By Dr Jean Strelitz, MRC Postdoctoral Fellow, MRC Epidemiology Unit

People with type 2 diabetes have a higher risk of heart disease and premature death. People with type 2 diabetes are increasingly encouraged to lose weight, as evidence from numerous clinical trials shows that weight loss substantially improves blood sugar levels. Indeed, a recent trial of intensive weight management in people with type 2 diabetes in the UK achieved remission in about half of the participants with type 2 diabetes, so that they no longer needed to take drugs to manage their blood sugar.  What remains unanswered, is whether weight loss can also help lower patients’ risk of heart disease.

Unanswered questions on weight loss and heart disease.

While weight loss can improve blood sugar levels, questions remain regarding the impact on downstream consequences of diabetes such as heart disease and premature mortality.

To address this we undertook a systematic review of the published literature of observational  studies and intervention trials reporting weight loss and other weight changes and heart disease among people with type 2 diabetes. To be included in our analysis weight data had to be collected at least two occasions over the course of the study to measure weight changes, and we identified 17 studies on this topic that met our criteria, 14 of which were observational studies and 3 behavioural intervention trials. We didn’t include studies of bariatric surgery because this has other health impacts on heart disease risk unrelated to weight loss. We instead focused on studies of behaviour-based weight loss.

Results from our review showed that weight gain among people with type 2 diabetes was associated with increased risks of heart disease and death, but the results for weight loss were more mixed. Several studies distinguished between intentional weight loss and unintentional weight loss, finding that unintentional weight loss was associated with a higher risk of death from all causes, consistent with this weight loss being a symptom of an underlying illness.

Intentional weight loss and unknown consequences

Our review found that there have been few studies that assessed whether intentional weight loss protects against heart disease and death. Indeed the three behavioural interventions targeting weight loss showed no impact on the risk of cardiovascular disease events such as heart attack or stroke during 5-10 year follow up periods.

Studies showed conflicting results and were influenced by bias, highlighting the need for high-quality research to inform weight loss guidance for patients.  Differences between the studies regarding the duration of weight loss, whether the study accounted for unintentional weight loss, the duration of follow-up for heart disease risk, and other individual characteristics contribute to differences in the findings. There was evidence of moderate bias in most of the studies we included, due to factors such as the method of weight assessment used, and whether the study controlled for common confounding factors like smoking.

Our review suggests that preventing weight gain in people with type 2 diabetes may reduce risk of heart disease and mortality. However, while there is growing evidence for the short-term benefits of behavioural weight loss interventions on risk factors such as blood sugar levels, there is a lack of evidence to support such interventions for preventing heart disease and death in adults with type 2 diabetes. Another recent paper from our group found in a study of more than 2,000 people with type 2 diabetes that a large amount of weight loss (more than 10% of body weight) during the five-year period after diabetes diagnosis was associated with a two-fold increased risk of premature death from any cause. The risk of death after weight loss was highest among participants who did not have obesity at the time they were diagnosed, suggesting obesity could be a particular factor in how patients are affected by losing weight.

Time for a more tailored approach to weight loss

Taken together with the results of our systematic review this suggests that we need more evidence to inform weight loss advice and support for people with  type 2 diabetes, as some may be affected differently from others. Considering that weight loss may affect patients differently, a more tailored approach that reflects how individuals with type 2 diabetes may respond differently to weight loss may be more effective.

In order to determine which patient groups will benefit from behavioural weight-loss interventions, and what amount of weight loss is most effective in preventing heart disease, long-term follow up of behavioural intervention studies is needed. Accumulating this evidence will take time, but it will inform policy concerning weight management advice, help us to allocate health service resources more effectively, and enable us to better support people with diabetes.

 Find out more

• Jean Strelitz, Emma R. Lawlor, Yue Wu, Annabel Estlin, Giri Nandakumar, Amy L. Ahern, Simon J. Griffin “Association between weight change and incidence of cardiovascular disease events and mortality among adults with type 2 diabetes: a systematic review of observational studies and behavioural intervention trials” Diabetologia, 02 Dec 2021 https://doi.org/10.1007/s00125-021-05605-1
• Type 2 diabetes weight loss recommendations could be harmful for some, depending on BMI – Jean Strelitz, MRC Epidemiology Unit Research Blog, 16 December 2020
• Type 2 diabetes: losing even a small amount of weight may lower heart disease risk – Jean Strelitz, MRC Epidemiology Unit research blog, 13 May 2019.