There have been many widely-reported criticisms of the low carbohydrate diet in the past year, and these still surface now and then in various news shows and publications. I have seen news reports that have absolutely no scientific substance despite a great fanfare, and have also seen comments by nutrition experts and others that are based on scientific misinterpretation.
I believe it is important for those individuals who want to use a low carbohydrate diet as a maintenance plan to understand enough of the science behind the frequent criticisms to recognize whether they are valid or not. I present some of the more common ones I have heard here:
This belief arises from incorrectly reversing a known medical fact. It is known that with certain types of kidney disease protein should be restricted in the diet because the unhealthy kidneys cannot dispose of the nitrogen break-down product efficiently. However, the reverse assumption that protein in the diet will cause this condition is totally incorrect. Healthy kidneys should be able to deal with any amount of nitrogen that is delivered to them.
Diabetics are prone to kidney disease, which is more likely to occur if their blood sugar levels are too high. However, if there is no evidence of current kidney disease, a low carbohydrate diet is an ideal way to help control blood sugar levels and avoid the onset of kidney problems.
This is the statement I have seen most commonly from physicians and other health experts. It comes from considering studies showing negative effects of fat intake on cholesterol, heart disease and cancer without recognizing that the studies being quoted were performed on diets that were not limited in carbohydrates.
In reality, studies that were performed on diets low in carbohydrate reveal that dietary fat promotes the production of HDL cholesterol - the one that prevents heart disease. At the same time, limiting carbohydrate in the diet results in decreased levels of LDL cholesterol, the one which produces atherosclerosis. (This is discussed more in detail in the section on cholesterol.)
As for cancer, I know of no studies that examine whether the amount of fat in a low carbohydrate diet has the same effect on cancer risk as in a diet that obtains 50% of calories from carbohydrate. Based on the metabolic processes in the human body, I suspect we would see a very different picture.
So when you see statements about the high fat content of a low carbohydrate diet, remember that the other side of the equation - the low carbohydrate content - must be considered also in order to be scientifically valid.
I must admit, this criticism is correct for some of the popular low carb plans promoted by various authors, because they restrict the total caloric intake. (For details, see the comparison of popular low carb plans.)
Ketones are the breakdown products of fat when it is used for energy. One of the major principles of a low carbohydrate diet is that the body is required to use fat for energy because not enough glucose is supplied by dietary carbohydrate. This same situation occurs every night while we sleep and are not eating anything, so having ketones in the bloodstream is a natural state. The difference is the quantity of ketones in the natural state versus a state of ongoing ketosis.
Let us consider a low carb plan where only carbohydrate is limited, and both protein and fat are eaten as desired to satisfy hunger. This would still lead to some ketone production when fat is used for fuel, however, there is no scientific evidence that this level of ketones would inhibit the appetite enough to prevent ingestion of adequate calories to meet the body's needs.
In other words, starvation = ketones, but ketones do not = starvation. Additionally, it is likely that the the major appetite control in an unrestricted low carb diet is the hormonal effect of dietary fat on brain neurotransmitters.
As noted above, it is likely that an individual on a low carb diet will consume fewer calories because of the appetite control of the fat intake, and of the ketones to some degree. But there are other factors at work that are equally important.
In a low carb diet, the body's glucose needs are partially met by converting dietary protein to glucose. It is a known scientific fact that some of the energy of the protein is lost in this conversion process. It actually requires 1.6 grams of protein to produce 1 gram of glucose.
Here is an example:
Suppose you eat a meal that contains 28 grams of carbohydrate (like a baked potato) and 56 grams of protein (like an 8 oz lean steak). Both protein and carbohydrate are known to provide 4 calories per gram, so the total for this meal would be 336 calories.After digestion, the body converts the 28 grams of carbohydrate to 28 grams of glucose, for 112 calories. Let's assume you get a full 4 calories per gram of protein when it is used as energy (it is actually somewhat less), which means you get 224 calories from the steak. That is a total of 336 calories.
Now suppose instead you ate only a 12 oz steak and no potato. This would be 84 grams of protein (7 grams of protein per ounce of meat), or the same total of 336 calories for the meal.
After digestion, the body will convert some of the protein to glucose to meet its baseline needs (mainly for brain activity). Let's assume it produces the same 112 calories as we got in the previous meal, or 28 grams of glucose. Since it requires 1.6 grams of protein for each 1 gram of glucose produced in this process, it will require 44 grams of protein to accomplish this. This leaves 40 grams of protein to be used as energy. Again, assuming we get the full 4 calories per gram, this gives us 160 calories of energy from the protein. The final effect is that we have now obtained only 272 calories of energy from this 336-calorie meal. The rest of the energy was used in converting the protein to glucose.
An additional factor involves the ketones that are produced when fat is used for energy. When excess amounts of ketones are present in the bloodstream, they are excreted by the kidney. Because ketones represent a portion of the 9 calories per gram of energy that is stored in the fatty acid molecules, this also represents a loss of calories.
These scientific principles explain why it is possible to lose weight on a low carb diet without a restriction in calories, and even with an increase in caloric intake!
A word of warning - over the years numerous dietary supplements or specific foods have been advertised as being "fat-burning", which sounds like the process described above. Be aware that there is no single food, "natural" product or vitamin supplement that can take advantage of this process. It is a result of the composition of the complete dietary intake.
Additional explanations about
these concepts are provided in "The IDEAL DIET for Human Health." This
120-page book reveals the known scientific facts about human nutrition and
metabolism in layman's terms, explaining why low carbohydrate diets are the
healthiest for most people. (More
information about the book and newsletter)
When you understand the science, you can interpret these and other criticisms (and there will undoubtedly be more) with the security that comes with knowledge.
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