Efficacy of low- and very-low-calorie diets in overweight and obese patients with type 2 diabetes: a meta-analysis of intervention studies

Background and aims

In patients with type 2 diabetes, dietary recommendations based on caloric restriction with very-low-calorie diets (VLCD; ≤800 kcal/day) are mainly based on evidence from observational studies. We undertook a comprehensive systematic review and meta-analysis of relevant interventional studies to help clarify the evidence about the efficacy of caloric restriction on body weight in type 2 diabetes.

Materials and methods

We electronically searched articles on Medline, EMBASE, and CINAHL up to March 2018 to identify interventional studies (single or multiple arms) reporting the effect of Low- (LCD; ≤1600 kcal/day) and VLCD diets on the outcomes body weight and BMI. Given the non-linear effects of diets over time, we modelled the outcomes using restricted cubic splines and accounting for study-specific estimate precision (inverse of the variance). Egger’s test was used to assess publication bias.

Results

Of 803 records identified, 47 met the inclusion criteria comprising 55 study arms and 3883 participants (45% male); mean age was 51.9 (SD 7.0) years and the mean duration of diabetes 7.0 (SD 3.8) years. The median duration of intervention was 56 (IQR 28-84; range 6-112) days and the mean daily target was 729 (SD 381, range 23.2-1600) kcal. Studies were published between 1978 and 2017 and were generally of low-moderate quality. There was a significant publication bias for body weight (Egger’s p<0.001) but not for BMI (p=0.057).

For 800 kcal/day, the modelled reduction was already evident at 14 days and progressively higher at 60, 90, and 120 days while for 1200 the effect was present only from 2 months onwards (Figure). Conversely, for 1600 kcal/day, there was no effect at 14 and 60 days, a small reduction at 3 months, and an uncertain effect at 120 days. BMI followed the same pattern of body weight change.

Conclusion

These results from interventional studies support evidence for efficacy of VLCDs and some LCDs only in short-term studies. A lack of high-quality studies and the possibility of publication bias compound the uncertainty over the true effect of diets on body weight and BMI. This highlights a need for RCTs with larger sample size and longer duration to confidently quantify the efficacy of VLCDs and LCDs in overweight patients with type 2 diabetes.