How to stay slim in your 30s, 40s and 50s Exercises Training Methods Weight loss by admin - 3 June 20182 June 20180 How to stay slim in your 30s, 40s and 50s Can you beat age-related weight gain? We asked the experts for their diet and exercise tips for women in their 30s, 40s and 50s.What is the ‘middle age spread’?The term ‘middle-age spread’ has been etched into ageing lore, yet unflattering connotations ignore the naturalness of physiological change. Expecting to weigh the same at 30 as 18 is folly according to clinical psychologist Louise Adams from Treat Yourself Well.”Our body weight at age 18 is for many of us the lightest we have ever been,” says Adams. “We may not have stopped growing at that point and may not have reached full maturity.