Eat Balanced
You have all heard of "RDA," the recommended daily allowance of nutrients...NONSENSE! They are too low. These daily allowance, until resently, were called "Minimum Daily Requirements." Then the PR people for the food industry realized that people wanted more than the minimum and the nutitional value of their factory foods was decreasing. So 'Minimum' was changed to 'Recommended' and the numbers stayed the same.
The same government agency that assigns RDAs also assigns nutrient levels for research animals in government labs. For research monleys, the agency recommends optimum intake levels. As a result research animals are fed a diet which is higher in nutrients than the recommended RDA for humans.
I am sure you have heard nutrition "experts" tell you that you can get all the nutrients from a normal diet, if you include things like rutabaga, caviar, mutton and persimmon. They are shills for various producer groups.
The next time you here one of these industry shills remind yourself that it takes 20 oranges per day to supply a single gram of vitamin C and you will get more vitamin C from a fork full of broccoli than from an orange.
The RDA will prevent you from diseases like beri-beri or rickets, but we have higher goals than that. For our purposes a balanced diet is determined by setting our goals - slimming the waistline and increasing cognition. Assessing where we are to start and determining how to get there. These are very individual decisions. I can tell you what I am doing for me, but what you do for you is your decision and your responsibility.
Inform yourself but be aware that your internet search options have devolved into paid placements. The first forty listing on any given topic on Google, for example, have paid to be there (except mine, of course. For the categories important to me, etresoi.ch heads the list and we do not pay or get paid by anyone.) I have found a good alternative; if you wish to do serious research try http://scholar.google.com (mine comes up in French but yours should come up in whatever language is your browser's default.)