A University of Sydney study found that older adults who reduced dietary fat or animal-based protein for just four weeks showed measurable reductions in biological age. The findings offer an early look at how diet could reshape aging outcomes later in life.
A short-term dietary shift may be enough to move the needle on how quickly — or slowly — the body appears to be aging, according to new research out of the University of Sydney.
Scientists found that adults between the ages of 65 and 75 who reduced either their dietary fat intake or their consumption of animal-based protein for just four weeks showed signs of a lower “biological age,” as measured through a panel of blood biomarkers. The study, published in the journal Aging Cell, was led by Caitlin Andrews, a postdoctoral researcher in the University of Sydney’s School of Life and Environmental Sciences.
While everyone ages chronologically at the same rate, biological aging — how the body’s systems are actually holding up — varies considerably from person to person. Researchers can estimate biological age using biomarkers like blood cholesterol, insulin levels and C-reactive protein, a marker of inflammation. A lower biological age relative to one’s chronological age is generally associated with better health and a longer life.
How the Study Worked
The trial, conducted at the University of Sydney’s Charles Perkins Centre as part of the Nutrition for Healthy Living study, enrolled 104 non-smoking participants with no major health conditions such as type 2 diabetes, cancer or kidney disease. All participants were non-vegetarians with a BMI between 20 and 35.
Participants were randomly assigned to one of four diets, each deriving 14% of total energy from protein. Two diets were omnivorous — drawing protein equally from animal and plant sources — and two were semi-vegetarian, with 70% of protein coming from plants. Within each category, participants were further split into high-fat/low-carbohydrate or low-fat/high-carbohydrate plans, producing four groups: omnivorous high-fat (OHF), omnivorous high-carbohydrate (OHC), semi-vegetarian high-fat (VHF), and semi-vegetarian high-carbohydrate (VHC).
The OHF group’s diet most closely resembled what participants were already eating before the study began, and this group showed no meaningful change in biological age biomarkers. The other three groups, each of which made more significant dietary shifts, all showed reductions. The OHC group — eating a diet with roughly 53% of energy from carbohydrates and only 28-29% from fat — produced the most statistically confident results.
Why It Matters
Researchers used data from 20 different biomarkers to calculate a composite biological age score for each participant. The speed at which three of the four dietary groups showed improvement — in just one month — is notable, suggesting the body may respond to dietary changes more quickly than previously understood.
That said, the authors are careful to frame these findings as preliminary. Whether a reduced biological age score in biomarkers actually translates to lower disease risk or a longer life remains to be seen.
“Longer term dietary changes are needed to assess whether dietary changes alter the risk of age-related diseases,” senior author Alistair Senior, an associate professor in the School of Life and Environmental Sciences and the Charles Perkins Centre, who supervised the research, said in a new release.
Andrews struck a similarly cautious tone while acknowledging the promise of the findings.
“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,” Andrews said in the news release.
Andrews also pointed to what comes next for this line of research.
“Future research should explore whether these findings extend to other cohorts and whether the changes recorded are sustained or predictive of long-term outcomes,” added Andrews.
What This Means for Young People
Although this study focused on adults aged 65 to 75, its implications reach beyond that cohort. Dietary patterns established in young adulthood often persist for decades, and research increasingly points to earlier lifestyle choices as key drivers of how people age over the long term. For college students and young professionals navigating everything from dining halls to first apartments, evidence that food choices can measurably affect the body’s aging clock adds weight to the case for building healthier eating habits now.
The study’s authors call for broader trials that test these findings across different age groups and over longer periods. For now, though, the evidence adds to a growing body of research linking diet quality — particularly reductions in saturated fat and animal protein — to healthier aging outcomes.
Source: University of Sydney