Diets with low glycemic index or glycemic load may benefit patients with diabetes

Patients with moderately controlled type 1 and type 2 diabetes may benefit from diets with low glycemic index (GI) or glycemic load (GL), according to a recent study.

Researchers performed a systematic review and meta-analysis of randomized controlled trials published up to May 13, 2021, to inform an update of the European Association for the Study of Diabetes' clinical practice guidelines for nutrition therapy. Trials were eligible if they were at least three weeks in duration and looked at the effects of diets with low GI or GL in patients with diabetes. The primary outcome was HbA1c, while secondary outcomes included other markers of glycemic control, such as fasting glucose and fasting insulin levels; blood lipid levels; adiposity, as measured by body weight, body mass index (BMI), or waist circumference; blood pressure; and inflammation, as measured by C-reactive protein level. The study results were published Aug. 5 by The BMJ.

Twenty-nine trial comparisons involving 1,617 outpatients with type 1 and type 2 diabetes were included. Median follow-up was 12 weeks, and median age was 56 years. Most patients were overweight or obese and had moderately controlled type 2 diabetes that was treated with hyperglycemia drugs (69%), insulin (14%), or both (7%), while 10% of patients were treated with diet alone. Low GI/GL dietary patterns reduced HbA1c versus control diets with higher GI/GL (mean difference, −0.31%; P<0.001). Body weight, BMI, and levels of fasting glucose, low-density lipoprotein (LDL) cholesterol, non-high-density lipoprotein (HDL) cholesterol, apolipoprotein B, triglycerides, and C-reactive protein level were also lower with low GI/GL dietary patterns (P<0.05), but no difference was seen in blood insulin level, HDL cholesterol level, waist circumference, or blood pressure. There was a positive dose-response gradient for the difference in GL and HbA1c improvement and for absolute dietary GI and systolic blood pressure improvement (P<0.05).

The researchers noted that the evidence indicated serious inconsistency for the effect of a low GI/GL diet on LDL cholesterol level and waist circumference, as well as imprecision in pooled estimates across most outcomes, among other limitations. The authors suggested their findings were most relevant to adults with type 2 diabetes. They graded the certainty of evidence as high for the diets' effect on HbA1c and HDL cholesterol, moderate for most other outcomes, and low for fasting insulin, LDL cholesterol, and waist circumference. “Our synthesis shows that low GI/GL dietary patterns are considered an acceptable and safe dietary strategy that can produce small meaningful reductions in the primary target for glycaemic control in diabetes, HbA1c, fasting glucose, and other established cardiometabolic risk factors,” the authors wrote. They called for larger randomized trials to examine whether improvements in these intermediate cardiometabolic risk factors translate to reductions in clinical outcomes.