The PREVIEW study has the main objective of finding an effective means of prevention of obesity and type 2 diabetes (T2D) over the entire lifespan of an individual¹. This large investigation is based on the premise that the likelihood of not getting diabetes has been associated with exercise, modest weight loss and Nordic nutritional recommendations, since diets that have a low glycaemic index and high protein intake seem to be associated with greater weight loss than other types of diets.

• PREVIEW is investigating if a diet that is high in protein with a low glycaemic index, in combination with moderate or high intensity physical activity, can reduce the incidence of T2D in children, adults and the elderly who are overweight with prediabetes compared with current recommendations of less protein and a moderate glycaemic index.

Type of study, patients, and inclusion criteria

• PREVIEW is a 3-year, randomised, controlled multicentre trial including up to 2,500 participants, testing the hypothesis that a high protein, low glycaemic index diet will be superior to the recommended diet for weight maintenance and prevention of T2D.
• PREVIEW randomised subjects to one of four intervention groups:
  • High protein (25% energy), moderate carbohydrate (<50% energy), low glycaemic index (<50) diet with high intensity physical activity (75 min/week);
  • High protein (25% energy), moderate carbohydrate (<50% energy), low glycaemic index (<50) diet with moderate intensity physical activity (150 min/week);
  • Moderate protein (15% energy), moderate carbohydrate (55% energy), medium glycaemic index (>56) diet with high intensity physical activity (75 min/week);
  • Moderate protein (15% energy), moderate carbohydrate (55% energy), medium glycaemic index (>56) diet with moderate intensity physical activity (150 min/week).
• Subjects were followed for 36 months.

Patient population

Adults

• 5,472 adults were screened.
• 2,326 adults were eligible.
• Two-thirds were women.
• Mean age 52 years.
• Mean BMI 35.4 kg/m².
• During the lead-in period of two months, patients were prescribed a low calorie diet, during which a mean weight loss of 10.7 kg was achieved.
• 79% of all eligible subjects achieved  ≥8% weight loss on a low calorie diet.

Children

• 139 children (10-18 years) randomised.
• Explorative study.

Primary endpoint

• Adults: incidence of T2D over 3 year.
• Children: HOMA-ID at 2 years.

Secondary endpoints

• Anthropometry, laboratory parameters, urine, faeces, physical activity, sleep, stress, behavioural questionnaires.

Primary endpoint

• There were no significant differences in developing T2D between the two types of dietary intervention groups (high-protein vs. low-protein).
• The probability of not developing diabetes was 96%.
• There were no significant differences in developing T2D among all 4 intervention groups.
• The cumulative incidence rate of developing T2D was 4%.
• 22% of subjects completing the study did not have pre-diabetes by the end of the 3-year intervention.

Secondary endpoint

During the course of the study:

• There were no significant differences between the four groups in body weight.
• There were no significant differences between the four groups in fasting glucose, insulin levels, 2-hour glucose or HbA_1c levels.
• There were no significant differences between the four groups in HOMA-IR.
• Measured by protein intake from 24-hour urine, good compliance with the diet in the different groups seemed to emerge.

• There were fewer T2D cases than expected after 3 years of intervention: only 62 subjects of the 2,326 participants developed T2D by the end of the study, and the probability of not developing diabetes was 96%.
• There was overall sustained weight loss maintenance (after the 8-week lead-in) using diet, physical activity and behavioural modification tools.
• Insulin was reduced by about 25%; 2-hour glucose was reduced by about 8%.
• There were no differences between the 2 diet groups, the 2 physical activity groups or the 4 groups taken individually.