Low-fat diets, and diets that restrict one category of nutrients in general, do a poor job of reducing weight and keeping it off for a year or more, according to a new review of clinical trials conducted by researchers from Brigham and Women’s Hospital in Boston.
Evidence of the success of diets based on nutrient restriction, like low-fat and low-carb diets, has been mixed.
Over one year or more, low-carb diets yield a couple more pounds of weight loss on average, but that’s not meaningful for most people, the researchers said.
The reviewers included 53 randomized controlled trials comparing low-fat and higher-fat dietary interventions that collected weight change data for at least one year. The studies included a total of more than 68,000 people.
Low-carb diets tended to lead to about 1.15 kilograms, or 2.5 pounds, more weight loss than low-fat diets in 18 comparisons. Low-fat diets only won out in weight loss when compared to a group of people who were not dieting.
Low-fat diets were no more effective than other higher-fat diets. Low-fat and higher-fat diets also had similar effects in weight maintenance trials.
The research team restricted diets to prescriptions at least one year in duration.
People start diets and do relatively well when they first begin over a month or two, then slowly lose steam as they relapse back to the way they used to eat.
However, within any one study, some individuals were very successful while others did not lose any weight, or even gained weight, so the overall average weight loss was small.
Focusing on restricting certain nutrients over the long-term can be hard to maintain, which makes low-fat and low-carb diets less successful, the researchers said.
People should try to choose a diet they can stick to long-term rather than treating it like a short-term fix.
Source: The Lancet Diabetes and Endocrinology, online October 29, 2015.
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