A study published in the journal Aging Cell has found that a high-carb diet and biological age are meaningfully connected, with participants who followed an omnivorous, higher-carbohydrate eating pattern showing the greatest reductions in age-related biomarkers after just four weeks. The research was conducted by the University of Sydney.
The study recruited 104 adults in their mid-60s and 70s, with participants’ BMI ranging from 20 to 35, according to ScienceDaily. Researchers randomly assigned them to one of four diets for four weeks, with 26 participants per group. Each person consumed 14% of their total calories from protein. Two diets were omnivorous, drawing on an equal mix of plant and animal sources; two were semi-vegetarian, with 70% of protein from plant sources. Within each of those categories, participants followed either a higher-fat, lower-carbohydrate plan or a lower-fat, higher-carbohydrate one.
What the High-Carb Diet Biological Age Study Actually Found
Biological age, as used here, is a measure of how old a person’s cells appear based on biomarkers including insulin levels, blood pressure and cholesterol. It is different from chronological age, which is simply the number of years a person has been alive. There is no single standardised method for calculating it, and it does not currently feature in routine clinical practice.
The omnivorous high-carbohydrate group, known in the study as the OHC group, consumed 14% of calories from protein, up to 29% from fat, and 53% from carbohydrates. Crucially, carbohydrates across all four diets were described in the study as primarily complex carbohydrates from whole, minimally processed sources. The OHC group’s reduction in estimated biological age was also measured with the highest degree of statistical confidence of any group in the trial, according to the University of Sydney.
Participants following the omnivorous high-fat diet, which most closely resembled a typical Western diet, showed no meaningful change in biological age markers over the four weeks. That diet included fewer servings of fruits, vegetables and legumes than the other three. The other three groups all recorded reductions in their estimated biological age based on biomarker results.
ScienceDaily reports that, taken together, the findings suggest reducing dietary fat, animal-based protein, or both may influence ageing-related biomarkers in older adults over a relatively short period. That is a broader conclusion than the headline carbohydrate finding alone, and it points toward overall dietary pattern rather than any single macronutrient as the driver.
Why Researchers and Dietitians Urge Caution
The study’s own authors are careful about how the findings should be read. Caitlin J. Andrews, PhD, study co-author and researcher at the University of Sydney’s School of Life and Environmental Sciences, is clear on what the biomarker shifts actually mean. “These are years of estimated biological age, not years of life, so it means the blood results looked like those of a younger person,” she explains. The researchers also wrote in the study that “caution is warranted in interpreting such changes as evidence of biological age reversal.”
The trial was small, with only 26 participants per group, and the four-week intervention period is short. Whether the observed biomarker shifts reflect lasting changes in the rate of ageing is not something the study can confirm.
Jessica Cording, RD, registered dietitian and author of The Little Book of Game-Changers, puts the carbohydrate finding in context. “People tend to think of bread, rice, pasta, and sugar as carbs, but they often forget that vegetables, fruit, nuts, seeds, and legumes also have carbohydrates,” she says. She suggests the results may be “reflecting more whole foods in a person’s diet,” adding: “It’s not just about the carbs.”
Sandra Zhang, RDN, LDN, registered dietitian and nutritionist at the Frances Stern Nutrition Center at Tufts Medical Center, points out that eating more carbohydrates may also mean higher fibre intake from plant foods, but that is not guaranteed. She notes that different types of fats, carbohydrates, fibre and protein all influence inflammation processes, making dietary quality as important as macronutrient ratios.
Andrews agrees, framing the broader picture plainly: “The benefits across the study tended to be associated with the diets that moved further away from a typical Western diet toward more minimally processed, whole food diets.” She adds that foods such as vegetables, fruits, legumes and whole grains tend to be higher in fibre, more filling and associated with better long-term health than heavily processed carbohydrate-rich alternatives.
Separate research from the Tabriz University of Medical Sciences, published in the European Heart Journal, has also linked eating up to six servings of whole grains a day with lower cholesterol, blood sugar and body weight, each of which can influence biological age markers.
On the protein side, both Cording and Zhang caution against abandoning animal sources entirely. “Plant-based proteins do carry the benefits of low-fat and high-fiber, but they are not necessarily easily absorbed and complete, especially for the elderly,” Zhang says. Cording recommends a balance: “Make room for beans, nuts, and seeds, along with lean meats. There is room for all of it.”
Perhaps the most grounded takeaway comes from Cording on the speed of the results. “Four weeks is nothing,” she says. “It reinforces that you don’t need to eat perfectly for years before your body starts to benefit from you making better food choices.”
