The purpose of this study is to investigate the effect of a diet with either high or low glycemic index (GI) on ad libitum (free) food intake, body weight, fat mass and fat-free mass, risk markers for diabetes and cardiovascular diseases, energy expenditure and substrate oxidation after 10 weeks´ intake in slightly overweight subjects.

Experimental design Two matched groups are given high-GI or low-GI foods to their own diet throughout 10 weeks in a parallel design. A number of measurements are done before, during and at the end of the 10 weeks' intervention.

Subjects A total of 50 slightly overweight (body mass index, BMI = 25-30 kg/m2) women, 20-40 years of age participate. Subjects are randomized according to body weight, composition, age, sex and physical activity level into two matched groups.

A representative subgroup of 15 subjects is randomized from each diet group (a total of 30 subjects) for measurements of energy expenditure and substrate oxidation by ventilated hood as well as postprandial blood sampling.

Experimental diets Subjects eat their own diet until the intervention starts and perform a 7-day weighed dietary record for determination of habitual food intake. At the beginning and every 2 weeks during the 10 weeks' intervention all subjects are instructed in consuming a low-fat (<30 E%), high-carbohydrate diet (>55 E%) by a dietician. Subjects are each week given an amount of carbohydrate-rich foods with either high or low GI with instructions to consume a minimum amount of these every day. We aim at controlling about 75% of the subjects' total carbohydrate intake. The exact amount of test foods eaten is noted every day by the subjects by use of a diary and a diet scale. Instructions in food intake and cooking recipes are given by the dietician. A positive list and a negative list of food items is provided for each study group.

Besides the fixed minimum amount of experimental foods subjects can eat at liberty. Another 7-d dietary record is performed at week 5 and week 10 to register ad libitum food intake. To further validate the dietary records 24-h urine samples are taken during the registrations. Lithium will also be added to the experimental foods in week 4-5 to follow compliance during the study.

Measurements

All subjects:

Week 0, 2, 4, 6, 8, 10 we measured body weight,fat mass and fat-free mass using bio-electrical impedance.In week 0 and 10 we measured body composition by DEXA-scan, W/H-ratio and sagittal height. Blood samples fasting in week 0 and 10 (Glucose, insulin, triacylglycerol (TAG), non-esterified fatty acids (NEFA), leptin, T-cholesterol, LDL-chol, HDL-chol, fructosamine, glycated hemoglobin, GIP, GLP-1, GLP-2, ghrelin, factor VIIc, factor VIIb, PAI-1, Apo A IV.). Blood pressure in week 0 and 10 (fasting systolic and diastolic BP and heart rate). 24-h urine sample is collected in week 0, 5 and 10. Feces is collected in the subgroup in week 0 and 10.

Subgroup:

Week 10: Ventilated hood for measurement of fasting and 4-h postprandial energy expenditure and substrate oxidation. Postprandial appetite scores for hunger, satiety, fullness, prospective consumption, desire for something sweet, fatty. Postprandial blood samples for 4 hours after breakfast (30, 60, 90, 120, 180, 240 min): Glucose, insulin, NEFA, TAG, leptin, glucagon, GIP, GLP-1, GLP-2, ghrelin, paracetamol. At 240 min: factor VIIbt, PAI-1, Apo A IV.

Inclusion Criteria:

• healthy, slightly overweight (body mass index, BMI = 25-30 kg/m2) women, premenopausal, non-alcoholic (< 14 units alcohol/w)

Exclusion Criteria:

• smoking, elite athletes, food allergies, pregnant, lactating, on medication, blood donation 3 months before, during and 3 months after the completion of the study