# When a calorie is not just a calorie > https://doi.org/10.1016/j.cmet.2023.06.008 https://doi.org/10.1016/j.cmet.2023.06.008 When a calorie is not just a calorie: Diet quality and timing as mediators of metabolism and healthy aging. ## Abstract > An epidemic of has affected large portions of the world, increasing the risk of developing many different age-associated diseases, including , [cardiovascular disease](https://wiki.g15e.com/pages/Cardiovascular%20disease.txt), and [diabetes](https://wiki.g15e.com/pages/Diabetes.txt). In contrast with the prevailing notion that "a calorie is just a calorie," there are clear differences, within and between individuals, in the metabolic response to different macronutrient sources. Recent findings challenge this oversimplification; calories from different macronutrient sources or consumed at different times of day have metabolic effects beyond their value as fuel. Here, we summarize discussions conducted at a recent NIH workshop that brought together experts in , macronutrient composition, and time-restricted feeding to discuss how dietary composition and feeding schedule impact whole-body metabolism, longevity, and healthspan. These discussions may provide insights into the long-sought molecular mechanisms engaged by calorie restriction to extend lifespan, lead to novel therapies, and potentially inform the development of a personalized food-as-medicine approach to healthy aging.