Many books insist that a natural diet of 2000 calories can't supply the necessary nutrients for a healthy diet, that a multi-vitamin supplement is necessary. Since we humans have had no artificial supplements in our diets until very recently, I decided to investigate.
I started with the nutrients in a list of 180 essentially natural foods that I normally eat (they are in my database because I like them), that are analysed by the USDA and for which there are widely accepted recommendations for my daily requirements. I wrote an optimization program to vary the percent of each food in a diet until all requirements were met, with no excess undesireable nutrients such as cholesterol (shown in red below). Maximum saturated and minimum monounsaturated lipids were each maintained at 10% of total calories, and dietary fiber requirement was reduced proportionately to total calories. The total calories was reduced until the optimization failed.
The program promptly found a diet with only 470 calories per day!
This first diet called for essentially every food in my database, many in precise but tiny quantities. And, it called for 27% of calories to come from spinach. No dietician would recommend relying so much on a single food. So, two constraints were added, that no food form more than 10% of the diet, and that any food needed at less than 0.5% of the total diet, one serving per month at this calorie level, should be eliminated. Few essential nutrients are stored in our bodies for longer than this.
Here is a typical result, a diet of 540 calories per day with no artificial supplements whatsoever:
| food | % of calories | nutrient | % of RDA |
|---|---|---|---|
| chard | 10 | A | 344 |
| spinach | 10 | B1 | 100 |
| cod | 8 | B2 | 163 |
| lettuce | 7 | B3 | 104 |
| ham | 6 | B5 | 100 |
| hazelnut | 6 | B6 | 125 |
| mushroom | 5 | B8 | 211 |
| collard | 4 | B12 | 452 |
| oyster,can | 4 | C | 232 |
| herring,can | 3 | D | 100 |
| milk,dry | 3 | E | 103 |
| ocean perch | 3 | K | 3370 |
| pollock | 3 | saturated | 46 |
| sole/flounder | 3 | monosaturated | 100 |
| broccoli | 2 | omega-6 | 16 |
| haddock | 2 | omega-3 | 177 |
| mackerel,can | 2 | cholesterol | 76 |
| pork,trimmed | 2 | Ca | 100 |
| salmon,sockeye,can | 2 | Fe | 229 |
| almond | 1 | Mg | 136 |
| beef liver | 1 | P | 150 |
| brussel sprout | 1 | K | 100 |
| chicken liver | 1 | Na | 62 |
| cod liver oil | 1 | Zn | 100 |
| cucumber | 1 | Cu | 265 |
| goat | 1 | Mn | 207 |
| ham,can | 1 | Se | 202 |
| oil,sunflower | 1 | I | 168 |
| salmon,pink | 1 | F | 90 |
| shrimp | 1 | Hg | 49 |
| tofu | 1 | fiber | 293 |
| tomato | 1 | protein | 110 |
| tuna,can | 1 | tryptophan | 130 |
| zucchini | 1 | threonine | 121 |
| isoleucine | 142 | ||
| leucine | 101 | ||
| lysine | 114 | ||
| methionine+cystine | 100 | ||
| phenylalanine+tyrosine | 119 | ||
| valine | 119 | ||
| lutein+zeaxanthine | 1040 | ||
| flavonoids | 103 |
Problems with nuts? You can still have a diet of 540 calories per day. Don't like spinach because you can't be bothered washing it properly? 600 calories per day suffices. Vegetarian? 900 calories per day if milk products are OK.
So, any claim that vitamin supplements are necessary for healthy people is total nonsense, so much so that the competence of anyone who makes it has to be called into question.
It is not possible, however, to be a vegan (no animal-sourced food whatsoever) and get all required nutrients from natural sources, as there is no reliable such source of Vitamin B12, essential for memory function.
There are over 6000 foods in the USDA database. There will be thousands of diets that can supply all the nutrients anyone needs with natural foods, as long as you don't have a medical problem such as malabsorption of some nutrient.
There are other nutrients that are not tested for by the USDA or that don't have established RDA's, yet are suspected to be useful for nutrition: antioxidants other than beta-carotene, vitamin C and vitamin E; ellagic acid; lycopene; organosulfides; pectins; phytoestrogens.... But, when I Google them, I find routine mention of foods I regularly eat as good sources. So, I don't worry about them. I don't think any other healthy person needs to either.