Mainstream groups such as the American Heart Association and the American Dietetic Association 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 diet books take a very different approach. The Atkins diet, the Zone diet, Protein Power , and numerous other dietary approaches turn thumbs down on low-fat. Instead, these methods recommend cutting down on carbohydrates. According to proponents of these theories, when you reduce the carbohydrates in your diet (and, correspondingly, increase protein and/or fat), you will find it much easier to reduce your calorie intake, and you 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 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-carbohydrate or a low-fat diet. 1 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 JAMA 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. 4-9,11-15,18,20-21,29 In some studies, one particular diet method may do better than others. But, in other studies, a different diet stands out.

For example, researchers reviewing 13 studies comparing low-carb against low-fat/low-calorie diets in overweight subjects for at least 6 months concluded that the low-carb diets tended to perform better at reducing weight and cardiovascular disease factors for up to 1 year. 31 But, in a subsequent trial involving 144 obese subjects with diabetes, researchers found that a low-carb diet did not result in greater weight loss when compared to a low-fat diet over a 2-year period, nor did it perform any better at improving blood cholesterol or glucose levels. 32

As research continues, a consensus has yet to emerge among nutrition scientists as to which diet performs better overall. Many of the studies cited above 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 cholesterol profile differs between the two approaches. Low-fat diets tend to improve total and LDL cholesterol levels, but worsen HDL and triglyceride levels, while low-carb, high fat diets have the opposite effect. 22

The Mediterranean diet, which is relatively high in fiber and monounsaturated fats (eg, 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. 30 It also seems to have the added advantage of benefiting diabetic patients more than the other two diets.

However, if one undertakes a low-carb (or low-fat) diet that does not cause weight loss, 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 a bit of evidence that a low-carb, high-monounsaturated fat diet reduces blood pressure to a slightly greater extent than a high-carb, low-fat diet. 19 Contrary to claims by some low-carb proponents, low-fat, high-carb diets do not seem to metabolically backfire and promote weight gain. 16

Therefore, based on the current state of information, it seems that the most sensible course is as follows: If you need to lose weight, experiment with different diets, and see which one allows you to most easily cut calories (and keep them cut). If the low-carb diet approach works for you, stick with it. However, if it does not help you lose weight, you probably should not continue it indefinitely.

Note : Any form of extreme dieting can cause serious side effects or even death. We strongly recommend that 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. 2,3 )

In addition, people who take the blood thinner warfarin (Coumadin) may need to have their blood coagulation tested after beginning a high-protein, low-carbohydrate diet. Two case reports suggest that such diets may decrease the effectiveness of warfarin, requiring a higher dose. 10 Conversely, if you are already on warfarin and a high-protein, low-carbohydrate diet and go off the diet, you may need to reduce your warfarin dose.

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