Key Points New research suggests that diets lower in protein may support healthy aging. Among other things, a lower protein intake was linked to better metabolic function, nutrient signaling, and cellular health. One piece of the puzzle seems to be fibroblast growth factor 21 (FGF21), a hormone that rises as protein intake drops. Lisa Moskovitz, R.D., founder of NY Nutrition Group and the author of The Core 3 Healthy Eating Plan, agrees. “Cutting back too much could increase the risk of muscle loss, so this is not a reason to drastically reduce protein intake.”