No. of Recommendations: 5
Healthcare is a major part of the U.S. economy (now about 19% of GDP), and obesity can affect health.
A new obesity definition is making the rounds, resulting in an increased rate in the U.S. (69% with the new definition vs. 43% with the old definition). The new definition includes a waist measurement, which makes sense to me (although my doctor does not measure it). Belly fat is more unhealthy than thigh fat.
The lowest mortality is in the BMI range of 25–30 which is considered "overweight". The mortality study shows that just dividing the population into obese/not obese is not useful. At least 5 groups are needed:
mortality
BMI Category BMI Range hazard ratio
Underweight Below 18.5 1.5
Healthy 18.5 to 24.9 1.2
Overweight 25.0 to 29.9 1.0
Obesity 30.0 to 34.9 1.3
Extreme Obesity 35.0 or above 2.0
BMI lower than 20 or above 35 has increased mortality hazard ratio. BMI is proportional to weight. With 5' 9" height, 27.5 +/- 5 BMI range converts to a 186 +/- 34 lb. low-mortality target.
=== links ===
Implications of a New Obesity Definition Among the All of US Cohort, October 2025
"68.6% had obesity according to the new definition vs 42.9% according to the traditional definition, due to inclusion of individuals with anthropometric-only obesity. Among the overall cohort, 108650 individuals (36.1%) had clinical obesity according to the new definition; this prevalence increased with age, as 24498 of 45018 individuals 70 years or older (54.4%) had clinical obesity."
https://jamanetwork.com/journals/jamanetworkopen/f...Definition and diagnostic criteria of clinical obesity, March 2025
"Current BMI-based measures of obesity can both underestimate and overestimate adiposity and provide inadequate information about health at the individual level, which undermines medically-sound approaches to health care and policy. ... We recommend that BMI should be used only as a surrogate measure of health risk at a population level, for epidemiological studies, or for screening purposes, rather than as an individual measure of health. Excess adiposity should be confirmed by either direct measurement of body fat, where available, or at least one anthropometric criterion (eg, waist circumference, waist-to-hip ratio, or waist-to-height ratio) in addition to BMI, using validated methods and cutoff points appropriate to age, gender, and ethnicity."
https://www.thelancet.com/journals/landia/article/...(24)00316-4/abstract
Impact of Body Mass Index on All-Cause Mortality in Adults: A Systematic Review and Meta-Analysis, 2024
"Results: The meta-analysis showed a U-shaped relationship between BMI and all-cause mortality risk, with the lowest mortality in the BMI range of 25–30 kg/m2. Subgroup analysis showed a J-shaped relationship, with greater risk in the highest BMI range (>35 kg/m2). Among the elderly, BMI values <20 kg/m2 were associated with the highest risk. Among diabetic patients, a U-shaped relationship was noticed, again with the highest risk in the lowest (<20 kg/m2) and highest BMI range (>35 kg/m2). Among patients with cardiovascular disease, the risk increased with BMI values <25 kg/m2 but did not noticeably change for BMI exceeding that value. Among cancer patients, the relationship was less pronounced than in other subgroups, with a slightly higher risk (>35 kg/m2). Conclusions: Our results show that the lowest mortality is observed among patients with BMI 25–30 kg/m2. Reduction of body mass should not be a universal recommendation in clinical practice, but it should be individualized. ... This phenomenon is known as the “obesity paradox”, and clearly shows that the association between body mass and mortality is much more complex than previously thought."
https://pmc.ncbi.nlm.nih.gov/articles/PMC11051237/BMI Category BMI Range
Underweight Below 18.5
Healthy 18.5 – 24.9
Overweight 25.0 – 29.9
Obesity 30.0 or above
https://www.nhlbi.nih.gov/calculate-your-bmi 