Which diet for weight reduction in type 2 diabetes?

With type 2 diabetes and obesity being closely linked, dietary advice and intervention for most people with type 2 diabetes should aim for both weight loss and improvement in glycaemic control. However, the majority of people who attempt it are unable to lose weight and/or maintain the weight loss. There are many reasons for this, involving multiple factors. A key factor is the inability to maintain a strict diet, as many diets exclude common foods. The panoply of different diets means that many obese individuals try several different approaches, each of which is associated with failure; this in turn jeopardises the next attempt at weight loss.

As carbohydrate intake is linked to glycaemia, there is great interest in the use of low-carbohydrate diets in people with type 2 diabetes. Tay and colleagues (their study summarised alongside) conducted a single-centre, randomised trial to compare low- and high-carbohydrate diets in overweight and obese people with type 2 diabetes over 52 weeks. Intensive support was provided every 2 weeks in the first 3 months, followed by monthly visits. Key foods and food vouchers were provided to participants. The participants had individualised energy restriction targets of about 30% in both diets. The low- and high-carbohydrate diets consisted of 14% and 53% energy from carbohydrate, respectively. For the high-carbohydrate diet, low-glycaemic-index foods were emphasised. Participants were also provided with 60-minute supervised exercise classes on three non-consecutive days per week.

The mean age of the 115 randomised participants was >50 years. Both groups had reductions in weight, waist circumference, HbA_1c (by about 11 mmol/mol [1.0%], despite fairly good control at baseline), and systolic and diastolic blood pressure (about 6–7 mmHg). There was no significant difference in weight loss (around 9%) or waist circumference reduction (9–10 cm) between the two diets. However, the low-carbohydrate group had a significantly greater reduction in triglyceride levels and diabetes medication requirements. The low-carbohydrate diet was also associated with lower glycaemic variability and less time spent in the hyperglycaemic range, as measured using continuous glucose monitoring.

As in most previous studies, the most significant weight loss occurred in the first 24 weeks. However, unlike in many studies, the weight loss was maintained up to 52 weeks. In a separate analysis of this cohort (Tay et al, 2015), the authors examined the impact of the diets on renal parameters and did not observe any adverse effects.

The key message from this study is that calorie restriction in the context of an intensive lifestyle intervention translates to meaningful weight loss and improvements in diabetes outcomes. Calorie reduction plays a significant role in improvement of diabetes in the context of obesity (Steven et al, 2015). One approach in achieving significant weight loss is the use of low-energy diets (Rehackova et al, 2015; see page 14). When calorie restriction is combined with intensive lifestyle support it can result in clinically significant changes in key diabetes and cardiovascular parameters (Look AHEAD Research Group, 2013). The diet advised and extent of calorie restriction should take into account individual preferences and lifestyle, with a view to sustainability. Increasingly, there is evidence that people with type 2 diabetes can have significant weight loss and improved outcomes that are comparable to obese people without diabetes (Brown et al, 2015). Given these findings, the ever-present question is why evidence-based lifestyle interventions are not employed in the daily clinical care of people with type 2 diabetes.

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