New Delhi, Dec. 22 -- Many people notice a frustrating shift after they cross 30 - the same foods suddenly lead to belly fat, workouts don't deliver the same results, and even small "cheat meals" seem to show up on the waistline. According to Dr Saurabh Sethi, this change is not about willpower but biology.

The California-based gastroenterologist, trained at AIIMS as well as Harvard and Stanford universities, recently explained why metabolism slows with age - even when diet and activity levels remain unchanged.

Dr Sethi said that after the age of 30, the body naturally loses around 3-8% of muscle mass every decade. Since muscle is metabolically active tissue, less muscle means fewer calories burned at rest. "Even a loss of one kilogram ...