Glycated hemoglobin declined more in people who consumed low carbohydrate food than in those who consumed low-fat food in the short term. There is low to high (majority moderate) certainty for small improvements of unclear clinical importance in plasma glucose, triglycerides, and HDL concentrations favoring low carbohydrate food at half of the prespecified time points. Currently available data provide low- to moderate certainty evidence that dietary carbohydrate restriction to a maximum of 40% yields slightly better metabolic control of uncertain clinical importance than reduction in fat to a maximum of 30% in people with T2D.
van Zuren (2018). "Effects of low-carbohydrate compared with low-fat-diet interventions on metabolic control in people with type 2 diabetes: a systematic review including GRADE assessments." Am J Clin Nutr.