What is a low-carbohydrate diet?

Quick Answer
Weight loss and maintenance through diets that are low in carbohydrates.
Expert Answers
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Mainstream groups such as the American Heart Association and the American Dietetic Association traditionally endorse a unified set of dietary guidelines for people who wish to lose weight: Eat a low-fat diet and cut calories. However, many popular weight-loss and diet books take a very different approach. The Atkins diet, the Zone diet, Protein Power, and numerous other dietary approaches reject the low-fat guideline. Instead, these methods recommend cutting down on carbohydrates. According to proponents of these theories, when a person reduces the carbohydrates in his or her diet (and, correspondingly, increases protein or fat, or both), that person will find it much easier to reduce calorie intake and may even lose weight without cutting calories.

The controversy over these contradictions has been heated. Proponents of the low-fat diet claim that low-carbohydrate (low-carb) diets are ineffective and even dangerous, while low-carb proponents say much the same about the low-fat approach. However, an article published in the Journal of the American Medical Association suggests that neither side has a strong case. Researchers concluded, essentially, that a calorie is a calorie, regardless of whether it comes from a low-carb or a low-fat diet. They did not find any consistent evidence that the low-carb diet makes it easier to lose weight than the low-fat diet, but neither did they find any consistent evidence for the reverse. Furthermore, the authors of the review did not find any compelling reason to conclude that low-carb diets are unsafe, although they did point out that the long-term safety of such diets remains unknown.

Subsequent studies confirmed these findings for a variety of low-carb diets. In some studies, one particular diet method may do better than others, but in other studies a different diet will stand out. Researchers reviewing thirteen studies comparing low-carb with low-fat/low-calorie diets in overweight participants for a minimum of six months concluded that the low-carb diets tended to perform better at reducing weight and cardiovascular disease factors for up to one year. Nevertheless, a consensus has yet to emerge among nutrition scientists as to what diet performs better overall. Many of the foregoing studies suggest that if a diet causes weight loss, cholesterol will improve regardless of the diet used to achieve that weight loss. However, the manner of change in a person’s cholesterol profile differs between the two approaches. Low-fat diets tend to improve total and LDL (low-density lipoprotein, or bad) cholesterol levels, but they tend to worsen HDL (high-density lipoprotein, or good) cholesterol and triglyceride levels; low-carb, high-fat diets have the opposite effect.

The Mediterranean diet, which is relatively high in fiber and monounsaturated fats (such as olive oil) has also attracted the attention of nutrition researchers. There is good evidence that it is as effective as low-carb diets for weight reduction and probably more effective than low-fat diets. It also seems to have the added advantage of benefiting persons with diabetes more than the other two diets.

However, if a person undertakes a low-carb (or low-fat) diet that does not cause weight loss, that person’s cholesterol profile will probably not improve significantly. In addition, there is little to no evidence that the low-carb approach improves blood sugar control except insofar as it leads to weight loss. However, there is some evidence that a low-carb diet that is high in monounsaturated fats reduces blood pressure to a slightly greater extent than does a high-carb, low-fat diet. Contrary to claims by some low-carb proponents, low-fat, high-carb diets do not seem to backfire metabolically and promote weight gain.

Based on this information, it seems that the most sensible course to take to lose weight is to experiment with different diets and determine which one cuts the most calories (and keeps them cut). If the low-carb diet approach works, one should continue with it. However, if it does not help one lose weight, it should not be continued indefinitely. Additionally, most health experts suggest that dieting according to fads is ineffective, as any immediate weight loss is typically not sustained long term. Instead most recommend that following a balanced diet in combination with regular exercise and other healthy habits is the best way to manage weight and promote overall well-being.


Any form of extreme dieting can cause serious side effects or even death. All people who intend to adopt an unconventional diet should first seek medical advice. Furthermore, people with kidney failure should not use low-carb, high-protein diets, as high protein intake can easily overstress failing kidneys. (High-protein diets are probably not harmful for people with healthy kidneys.)

In addition, people who take the blood thinner warfarin (Coumadin) may need to have their blood coagulation tested after beginning a high-protein, low-carb diet. Two case reports suggest that such diets may decrease the effectiveness of warfarin, requiring a higher dose. Conversely, a person who is already on warfarin and a high-protein, low-carb diet and then goes off the diet, may need to reduce his or her warfarin dose.


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