High-Carb Diet May Reverse Biological Age by 3.5 Years in 4 Weeks An Australian study finds that a high-carb diet may reduce biological age by 3.5 years in just four weeks, offering new hope for slowing ageing. A recent Australian study published in the journal Aging Cell suggests that a high-carbohydrate diet may reduce biological age by an average of 3.5 years in just four weeks. The research, involving 104 adults aged 65 to 75, adds to growing evidence that diet can influence the ageing process. Study Details and Dietary InterventionsThe study, led by Caitlin Andrews from the University of Sydney’s School of Life and Environmental Sciences, divided participants into four groups, each following a different diet for four weeks: omnivorous high-fat (OHF), omnivorous high-carbohydrate (OHC), semi-vegetarian high-fat (VHF), or semi-vegetarian high-carbohydrate (VHC). All diets consisted largely of minimally processed foods, with carbohydrates from whole foods such as wholegrains, legumes, and fruits and vegetables. These were not weight-loss diets, although most participants lost weight.Biological age was calculated using clinical measurements such as blood pressure and 20 biomarkers, including cholesterol, insulin, and C-reactive protein, which is linked to inflammation. At the end of the study, those on the omnivorous high-fat diet showed no change, but participants in the other three groups reduced their biological age.The omnivorous high-carbohydrate diet had the most significant effect. It comprised 14 percent of calories from protein, 28 to 29 percent from fat, and 53 percent from complex carbohydrates. People on this diet finished, on average, about three-and-a-half years younger than they were at the study start, compared with those on the OHF diet. The semi-vegetarian diets resulted in an average reduction of three years.Protein Sources and Diet CompositionIn both omnivorous diets, half of the protein was from animal sources and the rest from plants. In the semi-vegetarian diets, 70 percent of the protein was from plants. Dairy was included in all four diets. A standard breakfast across groups was muesli with yoghurt. Semi-vegetarian options involved swapping red meat and poultry for legumes, soy, nuts, and seeds, but did not cut animal foods completely. For example, tikka masala was made with either chicken or tofu, and casserole with either lamb or beans.Caitlin Andrews explained that the trial was designed to be realistic. Debates about diet and ageing often get framed as either/or, such as plant versus animal protein or carbs versus fat. In reality, people eat both at once, so the trial allowed researchers to look at protein sources and the fat-to-carb balance together and see whether they interact to create a beneficial effect.On average, participants lost about 4lb over the four weeks, and 94 percent lost some weight. Andrews told Good Health that weight loss was seen across all groups, including the omnivorous higher-fat group, which showed no meaningful change in biological age, so weight loss alone does not explain the differences between diets.Mechanisms and Expert PerspectivesWhile it is not clear why those on a low-fat, high-carb diet did the best, the researchers were surprised by the speed of change. Andrews noted that four weeks is short, and they did not necessarily expect to see a shift in that window. However, some individual biomarkers like C-reactive protein are known to respond to diet within a relatively short timeframe. One factor is that the diets moved further away from a typical Western pattern toward more fibre-rich wholefoods.Dr Thomas Holland, a physician scientist at Rush University in Chicago, who is investigating the impact of lifestyle modifications on chronic diseases of ageing, said the findings from the University of Sydney backed up previous research. For example, a large-scale study published in Nature Medicine last year, which followed more than 100,000 participants for up to 30 years, found that people who had healthy long lives had a higher intake of fruits, vegetables, whole grains, unsaturated fats, nuts, legumes, and low-fat dairy products. Those who reported higher intakes of salt, trans fats, sugary beverages, and red or processed meats were less likely to reach 70.Dr Holland told Good Health that this makes complete sense because the diets that improved had several things in common, including lower saturated and trans fats and higher fibre and fruit and vegetables. He added that fibre, for instance, can help steady blood sugar levels and improve the gut microbiome.