The normal values for someone without diabetes are 70–100 mg/dL for fasting blood sugar and 4.0–5.6% for HbA1c. The observed improvements (−28.2 mg/dL and −1%) were therefore large and clinically significant.

These improvements seem attributable, at least in part, to the lignan sesamin. In studies of diabetic rats, sesamin lowered blood sugar by promoting the synthesis of glycogen and the secretion (by pancreatic beta cells) of insulin.^[2]^[3]

Moreover, the lignans and vitamin E in sesame seeds might improve glycemic control through this causal chain: increased activity of antioxidant enzymes in the liver → increased scavenging of free radicals → decreased oxidative stress → improved beta cell function → increased insulin secretion.^[4]

Although the lignan content of sesame seeds and sesame oil (which is extracted from the seeds) is highly variable, it tends to be lower in the seeds than in the oil.^[5]^[6] This may explain why, in the present meta-analysis, ground seeds/flour didn’t improve fasting blood sugar.

Another potential explanation is that the subgroup analysis looking at the effects of ground seeds/flour on fasting blood sugar lacked statistical power, since it contained only two trials. Both trials reported nonsignificant improvements that, combined in the subgroup analysis, trended toward statistical significance (p = 0.056); it’s therefore possible that, with more trials, statistical significance would have been reached.

Sesame seeds for glycemic control in people with type 2 diabetes Original paper