Low GI diet leads to important improvements for people with diabetes: Prof Jennie Brand-Miller


Low-glycaemic index and low glycaemic load diets result in small but clinically significant improvements in cardiometabolic risk factors, including blood sugar levels and body weight, for people with diabetes, according to a new meta analysis.

The study, carried out by researchers from Canada, the US and Spain, is the largest and most comprehensive analysis to date and is the first update on evidence surrounding low GI/GL dietary patterns in diabetes in more than a decade.

Commenting on the research Professor Jennie Brand-Miller, Professor of human nutrition at the University of Sydney told the limbic that there is a lot of ‘noise’ when it comes to diet recommendations for people with diabetes particularly because of the heterogeneity across nutrition study designs and cohorts, which invariably leads to inconsistent findings.

“We hear that some studies show positive associations while others show negative – some studies in this space are better than others and I think you would be forgiven if you might be confused as to whether low GI diets are favoured or not.”

The well-known nutritionist – who has written multiple books on the subject, manages the GI testing service at the University of Sydney and is President of the GI Foundation – said the updated meta analysis cuts through that noise.

“This latest meta analysis is good to see. Where others have included studies looking at low GI/GL diets for weight loss, insulin sensitivity and other factors this latest review is specifically relevant to people with diabetes.

It tells us a lot more than previous meta analyses have done and suggests that it is useful to recommend low GI/GL diets to people with diabetes because it will convey a whole lot of benefits – not just for glucose control but to all of the cardiovascular disease risk factors. It suggests that the diet is a useful evidence-based intervention.”

Study results

Published in The BMJ, the study included data from more than 1,600 adult participants with type 1 or 2 diabetes from 29 randomised controlled trials that looked at the effect of low-GI diets in diabetes.

Participants were mostly middle-aged, overweight or obese with moderately controlled type 2 diabetes treated with glucose lowering drugs or insulin.

All of the included trials examined the effects of a low GI diet or a low glycemic load diet for people with diabetes over a period of three or more weeks.

The pooled data showed that low-GI/GL dietary patterns were associated with small but clinically meaningful reductions in HbA1c.

Compared with people who consumed diets with higher GI/GL ratings, those who consumed lower glycemic diets had significantly improved glycaemic control as reflected in HbA1c level, which was the primary outcome of the study (mean difference, -0.31%; P < .001).

The research team said the finding would meet the threshold of ≥0.3% reduction in HbA1c proposed by the European Medicines Agency as clinically relevant for risk reduction of diabetic complications.

Those who consumed low glycaemic diets also showed improvements in secondary outcomes, including fasting glucose level, which was reduced by 0.36 mmol/L (-6.5 mg/dL), a 6% reduction in low-density cholesterol (LDL-C) (-0.17 mmol/L), and a fall in triglyceride levels (-0.09 mmol/L).

They also lost marginally more body weight, at -0.66 kg. Body mass index (BMI) was lower by -0.38, and inflammation was reduced (C-reactive protein, -.41 mg/L; all P < .05).

However, no significant differences were observed between the groups in blood insulin level, high-density lipoprotein cholesterol level, waist circumference, or blood pressure.

The improvements were evident over and above existing drug or insulin therapy, say investigators suggesting that a low-glycemic diet might be useful as an add-on treatment to help people with diabetes achieve therapeutic targets.

The researchers concluded that the evidence was high for a reduction in blood sugar levels and moderate for most other outcomes. They did note some limitations that may have affected results, such as imprecision in the evidence for the effect of low GI/GL dietary patterns on LDL cholesterol and waist circumference, and the small number of available trial comparisons for blood pressure and inflammatory markers.

However, overall they said the evidence ‘supports existing recommendations for the use of low-GI dietary patterns in the management of diabetes’.

Low carb compromise

For Professor Brand-Miller, that approach is a good compromise to the low or no carbohydrate diet.

“Low carbohydrate diets are getting a lot more air play both in the science and the media and in that respect people with diabetes are being told  that they should cut carbohydrates. While some people won’t mind that most people like carbohydrates and what GI does is try to guide the choice of carbohydrate rather than to knock it out of the diet altogether.”

She added that doing ‘a bit of both’ can also be useful.

“That’s demonstrated in this meta analysis, which includes studies where researches have both lowered the GI of the carbohydrate and they’ve lowered the total carbohydrate intake as well and that’s a nice way of including the carbohydrate foods a person might love, like pasta or bread, without telling them they have to cut them out completely.”

“Because food is an important part of enjoying life and we shouldn’t make recommendations that are going to interfere with that enjoyment unless we have a really solid basis for it. And, at the moment, I don’t think we have a solid basis for telling people to eat a very low carbohydrate diet.”

Investigators say the findings will help inform an update to the European Association for the Study of Diabetes’s guideline.

The study is published in theBMJ.

Disclosure: Professor Brand-Miller disclosed being the author of several books on GI diet for which she receives royalties.

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