Why low-fat diets don't work

Is a Low-Carb Diet Better Than a Low-Fat Diet?
Is a Low-Carb Diet Better Than a Low-Fat Diet?

You don't have to eat egg-white omelets and cardboard-esque low-fat chips to slim down. And, what's more, you shouldn't. Why? It turns out that following a low-fat diet isn't an effective way to try to lose weight over the long-term.

That's the word from a new meta-analysis published in The Lancet Diabetes & Endocrinology. For the review, researchers from Brigham and Women's Hospital and the Harvard T.H. Chan School of Public Health in Boston combed through 53 randomized control trials comparing the weight-loss outcomes of 68,128 participants who had followed a low-fat or higher-fat diet. The results: Low-fat diets were actually less effective than higher-fat eating strategies at helping people lose weight and keep it off for a year or more.

"As a nation, we've been following low-fat advice for years, but as a nation we are also becoming more and more obese," explains lead study author Deirdre Tobias, a researcher in the division of preventive medicine at BWH. "It's clear that the low-fat approach isn't working."

But if too much fat on our frames is the problem, why isn't eating less fat the solution? "Largely, because a food's fat content doesn't do a lot to determine if it's actually healthy or not," Tobias explains. For instance, high-fat foods like avocados, eggs, olive oil and cheese can be part of a healthy diet. But low- and fat-free foods like "diet" ice cream and gummy worms probably aren't doing anyone's waistline any favors.

Unfortunately, when many people try to follow a low-fat diet, they eliminate those high-fat healthy foods and fill up on low-fat processed foods, rather than whole foods like fruits, veggies and lean meats, which just happen to be low in fat, she says. And many low-fat processed foods, even if they contain less saturated or trans fat, often pack more sugar than their full-fat counterparts. (No, fat-free cookies aren't necessarily any healthier than fatty ones.) It's consumption of that added sugar that most health experts are now implicating in our nation's growing waistlines.

"When you eliminate one food group or macronutrient like fat from your diet, it's very easy to overdo it on another food group, primarily carbohydrates," explains Holly Herrington, a registered dietitian in the Center for Lifestyle Medicine at Northwestern Medicine in Chicago. "And people don't tend to overeat healthy carbs like whole grains, beans and fruits. They overeat refined carbohydrates like candy, white pasta and white bread, which are linked with weight gain." According to data from the National Health and Nutrition Examination Survey, Americans eat about 20 teaspoons of sugar every day.

What's more, eating some fat, especially unsaturated fat from plant foods, can actually benefit your weight-loss efforts – and your health. "Fat in itself is a major source of energy," Herrington says. Without it, your body's metabolic functions would falter. You would feel fatigued and simply not have the energy to work out. Cravings would be inevitable. Plus, since many nutrients including vitamins A, D, E, and K are fat-soluble, meaning that the body can't absorb them unless you also consume dietary fat, cutting fat from your diet could also deprive your body of other vital nutrients.

What's more, fat is incredibly satiating, which is especially important for those trying to lose weight. "Since fat takes a long time to break down in the stomach, it can help people feel fuller for longer after their meals to prevent overeating. That's why, when we look at people who follow low-fat diets, they often feel they are more hungry than people who do incorporate a moderate amount of fat into each meal," Herrington says.

But that doesn't mean you should eat all of the fat your taste buds desire, either. After all, every gram of fat contains 9 calories, 5 more than a gram of carbohydrates or protein. So, if you don't watch your portion sizes, it can be easy to over-consume calories when filling up on fat, Tobias says. And no matter how healthy unsaturated fat can be – and saturated fat when from whole foods – it's still important to limit intake of trans fats, often lurking in processed foods as partially hydrogenated oils.

The bottom line: Healthy foods are healthy, and unhealthy foods are unhealthy – no matter how much fat they do or don't have in them.

"The focus on eating low-anything isn't particularly effective. Instead of trying to find a new ratio or exact percentage of fat or carbs or protein you need, just focus on whole, healthy foods." Tobias says. "Ask yourself, 'What foods should I be eating?' That would be a far more effective strategy for losing weight over the long-term."

Copyright 2015 U.S. News & World Report

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