My biology teacher told me that protein supplements are useless, because you get enough protein normally, so you just pee it out. He is not just saying this either. He has many years of teaching knowledge, a college education for P.E., and he is an amazing and well learned track coach, so I know he is not telling us something he just heard. What do you think about this?
Chodantraceur, you can print this reply out for your PE teacher so can revise his views.
As Chris mentioned, that's a misguided view that is not in accordance with all the scientific evidence.
For the most part you can "survive" even with almost no protein at all, but there is a difference between survive and thrive, and all data shows you can do much better with more protein than what most people tend to eat.
If you can get it all from your diet without making bad nutritional choices (e.g., too many calories because your main protein source is say McDonalds) and without going broke (good quality protein-rich food tends to be more expensive), then go for it.
If you can't quite make it all from food, and often you can't, protein supplements are a great easy way to round you up to the ideal amount without messing up your caloric max or your wallet.
The minimum is considered ~50 grams a day to avoid going into protein deficiency, and that's for sedentary people and just to avoid becoming sick in the long run, not to be as fit as you can be.
If you are active or training you need much more, and there is an even higher threshold before you stop seeing benefits from adding more proteins to your diet.
Talking in numbers, if your weight is say 150lb and physically active you would need at least 100-150g of protein a day. And that of course depends on the intensity of the training and amount of muscle growth too. A bodybuilder for example has an even greater protein need to be able to put on that much muscle. But for the average lighter training, at ~160g you can see evidence that adding more proteins on top of that starts to be wasted. That's based on total body protein synthesis measurement and on aminoacid oxidation which is when your body starts to convert excess protein material into energy (and yes eventually the metabolites get passed through the kidneys but they are no longer proteins or aminoacids by then, as Chris said).
For people interested about where these numbers come from, here is one study on this
http://www.ncbi.nlm.nih.gov/pubmed/1474076and there are many more showing benefits at higher ranges for higher intensity.
Now, consider that one large egg, a very good source of protein, has only 6 g of protein, and you can see that if you add up all your protein sources (use something like
this) in your diet it's easy to fall short especially if you are active.
All this is also without going into protein quality, not all protein is equal and even if your cereal says it has X grams of protein, protein from grains is much less complete and lower quality by itself (compared to eggs, milk, cheese, meat/fish), while again protein powders are much more complete and high-quality so they are a good way to compensate as needed.
