We all get old eventually if we're lucky, but not always at the same rate.
While everyone's chronological age advances uniformly, biological age can vary depending on factors such as genes, the air we breathe, and the food we eat.
Diet is one of the modifiable factors linked to resilience to the rigors of aging. It can affect inflammation, metabolism, cardiovascular health, and other systems that tend to shift as we age.
These effects can make us seem younger than we really are at the cellular level.
According to a new study, nutritious food may provide this benefit even if your chronological age is already relatively high. Starting young might be best, but the results suggest that dietary changes in older age still offer an effective way to rapidly improve biomarkers linked to aging.
"It's too soon to say definitively that specific changes to diet will extend your life," cautions first author Caitlin Andrews, a nutrition scientist at the University of Sydney in Australia.
"But this research offers an early indication of the potential benefits of dietary changes later in life."
Andrews and colleagues used data from the Nutrition for Healthy Living (NHL) study, a randomized clinical trial that investigated the effects of dietary protein source and individual macronutrients on the health of older adults.
For the NHL study, researchers recruited people aged 65 to 75 with a body mass index between 20 and 35 and then randomly assigned them to one of four diets for four weeks, supplying all study participants' meals.
Each diet provided 14 percent of its energy as protein. Two were omnivorous (with protein split evenly between animal and plant sources), and two were semi-vegetarian (in which 70 percent of protein came from plants).
Within the omnivorous and semi-vegetarian groups, participants also received an additional diet to complement their protein intake, featuring either high-fat, low-carbohydrate or low-fat, high-carbohydrate fare.
This resulted in four overall diet types: omnivorous high-fat (OHF), omnivorous high-carbohydrate (OHC), semi-vegetarian high-fat (VHF), and semi-vegetarian high-carbohydrate (VHC).
Scientists can estimate your biological age based on biomarker profiles, or measures of physiological function, that may reveal more about your health and potential longevity than the mere duration of time since your birth.
The University of Sydney researchers analyzed NHL data to determine whether dietary changes in older people could influence biological age, which they estimated using the Klemera-Doubal Method.
The new study incorporated data from 20 biomarkers – including blood pressure, and blood levels of insulin, cholesterol, and C-reactive protein – to determine subjects' biological ages.
Of the four diet categories, OHF was most similar to the typical baseline diets subjects reported eating before the study began, researchers note. That may explain why it also had the least effect on their biological ages, with no significant change in relevant biomarkers.
The other three diets, however, did seem to reduce subjects' biological ages.
Those who ate the OHC diet showed a significant reduction, the study found, while the VHF and VHC groups exhibited similar reductions but did not always reach statistical significance.
It remains unclear if these effects would translate to durable protection against deteriorating health.
"Longer-term dietary changes are needed to assess whether dietary changes alter the risk of age-related diseases," says Alistair Senior, a nutritional ecologist at the University of Sydney.
These hopeful preliminary findings highlight the potential for further study.
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"Future research should explore whether these findings extend to other cohorts," Andrews says, "and whether the changes recorded are sustained or predictive of long-term outcomes."
The study was published in Aging Cell.