Keep your BMI between 20 and 25, and lose weight if you are overweight
- Moderate value
- Evidence A
- Buys life
- Disputed
- Free
- Takes time daily
- Long-term effort
In plain words
The chance of dying is lowest at a BMI of 20–25. At a BMI of 27.5–30 it is about 20% higher, at 30–35 about 45% higher, and at 35–40 nearly double. East Asians are more sensitive to excess weight: for every 5 points of BMI above 25, the risk is about 40% higher.
- Cost
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Free. Diet and exercise take time every day. This is the item in the section that takes the most willpower: you have to watch what you eat and keep moving over the long term, and keeping the weight off is harder than losing it.
- What you get
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Pooling individual data from 239 studies that followed people forward in time (observational, not assigning groups). This analysis kept only three kinds of people: never-smokers, people with no chronic disease at enrollment, and people who survived at least 5 years after enrollment. Result: the risk of death was lowest at a BMI of 20–25. BMI 25–27.5 was about 7% higher (HR 1.07). 27.5–30 was about 20% higher (HR 1.20). 30–35 was about 45% higher (HR 1.45). 35–40 was about 94% higher (HR 1.94). 40–60 was 2.76 times (HR 2.76). For people with a BMI above 25, each 5 kg/m² higher raised the risk in East Asian populations by about 39% (HR 1.39).
- Notes
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Disputed. One side holds that being a little heavy means living longer. Their pooled result: overweight people had about 6% lower risk of death, and mildly obese people about 5% lower. The disagreement is mostly about whether to remove three kinds of data: smokers, people who are already ill, and the first few years after enrollment. They are removed because seriously ill people lose weight first. After the 239-study analysis removed those three kinds, the risk from overweight reappeared. Also note that no randomized trial shows that losing weight itself lowers overall mortality. The benefits above come from comparing people of different builds side by side; they don't mean you will lower your risk by that much by losing weight. If you want to lose weight, you needn't worry about meal timing; neither breakfast nor 16:8 intermittent fasting has extra benefit, see §6.26 (don't count on breakfast or 16:8 to control your weight)
- Evidence grade
- A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.
- Sources
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- Global BMI Mortality Collaboration (2016). Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies in four continents. Lancet. https://doi.org/10.1016/S0140-6736(16)30175-1
- Flegal KM 等 (2013). Association of all-cause mortality with overweight and obesity using standard body mass index categories: a systematic review and meta-analysis. JAMA. https://doi.org/10.1001/jama.2012.113905（争议方）
Mentioned in
- Lose weight, quit smoking, and keep blood pressure and blood sugar under control; erectile function can improve along with them
- Don't count on eating breakfast or 16:8 intermittent fasting to control your weight; choose meal times you can keep up long term
- Don't use extreme dieting, fasting or induced vomiting to control your weight; if you want to lose weight, do it on the exercise side
Translated from the Chinese original. Original book, section 2, tip 32. This section is about health and medicines. It is general information, not a substitute for a doctor’s diagnosis or prescription. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer