The skinny on low-fat diets

Matt Ruscigno
Environmental Nutrition

Low-fat diets have been around for decades, with the hope of cutting weight, as well as disease risk. Most of the research on low-fat diets (less than 30 percent of calories from fat) has not been fruitful, though some studies indicate that very low-fat diets may be an option for heart disease treatment.

The low-fat diet era

In the late 1980s, a public health campaign pushed to reduce dietary fat, as it is the most calorically dense macronutrient and contains more than twice the calories per gram than carbohydrate or protein. Quickly, low-fat food products were developed, including some with more calories than the full-fat versions. A few decades later, a body of evidence shows that a low-fat diet does not help in weight loss or chronic disease risk reduction. For example, data from the Women’s Health Initiative, an eight-year trial including almost 49,000 women, found that a low-fat diet did not result in weight loss or protection against breast and colorectal cancer or cardiovascular disease.

Some fats are beneficial. Our bodies require a certain amount of essential fatty acids for normal body function, such as maintaining cell membranes and healthy skin and hair. Fat also is needed for the absorption of the fat-soluble vitamins, A, D, E and K, as well as some phytochemical compounds. The U.S. Dietary Guidelines recommend dietary fat levels should be no lower than 20 percent of calories to meet the body’s needs. But the type of fat may be more important than limiting fat. For example, monounsaturated fats found in nuts, seeds and olive oil, and polyunsaturated fats found in vegetable oils, are associated with improved lipid biomarkers. Fat also helps increase satiety and the palatability of foods.

Evidence on very low-fat diets

In the last 15 years, some research has pointed to benefits from a very low-fat diet, particularly among people with existing cardiac conditions. Dean Ornish, M.D., founder of the Preventive Medicine Research Institute, has published research showing that coronary artery disease could be halted and even reversed using a holistic approach, including a very low-fat (about 10 percent of total calories), mostly vegetarian diet, stress-reducing techniques and exercise.

Caldwell Esselstyn, M.D., a cardiac surgeon at the Cleveland Clinic, published a study that found very low-fat diets composed of whole plant foods and free of added oils, nuts, seeds and avocado (less than 10 percent of calories from fat) markedly reduced body weight and improved disease biomarkers (Journal of Family Practice, 2014). In his study, 198 cardiac patients, followed for an average of 3.7 years, were split into two groups where 177 adhered to the low-fat diet and 21 did not. The low-fat group had an average weight loss of 18.7 pounds and 22 percent showed full coronary artery disease reversal.

However, there are limitations in this research, including lack of a control group.

The bottom line

Moderate intake of healthy fats is part of an optimal eating plan, though intriguing research suggests that very low-fat diets comprised of mostly whole plant foods may offer benefits for those with existing heart disease.