Low-calorie diet and exercise improve blood sugar levels in people without impaired glucose tolerance (IGT) or diabetes

Zhang X,  Imperatore G, Thomas Wvet al. Effect of lifestyle interventions on glucose regulation among adults without impaired glucose tolerance or diabetes: A systematic review and meta-analysis Diabetes Research and Clinical Practice. 2017;123:149-164.

Review question

Do lifestyle changes like exercising and eating a low-calorie diet improve blood sugar levels in people who do not have impaired glucose tolerance (IGT) or diabetes?

Background

In people with diabetes, the body does not properly produce and/or respond to the hormone insulin, leading to high blood sugar levels. People are more likely to develop diabetes if they have an unhealthy diet, low activity levels, overweight or obesity, or IGT (a type of “pre-diabetes”). People with IGT have some resistance to insulin and higher blood sugar levels than normal. Research has shown that lifestyle changes can help improve blood sugar levels and prevent diabetes in people with IGT, but few studies look at whether lifestyle changes can also help control blood sugar in people without IGT or diabetes.

How the review was done

This is a review of 79 randomized control trials that included a total of 15,618 participants. 57 of the trials were combined in a meta-analysis.

• Average age of participants in the studies ranged from 30 to 70.
• All participants were adults who did not have IGT or diabetes. Most of the studies included participants with risk factors for diabetes, such as overweight or obesity and inactive or sedentary lifestyle.
• Study participants participated in programs focused on either: a) increasing physical activity; b) following a low-calorie (<1500 calorie) diet; or c) increasing physical activity and following a low-calorie diet.
• Researchers measured how much these programs changed participants’ blood sugar levels and other risk factors for diabetes (including weight loss) after at least a year.
• Results were compared to control groups who did not participate in diet and/or exercise programs.

What the researchers found

Lifestyle changes helped lower the blood sugar levels of people without IGT or diabetes. Diet programs and combined exercise and diet programs were better at lowering blood sugar than exercise programs alone. People had similar drops in their blood sugar levels regardless of their blood sugar levels before they started the programs. Lifestyle changes also decreased other risk factors for diabetes, specifically by leading to weight loss and increased insulin levels and/or responsiveness to insulin. This review was not able to prove whether lifestyle changes prevent the development of diabetes in people without IGT as effectively as in people with IGT.

Conclusion

Low-calorie diets and low-calorie diets combined with exercise appear to be an effective way to control blood sugar levels in people without IGT and diabetes. This may mean that these lifestyle changes can decrease the risk of developing diabetes in people without IGT; more research is needed to confirm this.