How Much Fat Should You Eat?

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Meksawan K, Pendergast D, Leddy J, et al.: Effect of low and high fat diets on nutrient intakes and selected cardiovascular risk factors in sedentary men and women. J Am Coll Nutr 23:131-140, 2004.

What is the problem, and what is known about it so far?

Many doctors don't agree on the ideal amount of fat a person should eat.

Researchers know that fats and carbohydrates are important nutrients and provide the good cholesterol that rids the body of bad cholesterol. Fat also provides essential elements and energy for muscular work. Still, many diets recommend eating low amounts of fat to lose weight and improve heart health.

Researches wanted to find out how changing the amount of fat a person eats affects their nutrition and heart health.

Who was studied?

Participating in the study were 11 healthy volunteers (5 men and 6 women), who did not have high blood pressure, heart disease, diabetes, or other metabolic disorders and who did not take any medications.

How was the study done?

The standard recommended diet calls for 30% of a person's total daily calories to come from fat. The researchers looked at the effects of decreasing fat intake to 19% in one group and increasing fat to 50% of a person's diet in another group.

The participants filled out a health questionnaire and had a physical exam. They were randomly put into one of the two diets (19% fat or 50% fat). Each diet lasted 3 weeks.

Participants kept diaries of what they ate and drank and how much they exercised. At the beginning and the end of each diet, the participants gave blood samples and researchers noted their weight, heart rate, and oxygen consumption.

What did the researchers find?

The participants who followed the 19% fat diet ate significantly fewer calories than the other group and lost an average of 1.3 pounds during the study period.

Participants who followed the 50% fat diet ate more protein, which improved the participants' levels of essential fatty acids, vitamin E, and zinc.

Those on the 19% fat diet had lower HDL (“good”) cholesterol.

Interestingly, the participants on the 50% fat diet did not increase their body fat, heart rate, blood pressure, blood triglycerides (fat in the blood), and total cholesterol. However, both the good and bad cholesterol levels were highest in these dieters.

What were the limitations of the study?

The food diaries were self-reported and relied on the participants' memory of what they ate and drank. Self-reported diaries can be inaccurate.

Also, the number of participants was small. A similar study that includes more people may result in a different outcome.

What are the implications of the study?

A low-fat diet might not provide enough calories, essential fatty acids, and some nutrients (especially vitamin E and zinc) for a healthy person. It also lowers HDL cholesterol (“good” cholesterol, which rids the body of LDL “bad” cholesterol).

In addition, increasing how much fat a person eats and drinks (to as much as 50% of their daily calories) may improve nutrition and may not put them at a higher risk for heart and blood vessel disease as previously thought.

Eating and drinking less fat may not benefit the general population if they continue to eat a lot of calories. New dietary recommendations should include the concepts of good carbohydrates and fat versus bad carbohydrates and fat.