Metabolism: how it works and what affects it

Guides

What metabolism actually is, what genuinely affects it, and which common claims the evidence doesn't support.

Written by UCLH Health Editorial Team, Health writers & editors Published 1 March 2026 Updated 19 June 2026

Metabolism is the set of processes your body uses to turn food and drink into the energy it needs to function. It's working constantly — to keep your heart beating, your lungs breathing, your brain active, and your cells maintained — not only when you're moving around.

This guide focuses on what the evidence supports and steers clear of quick-fix claims, of which there are many in this area.

What "metabolic rate" means

Your basal metabolic rate is the energy your body uses just to keep its essential functions running at rest. For most people, this resting energy use accounts for the largest share of the energy they burn each day — more than exercise does for the typical person.

What actually affects it

Several things influence how much energy your body uses, including:

• Body size and composition — larger bodies, and bodies with more muscle, tend to use more energy at rest.
• Age — energy needs generally change across the lifespan.
• Activity — movement of all kinds adds to the energy you use.

What the evidence doesn't support

There's no single food, drink, or supplement that reliably and meaningfully "boosts" your metabolism in a way that transforms your health or weight. Claims promising to do so usually overstate small, short-lived, or insignificant effects. The dependable foundations remain regular movement, enough good-quality sleep, and a balanced way of eating.

A couple of popular claims are worth addressing directly. Apple cider vinegar is often sold as a fat-burner or appetite suppressant — our guide looks at what the evidence really shows. And while fibre won't "speed up" your metabolism, soluble fibre such as psyllium husk can genuinely help with fullness and steadier digestion, which matters more for most people than any metabolic trick.

What actually helps, in practice

If the goal behind "boosting metabolism" is usually managing weight and energy, the evidence points to a few unglamorous but reliable levers:

• Build and keep muscle. Because more muscle tends to raise resting energy use, our guides to muscle health and high-protein foods are more useful here than any "fat-burning" product.
• Protect your sleep. Poor sleep affects appetite and energy; our guide on sleeping better and managing insomnia covers the basics.
• Get the foundations right. Adequate vitamin D is part of general health, though it is not a weight-loss aid — the guide explains the NHS advice.

If you want advice tailored to you, a doctor or a registered dietitian is the right place to go.