I became interested in the health value of fermented foods after I noticed a curious coincidence. Humans have three mysterious food preferences: for (a) sour food, (b) food with umami flavor, and (c) food with complex flavor. I realized that all three preferences made bacteria-laden food more attractive. Bacteria change sugars to acids, increasing sourness. They break down proteins, creating glutamate, which produces umami flavor. And the many chemicals they introduce into a food make its flavor more complex. After I noticed this, I came across many studies that supported the idea that fermented foods are good for health. I also found studies that suggest the bacteria in our digestive system are crucial to health.
This raised the question: What fermented foods to eat? How many? How often? To begin to answer these questions, it would help to know how bacteria in our food help us be healthy. There were two obvious answers:
1. Stimulate the immune system. The bacteria in fermented food are inherently safe: they are specialized to reproduce on/in food, which is so different than inside the human body. But the immune system doesn’t know this. If this was one benefit of fermented food, you could study which ones to eat by measuring immune system activation. Unfortunately, that is nearly impossible.
2. Improve digestion. Many people have digestive problems and some of them are helped by fermented foods. Obviously they contain bacteria that digest food. I don’t have digestive problems so I can’t study this by figuring out which fermented foods help.
Recently, I have begun to think there is a third reason:
3. Place competition. To make us sick, outside bacteria need to stick inside us. To digest our food, the surfaces of our digestive system, such as the inside of our intestines, is much more porous than other surfaces, such as our skin. It is our digestive system, therefore, that is most vulnerable to dangerous microbes. The totally-safe microbes in fermented foods compete for sticky spots with other, more dangerous microbes. If there are plenty of safe bacteria — say, billions in a serving of yogurt — they may do a lot to protect us against the dozen or so similar dangerous bacteria we might get from touching the same surface as a sick person. I think of a wooden floor where the lumber is not quite well-fitted. If you want to protect what’s below that floor from black sand (dangerous), an excellent method would be to pour an enormous amount of white sand (safe) on the floor.
If Effect #3 (place competition) is the main reason fermented food protects us from disease, it implies that dead bacteria work as well as live bacteria (in contrast, live bacteria do not digest food, Effect #2). This might explain the potency of alcoholic beverges such as wine, where most of the bacteria are dead. It also suggests that what matters is diversity of where bacteria stick and how much they stick. It might someday be possible to feed people (non-radioactive) bacteria and learn where in the body they end up.
Your second point (harmless bacteria stimulate the immune system while being harmless) reminds me of a possibility for why very spicy food gets liked– it’s pain without danger.
I have a half-baked theory that inadequate digestive flora leads to obesity: it makes foods with lots of white flour and sugar more palatable because they’re easily digested by such people. Denser foods like meats with a lot of fat and high protein or raw fruits and vegetables don’t digest so easily so they avoid them. Then they get addicted to the blood sugar spikes. No idea if this makes sense or not but there you are.
Seth: As Nancy says, lots of people avoid carbs but are still fat. Alex Chernavsky tried a low-carb diet. Initially he lost a lot of weight. After a year or so he started to regain the lost weight. At that point he changed his diet. Short-term weight loss caused by his low-carb diet was not easily sustained for a long time. I don’t agree that simply eating white flour and sugar is fattening (or avoiding them is thinning). It’s more complicated than that.
Probably a half-baked theory, or at least you’d need to check on a good sample of fat people.
Simple carbs aren’t good for me, so I don’t eat a lot of them. I like fat and protein more. I’m still fat.
Your theory might apply to some proportion of fat people, but biology is complicated.
Really enjoy reading your stuff here on fermented foods.
As for your theory about why bacteria is healthy for us, apropos point number 3, this sounds to me like exactly the same reasoning for the medical technique of fecal transplant https://www.slate.com/articles/health_and_science/medical_examiner/2011/01/the_enema_of_your_enemy_is_your_friend.html
We can add this to the list of “evolutionary” ways that modern living has
short changed human physiology.
1. Industrial foods are unnatural.
2. Artificial light disrupts circadian rhythms.
3. Artificial heat prevents cold adaptation.
4. Modern refrigeration restricts the need for food storage via fermentation.
Are there any I missed?
Seth: I think you’ve missed about a hundred. For example: 1. Modern living reduces human contact in the morning. 2. Modern timing of food interferes with sleep.
Modern news contributes to constant anxiety.
Human contact in the morning — or any other time — irritates the snot out of me. But I love peace and quiet. I don’t have a TV or a radio, and I keep the sound turned off on my computer.
You’re the psychologist, Seth, but is there really anything wrong with enjoying peace and quiet? If I’m happy, what’s wrong with that?
A while back you mentioned the Nobel Prize in medicine. This could be interesting to you:
https://www.rationaloptimist.com/blog/induced-pluripotent-stem-cells-change-the-ethical-debate.aspx
A possible 4th reason we like fermented foods. (not my idea).
New microbes are a source of genetic material for our epigenetic mechanisms to use for genetic adaptations to environmental stresses. IE they are inventory in our junk DNA parts list.
The fermented foods are producing enzymes that aid in the absorption of nutrients and digestive capacity.
“1. Industrial foods are unnatural.” All cooked foods are unnatural.