Obesity, the metabolic syndrome, pre-diabetes and type 2 diabetes are important risk factors for the development of coronary artery disease and stroke. Excessive body fat, together with inactivity, can account for almost 90% of all new cases of type 2 diabetes, and these are the most important potentially modifiable risk factors. It is well established that the dietary risk factors for weight gain are large portion sizes, sugar-rich soft drinks, high intakes of energy-dense foods poor in fibre and whole grain, and low intakes of fruit and vegetables, but many popular books advocate carb restriction and increased intake of fat and protein, and claim this approach to be more effective for weight control than the low-fat concept. However, insufficient carbohydrate intake may impair physical and mental performance and little is known as to whether slight changes in protein to carbohydrate ratio (with a fixed normal fat content) under ad libitum conditions (i.e. with no “calorie counting”) can control body weight.

In the large-scale pan-European, randomised, controlled, dietary intervention Diet, Obesity and Genes study (DiOGenes) we enrolled families with at least one obese adult. Adults followed an initial 8-week 800 kcal/d weight-loss program, and were then randomised to one of five ad libitum diets (6-months intervention period) contingent upon a weight loss of ≥8%. The diets were Low Protein (LP)/Low Glycemic Index (LGI), LP/High GI(HGI), High Protein(HP)/LGI, HP/HGI or Control. A total of 780 adults were randomised to the diets and 559 adults completed the intervention period. Mean weight loss at the end of the 8 week intervention was 11 kg, and blood lipids, CRP and blood pressure improved substantially. During the subsequent 6 month weight maintenance period the HGI, LP and control diet groups gained most weight, whereas the HP and LGI groups did better, but only the HP/LGI group maintained the weight loss without regain. The diets had no major effects on cardiovascular risk factors  other than CRP blood levels, which further decreased by ~30 % in both LGI groups. The HP/LGI diet produced a reduction in body fatness in the ~800 children, and a 14% spontaneous reduction in prevalence of overweight and obesity. One-year results will be presented. The on-going PREVIEW European multicentre trial will assess the efficacy of the DiOGenes diet combined with exercise in preventing of type 2 diabetes.