Low-fat diets came into popularity in the 1970s and 1980s on the idea that fat would make you fat and cause heart disease. Consumer books like the Scarsdale Diet and Pritikin Diet fanned the fuels of the fire and eventually thousands of individuals were seeking to reduce the amount of fat they ate as a way to improve health. By the 1990s, the federal government had signed-on and based the updated Food Pyramid on low-fat, high starch dietary principles.

The Dietary Guidelines for Americans generally recommend that 20 to 35 percent of daily calories come from fat. While the technical definition of a low-fat diet is debated, most resources state that below 30 percent of total calories is the upper end of the range.  The Therapeutic Lifestyle Change (TLC) diet supported by the American Heart Association is around 22 percent fat, and – on the more extreme end – the Ornish diet recommends less than 10 percent.

The basic theory of the low-fat diet is that fat at nine calories per gram has a lot more calories than carbohydrates or protein (which both have four).  Also, reducing dietary fat will tend to reduce intake of trans fats, saturated fats and dietary cholesterol that may have independent health risks. Because dietary fats and protein are often found together in foods (think steak, cheese, whole eggs, etc…), low-fat diets are also usually relatively high in carbohydrate and lower in protein than other diets. Many very low-fat diets are very close to strict vegetarian diets for this reason.

Despite the recent craze for high protein, carbohydrate restricted diets, there is research to support low-fat diets, which is partly why the debate rages on.  In studies that have looked at low-fat diets versus low carb diets, both tend to produce weight-loss, though (at least in the short term) low carb diets may produce more (1).  It is worth nothing that the largest study of a low-fat diet for weight-loss (The Women’s Health Initiative Dietary Modification Trial – which looked at 19,500 women for eight years) did not show any benefits for heart disease, cancer, or weight as compared to an unrestricted diet. However, while the goal for the trial was for women to eat 20 percent of calories from fat, the participants actually only reach 29 percent. Thus it is possible that what we mostly learned from this study is that the goal of 20 percent calories from fat is hard to achieve.

The basic risks of this kind of eating come from people including too many calories from simple carbohydrates (sugars and other empty calorie foods) and missing out of getting enough good or essential fats and fat-soluble vitamins. Fat-restricted diets have clear medical benefits for those with a medical condition that impairs fat digestion. This can include gallbladder disease, chronic pancreatitis or malabsorption.

In Health,

Dr. Jacques

About the Author
Dr. Jacques, a frequent author in the OAC’s quarterly publication, Your Weight Matters Magazine, is a Naturopathic Doctor with more than a decade of expertise in medical nutrition. Her greatest love is empowering patients to better their own health. Dr. Jacques is a member of the OAC National Board of Directors. 

1) William S. Yancy, Jr., Maren K. Olsen, John R. Guyton, Ronna P. Bakst, Eric C. Westman; A Low-Carbohydrate, Ketogenic Diet versus a Low-Fat Diet To Treat Obesity and HyperlipidemiaA Randomized, Controlled Trial. Annals of Internal Medicine. 2004 May;140(10):769-777.

2) Howard BV, Manson JE, Stefanick ML, et al. Low-fat dietary pattern and weight change over 7 years: the Women’s Health Initiative Dietary Modification Trial. JAMA. 2006; 295:39-49.