Weight management: what the evidence supports

How weight is assessed

What we know

The NHS uses body mass index (BMI) and waist-to-height ratio. For most adults a BMI of 25 to 29.9 is classed as overweight and 30 or more as obese. Lower thresholds apply to people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds (23 to 27.4 overweight, 27.5 or more obese), because health risks rise at a lower BMI.

The NHS also suggests keeping your waist to less than half your height. Waist size reflects fat stored around the organs, which is closely linked to cardiometabolic risk. BMI cannot tell muscle from fat, so it is a starting point, not a verdict.

What a realistic change looks like

• The NHS suggests aiming to lose weight steadily, at about 0.5 to 1kg (1 to 2lb) a week.
• Losing a small amount, 5 to 10% of body weight, can improve health.
• Sustained changes to eating and activity work better than short, severe diets.

Protecting muscle

Losing weight quickly or eating very little increases the share of weight lost from muscle. Strength exercises on at least two days a week, as the UK activity guidelines recommend, and enough protein help keep strength and mobility. Read why strength matters more with age.

Where the gut fits in

What may help

A fibre-rich diet can help with fullness and is good for gut health generally. Research on the gut microbiome and weight is active, but it has not produced a proven microbiome-based way to lose weight. See the gut microbiome: what we know and what we don't.

Medicines and specialist support

Weight-loss medicines are available on the NHS for some people, depending on BMI and weight-related health conditions, and are usually prescribed alongside diet and lifestyle advice. They are not suitable for everyone and need medical supervision. NHS weight management services are available in many areas, and in some you can refer yourself.

References

1. NHS. Obesity and Obesity: treatment. Accessed 29 September 2026.
2. National Institute for Health and Care Excellence. Overweight and obesity: prevention and management (NG246). Replaces CG189.
3. Department of Health and Social Care. UK Chief Medical Officers' physical activity guidelines. 2019.