About this paper
This is PHC's T2D-specific sister compilation to the general low-carb vs low-fat RCT summary — published and maintained alongside it as part of PHC's evidence section. It narrows the scope to RCTs carried out in people who already have type 2 diabetes, where the clinical stakes (HbA1c, medication load, complications) are highest.
PHC uses the same definitions as the parent table: low-carbohydrate diets are under 130 g of carbs per day, low-fat diets derive under 35% of calories from fat. Trials are tabulated with duration, participant numbers, weight outcome and HbA1c outcome, each linking to the original publication.
The results are more lopsided than in the general population. Across 22 RCTs with 1,661 participants, 20 favoured low-carb and only 2 favoured low-fat. Looking only at statistically significant results, 15 favoured low-carb — and not a single trial showed a statistically significant advantage for low-fat.
HbA1c, the primary glycaemic-control marker, moved sharply in the low-carb arms of these trials, with reductions reaching 28.4 mmol/mol in the most favourable study. This is clinically meaningful territory: reductions of that magnitude can move patients out of diagnostic diabetes ranges and support medication de-prescribing.
The policy implication PHC draws is that Diabetes UK and NHS dietary advice for T2D — which has historically centred on starchy carbohydrates and low-fat eating — is out of step with the RCT evidence in exactly the patient population where the consequences of mis-advice are most severe.
Like the parent table, the T2D summary is a living document. It is accompanied by a printable table, an infographic and a meta-analyses companion, and is explicitly aimed at clinicians who want to cite cause-and-effect evidence in consultations with diabetic patients.