Moderate-Fat Diets for Weight Loss?

Summarized by Robert W. Griffith, MD
April 23, 2004

Introduction

Being overweight or obese is associated with an increased risk of major diseases, such as coronary artery disease and diabetes. If you're trying to lose weight you'll probably be recommended a diet that restricts your total intake of calories (an energy controlled diet) and be advised to take less than 25% - 30% of your calories as fat. At least, that was until the Atkins diet became popular, and questioned the whole concept of low-fat diets. A study recently reported in the American Journal of Clinical Nutrition has now examined whether a moderate-fat diet, rich in mono-unsaturated fatty acids, is better than a low-fat diet in reducing the risk of cardiovascular disease.

What was done

Overweight and obese healthy men and women were enrolled in the study, which was done at Pennsylvania State University. They had normal lipid profiles at the start of the study. They were selected, at random, to take one of two diets. The first (low-fat) was designed to contain about 20% of the energy from fat, by replacing saturated fat with carbohydrates. The second (moderate-fat) contained about 35% of its energy as fat, by replacing saturated fats by mono-unsaturated fats. The amounts of protein, cholesterol, and fiber were kept the same in both diets.

During the first 6 weeks of the study the total diets were restricted to produce a steady rate of weight loss - 2 lbs (0.9 kg) a week - and for the subsequent 4 weeks they were increased sufficiently to achieve weight maintenance.

Blood samples were taken for lipid analyses at baseline and at the end of the 10 weeks study period.

What was found

There were 53 people in the study - one third of them men. Half of them were overweight (BMI scores over 25 but below 30), and half were obese (BMI scores over 30).

The average weight loss during the first 6 weeks was the same in the two groups, an average of 2.6 lbs (1.2 kg) per week. Most of the subjects continued to lose some weight during the 4-week maintenance period.

Both diets were effective in lowering total and LDL cholesterol during the weight-loss period; LDL cholesterol - the 'bad' cholesterol - was reduced by 18% in the low-fat and by 14% in the moderate-fat group, respectively. However, there were differences between the groups with regard to other lipids measured.

There were no relevant changes in HDL cholesterol - the 'good' cholesterol - in the moderate-fat diet group. In the low-fat group, however, there was a significant reduction (12%).

Both groups showed a significant decease in triglycerides during the weight-loss period. In the weight-maintenance period, however, the low-fat group regained their original triglyceride levels.

What does this mean?

These results demonstrate that considerably lowering your fat intake may affect your blood lipid profile, so that you have a somewhat increased risk of cardiovascular disease - higher triglycerides, reduced HDL cholesterol. (This effect on HDL cholesterol has been shown before in earlier studies.) And in this study the HDL didn't increase again during the maintenance phase.

On the other hand, a moderate fat diet blunts the weight-loss decrease in HDL-cholesterol, and is associated with a greater fall in triglycerides than a low-fat diet. As the authors of the study put it: ". . .results indicate that a moderate-fat weight-loss diet decreases cardiovascular risk".

This is encouraging news for those people trying to lose weight who are flirting with Atkins, South Beach, and other dietary regimens that allow more fat than earlier diets. There is no doubt that a moderate amount of fat will improve adherence and minimize weight fluctuations; if mono-unsaturated fatty acids are included, such as peanuts and peanut butter, so much the better. However, the guiding light for weight loss and maintenance must be calorie control, as before.

Source

• Effects of moderate-fat (free from monounsaturated fat) and low-fat weight-loss diets on the serum lipid profile in overweight and obese men and women. CL. Pelkman, VK. Fishell, DH. Maddox,  et al., Am J Clin Nutr, 2004, vol. 79, pp. 204--212

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