There are thousands of diet concepts on the market. I call them "diet camps". This is not a camp that you attend. It's a belief system. Typically, people in these diet camps do not budge from their respective camp. In fact, they will present all types of research that demonstrates "how right they are". They will also tell you what's wrong with all the other diet camps.
The spectrum runs form vegan (if it has a mother or a face, do not eat it) to paleo (meat eaters - fat ain't the villian). Interestingly, all of these diets work. That's the good news. However, all of them are partially correct. To a large degree, it's what they omit from their diet that plays a major role in their health.
They all omit or minimize these types of foods: fast food, junk food, processed food, sugar, soda, candy, cookies, cake, and more. And, they add a good dose of exercise. In regard to exercise, find one or more that you enjoy. For example, I enjoy running, biking, hiking, kayaking, and weight training. Bottom line: For good health, you must exercise.
In addition to the "diet camps", experts have advice about what to eat. They discuss nutrients, macro-nutrients, micro-nutrients, leptin, ghrelin, insulin, and much more. While that's important, it could not get much simpler than this: