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

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If you’ve ever tried to lose weight, you’ve noticed the myriad of diet options out there: keto, paleo, WW (formerly Weight Watchers), the Mediterranean diet, and many more.

Is there a way to tell which one works the best? Public health officials have been asking this question for decades. The answer emerging from the most recent data is unexpected: They all work, and what works best for you depends on a variety of biological and lifestyle factors.

Take, for example, a recent systematic review by the Cochrane Collaboration, a consortium of researchers and experts spread around the globe. The group recently pooled the available evidence to ask which type of diet works the best, low-carb or low-fat?

The researchers categorized low-carb diets as meal plans that restrict grains, cereals, legumes, dairy, most fruit, and some vegetables. These diets replace those carbs with foods higher in fat and protein including meat, eggs, and cheese. Some low-carb diets suggest eating as much as you want and others restrict food intake. Popular examples are the keto and paleo diets.

Low-fat, or balanced-carbohydrate diets, include moderate amounts of all of the types of foods: carbohydrates, proteins, and fats. They often require eating healthier foods – such as olive oil instead of butter – and encourage weight loss through reduced calorie intake. Examples include the DASH diet or WW.

For the review, researchers found 61 trials with nearly 7,000 participants who were considered overweight or obese. The shortest trials – 37 of them – lasted for six months or less. There were six trials that followed participants for two years.

Combining all of that data, researchers found that the two types of diets performed about the same. In the shorter duration studies, people who followed a low-carb diets lost on average about 2 pounds more than those who followed the low-fat diets (this amount is not statistically significant); over the long term, there was even less difference. The two diets also resulted in little or no differences in health indicators like blood pressure, unhealthy cholesterol levels, and blood sugar levels.

But there is a kicker: Although both groups lost weight on the whole, weight loss varied greatly for individuals. The low-carb diets worked much better for some people and not at all for others; the same held true for the low-fat diets.

This is because diets are not one-size-fits-all, explained Martha Field, assistant professor in the Division of Nutritional Sciences at Cornell University. In fact, nutrition researchers are discovering that many factors – genetics, gut microbiome, medications, lifestyle, and more – contribute to how each individual responds to a specific diet.

“As nutrition science has evolved, moving toward a more individualized approach is something we all see as an important goal,” she said. “When you get into the details and the variability from person to person, that’s what precision nutrition aims to understand.”

The National Institutes of Health has launched a new research campaign called Nutrition for Precision Health that is investigating individual responses to diet.

In the meantime, Field said, researchers don’t know enough yet to identify which diets work best for which people. But there are some general recommendations that probably apply to everyone according to the most current evidence: eat plenty of fruits, vegetables, and fiber; drink enough water; and keep as active as possible.

The take-home message: There isn’t one diet that works best for losing weight. But with all of the options out there, it’s possible to find the one that works best for you.