Weight and metabolic syndrome: what has evidence, and what is sold

The supplement industry sells weight loss and the evidence does not support most of it. Where effects exist they are small — a kilogram or two over months, with high heterogeneity — and the interventions with the largest effects are behavioural and not purchasable in a capsule.

Green tea catechins. Pooled analyses of green tea or catechin supplementation show a small reduction in body weight and waist circumference, usually a kilogram or less, with heterogeneity and a signal of publication bias. The effect is real and small.

Fibre. Increasing dietary fibre is associated with lower body weight and increases satiety, and it is one of the more reliable dietary levers. It also improves glycaemic and lipid measures.

Protein. Higher protein intake increases satiety and preserves lean mass during weight loss. The effect on total energy intake is moderate and real.

Metabolic syndrome as a whole. The interventions with the best evidence are a dietary pattern (Mediterranean or DASH), losing 5-10% of body weight, and 150 minutes a week of moderate activity. That combination reduces the incidence of type 2 diabetes substantially in randomised trials of people with impaired glucose tolerance. No supplement has that evidence.

What is sold and should be treated with suspicion. Thermogenics containing ephedra (illegal and dangerous), "fat burners" containing high-dose caffeine and synephrine, raspberry ketones, garcinia, and the endless cycle of new products. Stimulant weight-loss products have caused cardiac events and deaths. Adulteration with undeclared pharmaceuticals — including sibutramine and fluoxetine — is a documented and recurring finding in products marketed for weight loss.

The honest framing. A kilogram of weight loss from a supplement over three months is within the noise of daily weight fluctuation. Weight is not the only outcome that matters, and the metabolic measures — blood pressure, glucose, lipids, waist — respond to behaviour and matter more than the number on the scale. A product that promises substantial weight loss without behaviour change is either ineffective or adulterated, and adulterated is the more common explanation for the ones that seem to work.