The Truth About Carbohydrates
and Dieting
Judy Goffi MS, RD, CDE, LD

Recently popularized diets such as Atkin's, Protein Power and The Zone recommend severe restrictions of carbohydrates in favor of increases in fat and protein. The shared theme among these diets is that carbohydrates are bad because insulin is released as a result of carbohydrate ingestion. Insulin then supposedly takes the carbs and stores them as fat, rather than allowing the body to use them as energy.

The recommendation therefore becomes diets lower in carbohydrates - as low as 5-10% in some cases! Still, nearly every professional medical organization, led by the American Heart Association and the American Dietetic Association recommends that approximately 55-60% of your calories should come from carbohydrates. Why is this?

The simple fact is that when you lower your carbohydrate intake below 55-60%, you have to increase your protein and fat intake. The major medical institutions will not support this because the vast majority of medical research shows two things: a diet high in fat is unhealthy (1-5), and a diet excessively high in protein is unhealthy (6-9,11-12).

High fat diets are associated with an increased risk of cardiovascular disease (1-5). A recent comparison study of eight popular diet plans found that the low-carbohydrate diets had more than twice the amount of recommended saturated fat (13). All that saturated fat is a recipe for clogged arteries, which leads to cardiovascular disease.

And while a high carbohydrate diet (beyond 75%) does raise insulin levels which increases the risk of heart disease, there is no good evidence that high insulin levels make people fat.

As a result of the lower carbohydrate composition of these diets, protein is also increased to more than twice the recommended levels. Increasing protein levels to 40-50% of your caloric intake places tremendous stress on your kidneys (6-9,11-12) and liver (9,10). Studies have shown that high-protein diets result in adaptations such as kidney enlargement and increased filtration rate (6-9,11-12).

But what about the success of low carbohydrate diets?

It is unarguable that low carbohydrate diets are successful for weight loss, at least in the short-term. The question isn't whether or not this approach is effective, but why is it effective, is it safe, and are there long-term benefits or health risks?

The bottom line is that body weight depends on calorie balance. If you are eating more calories than you are expending, you are going to gain weight. Low carbohydrate diets work because they severely restrict calories, not because of what is supposedly happening to insulin levels.

By restricting carbohydrate intake to such a degree and subsequently increasing saturated fat and protein levels far beyond normal, low carbohydrate diets appear to be very unsafe in the long-term, especially for those with high levels of LDL cholesterol. Also, keep in mind that while effective at making you lose weight, these diets also rob you of important fiber, vitamins and minerals derived from fruits and grains.

JUDY GOFFI MS, RD, CDE, LD
Lead Dietitian Seneca Physical Therapy Inc., Beyond Fitness

 

REFERENCES:

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1. Grundy SM, Denke MA. Dietary influences on serum lipids and lipoproteins. J Lipid Res. 1990;31:1149-1172.
2. Mensink RP, Katan MB. Effect of dietary fatty acids on serum lipids and lipoproteins: a meta-analysis of 27 trials. Arterioscler Thromb. 1992;12:911-919.
3. Ginsberg HN, Barr SL, Gilbert A, et al: Reduction of plasma cholesterol levels in normal men on an American Heart Association Step I diet or a Step II diet with added monounsaturated fat. N Engl J Med. 1990;322:574-579.
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