Apart these consensuses, still few controversial issues remain, among them, the efficacy of glycaemic index in diabetic meal planning. A Cochrane review [23] assessed randomised controlled trials of 4 weeks or longer that compared a low glycaemic index, or low glycaemic load, diet with a higher glycaemic index, or load, or other diet for people with either type 1 or 2 diabetes mellitus, whose diabetes was not already optimally controlled. Eleven relevant randomised controlled trials involving 402 participants were identified. There was a significant decrease in the HbA1c; the weighted mean difference was −0.5 %. No study reported on mortality, morbidity or costs. The Cochrane concluded that a low glycaemic index diet can improve glycaemic control in diabetes without compromising hypoglycaemic events. However, some authors disagree with these conclusions and claim no or very limited benefit of a low glycaemic index diet [24].

Another controversial issue is about micronutrients (vitamins and minerals) supplementation in people with diabetes (compared with the general population) without underlying deficiencies. An antioxidant diet significantly improved endothelial dysfunction when supplemented with alpha-lipoic acid, unlike diet with placebo or controls [25]. However, routine supplementation with antioxidants, such as vitamins E and C and carotene, is not advised because of lack of evidence of efficacy and concern related to long-term safety.