Some people naturally gravitate to the style of eating that best supports their energy and stamina. Some thrive on fresh fruits, veggies, whole grains and plant protein, while others feel terrible unless they eat red meat and animal proteins. As a dietitian, I strive to match the right person with the right diet. For example, if your family history is positive for cancer, and you also have heart disease, it is amazing how the right diet can support prevention of both conditions at the same time. I think people worry that health conditions each have their own modifications, but often, one set of guidelines help the whole body which puts nutrition into a holistic context.
Exercise is extremely important, too.
You have to put the right foods into the body to feel good, but you also have to move that body and keep it in good shape. Most people start out too ambitious at the first of the year and try to do too much at once. Consequently, they burn out and stop exercising in a month. I did that once. I am still paying on a monthly membership to a gym that I used for two months and stopped going because the treadmill and the resistance equipment were too mechanistic and boring.