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.

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• Authors highlight current evidence on diets for T2D remission is limited but believe remission can be achieved if sufficient weight loss is maintained. The main contributor to HbA1c reduction and remission appears to be weight loss, irrespective of diet type.

• NICE Guidelines highlight the remission of diabetes occurs when a patient no longer satisfies the diagnostic criteria, without receiving glucose-lowering medication. By 2019 in one UK GP practice 27% of the practice population with T2D who followed a LCD for 23 months, lost weight and lowered their HbA1c to 48 mmol/mol (NICE target range) in conjunction with prescribed medication.

• This review highlights an opportunity for Nutritional Therapy Practitioners to successfully work with LCD approaches to support weight loss and improved HbA1c.

Introduction

This systematic review of meta-analyses aimed to evaluate dietary approaches for weight loss in those with a diagnosis of Type 2 Diabetes, including disease remission.

Methods

• 19 meta-analyses (MA) on weight-loss diets, involving 23 primary trials, were assessed using A Measurement Tool to Assess Systematic Reviews (AMSTAR) 2. Findings were synthesised by diet type and study quality (Cochrane Risk of Bias tool 2.0 and Risk Of Bias In Non-randomised Studies – of Interventions [ROBINS-I]) with GRADE applied.

• Time period of diets / length of observation / intervention: 1) Formula meal replacements (>12–52 wk), 2) LCDs ranged between (>8 wk to 4 years), 3) Very low energy diets (>8–12 wk), 4) High- protein (>4->8 wks), Mediterranean (>4->8 wk), high-monounsaturated-fatty-acid (>2wk), vegetarian (≥3wk) and low-glycaemic-index diets (≥6mo).

Results
Weight loss diets in the review included:

• Formula meal replacements (high quality, GRADE moderate) achieved 2.4 kg (95% CI −3.3, −1.4) greater weight loss over 12–52 weeks.

• Low-carbohydrate diets were no better for weight loss than higher-carbohydrate/low-fat diets (high quality, GRADE high).

• High-protein, Mediterranean, high-monounsaturated-fatty-acid, vegetarian and low-glycaemic-index diets all achieved minimal (0.3– 2 kg) or no difference from control diets (low to critically low quality, GRADE very low/moderate).

• Greatest weight loss was reported with very low energy diets (VLED), (400–500 kcal). However, this study found that low-carbohydrate diets (LCD) (21–70g of carbohydrate daily from 1000–1500 kcal) were no better for weight loss than higher-carbohydrate/low-fat diets.

Conclusion

This MA found that VLED and formula meal replacement appear the most effective approaches for weight management in T2D by providing less energy than self-administered food-based diets. Potential pathophysiological mechanisms highlighted by authors are HbA1c reduction and remission which appear to be from weight loss, with only small differences between diet types assessed over 3–12 months, irrespective of diet type. Authors highlight weight reduction is fundamental for T2D management and remission.

Study limitations: Many meta-analyses were of ‘low’ and ‘critically low’ AMSTAR 2 quality, predominantly through ‘no protocol reported’ (despite clear and sound methods) and no assessment of publication bias.

• While this study found a variety of dietary compositions can be used effectively for weight management with T2D, VLED was successfully used to achieve remission for T2D.

• Programmes with a ’total diet replacement’ induction phase were the most effective dietary approach for T2D remission (up to 61% of participants at 1 year).

• Authors state future research should provide implementation with optimal support in real-life settings for weight loss, prevention of weight regain and remissions, rather than seek subtle differences from macronutrient compositions.

• Future studies should report sufficient detail about macronutrient or micronutrient contents, or prescribed and reported energy intakes, including energy intake of nutrient-restricted diets.

• Most studies included European participants, such that findings may not be equally applicable to other ethnic and/or deprived communities. Durations of interventions varied, where weight regain is frequent over a longer period. Authors highlight evidence from clinical practice is needed to identify safe and effective approaches to achieve and maintain weight loss

• Authors highlight primary studies should use an RCT design, with data analyses conducted ‘blind’. They should define the intervention clearly (e.g., diets, physical activity, and behavioural and psychological support), and address separately the induction (usually 3–6 months) and maintenance (≥12 months) phases.