If you sit down and read about obesity and health, you realize that the evidence is complicated, which is why bio-medical researchers need to conduct big meta-analyses that combine many studies to get a handle on the issue. For example, this 2013 JAMA meta-analysis found that being a little overweight is associated with *lower* all-cause mortality, while being more obese increases mortality. Here is the findings section:
Random-effects summary all-cause mortality HRs for overweight (BMI of 25-<30), obesity (BMI of ≥30), grade 1 obesity (BMI of 30-<35), and grades 2 and 3 obesity (BMI of ≥35) were calculated relative to normal weight (BMI of 18.5-<25). The summary HRs were 0.94 (95% CI, 0.91-0.96) for overweight, 1.18 (95% CI, 1.12-1.25) for obesity (all grades combined), 0.95 (95% CI, 0.88-1.01) for grade 1 obesity, and 1.29 (95% CI, 1.18-1.41) for grades 2 and 3 obesity. These findings persisted when limited to studies with measured weight and height that were considered to be adequately adjusted. The HRs tended to be higher when weight and height were self-reported rather than measured.
Notice that the category of “any obese” (grades 1-3) only results in a modest increase in mortality (1.18 compared to a baseline of 1.00). In other words, weight has very non-linear and subtle relationship with mortality. This is not an isolated study, this comes up a bit.
Though it’s a little old, I recently found an interesting Nature article called “Healthy obese versus unhealthy lean: the obesity paradox” that provides some important context. Apparently, health researchers have this idea of “fat but fit.” To really understand if someone is healthy, don’t just use BMI, you need to understand how active or fit they are, which is measured in different ways. Here is the key clip:
The ideal situation is for all individuals to maintain a lean, metabolically healthy profile, and to avoid low fitness throughout adult life.17 However, substantial evidence suggests that patients with MHO have minimal to no increase in risk of CHD.6,17,19 Furthermore, patients with overweight or obesity who are fit have a better prognosis than underweight or lean patients,43,52 particularly those in the lower end of the normal BMI group (that is, BMI 18.5–22.0 kg/m2 ) who are unfit.43–46,52 In patients with cardiovascular diseases, a strong obesity paradox exists,1,7,8 (Ed. - numbers denote references in text, from page 7)
In other words, if you exercise and your metabolism is fine and you are a little chubby, you’re probably more than ok, especially compared to leaner inactive people.
Bottom line: If your doctor is mechanically going on BMI and not looking at the whole picture, gently suggest that they look again.
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I thought you might find this thread interesting: https://x.com/johnspeakman4/status/1547593316732006400