Energy-reduced Mediterranean diet with increased physical activity may significantly reduce risk of type 2 diabetes

1. In this secondary analysis of a randomized controlled trial, physical activity paired with an ad libitum energy-reduced Mediterranean diet was associated with significantly reduced incidence of type 2 diabetes among adults with overweight or obesity and metabolic syndrome.

2. The intervention was also associated with greater improvements in diet adherence as well as larger reductions in body weight and waist circumference.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Most studies showing the effect of lifestyle modifications on type 2 diabetes (T2D) involve weight loss through an energy-reduced, low-fat diet alongside increased physical activity, but few trials have examined weight loss through a relatively high-fat diet. A previous study found that a Mediterranean diet supplemented with extra-virgin olive oil or mixed nuts was associated with lower diabetes incidence had only a modest effect on body weight. This study aimed to determine whether weight loss intervention combining an energy-reduced Mediterranean diet with increased physical activity may reduce T2D incidence among adults with overweight or obesity and metabolic syndrome. After six years of follow-up, the weight loss intervention was associated with a nearly one-third reduction in T2D risk compared with a control Mediterranean diet without energy reduction, with a greater effect being observed in men. Both groups had increased adherence to the diet over time, although improvement was significantly greater in the intervention group. Similarly, the number of participants in both groups who reached their targets for almost all food items increased over time, although improvement was significantly greater among intervention participants. The intervention group also saw larger increases in physical activity and larger reductions in body weight and waist circumference. The generalizability of this study is limited by self-reporting of dietary adherence and a single-blinded design. Nevertheless, these findings suggest that increased physical activity alongside an energy-reduction Mediterranean diet may be a sustainable intervention for reducing risk of T2D and controlling body weight.

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Relevant Reading: Reduction in the Incidence of Type 2 Diabetes With the Mediterranean Diet: Results of the PREDIMED-Reus nutrition intervention randomized trial

In-Depth [randomized controlled trial]: This secondary analysis of the PREDIMED-Plus randomized controlled trial aimed to assess whether a weight loss intervention consisting of an ad libitum energy-reduced Mediterranean diet and increased physical activity may reduce T2D incidence. Participants were eligible if they were men aged 55 to 75 years or women aged 60 to 75 years, had a body mass index [BMI] ≥27 and <40 kg/m², did not have documented cardiovascular disease or diabetes, and met at least 3 criteria for metabolic syndrome. The energy-reduced Mediterranean diet included a planned reduction of 600 kcal/day, with 35% to 40% of calories being derived from fat. This study included 4746 patients without T2D (mean age, 64.9 years [standard deviation {SD}, 4.9]; 50% women). During a median follow-up of 6.6 years (interquartile range [IQR], 6.0 to 7.1 years), 629 participants developed diabetes. After 6 years, the absolute adjusted risk difference for incident T2D between the intervention and control groups was -2.4% (95% CI, -3.1 to -1.8), yielding a relative risk reduction of 31% (95% CI, 18% to 41%) in the intervention group compared with the control group. Subgroup analyses showed no statistically significant interactions for age, educational level, BMI, waist-to-height ratio, or baseline glucose level; a statistically significant difference was only seen for sex, with men having a greater risk reduction than women (p = 0.035). The mean difference in the erMedDiet score, which measures adherence to the study diets, between the intervention and control groups was 2.2 (95% CI, 2.0 to 2.3; p < 0.001). Mean body weight change over 6 years was -3.3kg (95% CI, -3.4 to -3.1kg) in the intervention group and -0.6 kg (95% CI, -0.7 to -0.4kg) in the control group, representing weight reductions of 3.7% in intervention and 0.6% in control. Furthermore, change in mean waist circumference was -3.6 cm (95% CI, -3.8 to -3.3 cm) in the intervention group and -0.3 cm (95% CI, -0.4 to -0.1cm) in the control group. Overall, this study suggests that a weight loss intervention consisting of an ad libitum energy-reduced Mediterranean diet and increased physical activity may significantly reduce risk of T2D incidence while also improving other markers of overall metabolic health.

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