BMJ 2018; 361 doi: https://doi.org/10.1136/bmj.k2340 (Published 13 June 2018)Cite this as: BMJ 2018;361:k2340

Conclusions

Although human populations have thrived on diets with widely varying macronutrient ratios, the recent influx of rapidly digestible, high-GI carbohydrates in developed nations has contributed to the epidemics of obesity and cardiometabolic disease. Moreover, the traditional starch-based diets of some developing countries have likely contributed to the rising risk of chronic disease, as decreased physical activity and higher body mass index are associated with rapid urbanization.

However, carbohydrate quality appears to play a more critical role in population health than carbohydrate quantity. A strong case can be made for consumption of high GL grains, potato products, and added sugars (mainly in drinks) being causally related to obesity, diabetes, cardiovascular disease, and some cancers. In contrast, non-starchy vegetables, whole fruits, legumes, and whole kernel grains appear protective. Nevertheless, the metabolic effects of total and high-GI carbohydrates may vary among individuals, depending on the degree of insulin resistance, glucose intolerance, or other inherited or acquired biological predispositions.

Despite much new knowledge about the metabolic effects of carbohydrate and areas of broad consensus, many controversies remain. Most long-term data derive from observational studies, which may be affected by confounding and other methodological problems. Most randomized controlled trials are short, rely on proxy measures, lack blinding, fail to control for treatment intensity across dietary groups, and have limited compliance. Additional relevant considerations in effectiveness studies include behavioral and environmental factors (e.g., food availability and affordability) that affect compliance. The resolution of these controversies (summarized in) will require mechanistically oriented feeding studies and long-term clinical trials, prospective observational research, and examination of economic and environmental impacts.