If you want ideal body composition for life, eat the way they did. Eat organic. Eat wild and range fed meats, organic free range poultry, and wild fish, large amounts of organic green vegetables, moderate organic fruit in season, That's it. Our ancestors did not have grains, or sugar, or processed carbs. It is senseless to believe that your genes can fare well on them.
Grains are a modern development from what were small, bitter, grass-like seeds, which grew bitter to prevent insects and animals, including our ancestors, eating them. We bred out the bitterness, increased the size and yield. And grains, breads, and cereals were born.
Of course, we then had to protect them from being eaten by pests. So the whole pesticide industry was born too. Opt out of these centuries of deception of the public for profit. Except for an occasional bit of flavor, eliminate ALL grains from your diet.
Sugar was rare in the hunter-gatherer diet (about 4% of calories, almost all from fruits and vegetables), I have documented many times that sugar was rare even 300 years ago. This abomination of food, and its spawn, such as high-fructose-corn-syrup, is the root of much of our disease today. Sugars are now one quarter of the calories in the average American diet. Eliminate sugar and sugar substitutes from your diet, all candy, ice-cream, sodas, cookies, cake, etc.
Difficult - Yes, because you have been carefully addicted to these so-called "foods", just as carefully as smokers were purposefully addicted to nicotine. Fortunately, just like nicotine, over six months to one year without the junk, your addiction will slowly fade, as new cells replace the old. Having never experienced the addiction, the new cells will not be bound by it.
I have used this information to help thousands of people over the last 30 years, many of whom have become lifelong acquaintances and friends. The periodic surveys we do of them show results that are fascinating to me as a scientist.
People who have made this nutrition their lifestyle, are much leaner than their peers, On Biomarkers of Aging, they are also biologically younger and healthier. Their interest in and use of the above foods to avoid has dwindled to almost zero. They do not report craving them or feeling deprived in any way. Many report that the taste of grains and sugar have become disagreeable.
You cannot do this by having "cheat days" or other media nonsense routines. You cannot do this by cutting food, and making up the difference with chocolate or candy. And you cannot do it by drugs, or fat-loss supplements, or stitching up your mouth (yes, it's a real procedure; look it up), or emptying your house of offending foods, or drinking water till it runs out your nose.
To adopt a healthy diet that matches your hunter-gatherer DNA, you have to exert your will. You have power aplenty latent in your brain. All you have to do is use it. Do not remain one of the mass of lemmings in our society, waddling hither and yon to the beck of every new weight-loss scam. Allow yourself to become lean and magnificent.