Which Diet Is Better, Low-Carb or Low-Fat?

It’s confusing. If you’re going to diet should you try a low-carb or low-fat diet? Or maybe you should eat like a caveman (Paleo diet) or an Italian (Mediterranean diet). Should you avoid sugar, cut out gluten, or perhaps go vegan? Several years ago a Kansas State University professor went on a junk food diet. He lost 27 pounds in 10 weeks eating Oreos, Doritos, Twinkies, etc. while limiting his daily intake to 1,800 calories but you probably shouldn’t try to replicate his diet.

Despite the plethora of diets much of the recent theorizing has focused on carbohydrates. It’s suggested that carbs are more likely to result in overweight because of the effect they have on insulin secretion. Popular diet books such as The Obesity Code, Always Hungry, and others advocate reducing carbohydrate consumption to promote weight loss.

A recent Harvard study found that lowering carbs resulted in increased energy expenditure during weight-loss maintenance. As is frequently the case, this type of study is subject to criticisms of the research methods used. In the real world, it’s difficult for researchers to control for genetics and accurately measure what people eat and the amount of physical activity they get.

In a new study, researchers in Lithuania used mice to compare low-carbohydrate to low-fat diets. The mice were inbred minimizing the effects of genetics. The food intake, activity level, and physical environment of the mice could be carefully controlled in the laboratory. For 18 weeks the mice ate as much as they wanted and gained weight. Then they went on a six-week “diet,” either low-fat or low-carb. The diets had equal caloric value and protein content; they only differed in their fat or carbohydrate content.

Both low-fat and low-carb diets resulted in similar weight losses. This was 30 percent better than control mice who had consumed a regular chow diet. For both diet groups weight loss was due to loss of fat. Glucose tolerance improved with both diets compared with the control mice and energy expenditure did not differ between the diet groups.

While human’s eating is more complicated, this study has the advantage of just isolating low-carbohydrate vs. low-fat dieting. All the other possible influences on weight loss were controlled so the findings indicate that it’s caloric restriction rather than the macronutrient composition of the diet that’s responsible for the loss.

The practical implication of this study is ignore the controversies about the optimal diet for weight loss. If you’re trying to lose weight, pick a reduced-calorie plan, Mediterranean, Paleo, South Beach, Ornish, etc. Some are healthier than others, but for weight loss, find one that you can live with. Just plan on maintaining it over the long-term.