Feeding the Thing That Feeds You

Why the gut microbiome matters, what it wants from your plate, and what quietly starves it

If you count all the cells in a person, roughly half turn out to be bacteria, most of them living in the gut. They're not intruders — they help digest food, make vitamins, and even change how medicines work in the body. They behave more like an organ — one we acquire rather than grow, and one we feed three times a day whether we intend to or not.

What it is actually doing down there

It finishes the digestion we cannot do ourselves. Human enzymes cannot break down most dietary fiber. Gut bacteria can, and when they ferment it, they release short-chain fatty acids, butyrate among them. Butyrate is the preferred fuel of the cells lining the colon. The lining of your bowel is fed, in part, by bacteria eating your vegetables.

It teaches the immune system. A large share of immune tissue sits along the gut wall, and in the first years of life it learns what to attack and what to leave alone partly from what it meets there.

It takes up space. A crowded gut is a difficult place for a pathogen to settle. Empty out the crowd and something opportunistic moves into the vacancy.

And it manufactures — vitamin K, several of the B vitamins, in amounts that count.

What a good one seems to prevent

Here I have to be careful, because this is the part of the science that gets oversold in magazines.

Low bacterial diversity travels alongside a long list of conditions: inflammatory bowel disease, irritable bowel syndrome, obesity, type 2 diabetes, colorectal cancer, and allergic disease and asthma in children. For most of them we still do not know whether the disturbed gut is the cause, the consequence, or a bystander that arrived with everything else.

Hence, the honest position is this: feeding your gut well is a sound bet with a plain mechanism behind it and no real downside.

What feeds it

Fiber and variety. Those are the two important things, and everything below is a way of getting there.

Plants, as many different ones as you can manage. The number worth aiming at is closer to thirty different plant foods in a week than to five eaten daily — malunggay, saluyot, kangkong, okra, monggo, squash, eggplant, whatever the market actually has that morning. Different bacteria eat different fibers. A narrow diet starves the minority species first.

Twenty-five to thirty grams of fiber a day. Most Filipinos eat well under that, and it is not because vegetables are expensive here. A lot of us are not used to eating vegetables.

Resistant starch. Rice that's cooked and then chilled overnight changes its structure, and part of it reaches the colon undigested — a rare case of yesterday's food being better for you. Refrigerate it, though; rice left out on the counter is a different story. Saba, oats and beans do the same work.

Let me explain further. Raw starch granules are tightly packed crystalline structures. Heat plus water makes them swell and lose that order, exposing the amylose and amylopectin chains to pancreatic α-amylase. Hot rice is highly digestible — glucose released in the small intestine is absorbed.

As the rice cools, the linear amylose chains re-associate into compact double helices and small crystallites. This new structure is not the original granule; it's tighter in a way amylase can't easily attack.

That retrograded fraction passes the small intestine largely undigested and arrives in the colon, where the resident bacteria ferment it into short-chain fatty acids — butyrate most notably, which is the preferred fuel of colonocytes. So starch that would have been glucose behaves instead like fiber.

Hence "better for you": lower glycemic load, plus substrate for the microbiome. And the crystallites are reasonably heat-stable, so reheating doesn't fully reverse it — which is why sinangag made from day-old rice keeps some of the benefit.

Fermented food. Kimchi at fifty to a hundred grams a day. Yogurt with live cultures. Yakult, which does contain a genuine strain of Lactobacillus, and also about eight grams of sugar in that small bottle. One a day is a reasonable habit.

One correction while I am here: most probiotic organisms pass through rather than move in. Passing through still counts — they interact with the residents on the way — but no bottle permanently rebuilds anything. The permanent work is done by what you eat, daily and dully, for years.

What starves it

Ultra-processed food. Not because it is poison, but because it arrives almost fiber-free and takes the place of something that would have fed them.

Antibiotics taken for a viral illness. A single course can drop diversity for months, occasionally longer. Most colds, most sore throats and most coughs are viral. Take antibiotics when they are genuinely needed and do not feel guilty about it.

Alcohol in quantity, which shifts the population and irritates the barrier that population sits on.

Monotony. Eating the same five foods with great discipline still leaves most of the residents hungry.

You do not need to buy anything for this. Squash, monggo and kangkong are among the cheapest things in the market, and they are what the whole industry of supplements is imitating.

Eat like you are cooking for someone else. You are.