By the faculty of Harvard Medical School
Q: I’ve been on a low-fat diet for about a year now, and have
been slowly losing weight. Some of my friends recently started on
the Atkins diet and have been dropping pounds more quickly. Would I
be better off with low-carb dieting?
A: If weight loss were a sprint, low-carb dieting would win,
hands down.
By the faculty of Harvard Medical School
Q: I’ve been on a low-fat diet for about a year now, and have been slowly losing weight. Some of my friends recently started on the Atkins diet and have been dropping pounds more quickly. Would I be better off with low-carb dieting?
A: 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 an average of 9 to 13 more pounds than those on a low-fat plan.
No one is completely certain why, although one of the most likely explanations is that the low-carb approach is better at satisfying appetite for a time, making it easier to cut calories.
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.”
Heaviness is a lifelong issue for most people who are overweight or obese. A year of slimming down isn’t all that meaningful. Longer studies are needed.
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, 6.8 pounds. Percentage-wise, that’s a pretty small change, and the people remained at high risk for health problems from being overweight. The people in the NEJM study weren’t as heavy – they averaged about 215 pounds – but the results were pretty similar.
On the other hand, losing even a few pounds may be a bigger victory than it seems. People in these studies may have been gaining weight month after month and that trend was reversed, notes Dr. Frederick Samaha at the Philadelphia Veterans Affairs Medical Center and one of the authors of the study in the Annals.
Low-carb dieting should be called low-carb, high-fat dieting. Indeed, the original Atkins diet did not discourage people from eating red meat and dairy products which are rich in saturated fat, which raises blood levels of LDL (“bad”) cholesterol.
However, recent versions of the Atkins diet, as well as the South Beach diet, instead steer people toward healthier plant-based polyunsaturated and monounsaturated fats. It was reassuring that, in the recent studies, the 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 heart disease-related blood fats.
In the Annals study, the low-carb diet was better for blood sugar control for people with diabetes.
As with any study, calculating the result for the average person in the study can overlook the fact that some individuals had very different results from the average person.
For example, Samaha says someone in the low-fat group in his study lost 79 pounds – and that person was among the 34 percent 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.
So what do we know, scientifically, about low-carb diets? First, low-carb dieting can’t live up to the hype (what could?) but it has some merit: it seems better for short-term weight loss.
If you try the low-carb approach, make the fats in your diet polyunsaturated and monounsaturated fats, and make whole grains your main source of carbs.
Second, for reasons of taste, upbringing, genetics and other factors, the individual response to diets varies tremendously. Experiment. See what works for you. Talk with your doctor.
And by all means, get some exercise, too.
If you would like to e-mail questions to the Harvard Medical School Adviser, you can submit questions to the Harvard Medical School Adviser at www.health.harvard.edu/adviser.
