Does losing weight help you live longer?
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For a big waist or a lot of extra weight, yes. In the biggest US habits study, a BMI of 25 to 30 carried almost no extra risk, while 35 and over carried 67% more. Your waist tells you more than the scale does.
What we’d do
Measure your waist as well as your weight. If it’s large, lose fat slowly with changes to what you eat, lift weights so you keep your muscle, and keep walking. If you’re a little overweight but fit and strong, put your effort into fitness first, since in the same study doing no exercise carried far more risk than a few extra pounds.
Why the scale misleads
Weight is the number everyone tracks, so it feels like the number that decides your health. But a scale can’t tell muscle from fat, or the fat under your skin from the fat packed around your organs. Two people with the same BMI can carry very different risk.
The simple version
BMI is like judging a house by its weight. A heavy house might be solid brick or might be waterlogged. You learn more by looking at where the weight is, and for a body that means the waist.
What the big US study found
Harvard’s study of 123,219 adults compared BMI groups with a BMI of 23 to 24.9:
| BMI | Risk of dying, against 23 to 24.9 |
|---|---|
| 18.5 to 22.9 | 6% higher |
| 25 to 29.9 | 5% higher |
| 30 to 34.9 | 25% higher |
| 35 and over | 67% higher |
Exercise made a bigger difference in the same people. Doing none carried twice the death rate of moving 3.5 to 6 hours a week. In our calculator, a 50-year-old with a BMI of 30 to 35 gets back about 2 years by reaching a BMI under 25, and one at 35 or over about 5 years. Someone who does no exercise and starts moving 30 minutes a day gets back about 7.
The waist is the better check
A 2020 review in the BMJ pooled 72 studies with over 2.5 million people. Each 4 inches (10 cm) more around the waist went with 11% higher risk of dying, and the link held after allowing for BMI. A bigger waist-to-height ratio did the same. Measure at home with the waist check, and see how to know if you have visceral fat.
Two results that surprise people
Losing weight with diet and exercise didn’t cut heart events in one big trial. In Look AHEAD, 5,145 adults with type 2 diabetes and extra weight were assigned to an intensive program or to standard education. The program group lost 8.6% of their weight in the first year and kept off 6.0% by the end, with better blood sugar and fitness. After nearly 10 years, heart attacks, strokes, heart deaths and hospital stays for chest pain were no lower. The weight loss was real, and the hoped-for heart benefit didn’t show up in that trial.
Surgery added years, but not all of them. In the Swedish Obese Subjects study, 2,007 people who had weight-loss surgery lived about 3 years longer on average than 2,040 people who got usual care. They still lived about 5.5 years less than the general population.
Weight is one part of the picture, and a big waist is the part to act on. In the Harvard study, smoking now and doing no exercise each carried more risk than even a BMI of 35 or over.
4 sources
- Li Y and others, Impact of Healthy Lifestyle Factors on Life Expectancies in the US Population, Circulation, 2018pmc.ncbi.nlm.nih.gov
- Jayedi A and others, Central fatness and risk of all cause mortality: systematic review and dose-response meta-analysis of 72 prospective cohort studies, BMJ, 2020pubmed.ncbi.nlm.nih.gov
- Look AHEAD Research Group, Cardiovascular effects of intensive lifestyle intervention in type 2 diabetes, New England Journal of Medicine, 2013pubmed.ncbi.nlm.nih.gov
- Carlsson LMS and others, Life Expectancy after Bariatric Surgery in the Swedish Obese Subjects Study, New England Journal of Medicine, 2020pubmed.ncbi.nlm.nih.gov
