Most people need a mix of proteins, carbohydrates, vitamins and small amounts of fats, in nutritional terms. However that is the scientific perspective and therefore it is limited. Variety and higher quality food will boost you in so many ways. My rule of thumb is, what would I eat if I were living in nature and without any artificially made ingredients. While I can only ponder a day of living naturally, I suppose it would be somewhat like: wake up, munch some berries and maybe some plants. Explore the plains a bit caveman style. Munch a bird if I were fast enough. Then probably some random herbs or whatever was around. This sounds silly and strange I know, but compare that to what you ate yesterday. Now what seems a bit strange.
Refined sugars are so far from natural and should be avoided, it directly causes diabetes and many other health issues. It is very difficult for you're body to break down, so you release high amounts of insulin to aid. This depletes surrounding cells of nutrition using it to this high energy boost which lasts a short amount of time. Don't give up your favorite treat because of this, use it in moderation to keep yourself motivated towards your goals.
If getting in shape is your goal, the best diet i could think of is 6 balanced small meals throughout the day. Giving your body a constant source of energy rather than large meals which take a lot of energy to digest and that intense digestion is far less efficient in absorbing any nutrition in that food.
Focus on movement in whatever you're doing, by taking the stairs instead of the elevator, getting up and stretching every hour or so can help your body stay much more active. Also adding in short exercise periods like power walking or weight lifting, can help your health in leaps and bounds.
Be conscious of what you eat, what ingredients were in it, and how you feel after eating it. The most often the less processed the more your body will get out of it.
Thanks for reading.