Emphasise Whole Foods
Whilst there is no single diet which is perfect for everyone, there is one common denominator shared by almost any successful approach: fresh, nutritous food derived from good sources.
Some might do better on more plant foods, some might do better on more animal foods, many will fall somewhere between. Either way it is the emphasis on real food, derived from good sources which is important. Vegetables, fruits, whole-grains, nuts, seeds, beans, pulses, mushrooms, herbs, spices, eggs, meat, fish. Food that nature provides!
The one diet which reliably makes people overweight and sick is the modern Western diet built around highly processed foods and sugar-laden drinks which provide an abundance of calories and a shortage of nutrition.
Not only is real food more nutritious and by extension healthier.
It is also far harder to overeat.