Older adults between 65 and 75 experienced reductions in estimated biological age after following specific diets for just four weeks, according to new research from the University of Sydney published in Aging Cell.
Chronological age counts the years a person has lived, but biological age measures how well the body actually functions under the wear and tear of time. New findings from researchers at the University of Sydney’s School of Life and Environmental Sciences demonstrate that these physiological markers of aging can shift surprisingly quickly in response to targeted dietary adjustments.
The Nutrition for Healthy Living Study Design
The research drew on data from the Nutrition for Healthy Living study, which followed 104 participants aged 65 to 75 years. Every participant in the trial shared specific baseline characteristics: body mass index (BMI) ranging from 20 to 35, non-smokers, non-vegetarians, and free from serious complications such as type-2 diabetes mellitus, cancers, renal or liver disease, or food allergies and intolerances.
Participants were randomly assigned to one of four distinct diet plans. Each of the four diets derived 14 percent of total daily energy from protein.
- Omnivorous high-fat (OHF): Protein split evenly between animal and plant sources, with higher fat content.
- Omnivorous high-carbohydrate (OHC): Protein split evenly between animal and plant sources, with higher carbohydrate content.
- Semi-vegetarian high-fat (VHF): 70 percent of protein sourced from plants, with higher fat content.
- Semi-vegetarian high-carbohydrate (VHC): 70 percent of protein sourced from plants, with higher carbohydrate content.
Biomarkers and Biological Age Scores
To evaluate biological age, researchers analyzed 20 physiological biomarkers—including blood pressure, cholesterol, insulin, and C-reactive protein levels. These measurements were incorporated using the Klemera-Doubal Method (KDM) to establish baseline and post-intervention scores for each individual.
The results revealed a clear dividing line based on how significantly the experimental diets departed from participants’ prior eating habits. The OHF group, whose meals most closely matched their baseline diets, showed no meaningful change in their biological age biomarker profile.
Which Diets Produced the Strongest Changes?
By contrast, participants in the other three groups—all of which involved reducing dietary fat or cutting back on animal-based protein—demonstrated measurable reductions in biological age. The most pronounced effect was observed in the omnivorous high-carbohydrate group.
In that specific group, daily energy comprised 14 percent protein, 28 to 29 percent fat, and 53 percent carbohydrates. This high-carb group scored 3.5 to 4 years younger in biological age compared with the unchanging OHF group, and their improvement was estimated with the highest degree of statistical confidence.
Researchers emphasized that the high-carbohydrate diets excluded refined sugars and ultra-processed foods, relying instead on complex carbohydrates rich in fiber and lower in fat.
What the Findings Mean and What Remains Unknown
While the four-week timeline points to a high degree of metabolic malleability in older adults, the study authors urge caution against overstating the conclusions. Short-term biomarker improvements do not automatically guarantee long-term health transformations.
“Longer term dietary changes are needed to assess whether dietary changes alter the risk of age-related diseases.”
Associate Professor Alistair Senior, School of Life and Environmental Sciences and the Charles Perkins Centre
Additional commentary from the research team underscores that more investigation is required before issuing broad dietary prescriptions for longevity.
“It’s too soon to say definitively that specific changes to diet will extend your life. But this research offers an early indication of the potential benefits of dietary changes later in life.”
Dr. Caitlin Andrews, University of Sydney
Next Steps for Aging and Nutrition Research
Future investigations will need to determine whether these biological age reductions persist over extended periods and whether similar dietary adjustments yield comparable results in different age cohorts.
“Future research should explore whether these findings extend to other cohorts and whether the changes recorded are sustained or predictive of long-term outcomes.”
Associate Professor Alistair Senior, School of Life and Environmental Sciences and the Charles Perkins Centre
Whether these short-term physiological shifts can be successfully translated into sustained, multi-year disease prevention strategies remains the central question for subsequent trials.