Low-carb diets exert short-term effects on glucose control, weight loss

Patients with type 2 diabetes mellitus (T2DM) who follow low-carbohydrate diets achieve small improvements in glycated haemoglobin and weight, but these benefits are not sustained in the long term, a study has found.

Researchers conducted a systematic review of randomized controlled trials comparing low-carbohydrate diets (mild: 26–45 percent of total calories from carbohydrates; very low: <26 percent of total calories from carbohydrates and/or <130 g of carbohydrates daily) with a carbohydrate-balanced diet (45–60 percent of total calories from carbohydrates), with the intervention lasting at least 12 weeks. The meta-analysis included 37 trials comprising 3,301 patients.

Of the studies, 28 excluded patients with kidney disease and 19 excluded those with previous cardiovascular disease. Overall, average carbohydrate intake in low-carb diets was 36 percent of total energy.

Low-carb diets led to a marked reduction in HbA1c at 3 months (mean difference [MD], −0.17 percent, 95 percent confidence interval [CI], −0.27 to −0.07) but a significant increase at 24 months (MD, 0.23 percent, 95 percent CI, 0.02–0.44). There were no differences seen at 6 and 12 months.

Similarly, very-low-carb diets reduced HbA1c at 3 months (MD, −0.43 percent, 95 percent CI, −0.60 to −0.26) and 6 months (MD, −0.40 percent, 95 percent CI, −0.59 to −0.22), but not at 12 and 24 months.

Diets low on carbohydrates also helped individuals lower their body mass index at 6 months (MD, −1.35 kg/m², 95 percent CI, −2.18 to −0.52) but not at other timepoints.

A few trials evaluated renal function, so renal safety could not be assessed. Finally, cutting down on carbohydrates conferred no significant benefits for body weight, lipid profile, or blood pressure in the long term.