Here are few reasons why weight loss is a challenge after 40s
1) As we age our resting metabolic rate drops, there is reductions in the mass of individual organs/tissues and in tissue-specific organ metabolic rate contribute to a reduction in RMR that in turn promotes changes in body composition favoring increased fat mass and reduced fat-free mass. This is one of the main reason why we tend to gain weight around the abdominal area.
2) After 40s most of the women attain menopause, where their hormone estrogen levels drop & this changes body composition & type of obesity. There is increase in total and body fat & decrease in lean body mass. Also there is shift from gynoid obesity to abdominal obesity.
3) This shift in the type of obesity & body composition predisposes one to various lifestyle diseases. Some of the diseases slow your metabolism thereby reducing the weight loss.
4) If we were to compare the increase in intensity of exercise of 20, 30 & 40 year old person. The increase in intensity of exercise of 20> 30> 40 . And so weight loss would be faster of 20 year old person > 30 year old person > 40 year old person.
But still you can lose weight with healthy diet & exercise & prevent & treat various health problems