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Carbohydrates, Part I
[mod edit] Please use the appropriate quote tags when quoting outside sources - Topic moved to Health and Beauty[/mod edit]
Carbohydrates, Part I
|Carbs. Carbos. Carbohydrates. Never have so many people been so confused by a food category. Good for you? Bad for you? Fattening? Slimming? On the one hand you have advocates of the Pritikin Program, and the Dean Ornish Program for reversing heart disease, suggesting that 80% of our calories should come from carbohydrates. On the other hand you have the Hellers -- (Richard and Rachel) -- authors of Healthy for Life and The Carbohydrate Addict's Diet, suggesting that we cut back on carbohydrates as a means of reversing obesity, hypertension, diabetes, and even heart disease. So, who is right?
Who can forget Susan Powter's screaming infomercial promising that we can eat all the carbs we want -- and be thin -- as long as we cut out fat. But what about Barry Sears and The Zone. He advocates that we restrict our carbohydrate intake to only 40% of our calories, aiming for a 40-30-30 balance of nutrients. Who is right?
To further confuse the issue, there's disagreement about the subcategories of carbohydrates. Complex carbs are good, say some of the so-called experts, and sugars are bad. Some people go so far as to maintain the sugar is toxic, and responsible for everything from addiction, to cancer, to criminal behavior. Who is right? Let's wade through the hype and hoopla, and take a closer look.
We may well discover -- as is often the case with nutrition issues -- that nobody is totally right, and everybody is a little bit right. First, there is no perfect universal eating plan. To quote the cliche: "One man's meat is another man's poison." And, the needs of the individual are not static. Our needs change with the seasons, with our age, and with our health status at the moment.
First, the chemistry lesson....
Carbohydrates are those substances composed of molecules of carbon, hydrogen and oxygen (CHO.) Hence the name: Carbo (as in carbon) and hydrate (as in water.) And water, as you probably remember is H2O (hydrogen plus oxygen.)
Carbohydrates which are composed of only one or two molecules are called "sugars." Carbohydrates which are composed of many molecules joined together are called "starches."
Classification of Carbohydrates...
bullet Monosaccharides are single molecules of carbohydrate.
1. Glucose (also known as dextrose) is *lo** sugar.
2. Fructose (also known as levulose) is fruit sugar.
bullet Disaccharides consist of two molecules joined together.
1. Sucrose (or table sugar) is made from one molecule of glucose and one molecule of fructose.
2. Lactose (or milk sugar) c****ines glucose and galactose.
3. Maltose (made from sprouted barley) c****ines two molecules of glucose.
bullet Polysaccharides are composed of many molecules of glucose joined together.
1. Starch is the polysaccharide found in most plants.
2. Glycogen is the polysaccharide that humans and animals store in their muscle cells.
3. Fiber is a type of polysaccharide that humans can't digest because we don't have the necessary enzymes. Some types of fiber are water soluble (for example, apple pectin.) Some types of fiber are insoluble (for example, wheat bran.) Some insoluble fibers will soak up water (as bran does) and other insoluble fibers won't soak up water (for example, the outer cellulose layer on a kernel of corn.)
In general, sugars are sweet tasting. Starches aren't. An exception is lactose, or milk sugar. It does not taste sweet. However, Lactaid Milk which has had the lactase enzyme added to it, tastes sweet because the lactose has been split into glucose and galactose.
There are other types of carbohydrates called sugar alcohols. Manitol, sorbitol, and xylitol are found in small amounts in fruits and vegetables. The calorie content of sugar alcohols is virtually identical to regular sugars, however because they are absorbed so slowly they are treated like artificial sweeteners and often used in "sugarless" gums and candies. The down side of sugar alcohols is that they tend to trigger diarrhea.
Functions of carbohydrate...
Carbohydrates provide the body's main source of energy. Certain parts of the body - the central nervous system, parts of the kidney, and red *lo** cells - must have a constant supply of CHO for energy formation. Under normal circumstances these tissues are unable to burn other sources of fuel.
Fiber, although it is not a source of calories, adds bulk and texture. It slows down digestion time so that a meal has more satiety. (You stay full longer.)
Soluble fiber, from foods like apples and oatmeal, sets up a kind of gel filtration system in the intestinal tract. It binds with bile salts and other waste products and carries them out of the system. (Bile salts are the end product of cholesterol metabolism. Attaching bile to fiber helps to lower the bodies cholesterol level.)
Insoluble fiber, such as wheat bran, swells with water and helps to prevent constipation. It binds with substances such as estrogen and can remove excesses of this hormone from the body.
Digestion of carbohydrates...
Digestion of starch begins in the mouth. Saliva contains an enzyme called amylase which begins to break starch down into glucose molecules. The pancreas releases more amylase into the small intestine to complete the digestion of starch into glucose.
Also in the small intestine, there are enzymes which break disaccharides down into their component parts.
bullet Maltase divides maltose into glucose + glucose.
bullet Lactase divides lactose into glucose + galactose. Sucrase divides sucrose into glucose + fructose
FYI In nutrition, any word ending in ase is an enzyme.
Many adults no longer produce the lactase enzyme, or they don't produce enough of it, and they may have lactose intolerance as a result. When we are unable to digest lactose it tends to ferment in the intestine, resulting in gas, bloating, and diarrhea. Fermentation is the interaction between the lactose and the bacteria and/or yeast that reside in the intestinal tract. A byproduct of fermentation is always gas.
Among Asians, the incidence of lactose intolerance is 80-95%. Among Africans, 50-99% are lactose intolerant. As many as 85% of Native Americans may be lactose intolerant.
After digestion and absorption, monosaccharides are processed by liver enzymes:
1. fructose and galactose are converted to glucose
2. glucose is converted to glycogen, or fat for storage
3. glucose is used to meet energy needs of the liver
4. nitrogen and other elements are added to glucose to produce nonessential amino acids that make up body proteins
Meet the hunger hormone...
After a meal, once we start to digest what we have eaten, our *lo** sugar level starts to rise. And this rise in *lo** sugar triggers the pancreas to release insulin. It is insulin that triggers the production of liver enzymes that handle the disposition of glucose and the other monosaccharides (as described above.) Insulin is the hormone responsible for moving glucose out of the *lo** and into the cells where it will be used for energy. You can think of insulin as a key that unlocks the door on a cell and allows glucose to enter. If the pancreas doesn't produce enough insulin, or if the insulin that's available doesn't work properly, *lo** sugar rises above normal. The result is called hyperglycemia or diabetes.
When everything works as nature intended, *lo** sugar rises after we eat, and then gradually -- over the course of 3-5 hours -- the level drops back to where it was before we ate. When it drops, we typically experience hunger pangs, the body's reminder that we need to refuel. How long it takes for hunger pangs to kick in, depends on the following:
bullet How much we've eaten. Larger meals last longer.
bullet How much fat we've consumed. Fat slows down stomach emptying, and meals containing fat take longer to digest.
bullet How much protein we've consumed as part of the meal. A meal that includes protein will last longer than one without.
bullet How much fiber we've consumed. Fiber slows down the digestion and absorption of carbohydrates, and therefore a high fiber meal lasts longer than a low fiber meal.
bullet How much refined carbohydrate we've consumed at one sitting. Refined carbohydrate would include white flour products and candies. Some one who polishes off a pound of jelly beans will probably experience a rapid rise in *lo** sugar and a huge insulin response which will result in a rapid lowering of *lo** sugar. Hunger pangs will arrive more quickly after 1600 calories from jelly beans than after 1600 calories from ice cream.
The jelly beans are all sugar. There's no fat, fiber or protein to slow down digestion and make those jelly beans last longer. Ice cream is high in fat, and fat slows down digestion. Therefore, ice cream results in a slower rise in *lo** sugar, and ice cream has more "satiety" than jelly beans. (Satiety means its more filling,)
Back to reality: My goal is not to push you towards eating either jelly beans or ice cream, but to make you aware of how different foods are handled because of differences in composition. This will help you understand how different foods effect your appetite.
Carbohydrates, Part II
With a little carbohydrate chemistry under our belts, lets look at dietary sources of carbohydrate.
Plants are the primary source of dietary carbohydrates. Fruits, vegetables, grains, and beans. Milk and milk-based products also contain carbohydrate. There is a little carbohydrate in cottage cheese, but virtually none in most hard cheeses, since lactose -- the carbohydrate that occurs in milk -- is removed during processing.
Carbohydrate is an essential part of a balanced diet for most people. As we said last month, certain tissues of the body the brain and red *lo** cells must have a constant supply of carbohydrate for energy formation. The brain alone burns 600 calories worth of glucose per day just for thinking. (If you dont think its somewhat less.) In fact, glucose is so important that the body has the ability to manufacture it when it is not consumed in adequate amounts. Protein (in the form of amino acids) is converted to glucose in the liver. That process is called gluconeogenesis (pronounced: gluco - neo - genesis) which means, the creation of new glucose.
Having said that, because the body does have the ability to synthesize glucose, it is possible to survive on a diet that is low in food sources of carbohydrate. The aboriginal Eskimo, for example, survived on a diet composed almost exclusively of fat and protein. But, unless youre an Eskimo, I dont recommend that you go to that extreme.
The amount of carbohydrate an individual will require over the course of the day will depend in part on the total number of calories the person needs. That amount will vary because of age, metabolism, activity level, and body type. In general, most people do well consuming between 40 and 50 percent of their calorie intake in the form of carbohydrate.
Thin, high strung, body types tend to do well on higher intakes of carbohydrate, because carbohydrate raises serotonin levels and has a calming effect on the body. (This same thin body type must have adequate protein to stabilize *lo** sugar, mood, and energy levels.) Obese body types need proportionately less carbohydrate in order to lower insulin levels, and/or to overcome insulin resistance. They also need fewer total calories in order to lose weight, and cutting back on carbohydrate is one way to force the body to use stored fat as an energy source.
Natural vs Refined. Complex vs Simple.
Natural carbohydrates are whole food items, such as string beans, apples, carrots, and brown rice. Refined carbohydrates are processed food items such as crackers, cookies, jelly beans, and bread or pasta made with white flour. (Guess which group is considered healthier!)
Complex carbohydrates are whole food items, such as fruits, vegetables, legumes, and whole grains -- (oatmeal, wheat berries, barley, corn niblets) -- which take longer to digest and metabolize because of their complex structure, especially their fiber content.
Simple carbohydrates are those processed food items -- (white flour products, sugars) -- which are digested and metabolized quickly because of their lack of fiber.
The Glycemic Index.
The Glycemic Index is a comparative chart which looks at how quickly a food will raise your *lo** sugar. When a food raises your *lo** sugar quickly, it is said to have a high glycemic index score. When a food takes longer to raise your *lo** sugar, it is said to have a lower glycemic index score.
Example: Glucose has a score of 100. A Russet potato is 98. Bread and rice are 72. Sucrose (table sugar) is 59. Oatmeal is 49. An orange has a score of about 40. Cherries are 23. Peanuts are 13. (Fat is 0.)
When fat is c****ined with carbohydrate foods it slows down digestion, and blunts the glycemic effect of a meal. Example: A slice of bread with peanut butter will raise *lo** sugar more slowly than the bread by itself.
In general, we are encouraged to eat foods which have a low glycemic index score so that we have a slow rise in *lo** sugar, and a sustained source of energy. However, if you needed to raise your *lo** sugar in a hurry -- perhaps because of hypoglycemia, or insulin shock -- that would be the time to choose a food which scores higher on the glycemic index.
The glycemic index remains somewhat controversial. Some health processionals recommend we live by it. Others claim that its impact is insignificant. The good news is that it does encourage greater consumption of whole foods, such as fruits and vegetables, and fewer refined carbohydrate products.
Food and Mood
Carbohydrates -- although they are a major source of energy -- can also make us sleepy because of their impact on brain chemistry. Carbohydrate consumption can increase the neurotransmitter called serotonin, and serotonin has a calming, sleep inducing effect on the body. Protein consumption, on the other hand, can increase levels of dopamine and norepinephrine, the neurotransmitters responsible for mental energy. Being deficient in any, or all, of these brain chemicals can result in depression.
Heres how to put this information to use:
bullet Falling asleep after lunch? Try cutting back on your starch intake, and/or increasing your protein intake.
bullet Stressed? And cant get to sleep at night? Have a slice of toast with jam on it before retiring.
bullet Cant keep yourself awake during afternoon business meetings? Snack on nuts instead of a bagel.
And, lets not forget our original questions. Are carbohydrates good for us? Are they fattening? And how much do we really need?
Carbohydrates can be either good for us, or bad for us, depending on the quality of the foods we choose. Example: Fruits and vegetables contain vitamins, minerals and fiber, in addition to their carbohydrate content. Table sugar, and white flour products, contain calories, but little else.
Are carbohydrates fattening? They can be. Like anything else they arent fattening until we consume more than we can burn off. And unfortunately, many of us are somewhat addicted to carbohydrates. We love our bagels and pasta.. And our cookies, and soda, etc., etc. And we have no concept of portion control. We stop eating when the plate is empty, rather than when the hunger goes away. During the past 2 decades weve made the mistake of eating excessive amounts of starch, and not enough protein, and most of us have gained weight as a result.
If weight is an issue, take a look at your carbohydrate intake, and cut back if thats appropriate. But dont go to extremes. In general, dont go under 100 grams of carbohydrate a day. And forget about very high carbohydrate, low fat diets. Even if you lose weight, which is doubtful, youll be hungry, deprived, and depressed. Low fat diets just arent healthy long term.
Hypoglycemia & Insulin Resistance
At any point in time we have several teaspoons of glucose in our *lo** stream. It is constantly being used by the brain, and by *lo** cells, for energy. Muscles can burn glucose also, and they do, but muscles can also burn fat for fuel. Under certain circumstances, when glucose is in short supply, the body will attempt to limit the amount of glucose the muscles can use by making our muscle cells resistant to insulin.
Insulin is the hormone produced by the pancreas that moves glucose out of the *lo** and into the cells where it will be used for energy, or stored as glycogen (starch,) or converted to fat and stored. What happens to glucose once it is inside the cell depends on what the body needs and how much fuel is available at that moment.
Insulin is like a key that opens a door on the cell wall, allowing glucose to enter. Each time we eat our *lo** sugar starts to rise, and the pancreas again produces insulin so that we can move glucose into the cells. If the pancreas is unable to make insulin our *lo** sugar will rise too high, and we will have a condition called Type I Diabetes. In this condition it is necessary to take the hormone insulin to make up for what the pancreas cant produce.
But what if we dont eat any carbohydrate? Suppose, for example, we go on a high protein, low carbohydrate diet that requires us to eat meat, eggs, cheese, chicken and fish, and nothing else. Well, the body in its wisdom will suppress the release of insulin, because none is needed if we arent consuming carbohydrates. The body will also produce a number of hormones that make us resistant to insulin. Being resistant to insulin means that the insulin that is in your *lo** doesnt work. Its as if someone put putty in the keyholes so that the key no longer fits in the lock.
Why do we become resistant to insulin? Remember what I said a few minutes ago about having only a few teaspoons of glucose in your *lo**. If we havent eaten any carbohydrate, and we are using glucose for energy, the risk is that our *lo** sugar will drop too low, the brain will be deprived of fuel, and we could go into a coma and die. (Yikes!) When we become resistant to insulin, the glucose in the *lo** is reserved for use by the brain and *lo** cells, and the muscles are forced to burn fat instead.
This adaptive process enables us to survive in the absence of carbohydrate, and even during starvation. For most of us the problem is not the absence of dietary carbohydrate, its what happens when we reintroduce carbohydrate following a period of time without it.
Lets go back to our high protein diet. Imagine for a moment that weve been invited to someones home for a dinner party. Our hostess is Itallian. Shes serving pasta, Italian bread, pastries, etc. You get the picture, right? We think "Oh what the heck. Its only one night. Ill go back on my diet tomorrow."
Dinner is served. We eat. Our *lo** sugar starts to rise, and rise, and rise.... Remember, there is no insulin available to metabolize the carbohydrate weve just consumed. None of the liver enzymes that metabolize glucose are there either. You see, theyre only produced in the presence of insulin. Eventually, when our *lo** sugar is much too high up in the diabetic range the body starts to produce insulin. It produces 2-3 times as much as it usually does, and our *lo** sugar suddenly swings from a hyperglycemic high to a hypoglycemic low When *lo** glucose falls below normal, we may feel any one of several kinds of symptoms.
bullet Cerebral symptoms: sleepiness, spaciness These symptoms occur because of a lack of available glucose to the brain.
bullet Hunger pangs and/or a craving for sweets.
bullet Heart palpitations, tremulousness, anxiety. These latter symptoms are brought on by the release of adrenaline, and occur primarily in persons with low *lo** pressure.
This entire reaction is referred to as reactive hypoglycemia. It is so named because it is a reaction to the ingestion of food which typically occurs 2 and1/2 to 4 hours after a meal. In the example I gave, it is a reaction to the ingestion of carbohydrate following a period of carbohydrate deprivation. In other words it is a rebound reaction. It is this rebound reaction that triggers binge behavior in starvation dieters, and in people coming off of low carbohydrate regimes. And it is this same rebound reaction that causes afternoon hypoglycemia in non-breakfast eaters.
When you get up in the morning you are coming off of an overnight fast. Your liver has run out of stored glycogen and is in need of refueling. In non-breakfast eaters the body must suppress the release of insulin, and make us resistant to any insulin still in the *lo**. Several hours after lunch *lo** sugar bottoms out because of a delayed and excessive insulin response, and the individual is either falling asleep at his/her desk, raiding the nearest candy machine, or experiencing an anxiety attack brought on by an adrenalin surge.
Over time, people who skip meals especially breakfast and lunch are at high risk for weight gain and Type II Diabetes.
Always plan to eat regularly, and make certain to include protein in your diet 3 times per day. Plan to consume a minimum of 100 grams of carbohydrate daily, and dont go on or off a ketogenic diet (thats an extremely low carbohydrate diet) unless youre working with a clinical nutritionist.
[mod edit] Please use the appropriate quote tags when quoting outside sources - Topic moved to Health and Beauty[/mod edit]