Against a global backdrop of increasing levels of obesity1, it is important that public health messages to counter this serious problem really work. In a major collaborative venture, five European research centres recently carried out a study to test whether current advice to follow a low-fat diet actually reduced weight in a free-living situation.2
Current efforts to tackle obesity have focused on lowering the fat content of the diet. This is because high-fat diets are energy dense making it easier to overeat. However, there are some inconsistencies in the fat story and the importance of low-fat diets in the prevention and treatment of obesity has been questioned by some. Also, some clinical studies show that low-fat diets cause a drop in HDL (good) cholesterol and a rise in triacylglycerides, both of which are risk factors for heart disease, whereas other studies showed an improvement of the lipid profile.
In order to address these issues, and to provide a real life setting situation, the Carbohydrate Ratio Management in European National diets, or CARMEN trial was set up. Research Centres in The Netherlands, Denmark, the UK, Germany and Spain each recruited 80 overweight men and women for the study. A novel approach was used to make the study as realistic as possible but still allowing food intake to be properly monitored.
Each centre set up a small shop containing a selection of 100-150 foods of known nutritional composition. Food choices could be guided and recorded by using a barcode scanner but people were not restricted on how much they could eat. Foods not provided by the laboratory shop like bread, fresh fruit and vegetables and fresh meat were bought at conventional supermarkets and recorded at regular intervals.
During a five week adjustment period, every-one got used to the laboratory shop and were given foods providing a level of fat typical of each country. Subjects were then randomly assigned into 3 groups: a control group who continued on a normal fat diet; a low-fat, high sugar diet group, and a low-fat, high starch diet group. A total of 316 people completed the full six months on the diets.
People on the high sugar and high starch diets both successfully reduced their fat levels by 10% and 8% respectively. In both groups, the energy density of the diet dropped significantly.
The low-fat, high starch group reduced body weight by 1.8 kg and the low-fat, high sugar group by 0.9 kg while the control group gained 0.8 kg. Both groups achieved significant fat loss of 1.8 and 1.3 kg respectively. Interestingly changes in blood cholesterol and triacyglycerides did not differ significantly among the groups.
The CARMEN study demonstrated that when eating to appetite, and going about their normal lives, moderately overweight people were able to lose weight on a low-fat, high-starch or low-fat, high-sugar diet with no adverse affects on blood fat levels. The amount of weight lost was modest but in the context of a whole population this may relate to a significant reduction in the number of obese people who are at increased risk of disease. Prof. Saris from the Nutrition and Toxicology Research Institute Maastricht (NL) and CARMEN project co-ordinator, believes that the greatest impact of reducing dietary fat is likely to be on the prevention of weight gain rather than radical weight loss. Either way, current public health advice to reduce the level of fat in the diet is likely to help rather than hinder our attempts to keep in shape.
- World Health Organisation (1998) Obesity: preventing and managing the global epidemic. WHO; Geneva.
- Saris WHM Astrup A Prentice AM et al (2000) Randomised controlled trial of changes in dietary carbohydrate/fat ratio and simple vs complex carbohydrates on body weight and blood lipids: the CARMEN study. International Journal of Obesity.24; 1310-1318.