If you've tried a low-fat diet or a no-fat diet to optimize your health and perhaps lose a few pounds after the holidays, you're not alone. But an eating plan that treats fat as the enemy, cutting out everything from beef to dairy to avocados, might not live up to its promises—in part because our bodies need fats. We spoke with doctors and dietitians to get the skinny on low-fat diets. 

The Promise

Proponents say these plans can prevent or ease heart disease, lower cholesterol levels, control blood pressure—and help you lose weight and keep it off. 

The Truth

Without some dietary fat, you can become deficient in essential fatty acids and have trouble absorbing fat-soluble vitamins. And unsaturated fat actually helps protect your heart and reduce the risk of type 2 diabetes. A 2012 review of studies by the independent Cochrane Collaboration found that replacing saturated fat (found in animal products such as butter and ground beef) with unsaturated fat (found in fatty fish, avocados, nuts, and plant oils like olive oil) lowered the risk of heart attacks and strokes.

If weight loss is your goal, be aware that low- and no-fat foods aren’t always lower in calories. “Sometimes the reduced-fat or nonfat version of a product has added sugar and starch to boost the flavor and texture,” says Maxine Siegel, R.D., who heads Consumer Reports’ research on food and nutrition.

Go to Consumer Reports' 2016 Holiday Gift Guide for updates on deals, expert product reviews, insider tips on shopping, and much more. And be sure to check our Daily Gift Guide.

The Bottom Line

Stay away from no- or very-low-fat diets; they can ultimately be harmful. But if you’re like most Americans and have been consuming more than a third of your calories as fat, says David Seres, M.D., director of medical nutrition at the Columbia University Medical Center in New York and a member of Consumer Reports’ medical advisory board, reducing your overall intake and picking good-for-you fats is probably wise.

plant-based diet, which includes plenty of good fats, is healthy and associated with a decreased risk of disease. And if you're specifically looking to lose weight, here are 15 tips that actually work—no flavorless fat-free cookies required.

Editor's Note: A version of this article also appeared in the March 2015 issue of Consumer Reports magazine.