Weight loss and disease remission in T2D may differ between patients regardless of type of diet regimen chosen, say authors of a new analysis.
Weight loss strategies that include very low-energy diets appear to be most effective for weight loss and disease remission in persons with type 2 diabetes, according to an umbrella review published in Diabetologia.
The review of 19 meta-analyses led by Chaitong Churuangsuk, a doctoral student in the department of human nutrition at the University of Glasgow, also found that programs initiated with complete formula meal replacements were most effective for inducing T2D remission with normoglycemia achieved at 1 year by 61% of participants. Overall, the authors report, actual macronutrient content was not found to be important to the outcomes observed.
Citing the fundamental role of shedding pounds for T2D management and remission but also describing the conflicting data regarding which type of diet is best to achieve and maintain these results, Churuangsuk and colleagues set out to examine existing research.
They first conducted a systematic review of published meta-analyses of RTCs of different regimens for weight loss, synthesizing weight loss findings stratified by diet type and assessing meta-analyses for quality. They followed this with a second systematic review of any intervention studies reporting T2D remission with weight-loss diets and analyzed findings by type of diet and study quality. Both analyses searched databases through May 2021.
The authors report identifying 21 systematic reviews (with 19 meta-analyses), of weight loss diets (2-23 trials; n=100-1587). Of the meta-analyses, 18 reported direct comparison of specific diets. Filtered by quality metrics, most meta-analyses were found to be of critically low (n=7) to low (n=5) quality; 7 were assessed as high quality.
Overall Churuangsuk et al found that the greatest weight loss was associated with very low-energy diets of 400 to 500kCal/day for 8-12 weeks, resulting in weight loss 6.6 kg greater than seen with low-energy diets of 1000 to 1500 kcal/day (95% CI, –9.5 to –3.7).
Formula meal replacements achieved 2.4 kg (95% CI −3.3, −1.4) greater weight loss over 12–52 weeks and this evidence was considered of high quality.
Contrary to conventional wisdom, the investigators found that low-carbohydrate diets were no more effective for weight loss than higher-carbohydrate/low-fat diets and that evidence for this finding was of high quality. Compared to control diets, the authors' analyses found there was minimal (0.3–2 kg) or no difference in weight loss associated with high-protein, Mediterranean, high-monounsaturated-fatty-acid, vegetarian, and low-glycemic-index diets. They also qualify the quality of the studies reviewed as of low to critically low quality.
Investigators evaluated 373 records for evidence regarding T2D remission and found only 16 that met inclusion criteria. They found no studies that directly compared diet types.
The best 12-month remission rates (median 54%) were achieved among participants in RCTs that included initial low-energy formula "total diet replacement" (830 kcal/day for 12 weeks) followed by a relatively low-fat high carbohydrate diet and meal replacements for long-term maintenance. For RCTs reporting use of meal replacement, remission at 1 year was reported for a median 11% of participants and for RCTs of Mediterranean-style diets, for 15% of participants. Investigators did note, however, there is some concern for risk of bias in the studies analyzed and GRADE certainty was moderate to low.
Evidence for remission with ketogenic/very low-carbohydrate and very low-energy food-based diets (20% and 22%, respectively), according to authors, was flawed by “serious and critical risk of bias” and GRADE certainty was very low.
In their discussion the authors note that the findings “contradict” some widely held beliefs about popular weight-loss regimens. “In particular, ‘low-carb’ diets hold no overall advantage for weight loss when compared with higher-carbohydrate diets.
“However, we cannot conclude that any individual with type 2 diabetes, in any context, will do equally well with any diet advice,” they continue, “or that a skilled practitioner may not have greater success advising one diet type. The skills and empathy of practitioners may overcome any diet-specific effects on weight loss by providing consistent evidence-based support . Realistic trials are required, in which individuals are offered choices, perhaps using n = 1 randomized trial designs.”
Reference: Churuangsuk C, Hall J, Reynolds, et al. Diets for weight management in adults with type 2 diabetes: an umbrella review of published meta-analyses and systematic review of trials of diets for diabetes remission. Diabetologia. Published online November 17, 2021.