There are many schools of diet and some people have issues which means what works for some people, doesn't for others.
Eating lots of foods with added sugar is generally unhealthy though e.g. 5 grams of sugar in the ingredients e.g. Kind bars are fine.
Partially hydrogenated fats are very bad, as are rancid fats e.g. deep fried foods.
There is general agreement that the following are very healthy (if you tolerate them):
--green leafy veggies
--cruciferous veggies (broccoli, cauliflower, brussel sprouts)
--berries
--garlic, onions, allium family
--nuts especially walnuts
legumes e.g. beans, lentils are healthy if you tolerate them.
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Beyond that it gets more complicated and there are differing theories.
If you have "gut issues", then some foods e.g. grains, legumes may not work for you.
One simple thing to eat which can be very healthy is a "green smoothie". Try:
--1 tbsp. ground flax seeds
--1 cup mixed berries (unsweetened) or 1 banana and 1/2 cup berries
--1-2 cups raw spinach
Mayo clinic's recipe
http://www.mayoclinic.org/healthy-lifes ... p-20049958