Today's post will be one part nutrition lesson, one part common sense lesson, and eight parts rant.
One of the popular arguments in favor of certain diets has to do with the enzyme content of various foods. Some advocates of eating raw foods, for example, argue that raw foods are better because they contain more enzymes, and that ingesting those enzymes can help us maintain a youthful, healthful body. Now there may be many benefits to eating foods raw but the enzyme content is not one of them except in a limited situation. It cannot be, and anybody with a middle school understanding of biology and chemistry should be able to understand why not.
Let's do this step by step.
What are enzymes? Enzymes are proteins that act as catalysts for various chemical reactions in the body. This is a fancy way of saying that enzymes basically allow, or make, those reactions occur. Pretty much every step in every chemical reaction that goes on in your body would happen too slowly to support life unless there were enzymes around to speed them up. Since you're basically nothing more than a big, complicated bundle of chemical reactions, enzymes re pretty important. Incidentally, this is why you feel like crap when you generate a fever - enzymes work optimally within a narrow range of temperatures, and once your body temp goes above that range all the chemical processes that your body depends on slow down.
There are different enzymes in every part of every cell in your body. There are digestive enzymes that break down proteins, for example. Guess where you'll find them? In your gut! There are other enzymes that form melanin when exposed to sun. Guess where you'll find those? On your skin. If they switched places you could digest meat on your chest and get a tan inside your stomach, but luckily we have a complex web of control mechanisms to keep that from happening.
When you eat proteins four things can happen to them: they are either digested or not digested (most of which happens in the stomach) and either absorbed into the bloodstream or not absorbed into the bloodstream (most of which happens in the small intestine).
Proteins that aren't absorbed aren't a worry for us right now - you poop them out, which might be a waste of protein but isn't otherwise of consequence. Let's think about the proteins that are absorbed. Ideally, do you want whole (undigested) proteins passing from your small intestine into your bloodstream? Of course not. Sure, some of those proteins might be beneficial, but most won't be - you don't want digestive enzymes in your blood - they'd digest stuff that you need, like pretty much anything in your body that's made out of protein. So your body is usually careful about what it lets into the blood from your intestine. It will let amino acids through - that's what you get when a protein is broken down into small, small pieces. But unless you have a seriously leaky gut big proteins - like enzymes - can't make it into the blood. If they can't get into the blood, they can't get anywhere else, either.
So when somebody tells you that you can regain youthful levels of enzymes by eating raw meat or whatever they're crazy. If enzymes are getting from your food to your blood undigested then you have serious health problems - lots of allergens and other crap are getting into your system from your gut. The only exception is digestive enzymes. Enzymes that help with digestion - which occurs in the mouth and stomach - will obviously make it to the mouth and stomach if you swallow them. What they won't do is pass through the wall of the small intestine to get to your blood, which is fine - you don't want them in your blood!
If somebody tells you to eat Food X because it has beneficial enzyme Y (like, say, telomerase) which will do Z for you, they have absolutely no understanding of human physiology. Unless Z is "help you digest food."
Now there are lots of other nutrients that might get absorbed and do whatever for you, and they might be denatured by heat, which might turn out to be a good reason to eat raw foods. Just because a position is supported by bad arguments doesn't mean the position is wrong. There are bad reasons to eat a Paleo diet, too. So eating raw foods might be beneficial. But the talk about re-stocking your supply of enzymes from raw foods is... simply ignorant (again, unless we're talking about digestive enzymes that act in the stomach - those don't have to cross into the blood to work, so they're an entirely different story).