Summary

A comparison between low-fat and ordinary diet has been carried out for the Women's Health Initiative. This shows that those on the low fat diet lost a modest amount of weight. Overall, however, there were no differences in diabetes risk between the two groups, save for a trend towards reduced diabetes risk among those whose fat intake and weight loss were greater.

Introduction

Among women, the prevalence of diabetes can be expected to rise sharply with each decade of age after the menopause. And we know that women aged 50 or more who have diabetes will live fewer years than those without the disease. They are also more likely to develop heart disease. Previous work has shown that increased physical activity and low-fat diet can help ward off diabetes among those who have glucose intolerance. It has not been clear whether the reduced risk is because of low fat intake in itself or because of any accompanying weight loss or increase in exercise. Accordingly, the Women's Health Initiative Dietary Modification Trial was set up to investigate the effect of a low-fat diet applied without any weight loss goals or any increase in physical activity.

What was done

Researchers at the Fred Hutchison Cancer Research Center, Seattle, studied a group of 48,835 post-menopausal women. From 1993 to 2005, 29,294 of the women continued with their usual diet, while 19.541 were assigned to a low fat diet. In the latter, 20 % of calories came from fat and the women ate increased levels of fruits, vegetables and whole grains. Information was collected on weight and any diagnoses of diabetes resulting in treatment.

What was found

Over the course of this study, new cases of treated diabetes were reported by 7.1 % of those in the low-fat diet group and by 7.4 % of those in the comparison group. Those who did have diabetes were older, heavier, less physically active and had higher blood pressure than those who did not have diabetes. But, overall, there was no difference in diabetes risk between the two groups. Further analysis suggested that the less the proportion of energy from fat, the less the risk of diabetes. But this link disappeared once the researchers accounted for the impact of any accompanying weight loss.

What this study means

This study was designed to assess the impact of changing dietary composition on diabetes risk and weight loss was not its goal. Inevitably, though, the women in the low-fat group did lose a small amount of weight (around 2.2 kilograms) and the researchers found that it was this, rather than the low-fat approach in itself, which accounted for the reduced diabetes risk. Nor did increased fruit and vegetable intake appear to reduce the diabetes risk, in itself. The message is that it is keeping to a healthy weight - however you do it - is the important thing in avoiding diabetes.