We probably couldn’t even begin to count the number of bodybuilders who’ve lived on boneless, skinless chicken breast and steamed rice or the amount of time those same bodybuilders spend eating such a diet. It’s not just bodybuilders that disregard the importance of a diversified diet. Many who are trying to lose weight or get into shape cling to a few foods and don’t eat anything else than that one or two meals.
Eating a lot of different foods is what we’re designed to do through evolution. One of the current theories about what drove monkeys to humans was the conversion of jungle to grassland. As this occurred, these primates learned to walk from jungle to jungle and had to eat whatever they came across. This is probably why we became omnivorous: When there’s little around to eat, they couldn’t be picky. So we evolved to eat a lot of different foods.
This evolution is now a necessity. We need a lot of different chemicals (both phyto- and zoo-) to function at an optimum level. This is where heavily oversimplified diets do us wrong. We don't get that diversity that we need to function properly. This trickles down to weight loss too. The better our bodies are nourished, the better they will break down the incoming foods. So make sure that you're getting a lot of different foods in your system.