It turns out that certain eating patterns we naturally gravitate towards can increase the amount of food that bypasses normal digestion, and serves as food for our gut bacteria.
Lots of research shows that when tannins are combined with starches, an interaction occurs that makes the starches less digestible, allowing the starches to pass into the large intestine whole, where they serve as prebiotic fiber.
Tannins are a class of plant polyphenols, usually credited with giving a bitter taste. Coffee and tea are very high in tannin content. The word tannin comes from German, for fir tree (oh, tannenbaum...). And tree-derived tannins have long been used to tan animal hides into leather due to a unique interaction that tannins have with animal proteins.
Plants produce tannins presumably as an evolutionary defense to prevent the likelihood of being eaten by animals. But, as Darwinian luck would have it, many animals developed a taste for tannins. The real winner, though, may be our gut bugs. For all we know, they may have engineered this whole elaborate scheme.
Tannins are found in most colorful plants and nuts. Foods often cited highest in tannins are:
- Most dried spices
- Beer and wine
- Coffee and Tea
- Fruit juices
- Honey (!)
2016 - Polymeric tannins significantly alter properties and in vitro digestibility of partially gelatinized intact starch granule.
2015 - Interaction of Sorghum Tannins with Wheat Proteins and Effect on in Vitro Starch and Protein Digestibility in a Baked Product Matrix.
2013 - Effects of sorghum (Sorghum bicolor (L.) Moench) tannins on α-amylase activity and in vitro digestibility of starch in raw and processed flours.
2012 - Interaction of tannins and other sorghum phenolic compounds with starch and effects on in vitro starch digestibility
1999 - Effects of red wine, tannic acid, or ethanol on glucose tolerance in non-insulin-dependent diabetic patients and on starch digestibility in vitro.
Research articles like these show a clear relationship between between tannins and starch digestibility. Most of this research was done to develop products for the food industry that can be added to snack foods, making them less fattening. Soon, some inventive company will no doubt be marketing a jar of powder that can be sprinkled on your food to make it less digestible. I find it ironic that nature spent billions of years perfecting a way to make animals want to eat less plants, and we are using these same chemicals so that we can eat more. Keep in mind, tannins are often referred to as "anti-nutrients" by the paleo-elite and other advice-giving dietary folks.
The list of antinutrients found in legumes, beans and soy is seemingly endless and includes: lectins, saponins, phytate, polyphenols (tannins, isoflavones), protease inhibitors, raffinose oligosaccharides, cyanogenetic glycosides, and favism glycosides. I know that this list appears somewhat formidable at first because of all the scientific terms, but don’t be worried – the concepts underlying how these toxins may impair our health are easily understood (Loren Cordain, 2015).
Also of note, the mode of action seems to be from several complex interactions. Tannins can reduce the amount of alpha-amylase we produce, or make it less effective at digesting starch. Tannins also physically bind with the starch granules, making them harder to digest. "Anti" nutrients. Yes. They. Are. But does that mean we should not be eating them?
First, let's look at a typical SAD meal:
Yummy, right? All those bright colors. I see a few things right with this meal, but mostly just wrong. Sesame seeds have long been eaten alongside bread. Sesame seeds contain lots of tannins, so this practice has roots. The secret recipe of Coca-Cola might contain some tannin-rich plant extracts, but we'll never know.
How about a more traditional meal?:
And for the sake of argument, let's say that the pizza crust is made from whole wheat flour, and the pepperoni is preservative-free, hand-made by some guy named Guido, and the tomato sauce is from sun-ripened, home-grown tomatoes. The spices, freshly ground. And that beer...well, it's perfect!
What I'm attempting to illustrate here is that foods we love often come packaged together with their natural tannin counterparts. But we bastardize our food to a great degree when we try to make it "healthier" or "tastier." Wheat flour used to be a pretty good food, but now it's refined and enriched in a way it's hardly a life-sustaining food.
So, here's the hack. Eat real food, and pair your starches with tannins from more real food. Some ideas:
- Whole wheat toast and jam
- A loaf of (homemade rye) bread and a jug of (Malbec) wine
- Fish tacos with cilantro, onions, and tomatoes on homemade "corn dodger" tortillas
- Oven-baked French fries dipped in homemade ketchup
While the science is heady, the concept is simple. Age-old traditional food pairings were chosen for reasons we are just now starting to understand. We seem to think we can outsmart nature to stay lean and healthy, but using artificial colors and flavors in place of natural tannins is a surefire way to get the science wrong. We need the goodness found in WHOLE foods, not refined, tasty treats.
Let's hear your ideas for the Great Tannin Hack in the comments!