Our physical condition is largely determined by nutrition. Most science of nutrition comes from the study of food nutritional content. Most studies on food content will break down food into a few categories, namely calorie content, fat content, protein content, and fiber content. Vitamins and minerals are grouped under trace elements, since their amount is relatively tiny in relation to the rest. When you consider about nutrition, one of your main questions should be the ratio and amount of nutrients you are getting in the foods you eat.

A balanced diet may comprise a ratio of  20-40% protein, 10-20% fat, and 50-60% carbohydrates, and 5-10% fiber, with the remainder being water, and you have trace elements like vitamins and minerals.  Having too much of protein, or too much of any of the nutrients can have adverse effects. The main thing is to have balance. Here's a little more on the nutritional content of foods like a sandwich, for example.