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67 Cards in this Set
- Front
- Back
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6 categories of nutrition
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Carbohydrate 4 kcal per gram
Known as Starches, Sugars and Fibers Fat (Lipids) 9 kcal per gram Known as Triglycerides, Phospholipids and Sterols (Fats and Oils) Protein 4 kcal per gram Made (synthesized) from basic building blocks called Amino Acids Vitamins 0 kcal Subdivided into two separate groups by solubility in water or fat so we have water-soluble and fat-soluble vitamins. Minerals 0 kcal Subdivided into two separate groups by the amount present in the body, Major or Trace. Water 0 kcal |
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Nutrient class
Carbohydrate |
Carbohydrate, fat and protein in foods are measured in grams and are considered the macronutrients. They provide energy to our bodies after we digest, absorb and metabolize them. There is a module dedicated to each of the macronutrients (Modules 4, 5, and 6).
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Nutrient class
Vitamins |
Vitamins are numerous and are divided into two categories as above. The fat-soluble vitamins include vitamins A, D, E, and K. The B complex and vitamin C make up the water-soluble vitamins. The chemical structures of vitamins are complex and we need specific forms of each vitamin (called the active form) to serve our body and keep us healthy. More on vitamins in Module 7.
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Nutrient class
minerals |
We also require certain minerals for good health. Minerals differ from carbohydrates, fats, proteins and vitamins in that they are considered inorganic (do not contain carbon and hydrogen). Minerals are elements you can find on the periodic table (if you remember back to high school chemistry or BIO 101). The minerals will be further studied in Module 8.
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Nutrient class
water |
The most vital of these six listed nutrients is water. We are always losing water from the body by way of urine, sweat, feces and the breath we exhale, so it must be constantly replaced because we do not store an excess of it. Most of our bodies are 60-70% water. Water in this context is the same as fluid. We can only live a short period of time (a few days) without fluids yet we can live for weeks without food. This shows you how important water is to our health and life. Water is discussed in Module 8 with the minerals.
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Calorie
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the amount of heat necessary to raise the temperature of 1000 grams of water one degree Celsius
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essentials nutritients definition
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the body can't make them so they must be consumed from the diet.
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How to calculate caloriese in grams
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You need to get used to the math involved in the field of nutrition. Here is a sample calculation using information concerning the caloric value of carbohydrate, protein, and fat from the last section. How do you calculate the fuel (energy) content of a 2 ounce serving of bread containing 32 grams of carbohydrate, 6 grams of protein and 2 grams of fat?
Carbohydrate has 4 kcals for each gram so... 32 grams carbohydrate X 4 Calories/gram = 128 Calories in carbohydrate Protein also has 4 kcals for each gram... 6 grams protein X 4 Calories/gram = 24 Calories And, fat has 9 kcals per gram (more than twice that of protein or carbohydrates)... 2 grams fat X 9 Calories/gram = 18 Calories Total (add) the Calories from carbohydrate, protein and fat (128 + 24 + 18) and you will discover that the fuel (energy) in a 2 ounce serving of bread will provide 170 Calories. Using this information, could determine the percentage of carbohydrate, fat or protein in the bread. If you want to know what percent of the whole, you look at the Calories from that macronutrient as part of the whole. For example, to find the percent carbohydrate, you divide the carbohydrate kcals by the total kcals to get the fraction that is carbohydrate (carb/total), then multiply by 100 to make the fraction a percentage. 128 kcals (from carbohydrate) / 170 kcals total= 0.753 or 75% |
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Appetite
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is considered a psychological response to the environment. Typical appetite stimuli include stress, depression, time of day, media advertisements and many other stimuli. Good examples of appetite changes are shown by the people who eat way too many calories because s/he is depressed, or the people that run to Taco Bell at 10 pm because the tv commercial looked so appealing! In these cases, the person may not be experiencing hunger but are seeking the food based on what their brain thinks about the current situation.
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phytochemicals
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These substances in foods (besides the carbohydrates, protein, fats, vitamins, and minerals) give foods the flavors, textures, colors we associate with them and may contribute some special health benefits. Vegetables, fruits, whole grains, herbs, nuts, seeds, and spices contain abundant phenolic compounds, pigments, natural antioxidants, and lots of other chemicals associated with a reduced risk of cancer and/or heart disease. These food components, which are shown to offer special disease-preventing attributes, are collectively called phytochemicals. Sometimes we might consider foods high in these components to be functional foods. Functional foods are promoted because they have components that have health-promoting qualities. Good examples of phytochemicals you have likely heard about include: lycopene in tomatoes or lutein that is so tauted for good eye health and prostatic cancer prevention, resveratrol in red wines from the skin of the grapes that are a powerful antioxidant, and beta-carotene in the yellow and orange vegetables that is also an anti-oxidant.
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AMDR
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AMDR in Nutrition stands for Acceptable Macronutrient Distribution Ranges.It can also be understood as the calorie composition of a diet that gives adequate energy as required and other nutrients. For example AMDR for carbohydrate is 45%-65%, fat is 20%-35% and of protein is 10%-35% of your total Kcal intake.
Recommended Dietary Ranges* 2002 Guidelines Older guidelines Carbohydrate 45% to 65% of total calories 50% or more of total calories Fat 20-35% of total calories 30% or less of total calories Protein 10-35% of total calories 10-35% of total calories |
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DRI
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Today, the classic RDAs have been replaced by the new standard known as the Dietary Reference Intakes (DRI) which includes more components than just the RDA.
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AI vs RDA
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Second, RDAs (Recommended Dietary Allowances ) are defined as the average daily dietary intake sufficient to meet the nutrient requirement of approximately 98% of the population. In statistical terms, this is two standard deviations above the mean. The RDAs are derived from the EAR. Note we have not dropped the RDA from the requirements, we have simply added more information than the RDA provided for us. The RDA is designed to meet the need of almost all healthy people. When you look at an individual day and a particular nutrient, most recommend you get at least 70% of the required amount to fall within a safe place on the curve.
Third, AI (Adequate Intake) indicates that there isn't enough data to estimate an EAR, thus it is defined as the quantity of intake consumed by groups with no evidence of inadequate nutrient intake. The AI lies somewhere between the EAR and the UL. Nutrients with an AI do not have an RDA because there is not enough information to get the first step of the RDA.....the EAR. |
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Balance foods with physical activity as dietary guidelines message
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The newest guidelines have 4 overarching messages:
Build a Healthy Plate Cut back on foods high in solid fats, added sugars, and salt Eat the right amount of calories for you Be physically active your way |
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What agency oversees labeling
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FDA
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Daily Values Labeling
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Daily Values represent standards derived from the 1968 RDA (Recommended Dietary Allowances) known as the RDIs (Reference Daily Intakes) and DRVs (Daily Reference Values). The RDIs are used to provide label information about vitamin and mineral content of a food. The only vitamins and minerals required on labels are vitamins A and C and calcium and iron. The DRV's are for nutrients that have no dietary standards (RDI) such as fat, saturated fat, cholesterol, total carbohydrate and fiber and sodium, with the exception of protein that does have an RDA. These DRV's are numbers based on current nutrition recommendations established by the National Academy of Sciences and are meant to act as an upper limit in most cases. It is the RDIs that are carry over from 1968! Appendix A in the text outlines the values used as the references in labelling.
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Nutrition density
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Nutrient density reflects the nutrient content of a food in relation to its energy (kcal) content. This information is not listed on the food label. One has to calculate or approximate this value. The ratio is derived by dividing a food's contribution to nutrient needs by its contribution to energy needs. More simply said, this is the food that has more nutrient for the calories.
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Macronutrient RDA
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Acceptable Macronutrient Distribution Ranges for Adults (as a percentage of Calories) are as follows:
Protein: 10-35% Fat: 20-35% Carbohydrate: 45-65% |
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portal vein
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As blood passes through the digestive tract, it picks up water-soluble nutrients for delivery to the liver through the portal vein (colored green in picture). Nutrients that don't dissolve in water, the ones designated as "fat-soluble", are emptied into lymph vessels and reach the right side of the heart through a large vein (yellow in picture). Eventually most of the fat-soluble nutrients are delivered to the liver but it takes a number of laps around the body before the liver "sees" all of these nutrients. In other words, the nutrients that are released by digestion will eventually find their way to the liver: protal vein nutrients go directly to the liver and lymphatic nutrients get there with enough laps around the body. The liver processes these nutrients before they are released into general circulation .
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Endocrine System
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The endocrine system or hormone system participates in the regulation of metabolism, reproduction, water balance, and many other functions.
Hormones are the body's messengers. They are produced by specialized cells within endocrine glands as a result of some condition in the body that needs adjustment. Hormones can be permissive (turn on), antagonist (turn off) or synergistic (works in cooperation with another hormone) in performing a task. Glands release the hormone into the blood, and the blood carries the substance to a target to effect a change. Once the desired change has occurred, the hormone production is decreased. Hormones can be very specific to affect a specific type of cell or tissue, or hormones can be more general and influence a lot of different cells. |
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insulin hormone
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The hormone insulin is produced by specialized cells in the pancreas in response to increasing levels of glucose (sugar) in the blood. Insulin is released into the blood and travels to muscle cells, fat (adipose) cells, and special cells in the liver. Insulin opens the cell "door" in these target cells to allow glucose to enter. As the blood is cleared of extra glucose and the concentration returns to normal, insulin production decreases.
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A few of the hormones affect all or almost all the cells in the body.
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Growth hormone from the pituitary gland in the brain causes growth in all parts of the body.
Thyroid hormones from the thyroid gland, located in the neck, controls the body's metabolic rate. This hormone is also known as thyroxin. It has become quite clear in the lastten or so years that our fat stores of the body are critically important in the endocrine system. Some hormones, such as leptin, are released from the fat stores signalling the brain that we have adequate energy stores on board. In response, the brain works to regulate the feeding center accordingly. The endocrine system allows us to maintain homeostasis or our normal state of being, the status quo of balance. It is automatic! We are unaware of hormones being turned on or off, nor are we aware of their action. If hormone control is automatic, how does nutrition fit into the scheme? Fasting, eating, and exercise can change levels of hormones in the body. Hormones also control the process of digestion. Hormones are released as food travels down the digestive tract. These hormones respond to the composition of the diet and cause release of digestive substances as needed. These actions help change the nutrients in food into more simple substances that can absorbed. The Hypothalamus regulates the heart rate, body temperature, water and salt balance, hunger, sleeping and wakefulness, emotions, and controls the release of various hormones in the pituitary gland. The pineal gland is responsible for circadian rhythms in the body, rhythms of physiological activity that fit into a 24-hour cycle. As you can see, these two parts of the brain are likely important to eating habits. The adrenal glands sit on top of the kidneys. The outer part of the adrenal glands secretes corticosteroids, hormones that regulate mineral balance in the body. The inner part of the adrenal glands secrete hormones to activate the 'fight or flight" response. See the next section for action details. |
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peristalsis
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waves of muscle contractions, followed by muscle relaxation, forcing the bolus of food on its way down the digestive tract.
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chyme
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The contents of the stomach are vigorously mixed with gastric juice containing water, acid, and enzymes. This produces a semisolid product or slurry called chyme. Hormones regulate the speed and amount of chyme that can leave the stomach and empty into the small intestine at one time. There are many factors that determine how fast the stomach can empty, we call this emptying "gastic emptying".
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enzymes
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A protein catalyst that speeds up the rate of a chemical reaction. It is not altered by the reaction
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Large intestine function
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The large intestine absorbs water and some minerals from chyme. It collects any material that won't be absorbed and "packages" it for disposal. The waste material is called feces. Muscle activity that moves the contents of the colon forward is very sluggish compared to peristalsis and is usually referred to as haustrations. None the less, it is important because it rolls and mixes the contents of the colon, and divides it into smaller particles in preparation for elimination from the body.
There are no villi in the large intestine, but there are large numbers of mucus producing cells. The mucus holds the fecal matter together. Mucus also protects the large intestine from bacterial activity. Beneficial bacteria in the large intestine breakdown many foodstuffs that escaped digestion in the small intestine so that they can be absorbed or used as fuel. Don't confuse the action of the bacteria in the colon with the true digestion that occurred in the small intestine. As you likely realize, feces are the indigestible portions of foods. They consist of a small amount of water, minor amounts of carbohydrate, protein (tough connective tissue) and fat that escaped absorption, and bacteria. Most of the carbohydrate is in the form of fiber and undigested starch. Dead cells from the intestinal tract are also present in the feces and get discarded. (Our small intestinal cells turnover about every 2-3 days, that is an amazing rate!!) |
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Villi purpose
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The lining of the small intestine is folded many times so it has an increased surface area for absorption. The finger-like projections called villi protrude from the surface. There are unique cells lining the villi of the intestinal tract that specialize in the absorption of nutrients released from food. These cells are organized in a finer-like projection called the villus. The villi (plural) are one cell thick and absorb the nutrients to deliver them to the blood or lymph (depending on the solubility of the nutrients).
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Small intestine purpose
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is the organ where almost all of the digestion of food and absorption of nutrients takes place. The small intestine has three distinct sections: duodenum, jejunum and ileum. Chyme is moved through the small intestine by peristaltic waves so that it can be mixed with the digestive juices within the small intestine. These juices contain enzymes for digesting carbohydrates, proteins and fat, and the preparation of vitamins and minerals for absorption. The lining of the small intestine is folded many times so it has an increased surface area for absorption. The finger-like projections called villi protrude from the surface. There are unique cells lining the villi of the intestinal tract that specialize in the absorption of nutrients released from food. These cells are organized in a finer-like projection called the villus. The villi (plural) are one cell thick and absorb the nutrients to deliver them to the blood or lymph (depending on the solubility of the nutrients). Most digestion happens in the duodenum (short first section) because it receives stomach contents and pancreatic enzymes. The longer two sections (jejunum and ileum) continue the digestion and provide a surface area for absorption.
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Sphincters
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The flow of chyme or feces is also controlled by specialized muscles that form rings around the entrance or exit of individual organs. These are called sphincters. There are four of these along the digestive tract. These sphincters separate the esophagus from the stomach, the stomach from the small intestine, the small intestine from the large intestine, and two terminal sphincters in the anus.
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GERD
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One sphincter that can cause a lot of trouble, the lower esophageal sphincter, often fails to prevent the backflow of the stomach contents into the esophagus. The stomach acid flows up the esophagus causing a burning sensation called heartburn or GERD (gastro esophageal reflux disease). If this condition persists for a long time medical attention is needed. Medications to reduce acid output by the stomach are frequently prescribed for this condition. We now know that untreated GERD may initiate esophageal cancer.
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mucus purpose in stomach
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There are no villi in the large intestine, but there are large numbers of mucus producing cells. The mucus holds the fecal matter together. Mucus also protects the large intestine from bacterial activity. Beneficial bacteria in the large intestine breakdown many foodstuffs that escaped digestion in the small intestine so that they can be absorbed or used as fuel. Don't confuse the action of the bacteria in the colon with the true digestion that occurred in the small intestine.
If you rub your tongue around the inside of your mouth, you become aware of a moist substance known as mucus. Mucus coats the digestive tract from mouth to anus, so all the chemicals associated with digestion are separated from the cells that make up the tract. Only when food is in the digestive tract are the digestive chemicals released. It is important that the body has protection from this harsh environment. Still, the cells lining the digestive tract have a very short life span, about 2-3 days. The stomach produces gastric juice containing an important chemical related to digestion called hydrochloric acid (HCl). |
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production/storage of bile
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The liver is an accessory gland and it produces a substance called bile. Bile is delivered to the small intestine by way of a tube called the bile duct. Bile is very much like soap: it takes large particles of fat and breaks them into small lumps so they can be suspended in water. When you wash your hands, you use soap to break up large fat particles into smaller ones and then you rinse away the dirt. This process of breaking fat into small particles is known as emulsification.
Before the bile is delivered from the liver to the small intestine, it is diverted to a storage site, a sac called the gallbladder. (This sac is tucked into the bottom side of the liver.) When fat enters the small intestine, a hormone is released that tells the gall bladder to contract because bile is needed. The contraction causes a small amount of bile to be squirted out into the intestine and the fat can be emulsified. Without emulsification, fat would not be properly digested, so it would not be absorbed. When a person has a gall bladder "attack", it is usually in response to a high fat meal and the gall bladder is trying to squirt bile through tubes that are blocked. Continued contraction of the gall bladder is quite painful. |
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Digestive enzymes by pancreas
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The pancreas manufactures a variety of digestive enzymes capable of breaking apart carbohydrates, proteins, and fats (lipids) into small fragments. The pancreatic duct carries the enzymes from the pancreas into the small intestine. The pancreas also manufactures sodium bicarbonate (baking soda). The same duct carries sodium bicarbonate from the pancreas to the small intestine. This alkaline substance is needed to neutralize the acid chyme as it enters the small intestines from the stomach. Just before this pancreatic duct empties into the small intestine, it is frequently joined by the bile duct that delivers bile from gall bladder. The juice that enters the small intestine is a mixture of sodium bicarbonate, digestive enzymes and bile.
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epiglottis
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A flap-like structure on top of the larynx. During swallowing it covers the entrance to the windpipe.
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Digestive enzymes by pancreas
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The pancreas manufactures a variety of digestive enzymes capable of breaking apart carbohydrates, proteins, and fats (lipids) into small fragments. The pancreatic duct carries the enzymes from the pancreas into the small intestine. The pancreas also manufactures sodium bicarbonate (baking soda). The same duct carries sodium bicarbonate from the pancreas to the small intestine. This alkaline substance is needed to neutralize the acid chyme as it enters the small intestines from the stomach. Just before this pancreatic duct empties into the small intestine, it is frequently joined by the bile duct that delivers bile from gall bladder. The juice that enters the small intestine is a mixture of sodium bicarbonate, digestive enzymes and bile.
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epiglottis
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A flap-like structure on top of the larynx. During swallowing it covers the entrance to the windpipe.
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Fat soluble vitamins
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The 4 fat-soluble vitamins, A, D, E, and K can enter the body only with the aid of fat. If anything interferes with the digestion or absorption of dietary fat, it will be reduce absorption of the fat-soluble vitamins.
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Lymph soluble nutrients
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The fats consumed in a meal will be digested into monoglycerides, free fatty acids and cholesterol.
Some of the end products of fat digestion (monoglycerides, cholesterol, and some of the free fatty acids) don't dissolve in water. This being the case, they are "packaged" into special carriers (chylomicrons) and enter into the body by way of the other circulatory system, the lymph. |
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Simple carb
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The simplest form of carbohydrate are three monosaccharides; the most important of the three being glucose, because it is this sugar that is found in the blood. "Monosaccharide" means a basic single unit of sugar, which is simple, and requires no digestion . It can be absorbed into the body without any change in its chemical structure.
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Another name for dietary fibers not digested by our enzymes
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Indigestible carbohydrates
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Relationship of starch to glucose
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Function of glucose: Glucose is the body's primary energy source. It is cellular fuel.
Food Sources of glucose: There aren't very many, although honey contains glucose. Glucose makes up the semi-fluid centers found in chocolate-coated cherries. We obtain almost all of our glucose from either starch or sucrose. Food starch is 100% glucose. Sucrose is 50% glucose. |
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Why do we drink water with high fiber diet
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We drink water because fiber absorbs water to soften stool
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Amylase
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Starch begins to be hydrolyzed (broken down) in the mouth. When we chew a cooked starch, such as a cracker, an enzyme in the saliva called salivary amylase begins to break the starch apart and releases a few maltose units. Swallowing the cracker stops the starch digestion when the bolus reaches the stomach. The acid in the stomach destroys the biological activity of the enzyme.
When the starch reaches the small intestine another amylase is released and digestion continues. This amylase is produced by the pancreas. It travels into the small intestine by the pancreatic duct and attacks the starch so that all the starch is hydrolyzed into maltose. |
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Lactose intolerance cause and symptoms
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Lactose, the sugar found in milk, is digested by the enzyme lactase in the intestinal microvilli. Many adults find that their ability to produce the enzyme is limited. This lactase deficiency is common among Asian, African and Native American populations.
The condition "lactose intolerance" causes much undigested lactose to remain in the intestine. Remember the bacteria of the large intestine can digest some of the fiber or sugars not absorbed in the small intestine. Diarrhea, gas and cramps are some of the symptoms of the disease. The term lactose intolerance has been replaced with lactase insufficiency. |
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Food sources cause lactose intolerance
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In order to control symptoms, the person avoids milk and milk products containing lactose. Yogurt is better tolerated than milk because much of the lactose has been converted to lactic acid by microorganisms in the product. Certain hard cheeses are lactose-free. One can buy lactase tablets and add them to milk, although the modified milk has a distinctly sweet taste. Many soy or rice milk products are a nice substitution for these folks. Usually, people can tolerate some milk if taken with other foods.
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Hyperglycemia and Hypoglycemia treatment
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Carefully designed diet to control blood glucose levels. This diet needs to be a mixture of fat, carbohydrates and protein.
Diet high in "complex" carbohydrates and fiber. It is common to use the glycemic index to gauge the entry of carbohydrate from a food into the blood stream. See Table 4-4 and page 140 of the text. Regular exercise. Insulin injections for type I diabetes. One of the many oral medications and possibly insulin injections for type 2 diabetes. |
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Recommended intake of carbs per day
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In order to prevent ketosis, one probably needs a dietary intake of 50 to 100 grams of carbohydrate per day. The current recommendation is that every person (adult) have at least 130 g per day. Health authorities usually recommend a carbohydrate intake of 55% to 60% of total kilocalories though the recent DRIs include a greater range for good health. On a 2000 kcal diet, 55-60% is 275-300 grams of carbohydrate per day. Remember the current acceptable macronutrient distribution range (AMDR) is 45-65% daily. Athletes definitely want to eat the top end of the range to be sure the muscle has plenty of glycogen (muscle fuel)!
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Fiber recommendation for adults
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Americans have an average intake of 14 to 15 grams of fiber per day. Health authorities and the DRI recommend a dietary intake of 25 grams for women and 38 grams for men per day. The daily value (DV) for a 2000 kcal diet is 25 grams. Fiber is like a good workout for your colon. It is also important to note that you can eat too much fiber. If your diet exceeds 50-60 grams of fiber per day, you could be binding important minerals and inhibiting their absorption.
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function of glucose
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Function of glucose: Glucose is the body's primary energy source. It is cellular fuel.
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glycogen
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Another form of complex carbohydrate, which is of animal origin, is called glycogen or animal starch.
This carbohydrate is a highly branched starch. Formation of glycogen: like plant starch, glycogen is made from individual glucose units and is formed in liver and muscle tissue. Function: Glycogen is the storage form of carbohydrate in humans and other animals. Glycogen in muscle and liver tissue provides a constant supply of glucose, so that we can go without eating between meals, and most of overnight. In other words, we always have a supply of glucose available in the form of glycogen. |
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Digestion after food enters mouth steps
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Starch begins to be hydrolyzed (broken down) in the mouth. When we chew a cooked starch, such as a cracker, an enzyme in the saliva called salivary amylase begins to break the starch apart and releases a few maltose units. Swallowing the cracker stops the starch digestion when the bolus reaches the stomach. The acid in the stomach destroys the biological activity of the enzyme.
When the starch reaches the small intestine another amylase is released and digestion continues. This amylase is produced by the pancreas. It travels into the small intestine by the pancreatic duct and attacks the starch so that all the starch is hydrolyzed into maltose. Another enzyme (maltase) breaks down the maltose into 2 glucose units. |
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Monosaccharides and how it is handled after absorption in liver
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No matter what kind of sugars or starches we eat, by the time they are digested, only glucose, fructose and galactose remain. The monosaccharides are absorbed into the intestinal cells, picked up by the blood and delivered to the liver via the hepatic portal vein.
A small amount of starch escapes digestion. In the large intestine, the undigested starch is "food" for the resident bacteria. It may be that this undigested starch provides energy to the cells that make up the large intestine. A word about the sugar in milk, lactose. The enzyme (lactase) that digests lactose is produced on the surface of intestinal cells. When lactase breaks down lactose, the monosaccharides glucose and galactose are released. These two monosaccharides are absorbed from the small intestines into the blood. But, when lactase activity is low or nonexistent, the lactose can't be digested and the sugar moves into the large intestine where it becomes food for resident bacteria. These bacteria metabolize the sugar to form acids and gases, sometimes with resulting discomfort (gas & diarrhea). The digestion of dietary fibers is quite a different story. There is no digestion of dietary fiber in the mouth, stomach, or small intestine. When the fibers enter the large intestine, soluble fibers are attacked by the bacteria. Actually, they are fermented, and some carbohydrates are changed into fatty acids and gases. Fatty acids are a type of lipid, so they can be absorbed by the walls of the large intestine. |
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Epinephrine influences blood glucose
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Epinephrine, produced by the adrenal gland, provides glucose and fat for immediate use.
As demonstrated in module 3, the hormone epinephrine is produced by the adrenal glands. This hormone is responsible for the "Fight or Flight" reaction. Under the influence of epinephrine, the liver releases large quantities of glycogen, which breaks down and pours glucose into the blood to make it possible for instant physical and mental response. Epinephrine is another hormone that affects blood glucose levels causing an immediate increase in blood glucose. |
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Undigested disaccharides (fiber)
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While fibers do not represent a significant source of energy (fuel), they play several important roles. First, the insoluble fibers decrease the amount of time it takes a bolus of food to make its way down the length of the GI tract. This means that there is less time for the GI tract to be exposed to harmful components in the diet (cancer-promoting chemicals). Second, dietary fibers absorb water as they move down the tract, which ultimately softens the stool and makes it easy to eliminate. It prevents constipation.
There are many advantages to soluble fibers. The soluble fibers remain in the stomach for a longer time than other carbohydrates (delays gastric emptying), which gives a feeling of being full for a longer period of time after a meal. Soluble fibers delay glucose absorption in the small intestine, so blood sugar levels are more evenly maintained. This is sometimes called the glycemic index of a food. Foods with high glycemic index are low in soluble fiber and high in simple sugar so enter the bloodstream rapidly. Low glycemic index foods are higher in soluble fiber and allow glucose into the blood much more slowly. And, soluble fibers help to keep blood cholesterol levels in check because they may bind cholesterol from the bile in the small intestine and carry it to the large intestine for elimination. |
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Saturation Fatty acid bonds
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First, fatty acids are classified as to being saturated or unsaturated. A fatty acid is saturated if it has no double bonds on the carbon chain. The chemical bonds between the carbons (little C's) are all single bonds.
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Monosaturated fatty acids
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One or more double bonds make the fatty acid "unsaturated". Further classification designates unsaturated fatty acids as either monounsaturated
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Polysaturated fatty acids
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polyunsaturated (2 or more double bonds).
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essential fatty acids definition
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These two fatty acids, Alpha-Linolenic acid (omega-3 fatty acid) and Linoleic acid (omega-6 fatty acid) are designated essential fatty acids because humans can't produce these fatty acids in the body (it is easier to abbreviate these as n-3 and n-6 fatty acids). Becasue they are "essential", we need a dietary source of them. They have special functions important to the body.
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chylomicrons
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Lipoprotein made of triglycerides and cholesterol surrounded by a shell of phospholipids and proteins. They are made in the intestinal wall from absorbed dietary lipids, and travel through the lymphatic system to the blood by way of the right side of the heart. (Transports lipids from the intestinal cells to the body.)
The long chain fats of the micelles (monoglycerides and fatty acids at this point) move into the cells lining the small intestine. Inside the intestinal cells, new triglycerides and new phospholipids are synthesized from the absorbed micelle products. These fresh, new lipids form particles called chylomicrons (ki''lo-mi'kronz). It is amazing how many times the body takes fats apart and puts them back together in order to digest, absorb and metabolize them. |
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fat absorption and chylomicron transport
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Once in the blood, a special enzyme (lipoprotein lipase) from inside the capillaries breaks up the triglycerides into glycerol and fatty acids. (Notice the hydrolysis or breakdown reaction again!)
Muscle cells, fat cells (adipocytes) and liver cells absorb the fatty acids from the chylomicrons in blood. Muscle cells use the fatty acids as fuel. Adipose cells put the fatty acids together again and store them as triglycerides. Excess fuel from the chylomicrons accumulates in the liver, where it is ultimately converted to new triglycerides and new cholesterol. |
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Hydrogenation and trans fatty acids and effect on LDL cholesterol
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LDL and HDL particles are sometimes referred to as "bad" and "good" cholesterol. As we just learned, each type of cholesterol particle has a specific job.
Normally, LDL particles are taken up by cells in need of cholesterol or cleared by the liver. If our liver cannot clear these fast enough, our blood levels of LDL become too high. Excess LDLs (with their load of cholesterol) will encounter scavenger cells in blood vessels. These specialized cells engulf the LDL particles to remove them from the blood. To keep them from reentering the blood, they are oxidized. This is the beginning of a process that leads to the formation of plaques within the blood vessel. As cholesterol is continually embedded in blood vessels (namely arteries), the cholesterol is combined with protein, white blood cells, smooth muscle cells, other lipids and calcium to form a substance called plaque. It is assumed that the plaque was originally deposited to repair some injury to the lining of a blood vessel. Plaque has two major effects on the inside of the artery. First, the plaque becomes thick and hard causing the elastic tissue in the vessel to become stiff and inflexible. Second, the plaque narrows the opening (lumen) of the artery reducing the amount of blood that can flow through the vessel to target sites. |
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VLDL HDL jobs and functions
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Excess fuel from the chylomicrons accumulates in the liver, where it is ultimately converted to new triglycerides and new cholesterol. These freshly made lipids are also packaged into VLDLs (very low density lipoproteins). The fuel source can be any excess carbohydrate, fat (lipid), protein or alcohol. The VLDLs are like the chylomicrons, just smaller. Just like the chylomicrons, enzymes within the capillaries break the triglycerides down into glycerol and fatty acids. The fatty acids are claimed by either cells that need fatty acids for fuel or cells that can store fatty acids as new triglycerides (mainly adipose tissue).
When VLDLs have released their load of triglycerides, they are much smaller particles. What is left is essentially cholesterol, forming particles called LDLs (low density lipoproteins). The job of LDL is to transport cholesterol to cells that need cholesterol; cells that use cholesterol may make steroid hormones, vitamin D and cell membranes. Like the other particles, LDL is transported in the blood. We know LDL for the negative effects on the arteries when it accumulates and oxidizes in the arterial walls resulting in atherosclerosis. Our liver cells are responsible for clearing the LDLs and the cell membrane controls the uptake of the LDLs. If the cell membranes of the liver have a high saturated fatty acid content, it is not very fluid and is less effective at clearing the LDLs, so the LDLs hang out in the blood longer. The longer LDLs hang out in the blood and the higher the concentration of them, the more likely they will accumulate in the arteries. Thus, we consider a high saturated fat diet to be the culprit in "heart disease". HDLs (high density lipoprotein) are the smallest of the lipid transport particles and should be known as the good guys. Formed in the small intestine and liver, their job is to pick up excess cholesterol in the body and deliver it to the liver for degrading and disposal. HDL is a scavenger. We know HDL for their positive effects in our fight against heart disease. |
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Hydrogenated fats
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Most of the oils produced in this country are converted to "vegetable fats" by a process of hydrogenation. Unsaturated fatty acids that make almost all oils liquid at room temperature can be saturated with the addition of hydrogen. By adding hydrogen to the carbon-to-carbon double bonds, it is possible to create single bonds, thus producing a solid fat at room temperature. This picture demonstrates how the process is done.
This is the chemical representation of the changes that take place when hydrogen is added. This process of hydrogenation is responsible for producing smoother and easier to spread peanut butter, margarine and shortening. However, hydrogenation of oils makes the fat more unhealthy, here is why: The natural form of unsaturated fatty acids is called cis. At the double bond the carbon chain folds back on itself. The hydrogens are on the same side of the chain like those in the yellow box below. During hydrogenation, some of the double bonds on the carbon chains stretch out to the unnatural form called trans. Note in the picture above, the hydrogens of the trans fat (green box) are on opposite sides of the chain. Trans fatty acids are just as bad as saturated fatty acids at increasing LDL levels in the blood. |
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Fats of saturated and unsaturated at room temp
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Generally, "fats" are solid at room temperature and include such lipids as beef tallow. Most animal sources of fat are high in saturated fat thus are solid at room temperature. "Oils" liquid at room temperature and corn oil is la good example. Plant fats tend to be higher in monounsaturated and polyunsaturated fatty acids thus are more liquid at room temperature.
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Liver regulation of cholesterol
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Chemical digestion of lipids takes place primarily in the small intestine. The action of the pyloric sphincter and bile are the key factors in breaking up large lipid droplets from foods. The warming of lipids in the mouth and stomach turn any solids to liquids.
Bile acids are made from cholesterol in the liver. They make up a fluid called bile, which is an emulsifying agent. Bile is stored in the gallbladder until a hormonal signal is received that bile is needed in the small intestine. The gallbladder squeezes down and bile is squirted into this portion of the digestive tract. The hormonal signal is initiated by the presence of fats in the stomach and small intestine. This is very smart of our bodies because we need bile when we eat fat! The gallbladder squirts bile into small intestine via the common bile duct. The bile acids help emulsify the dietary lipids in the digestive tract by keeping small droplets in little packages called micelles. Here is the structure of that micelle. Remember, because phospholipids like lecithin are fat friendly inside and water friendly outside, this make the perfect package to transport these small droplets of fat. If the fat droplets were left without a package or cover, they would come back together in one large droplet! Emulsifiers help spread the fats out! In this case, it allows enzymes better acess to the fats. In the meantime, the pancreas release pancreatic juice with lipid-digesting enzymes called lipase. Notice that this is lipid with the suffix "ase" which you should guess means lipid-digesting. Because the fats are in small droplets or micelles, pancreatic lipase can attack the emulsified fat particles and change them into monoglycerides and free fatty acids so they can be absorbed through the intestinal wall. Once bile has accomplished the task of helping fat digestion, bile is reabsorbed in the colon and recycled back to the liver via the hepatic portal system. Any bile that is not reabsorbed will be excreted in our feces. This can be an important disposal of cholesterol for some people. |
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Animal cholesterol
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Dietary sources of cholesterol are foods of animal origin. Milk (but not skim milk), cheese, beef and eggs contribute a significant amount of cholesterol to the diet, not because they are especially high in cholesterol, but because they are consumed in such large quantities. Organ meats such as brains, kidney and liver contribute very large quantities of cholesterol to the diet, but are not a significant source of cholesterol because they are foods that are seldom consumed.
Don't forget, foods with saturated fats are almost sure to be accompanied by cholesterol! |
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Pancreatic Lipase
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In the meantime, the pancreas release pancreatic juice with lipid-digesting enzymes called lipase. Notice that this is lipid with the suffix "ase" which you should guess means lipid-digesting.
Because the fats are in small droplets or micelles, pancreatic lipase can attack the emulsified fat particles and change them into monoglycerides and free fatty acids so they can be absorbed through the intestinal wall. |
