Low carb diet research

Critics of the low carb diet

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:

False data

Too much protein can cause kidney disease, especially in diabetics

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.



A low carb diet is hazardous because it is high in fat, which can cause heart disease and cancer

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.

Magic of weight loss

A low carb diet causes weight loss because your calories are so limited that you are in a state of starvation. You do not feel hungry because of ketones created by the starvation.

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.



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