点击显示 收起
Department of Medicine
Oregon Health and Science University
Mailcode L465
3181 SW Sam Jackson Park Road
Portland, OR 97239-3098
E-mail: connorw{at}ohsu.edu
Dear Sir:
We thank McCarthy for his comments regarding our study "Effects of a low-fat diet compared with those of a high–monounsaturated fat diet on body weight, plasma lipids and lipoproteins, and glycemic control in type 2 diabetes" (1). We agree that the results from the studies of Barnard et al (2, 3) are consistent with our findings. In those studies, the amount of dietary fat was limited to 10% of total energy, and the amount of carbohydrate was very high—75% of energy. In our study, dietary fat was restricted to 20% of total energy, and carbohydrate provided 65% of energy. This contrasted with the high–monounsaturated fat group of our study, who consumed 40% of energy as fat. There are at least 2 important effects of a high dietary fat consumption: one direct and one indirect. Unlike carbohydrate, except for fructose, dietary fat does not induce satiety; thus, the hormonal cues to stop eating are not operative (4). In our study, the diabetic subjects on the low-fat diet consumed 212 kcal less energy than they did on the high–monounsaturated fat diet. They then lost 1.53 kg of weight from the low-fat diet because of this energy deficit. Second, if less dietary fat is consumed, carbohydrate-containing foods rich in fiber and water can be increased. High-carbohydrate diets do induce satiety (4). The high-fiber content of the high-carbohydrate diet promotes weight loss and better lipid and diabetic control (5). All of these factors, we believe, led to more weight loss from the low-fat diet (20% of energy as fat and 65% as carbohydrate) than from the high–monounsaturated fat diet in the diabetic patients in our study. Contrary to the recommendations of the American Diabetes Association (6), we suggest that the amount of fat in the diabetic diet should be low and not flexible even if the source of fat is monounsaturated. Weight loss, the major goal in the treatment of type 2 diabetes, would be much more likely to occur if the diet is low in fat and high in complex carbohydrate and fiber, as in our study. Noteworthy was that the ad libitum low-fat, high-carbohydrate diet in our study was not associated with an increase in plasma triacylglycerol concentrations or with any impairment of diabetic control.
In view of the current interest in low-carbohydrate diets (eg, the Atkins diet), which are extremely high in fat (66% of energy), the long-term effects may not be salutary, given the lack of effect of fat on the satiety centers in the brain. What needs to be considered are the long-term effects of any dietary change.
Low-fat, high-carbohydrate, high-fiber diets may be useful not only in the treatment of but also in the prevention of type 2 diabetes mellitus. In 2 large prospective studies, the Finnish Diabetes Prevention Study (7) and the US Diabetes Prevention Program (8), persons with impaired glucose tolerance or elevated fasting plasma glucose concentrations but without frank diabetes, who received counseling to decrease dietary fat and increase fiber intake and physical activity, lost more weight and had a 58% decreased progression to diabetes compared with control subjects. From an epidemiologic viewpoint, human populations consuming diets low in fat and high in fiber and complex carbohydrates have low rates of type 2 diabetes and obesity. This suggests that such diets may protect against the development of diabetes. Other lifestyle factors, such as increased physical activity, may also be operative in these populations.
An important question is whether the results of short-term dietary studies such as our own have long-term applicability. Critical issues include whether low-fat, high-fiber diets can be adhered to long-term and whether or not weight loss would continue beyond the relatively brief intervention periods studied. Extrapolation from unpublished data from our study suggests that had the study been continued for longer than 6 wk, subjects on the low-fat diet may have continued to lose weight, while subjects on the high–monounsaturated fat diet would have stabilized. Astrup et al (9), in a meta-analysis of 16 intervention trials of 2-12 mo duration in nondiabetic subjects, showed that ad libitum consumption of a low-fat diet resulted in weight loss (3.2 kg more than in the control group) and decreased energy intake compared with control groups. The National Weight Control Registry has compiled a national roster of persons who had lost an average of 30 kg for an average of 5.5 y. Persons who successfully maintain weight loss long term share several common behavioral characteristics, including the consumption of a low-fat diet and a high level of regular physical activity (10).
In conclusion, the available evidence suggests that low-fat, high-fiber, high-complex-carbohydrate diets can be adhered to over the long term and will result in a modest, but significant, weight loss in healthy and diabetic persons. The results from our study and others suggest that such diets may be useful in the treatment and the prevention of type 2 diabetes, obesity, and the metabolic syndrome.
ACKNOWLEDGMENTS
The authors had no financial or personal interest in any company or organization connected in any way with the research represented in this article, including serving as an expert witness or public advocate, grantee, shareholder, option holder, advisor, consultant, employee, or officer.
REFERENCES