by Marion Nestle
Sep 4 2014

The diet wars: same old, same old

To my great surprise, a new clinical trial finding that low-carbohydrate diets help people lose weight has been getting a lot of press. Its conclusion:

The low-carbohydrate diet was more effective for weight loss and cardiovascular risk factor reduction than the low-fat diet. Restricting carbohydrate may be an option for persons seeking to lose weight and reduce cardiovascular risk factors.

This is news?

The trial, conducted by authors who previously published a meta-analysis that came to the same conclusion, told people to eat either a low-carbohydrate diet of less than 40 grams a day (the amount of sugar in one 12-ounce soda) or a “low-fat” diet of 30% of calories from fat or less.

They didn’t do either, of course (for one critic’s analysis, see examine.com).

I put quotes around “low-fat” because 30% of calories is not exactly what I would call low—lower, for sure, but not low. After a year, the low-carb dieters lost about 3.5 kg more than did the “low-fat” dieters.  They also showed greater improvements in their risk factors for cardiovascular disease.

As I told Andy Bellatti

The folks eating the low carbohydrate diet…were eating less, and probably a lot less.  It’s easier for some people to lose weight if they cut out whole categories of food, in this case, carbohydrates.  But is this a long-term solution?  For that, we need to see results for several years.   Studies that examine the effects of different kinds of diets—and there have been many—typically find that all work to the extent that they cut calories, but that people have trouble sticking to extreme diets, which the low-carb one was in this study.  Personally, I like carbs and would rather cut my calories some other way, but that’s just me.  The bottom line: if you want to lose weight and are having trouble doing it, you need to eat less.

This profoundly boring conclusion, discussed at length in my book with Malden Nesheim, Why Calories Count: From Science to Politics, has just been confirmed by yet another meta-analysis.  This one doesn’t seem to be getting much press, however.

It reports significant weight loss with any low-carbohydrate or low-fat diet.

Weight loss differences between individual named diets were small. This supports the practice of recommending any diet that a patient will adhere to in order to lose weight.

An accompanying editoria,  “A Diet by Any Other Name Is Still About Energy,” points out that study investigators only rarely analyze for how well participants in these studies actually adhere to the different diets, and for how long.

This makes it impossible for readers to figure out whether the weight loss was due to the specific components excluded from the diet or to the level of adherence.

In other words, whatever helps you eat less, helps you lose weight.  Go for it.