Diet: what actually works

DIETFITS (2018) randomised 609 adults to a healthy low-fat or healthy low-carb diet for a year, both coached toward whole foods. Result: −5.3 kg vs −6.0 kg — not a significant difference. It had pre-registered that a gene pattern and insulin level would predict who did best on which diet. Neither did. Individual results ranged from −30 kg to +10 kg within both arms, driven by adherence, not assignment.

Pooled across dozens of trials, low-carb vs low-fat differ by roughly ~1 kg at 12 months — clinically trivial next to the 5–10 kg swings adherence produces. The 2007 A-TO-Z trial gave Atkins a modest early edge over the weakest comparator, but that edge largely vanished once diet quality was equalised. The honest headline: pick a high-quality pattern you can sustain. Evidence ●●●●●

This is where low-carb is under-sold, not over-sold. In type 2 diabetes it produces the largest short-term drops in blood sugar of any dietary approach — one continuous-care program cut HbA1c from 7.6% to 6.3% with ~12% weight loss and got most patients off insulin. It also reliably lowers triglycerides and raises HDL. Caveat: in lean, metabolically healthy people, LDL cholesterol can rise sharply (the ‘lean-mass hyper-responder’ pattern) — reversible by adding carbs back, but worth monitoring. Evidence ●●●●○ for glycaemia

Both are excellent patterns whose headline benefits are not primarily about the scale. Mediterranean eating is strongest for cardiovascular risk and only modestly slimming (~1.8 kg vs control, and mainly with calorie restriction). DASH was built for blood pressure (it lowers it largely independently of weight). Choose them for those endpoints; expect weight loss only if you also hold a deficit.

Low-carb diets move the scale fast in week one — but that is mostly glycogen and water (see section 1), not a metabolic head start. Motivating, but don’t mistake it for fat.

Across the whole literature, a durable fat-loss diet looks unremarkable: protein-forward, fiber-rich, built on mostly whole foods, in a modest deficit, following a pattern you can actually maintain. Then layer the specific-job logic: diabetes or high triglycerides → lean lower-carb; high blood pressure → DASH; cardiovascular risk → Mediterranean.