The PREVIEW intervention study: Results from a 3-year randomized 2 x 2 factorial multinational trial investigating the role of protein, glycaemic index and physical activity for prevention of type 2 diabetes.

Diabetes, obesity & metabolism. 2021;23(2):324-337

Plain language summary

The main risk for the development of type 2 diabetes is being overweight or obese. Strategies to decrease weight are important to prevent its development or reverse disease. This long-term, randomised control trial of 2326 adults with prediabetes, aimed to compare the effectiveness of different maintenance diets, after initial weight loss; one which was high protein and low glycaemic index, and the other which was moderate protein and moderate glycaemic index. These diets were then combined with either moderate intensity or high intensity exercise. The results showed that after 3 years, the incidence of type 2 diabetes was low and did not differ between the diet and exercise groups. However, more individuals achieved normal blood sugar levels when on a moderate protein diet combined with moderate exercise and when on a high protein diet combined with moderate exercise. The high protein diet with high intensity exercise was the least effective at maintaining normal blood sugar levels. The amount of weight lost was the same no matter what combination of diet and exercise. It was concluded that the incidence of type 2 diabetes was lower than expected with the diet and exercise regimes and did not differ between the diets. This study could be used by healthcare professionals to introduce a long-term protocol combining weight loss, healthy eating, and physical activity to pre diabetic individuals who want to reduce their chance of developing type 2 diabetes.


AIM: To compare the impact of two long-term weight-maintenance diets, a high protein (HP) and low glycaemic index (GI) diet versus a moderate protein (MP) and moderate GI diet, combined with either high intensity (HI) or moderate intensity physical activity (PA), on the incidence of type 2 diabetes (T2D) after rapid weight loss. MATERIALS AND METHODS A 3-year multicentre randomized trial in eight countries using a 2 x 2 diet-by-PA factorial design was conducted. Eight-week weight reduction was followed by a 3-year randomized weight-maintenance phase. In total, 2326 adults (age 25-70 years, body mass index ≥ 25 kg/m2 ) with prediabetes were enrolled. The primary endpoint was 3-year incidence of T2D analysed by diet treatment. Secondary outcomes included glucose, insulin, HbA1c and body weight. RESULTS The total number of T2D cases was 62 and the cumulative incidence rate was 3.1%, with no significant differences between the two diets, PA or their combination. T2D incidence was similar across intervention centres, irrespective of attrition. Significantly fewer participants achieved normoglycaemia in the HP compared with the MP group (P < .0001). At 3 years, normoglycaemia was lowest in HP-HI (11.9%) compared with the other three groups (20.0%-21.0%, P < .05). There were no group differences in body weight change (-11% after 8-week weight reduction; -5% after 3-year weight maintenance) or in other secondary outcomes. CONCLUSIONS Three-year incidence of T2D was much lower than predicted and did not differ between diets, PA or their combination. Maintaining the target intakes of protein and GI over 3 years was difficult, but the overall protocol combining weight loss, healthy eating and PA was successful in markedly reducing the risk of T2D. This is an important clinically relevant outcome.

Lifestyle medicine

Fundamental Clinical Imbalances : Hormonal ; Immune and inflammation
Patient Centred Factors : Mediators/Type 2 diabetes
Environmental Inputs : Diet ; Physical exercise
Personal Lifestyle Factors : Nutrition ; Exercise and movement
Functional Laboratory Testing : Blood

Methodological quality

Jadad score : 3
Allocation concealment : Yes