There is no direct or unique causal link between intake of sugars and risk of type 2 diabetes. Research shows that weight gain due to excess energy from any source is a risk factor for type 2 diabetes. New research finds that high dietary glycemic index (GI) and glycemic load (GL) is a factor that likely contributes to type 2 diabetes incidence, while low dietary GI and GL can reduce the risk of type 2 diabetes.

Key research

Lean MEJ & Te Morenga L. (2016). Sugar and Type 2 diabetes. British Medical Bulletin, 120(1):43–53.
Much of the association between sugars and T2DM is eliminated by adjusting data for body mass index (BMI). However, BMI adjustment does not fully account for adiposity. Excess sugar can promote weight gain, thus T2DM, through extra calories, but has no unique diabetogenic effect at physiological levels.

Rippe JM & Angelopoulos TJ. (2016). Sugars, obesity, and cardiovascular disease: results from recent randomized control trials. Eur J Nutr, 55:45-53.
This review of randomised trials, systematic reviews and meta-analyses does not support a link between sugar consumption at normal levels and various adverse metabolic and health effects including those on energy-regulating hormones, obesity, CVD, diabetes, liver fat accumulation and neurologic responses.

Livesey G, Taylor R, Livesey HF, et al. (2019). Dietary glycemic index and load and the risk of type 2 diabetes: assessment of causal relations. Nutrients, 11(6):1436.
All nine of the Bradford-Hill’s criteria for causality were met for GI and GL indicating that the authors can be confident of a role for GI and GL as causal factors contributing to incident T2D. In addition, neither dietary fibre, cereal fibre nor wholegrain were found to be reliable or effective surrogate measures of GI or GL. The cost–benefit analysis suggests food and nutrition advice favours lower GI or GL, and would produce significant potential cost savings in national healthcare budgets.

Jayedi A, Soltani S, Jenkins D, et al. (2020). Dietary glycemic index, glycemic load, and chronic disease: an umbrella review of meta-analyses of prospective cohort studies. Crit Rev Food Sci Nutr, Dec 1: 1-10.
This umbrella review of meta-analyses found a positive association between dietary GI and the risk of type 2 diabetes, coronary heart disease, and colorectal, breast, and bladder cancers, as well as between dietary GL and the risk of coronary heart disease, type 2 diabetes, and stroke. There was no significant association with cancers at other sites. The certainty of evidence ranged from very low to low. 

Other research

Livesey G, Taylor R, Livesey HF, et al. (2019). Dietary glycemic index and load and the risk of type 2 diabetes: a systematic review and updated meta-analyses of prospective cohort studies. Nutrients, 11(6):1280.
Critical analyses of prospective cohort studies provide robust evidence that diets higher in glycemic index (GI) and load (GL), independently of dietary fiber, substantially elevate the risk of type-2 diabetes among healthy populations of men and women.

Biggelaar LJCJ, Eussen S, Sep S, et al. (2017). Associations of dietary glucose, fructose, and sucrose with β-cell function, insulin sensitivity, and type 2 diabetes in the Maastricht study. Nutrients, 9(4):380.
Higher intake of glucose, not fructose and sucrose, was associated with higher insulin sensitivity, independent of dietary fibre. No convincing evidence was found for associations of dietary glucose, fructose, and sucrose with β-cell function in this middle-aged population.

Rippe JM & Angelopoulos TJ. (2016). Added sugars and risk factors for obesity, diabetes and heart disease. Int J Obes, 40:S22-S27.
The normal added sugars in the human diet (for example, sucrose, high-fructose corn syrup and isoglucose) when consumed within the normal range of normal human consumption or substituted isoenergetically for other carbohydrates, do not appear to cause a unique risk of obesity, diabetes or cardiovascular disease.

Imamura F, O'Connor L, Ye Z, et al (2015). Consumption of sugar sweetened beverages, artificially sweetened beverages, and fruit juice and incidence of type 2 diabetes: systematic review, meta-analysis, and estimation of population attributable fraction. BMJ: 351:h3576.
Habitual consumption of sugar sweetened beverages was associated with a greater incidence of type 2 diabetes, independent of adiposity. Although artificially sweetened beverages and fruit juice also showed positive associations with incidence of type 2 diabetes, the findings were likely to involve bias.