Younger Biological Age Linked to Greater Weight Loss in Fast
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- Steve Horvath at UCLA and colleagues ran a 12-day medically supervised fast on 32 healthy volunteers aged 25–72 who consumed just 200–250 calories a day in the form of fruit juice, vegetable broths and honey, with Horvath warning "this is not something to try at home."
- The team tracked biological age using 12 different epigenetic clocks, which produced incongruous results — some clocks ticked older, suggesting stress on the body, while one clock built to detect BMI changes ticked younger.
- Volunteers deemed to have a younger biological age at the start of the study lost more weight than those who were biologically older, a result the researchers said they were not expecting.
- Robin Mesnage at King's College London explained that eating within three narrow windows (7–9am, 11.30am–1pm, 6.30–8pm) pushed participants into a fasting metabolic state, shifting the body from burning food to burning stored fat.
- Paulina Correa-Burrows at the University of Chile said biologically younger people tend to have more efficient mitochondria and better nutrient-sensing pathways, but cautioned that the small sample size makes the results inconclusive.
- Horvath said the mechanism is unknown but most likely involves metabolic adaptability — the ability to swiftly switch between fuel sources when calories are scarce — and now wants to test whether younger biological age also predicts weight loss under less restrictive diets.
Why it matters: With 12 different epigenetic clocks delivering conflicting signals and a sample of just 32, the weight-loss link is intriguing but far from settled — the practical payoff is that future diet programs could be matched to a person's biological age rather than prescribed identically to everyone, and Horvath explicitly flagged that as the next research question.
