Research Update: Mediterranean Diet Vs Low Fat Diet For Weight Loss

A Randomized Controlled Trial Of A Moderate Fat, Low Energy Diet Compared With A Low Fat, Low Energy Diet For Weight Loss In Overweight Adults
McManus K, et al.
International Journal of Obesity 2001 25:1503-11.

Objective: To compare the efficacy of a low fat diet and a moderate fat diet for long term weight loss.

Study Population: 101 overweight men and women (BMI between 26.5 and 46).

Methods: Subjects were randomized to one of two weight loss interventions.  Both diets had a goal of 1200 calories per day for women and 1500 calories for men.  Both diets provided 15-20% of calories as protein.  The low fat diet provided 20% of calories as fat and 60-65% of calories from carbohydrate.  The moderate fat diet provided 35% fat and 45-50% carbohydrate.

Everything else about the interventions was identical, including physical activity recommendations, behavior modification advice, weekly nutrition counseling sessions and the recording of food to gauge compliance.  Measurements included body weight, BMI, waist and hip circumference, physical activity and nutrient intake.  These were taken at baseline, 6, 12 and 18 months.

Results: 1) After 18 months, the moderate fat group had lost 9.2 pounds, decreased their BMI by 1.6 points and decreased their waist circumference by 2.7 inches.        2) During this same period, the low fat group gained 6.4 pounds, increased their BMI by 1.4 points and increased their waist circumference by 1 inch.  3) After 18 months, only 20% of the low fat group was actively participating in the weight loss program while 54% of the moderate fat dieters were sticking with their plan.

Discussion: This is a beautifully designed study.  First of all, it was 18 months long so you can assess both weight loss and maintenance of lost weight.  All elements of the weight loss interventions were identical, including total calories, total protein, physical activity and the dietary counseling component.  The only difference between the two interventions is that one was low fat, high carb and the other was moderate fat, moderate carb.

The results are striking.  After 18 months, the moderate fat group was 15.6 pounds lighter than the low fat, high carb group.  It is also notable that only 20% of the low fat dieters were able to stick to their program long term, while over 50% of the moderate fat dieters were able to stick to their program.  This is the knock on low fat diets in general.  Early on, you can lose some weight with them, but it appears that most weight is regained fairly quickly.  It seems that people have a hard time sticking to the low fat plans.  This is most likely due to the increased hunger caused by the dramatic swings in blood sugar on these diets.

Take Home Message: Fat is not the enemy, people.  When chosen wisely with vegetable source of fat, a moderate fat diet (35% of calories) can help reduce the risk of heart disease and diabetes and even help you maintain your weight.  Losing weight is great, but keeping it off is better.  The research is beginning to mount that a moderate fat diet gives you a better chance of keeping your weight off than a low fat diet.