In a multicentre randomized controlled trial, Carbohydrate Ratio Management in European National diets (CARMEN), we assessed the long-term effects of the dietary carbohydrate / fat ratio and simple versus complex carbohydrate changes on body weight and blood lipids in 398 overweight-to-obese subjects (BMI 26-35 kg/m2). After a run-in period of 5 weeks, in which subjects consumed a control diet according to the national intake figures, they were randomly allocated to three groups. During a 6 months intervention period subjects consumed the same control diet as in the run-in period (CD-group), a diet with a low-fat and high simple carbohydrate content (SCHO-group), or a diet with a low-fat and high complex carbohydrate content (CCHO-group). The diets were supplied by a validated laboratory shop system.
During the run-in period average intake of fat and carbohydrate was 35.7 and 47.1 energy percentage respectively (SCHO and CCHO intake: 22.3 and 24.3 energy percentage). In the intervention period fat and carbohydrate intake changed significantly (p<0.001) in the SCHO- and CCHO-groups (fat: -10.2 and -7.9 energy percentage respectively; carbohydrate +8.4 and +4.7 energy percentage respectively) compared to the CD-group. The SCHO / CCHO ratio changed by means of an increased SCHO intake (+7.2 energy percentage; p<0.001) in the SCHO-group and an increased CCHO intake (+8.3 energy percentage; p<0.001) as well as a decreased SCHO intake (-3.5 energy percentage; p<0.01) in the CCHO-group, compared to the CD-group. As a result of these dietary changes, body weight and fat mass were reduced with 0.9 and 1.3 kg respectively (p<0.05) in the SCHO-group and with 1.8 and 1.8 kg respectively (p<0.001) in the CCHO-group, compared to the CD-group. Changes in the blood lipid values as well as glucose, insulin and leptin did not differ significantly between the groups.
In the debate about the importance of low-fat diets in the prevention and treatment of obesity in the CARMEN trial adds valuable information to the large body of evidence that ad libitum reduction of dietary fat leads to a modest but significant reduction of body weight and especially body fat which has an important public health impact. The concomitant increase in either simple or complex carbohydrates did not reveal significant differences between both experimental groups. This leaves the observed increase of simple carbohydrates with low-fat diets less of a concern.
