Many nutrition experts disagree with the basic premise of low-carbohydrate
diets—the notion that high-carbohydrate, low-fat diets cause obesity and other health problems. In one argument, some nutritionists point to the traditional
Japanese diet that is very high in carbohydrates, low in protein, and very low
in fat, yet is associated with good health and normal weight in people who
follow that diet. Rather than attributing obesity and other problems to
carbohydrate intake, these critics blame the overconsumption of calories (from
any source) and lack of physical activity as the primary causes of these health
disorders.
Critics concede that low-carbohydrate dieters often experience significant
weight loss during the initial stages of the diet. However, these critics argue
that these diets often have a diuretic effect (in other words, they promote water loss) and
that the initial weight loss is due to water loss, not fat loss. Recent research
suggests that some people may lose more weight over the course of several months
on a low-carbohydrate diet than on one that is equal in calories but higher in
carbohydrates, but few studies have been done to determine the long-term
effects, good or bad, of low-carbohydrate diets.
In addition, many authorities are concerned that a lower-carbohydrate diet
may result in higher calorie intake from fat, which could lead to more
difficulties with overweight, insulin resistance, high cholesterol levels, and
heart disease risk. Studies of low-carbohydrate diets that are also low in
calories and promote weight loss often do not support these concerns, but
research on the effects of higher calorie versions of these diets is scarce and
conflicting. Increased protein intake as a result of avoiding carbohydrates is
also a concern for some critics, since some high-protein diets may increase the
risk of osteoporosis, kidney
stones, and some cancers.
Critics also express concern that the lack of grains, fruits, and vegetables
in low-carbohydrate diets may lead to deficiencies of key nutrients, including fiber,
vitamin C, folic
acid, and several minerals.