Diet changes show promise for reversing biological age in older adults

A team at the University of Sydney set out to test whether what people eat might shift how their bodies age at the cellular level. They recruited 104 Australians between 65 and 75, divided them into four groups, and asked each group to follow a different diet for four weeks. The diets varied in two ways: whether the protein came mostly from animals or plants, and whether fat or carbohydrates made up the larger share of calories. After the month ended, the researchers measured 20 different markers in the participants' blood—cholesterol, insulin, inflammation—and used those numbers to calculate what they call biological age: a snapshot of how old the body actually is, as opposed to how many years someone has lived.

Biological age is a useful concept because it captures something chronological age cannot. Two people born in the same year can be in vastly different states of health. One might have strong cardiovascular function, stable metabolism, and low inflammation. The other might show signs of wear across all three. Scientists have learned to read these differences in blood work and other measurable features of the body, and when they combine enough of these signals, they can estimate whether a person's body is aging faster or slower than the calendar suggests.

The four diets in the study were constructed carefully. Each provided 14 percent of total calories from protein. Two were omnivorous—half the protein from meat, fish, and dairy, half from plants. Two were semi-vegetarian, with 70 percent of protein from plant sources. Within each of those pairs, one diet was higher in fat and lower in carbohydrates, the other the reverse. The participants themselves were healthy enough to enroll: no type-2 diabetes, no serious kidney or liver disease, no cancer, no food allergies. Their body mass index ranged from 20 to 35. None smoked.

What the researchers found was striking in its specificity. The omnivorous, high-fat group—the diet closest to what most participants had been eating before the study—showed no meaningful change in biological age markers. But the other three groups all showed measurable shifts toward younger biomarker profiles. The strongest effect appeared in the omnivorous, high-carbohydrate group, where participants ate a diet that was 14 percent protein, 28 to 29 percent fat, and 53 percent carbohydrates. In other words, reducing either the amount of animal protein or the amount of fat, or both, seemed to move the needle on aging-related health markers in just four weeks.

But here is where the researchers became careful. A lower calculated biological age does not prove that aging itself has been reversed, or even slowed in any lasting way. The study lasted only a month. No one knows whether the changes in blood work will persist if people stick with these diets for months or years. No one knows whether a younger biomarker profile actually translates into a lower risk of heart disease, diabetes, or other conditions that come with age. The findings are preliminary—a signal, not proof.

Dr. Caitlin Andrews, who led the work, acknowledged the gap between what the study shows and what it cannot yet claim. "It's too soon to say definitively that specific changes to diet will extend your life," she said. "But this research offers an early indication of the potential benefits of dietary changes later in life." Her supervisor, Associate Professor Alistair Senior, added that longer-term studies would be needed to determine whether dietary changes actually alter the risk of age-related disease. The researchers are calling for future work to test whether these findings hold up in other populations and whether the changes they observed are sustained or predictive of real health outcomes down the road.