Most new science is descriptive, meaning, “I can’t explain it, but here’s what it looks like.” I recently bumped into that again on an issue for protein digestion.
So, here’s a question. How much does it matter what kind of protein you eat? Does it matter if it’s vegan, or milk-based, or meat-based, beyond getting a good balance of amino acids? What is truly toxic? Some body builders swear by dairy proteins, but those don’t break down much faster than others, and their amino acid proportions aren’t absurdly perfect.
In fact, protein digestion is murky. I don’t mean pre-digestion complications, such as allergies to peanuts, soy or seafood. No, this blog is about proteins you may not notice until they’re in the GI tract, such as gluten. Naturally some bloggers think gluten is evil incarnate. But the studies show some people have a gut reaction to gluten, and others react little if ever.
Once we start down this path it’s tempting to imagine exotic protein metabolism, such as for snake venoms that contain proteases and other harmful proteins. When I was a boy, first aid handbooks even taught the “cut-and-suck” method to treat snake bites. Somehow the caretakers survived, but it’s not clear how much (if any) venom protein reached their stomachs or blood. [Btw, handbooks now tell volunteers never to suck on snake bites. And current practice shrinks from even suction cups, though they removed as much as 40% of snake bite venom.]
So, really, how are proteins digested? It depends. Most food proteins get broken down by gut enzymes that begin as oversized proteins themselves and get clipped to become active digestively. The enzymes later pass through intestinal walls downstream – we don’t know just how – and then find their way back into the gut upstream. We use fruit enzymes (e.g., from papayas) for similar tasks to tenderize protein foods outside the body. Yet enzymes aren’t the only proteins that resist digestion or pass through gut walls. And that may be either good or bad.
One such group is a class called lectins (*not* to be confused with lecithin). These proteins seem to act as tactile sensors, so their home cells recognize visitors as friend or foe and react accordingly. Lectins are in many foods at low levels. Once in the gut, they act as signals that may alter the microbial ecology there, or alter hormone communications. Then they bind to tissue surfaces, and get leaked into the blood, where they continue to mess with hormones. Thus, they can mimic insulin, form clots, escalate cell growth, and trigger immune responses. Eventually, since lectins aren’t digested normally, surface cells absorb and break them down.
Any of several processes can mostly disarm lectins: moist cooking; fermentation; and sprouting. That’s key for beans and other legumes, where lectins often occur in the highest concentrations, but lectins are also found in other food categories: grains, dairy, fruits, and “nightshade” (Solanaceae) veggies such as tomatoes, potatoes, peppers, and eggplant.
Bottom line: next time someone tells you which proteins you should be eating (or not), take it with a huge grain of salt. What we think we know about it still has a lot of guesswork.
Circling-V ™ 