It is highly unlikely that you would use the word food without mentioning the word nutrition in the same sentence. This is because food nutrition essentially encompasses the entire food types that ne needs in total so as to remain healthy. When you hear about nutrition, what comes to you mind first?
With food nutrition, the whole idea is getting the various nutrients as we know them. In other words, we are referring to the carbs, proteins, vitamins and mineral salts. As you will find out, all these are essential and should be found in any of the food that you prepare to eat. If you have good that is lacking any of the above, then you will be deficient in one or more of the nutrients that will keep you healthy.
How much of the nutrients?
It really matters how much of the nutrients you are having as per the food nutrition. No matter how good a particular nutrient it, it must be consumed as per the body requirements and not as per the availability. So, you should not take excess sodium simply because a food contains plenty of it. You should be guided by the nutritional requirements of the body so that you do not either become malnourished or ill due to excess of a particular nutrient.
The serving size is essentially what has been described above, except that we are talking about the quantity of the food amount that you should have. In other words, we are referring to the portion. If you are serving, then you will be guided by the proportions of each of the food type that you need. These are measured in term of bottles, slices and so on. All these and many more measurements are helpful in determining the right food nutrition.