Optimum nutrition is a very complicated subject. At least, it is if you believe everything that dieticians and nutritionists would have you believe.
Really, it's not difficult at all. What makes it difficult is an attempt to make our modern, 21st century western diet fit into some sort of healthy template.
Once you come to understand the shenanigans and vested interests that have contributed to the way we eat today, you have the opportunity to simplify your nutrition plan and focus on what really gets results.
The basis of optimum nutrition is getting back to the foods that support human health.
Contrary to what dietary guidelines and various pressure groups have sold us since the 1970's and 80's, the foods that provide the greatest amount of nutrition and, therefore, best support human health are animal foods.
These foods provide us with a high level of very absorbable protein. Nothing in nature provides protein at those levels without potential negative effects. For example, the only food that comes close to animal foods for bio-available protein is soy. But soy also comes with a number of potential negative effects. One can argue all one likes about the levels and effects of phytoestrogens, but they're there and I don't like the potential risk. No other plant food comes close on the levels of bioavailable amino acids as there are in animal foods.
Also, leucine, the amino acid most important for muscle growth is far easier to get from animal foods.
Another factor to consider is the sheer amount of plant food you need to eat in order to get optimal amounts of nutrients. In contrast, you can get almost all the nutrients you need from 250g of beef!
Finally, there are at least 15 nutrients that you cannot get from plant foods. The most prominent of these is vitamin B12, but vitamins A and K, carnitine and creatine are found almost exclusively in animal foods.
Almost any vegetarian athlete who has supplemented with creatine has seen huge performance improvements.
Optimum nutrition matters more than all the training you do. You cannot outrun a poor diet.