Valter LongoPhD · biogerontologist, Professor of Gerontology, USC
Yes, keep BMI under 25
What it rests onBody composition is one of the outputs his Longevity Diet is tuned against, alongside the macronutrient split and the fasting periods, drawn from the observational longevity literature.
Source: pmc.ncbi.nlm.nih.gov ↗
Giles YeoPhD, MBE, FMedSci · Professor of Molecular Neuroendocrinology, MRC Metabolic Diseases Unit, University of Cambridge
No, and BMI is the wrong instrument for the question
What it rests onBMI cannot distinguish muscle from fat, and safe fat-carrying capacity is a genetically influenced trait that varies with ancestry, so the same BMI carries different risk in different people. He also cites the UK Parliament Women and Equalities Committee recommendation that individual BMI use be scrapped because it contributes to eating disorders and harms body image. Separately: 'Your weight is just a number on a scale. It doesn't tell you how fit or healthy you are.'
Source: sciencefocus.com ↗
Longo is writing for people optimising for longevity and is explicit that his diet is tuned as a package; Yeo is writing about clinical and self-assessment use of BMI in the general population, and is more concerned about the person at the low-risk end being told they have a problem. Both would accept that BMI works better across a population than within a person.
Both accept that excess fat mass causes metabolic disease, that waist or abdominal measures add information BMI lacks, and that the number is a proxy rather than the thing being measured. Yeo does not say weight is irrelevant; he says there is a personal threshold and that BMI does not locate it.
A validated, affordable individual measure of safe fat-carrying capacity, which Yeo names as the open research question and which would make both sides obsolete at once.
You do, and your call is dated, kept, and yours to change. Follow the people you already trust and what they publish turns into a short daily practice.
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