Carbohydrate restriction for diabetes: rediscovering centuries-old wisdom

Summary

This 2021 review in the Journal of Clinical Investigation argues that reducing dietary carbohydrates—especially very low‑carb (VLC) approaches—can meaningfully improve blood sugar control for people with diabetes, potentially at lower cost than conventional high‑carb treatment. It traces a centuries‑long history where carb restriction was standard before insulin was discovered, then fell out of favor as technology advanced—despite persistent post‑meal glucose spikes with high‑carb eating.

Key Findings

• Carbs drive after‑meal blood sugar spikes; fewer carbs mean smaller spikes and lower insulin needs.
• In type 1 diabetes (T1D), small randomized trials and case reports show VLC diets can yield near‑normal HbA1c, lower insulin doses, steadier glucose, and less time in hypoglycemia. The evidence is promising but limited by short duration and small samples.
• In type 2 diabetes (T2D), multiple meta‑analyses show reduced‑carb diets modestly lower HbA1c (around 0.5%) and often cut medication use; benefits appear even without major weight loss.
• Technology (rapid insulin, CGM, pumps, hybrid closed‑loop) helps, but many people still miss glycemic targets on high‑carb diets—especially adolescents—suggesting diet quality/amount remains crucial.
• Safety concerns for VLC (hypoglycemia, ketoacidosis, nutrient gaps, growth in children) are addressed: reports show low severe events when insulin is adjusted, nutritional ketosis is distinct from ketoacidosis, and careful diet planning can mitigate deficiencies; nonetheless, long‑term, well‑powered trials in T1D are needed.
• Lipids: triglycerides and HDL often improve with carb restriction; LDL responses vary. The paper notes ongoing debate and emphasizes that HbA1c and triglycerides were stronger CVD predictors than LDL in DCCT/EDIC analyses, but does not claim carb restriction eliminates cardiovascular risk.

Practical Applications for People with Diabetes

• Consider lowering total digestible carbs to reduce post‑meal spikes and insulin dose needs; pairing this with CGM can make benefits visible day‑to‑day.
• Emphasize carb quality (lower glycemic index/load) even if you don’t go VLC; this can modestly improve HbA1c and reduce hypoglycemia.
• If trying VLC, do it with medical supervision to adjust insulin or meds safely and to plan nutrient‑dense foods (non‑starchy vegetables, dairy, nuts, seeds, limited low‑sugar fruits).
• Pre‑bolus timing still matters: insulin action often lags glucose appearance; lowering carbs reduces this mismatch but doesn’t eliminate the need to time doses.
• Economic relevance: reducing rapid‑acting insulin needs and overall dose may lower out‑of‑pocket costs, a meaningful factor given high insulin prices.

Why It Challenges Conventional Wisdom

The review highlights that high‑carb recommendations grew with insulin’s availability and cholesterol concerns—not because high‑carb proved superior for long‑term diabetic outcomes. With modern monitoring showing how carbs drive glycemic variability, the authors argue it’s reasonable to revisit carb reduction as a primary lever—pending rigorous, long‑term trials.

Bottom Line

Carb restriction—especially very low‑carb—shows real promise for improving glycemia in T1D and T2D, often with lower insulin needs and steadier glucose. The approach looks cost‑effective and practical for many, but definitive long‑term safety and outcomes data are still required.