Tired of Starting Over? Universal Health and Beauty provides fitness information you can trust to guide your journey. So you can lose weight, build better nutrition habits, get strong, and build confidence for lasting health. Just In Why is It So Hard To Lose Weight After 40 After age 30, metabolism slows by about 2-5% per decade. So, at 40 years, you may burn 100-1500 fewer calories per day than in your 20s.