The Family Health Guide

Low carb vs. low fat

If weight loss were a sprint, low-carb dieting would win, hands down. Four recent studies have shown that at the six-month mark, low-carb dieters lose, on average, about 9–13 more pounds than those on a low-fat plan. But two studies have now shown that for weight loss, the two diets end up in a statistical tie after a year. In the first one, published in 2003 in the New England Journal of Medicine (NEJM), low-carb dieters spurted ahead of their low-fat counterparts during the first six months, only to regain pounds in the next six. In the second study, published in early 2004 in the Annals of Internal Medicine, the low-carb group kept off the pounds lost during the first six months, but the low-fat group caught up with them by continuing to lose weight. In the weight-loss race, low carb seems to be the hare and low fat, the tortoise.

But it's more complicated than that familiar fable with its moral that "slow and steady wins the race." The numbers of pounds being lost are relatively modest. The people in the Annals study were heavy to begin with: The average starting weight was about 288 pounds. After a year, the low-carb group (including the dropouts) had lost an average of 11.2 pounds and the low-fat group, just 6.8 (the difference between them didn't meet the test for statistical significance). The people in the NEJM study weren't as heavy —they averaged about 215 pounds — but the results were pretty similar. However, heaviness is a lifelong issue for most people who are overweight or obese, and losing even just a few pounds may be a bigger victory than it seems.

One of the chief objections to low-carb dieting has been that it would ratchet up levels of "bad" LDL cholesterol by encouraging people to eat food with higher saturated fat content. But both yearlong studies found that low-carb and low-fat diets had the same effect on LDL levels. And low-carb diets outdid low-fat diets with respect to other blood fats related to heart disease. Triglyceride levels fell further and the HDL results were better. In the Annals study, the low-carb diet was better for blood sugar control for people with diabetes.

Averages can be good summaries, but behind them there can be a lot of variation. Dr. Samaha says someone in the low-fat group in his study lost 79 pounds — and that person was among the 34% who dropped out of the study. At the other extreme, another person gained 31 pounds sticking with the low-fat diet program. There was a huge range among the low-carb dieters, too: from 65 pounds lost to 18 pounds gained.First, low-carb dieting can't live up to the hype (what could?) but it has some merit. You can improve upon it by sticking with polyunsaturated and monounsaturated fats as your fats and whole grains as your carbs. Second, diets have differing effects on cholesterol levels and metabolic factors. If you're serious about losing weight, you should talk to your doctor about getting a cholesterol test. The results may help you choose the best diet for you. Third, for reasons of taste, upbringing, genetics, and other factors, the individual response to diets varies tremendously. Experiment. See what works for you. And by all means, get some exercise, too.

September 2004 Update

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