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Letters to the Editor |
University of Washington School of Medicine Division of Metabolism, Endocrinology, and Nutrition Box 356426 Seattle, WA 98195 E-mail: purnell{at}u.washington.edu
Dear Sir:
Willett's (1) recent editorial points out the need for long-term studies (
1 y) to determine whether diets low in fat promote weight loss. As an example of a low-fat dietary intervention trial that does not support the hypothesis that graded weight loss results from a reduction in dietary fat as proposed by Bray and Popkin (3), he also cites the study by Knopp et al (2). This study failed to show an association between increasing weight loss and a progressively lower percentage fat intake (range: 22–28%). However, we emphasize that all groups undergoing dietary fat restriction in this study lost significant amounts of weight compared with baseline (range: 2–3 kg). This observation supports the conclusion that dietary fat restriction promotes sustained weight loss.
Several other studies lasting 1 y showed modest, but significant, sustained weight loss. Bray and Popkin included data from studies by Sheppard et al (4) and Siggaard et al (5) in their analysis. In another study, 14 subjects who lowered their fat intake to 21% of total energy intake for 1 y decreased their body weight by an average of 6.9 kg (6). More recently, in a 1-y follow-up study that included a control cohort, dietary fat restriction resulted in a significant decrease (from baseline) in fat intake from 28.4% to 22.7% of energy and in body weight from 69.6 to 67.2 kg (7). In the control group, no change in either of these variables was found at follow-up.
Those studies that measured energy intake showed that weight loss was associated with a spontaneous sustained reduction in daily energy intake (2, 4, 7). The fact that changes in the macro-nutrient content of the diet (lowering fat and increasing carbohydrate intakes) led to reductions in energy intake and long-term weight loss offers potentially important insight into the physiology of weight regulation (8, 9).
Dietary fat intake is only one environmental factor that affects the genetic expression of obesity. Therefore, it is not unexpected that dietary fat restriction results in a variable amount of weight loss, depending on one's genetic background. Schaefer et al (10) showed that when the subjects in their study switched from a high-fat to an ad libitum low-fat diet, they experienced a wide range of weight changes, from a gain of 1.5 kg to a loss of 13 kg, with an average loss of 3.3 kg. The notion of a low dietary fat "responder" being someone who loses >5% of their initial body weight and "nonresponders" being those who lose no weight is similar to other diseases whose expression is the result of gene-environment interactions. For instance, salt restriction may reduce blood pressure in up to 30–50% of subjects with "salt-sensitive" hypertension. Another example is subjects with hypercholesterolemia who are typically described as "dietary responders" if cholesterol concentrations decrease with restriction of dietary cholesterol and fat and as "nonresponders" if concentrations do not change. The above-mentioned studies support the view that dietary fat restriction in combination with regular aerobic exercise is sound advice that caregivers can give to their obese patients for the attainment of modest weight loss.
REFERENCES
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  M. J. Franz, J. P. Bantle, C. A. Beebe, J. D. Brunzell, J.-L. Chiasson, A. Garg, L. A. Holzmeister, B. Hoogwerf, E. Mayer-Davis, A. D. Mooradian, et al. Evidence-Based Nutrition Principles and Recommendations for the Treatment and Prevention of Diabetes and Related Complications Diabetes Care, January 1, 2002; 25(1): 148 - 198. [Full Text] [PDF]
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