In the short-term, low-carb diets decrease blood sugar levels in people with type 2 diabetes

Snorgaard O, Poulsen GM, Andersen HK et al. Systematic review and meta-analysis of dietary carbohydrate restriction in patients with type 2 diabetes BMJ Open Diabetes Res Care. 2017;5:e000354.

Review question

Do low-carbohydrate diets help people with type 2 diabetes lose weight, improve their quality of life or decrease their blood sugar and cholesterol levels?

Background

Carbohydrates (“carbs”) are nutrients that the body can quickly convert into sugar. They are found in many healthy and unhealthy foods, such as grains, vegetables, baked goods and sweetened foods and drinks. Low-calorie diets are recommended for weight loss and to improve blood sugar and cholesterol levels for people with type 2 diabetes. However, the ideal amount of dietary carbohydrates for diabetes self-management is unclear.

How the review was done

This is a review of ten randomized controlled trials conducted from 2008 to 2014, including a total of 1,376 participants. All the studies were combined in a meta-analysis.

• All participants had type 2 diabetes. Average age of participants was 58 and average body mass index (BMI) was >26 (overweight or obese).    
• Study participants followed diets in which carbohydrates made up less than 45% of total calories. The average target percentage was 25% carbohydrates.
• Participants reported their diet intake using food diaries and were instructed to replace carbohydrates with protein, fats or both.
• Researchers measured participants’ carbohydrate intake, as well as blood sugar levels, weight or BMI, cholesterol levels and self-rated quality of life at least three months after starting the diet.
• Results were compared to control groups who followed the standard diet of 45-60% carbohydrates.

What the researchers found

People following a low-carbohydrate diet had lower blood sugar levels than people following a higher-carbohydrate diet up to six months after starting their diets. There was a direct relationship between the percentage of dietary carbohydrates and blood sugar levels: people who ate fewer carbohydrates had lower blood sugar levels. There was also evidence that people on low-carbohydrate diets were also able to use lower doses of diabetes medication. The benefits were short-term, and it is not clear whether people are likely to adhere to low-carbohydrate diets in the long-term. The low-carbohydrate diets did not significantly improve cholesterol levels, weight or BMI, and quality of life.

Conclusion

Low-carbohydrate diets appear to be an effective way for people with diabetes to lower their blood sugar in the short-term.