In my 40s, I put on weight and looked decidedly chunky. Then I started having unpleasant reactions to some foods, the major one being wheat. I lost 1st through cutting out wheat from my diet. Then I became insulin resistant and as I have a strong family history of diabetes, I reduced sugar in my diet and lost another stone. I now weigh less than I did in my late teens and twenties. I have a waist, but my tummy isn't as flat. I do not exercise as much as I should, in fact very little recently due to health issues. So diet is a major factor to weight gain in middle age, as the body can no longer accommodate overeating. And muscles become less strong. Even my very slim, exercising DH has a slight paunch now he is 60+. I eat well, but take care as to what I eat. I eat a good breakfast, smaller lunch and dinner. I try not to snack, but.......! DH eats little and often. I do not eat a large dinner and never after 8pm, in order to give my digestive system a chance to do its job. I now feel uncomfortable if I over eat.