Almost no sugar, a bit less carbs generally (but complex ones), good protein, unsaturated fat.

Or a lot of fruit & vegetables, mainly vegetables. Dinner should be smallest meal. Also limit alcohol, thats sugar in different form.

Do sports, sleep well. That's it. If it can't be tackled by decades of such approach, no point worrying but doing so will improve every aspect of your life tremendously, including happiness and life satisfaction, thats 100% guaranteed.