A Registered Dietitian explains why carbs in their natural form are the human body’s preferred fuel source
by George Eisman, RD (co-written with Claire Holzner, MA)
For many years carbohydrates have been maligned as something to avoid in our diets. It’s time to set this notion to rest, and appreciate the value of carbohydrates as the best fuel source, in fact the only clean-burning fuel source for the human body to run on.
Our bodies can be fueled by four groups of chemicals: fats, proteins, ethanol alcohol, and carbohydrates. Of these, the only one that has no negative effects when used as a calorie source is carbohydrates. If you think carbs are fattening, know that the caloric density of these groups is: fat 9 calories per gram, ethanol alcohol 7, protein 4, and carbohydrates 4. Thus carbs are tied with protein as the least calorie dense source of fuel. The key to healthy carb intake is to assure that they come from whole plant foods with their fiber not only intact but still attached to the carbohydrate molecules (that is, not ground into flour or liquified). This assures that the carbohydrates are not digested and absorbed too quickly which can result in elevated blood glucose levels, not a good condition for the body to have to deal with.
What’s the problem with using the other sources of calories? Digesting fats in our bodies results in a buildup of by-products called ketones. One of the main ketones is acetone, which is also the principal ingredient in nail polish remover (!). Having a lot of these ketones build up in your system is not a good idea. Witness what happens when runners “hit the wall,” which means they have used up all the stored carbohydrate (it is stored as glycogen, which is a carbohydrate molecule similar to starch). Before a race, athletes try to build up their glycogen stores so they can use this as long as possible. Once they “hit the wall” their bodies will have to burn fat, which will result in build-up of ketones and thus discomfort. Excess ketones slow down the body in many ways, including suppressing appetite. People eating low-carb diets lose their appetites and tend to eat less after a while, so they temporarily lose weight. However, the short-term effects of ketone build-up and the long-term effects of fat clogging your arteries, sludging your immune system, and increasing risk of cancer make low-carb diets a bad choice.
Burning protein as a fuel source forces the body to de-aminate the amino acids which are the components of proteins. The liver removes the amino group from each amino acid so that the remaining part can be burned as fuel. About 60% of the amino acids yield a sugar particle, and the other 40% a fat particle. So fueling the body on protein amounts to eating a 60% sugar — 40% fat diet. The amino group that the liver removed from the amino acid is actually ammonia, a noxious chemical which must be eliminated from the bloodstream. The liver must deal with this ammonia by turning it into something slightly less toxic: urea, which is sent to the kidneys. Kidneys which are burdened with a high urea load wear out over time. Kidney failure is the seventh leading cause of death in the U.S. and the leading cause of death among body-builders and Native peoples of the Arctic region who eat a high-protein diet (a lot of fish). When people are hospitalized with kidney failure, the diet they are put on is a “low protein” diet, in order to give their kidneys a chance to recover. The “low protein” diet they are given is 20 to 40 grams of protein per day, which is not actually low. It is adequate but not excessive. The body needs only a little protein daily for building muscles and other tissues: less than one ounce (15-20 grams per day, an ounce equals 28 grams). All the other protein consumed beyond that small amount must be processed as described above. The average American eats well over 100 grams of protein per day, which far exceeds the generous U.S. Recommended Daily Allowance of 46 grams per day for women and 56 for men.
Consuming too much protein may also weaken our bones because the amino acids tend to make our blood acidic. The blood pH is normally slightly alkaline — about 7.35 (7.0 is neutral). When the blood becomes acidic, the body dissolves bone to buffer the acid and re-alkalize the blood. Bones are made up of calcium phosphate molecules, and it is the phosphate that serves as the alkaline buffer. The calcium gets detached from the phosphate and is released freely into the blood. This is not ideal as the heart can stop if calcium levels get too high. Thus the free calcium is sent to the kidneys for excretion. So you are urinating out calcium because you acidified your blood by eating unnecessarily high amounts of protein.
Using ethanol alcohol as a source of calories is also not a good idea. After killing some brain cells, the alcohol is sent to the liver and is turned into fat (which is why you get a fatty liver from drinking too much alcohol). Ultimately you are burning fat, which will result in the same ketone build-up described above.
This leaves us with carbohydrates as the only fuel source that burns cleanly. Carbohydrates are made up of an atom of carbon combined with a molecule of water. When you eat carbohydrates, fuel is generated for the body by the removal of the carbon from the water. The only waste products left after this process are carbon (which you combine with oxygen and breathe out as carbon dioxide) and water (which you urinate out). No ketones, ammonia, or acid build-up. However, refined sugars can cause an acid condition in the body. This is another reason to be sure that the carbohydrates you eat are unrefined, with the fiber attached. Flour products, even whole grain flours, generally have the fiber detached from the starch molecules, which can result in elevated glucose levels. Base your diet on foods that are rich in carbohydrates: true whole grains, beans, vegetables, and fruits (not juices), with moderate amounts of nuts and seeds. Ideal diets around the world historically have been found to consist of 80% of calories from carbohydrates, 10% from fat, and 10% from protein. This is not coincidentally the ratio found in whole grains and starchy vegetables, which have served as the staple foods of human beings for millennia, until we started eating large amounts of animal products daily.
So, no need to fear unrefined carbs! They are the best source of calories for our bodies. We stripped the king of his royal clothes (by refining carbs) and made him an outcast nutritionally. Time to let him keep his natural royal garb and serve us by giving us our good health back.
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