Glycemic Index, Body Weight and Health

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.