Ever since a ground-breaking experiment in which scientists demonstrated that mice with gut bacteria transplanted from an obese individual become obese (even when fed the same diets as their lean friends!), the study of the human gut microbiome has boomed.
Although there are still a lot of open questions, the state of our knowledge today points to some clear conclusions:
- a diverse, healthy microbiome fights our greatest modern epidemics such as obesity, cancer, heart disease, and diabetes;
- good bacteria manufacture chemicals that keep our cellular machinery young and exert positive influences on all our organs, keeping both mind and body fit;
- mood and metabolic disorders that keep people trapped helplessly in cycles of diet failure can be reversed with a focus on the microbiome;
- The human microbiome in developed peoples is an "ecological disaster zone."
We can save our microbiome, as long as its not too lateIn good news: studies indicate that with a change in diet, a healthy microbiome can re-establish itself. But there is a caveat: each generation that we get away from that healthy evolutionary garden of co-existent species in our intestines, the harder it is to recover microbiome diversity. Of particular concern: babies of mothers with a deficient microbiome during pregnancy may be born without any of many of the "good species" of bacteria present in their bodies. Our obsession with cleanliness and antibiotics further darkens the outlook. The bottom line: if a few representatives of a species is not present at some level, no amount of healthy diet can bring it back.
There is a large amount of uncertainty in this young science. A truly diverse microbiome can have as many as 100 million species in it, although numbers like 1000 or 10,000 are more commonly reported in studies from the project to "map the human microbiome," which we are increasingly learning is really a project to "map the Westernized microbiome." With such complexity, finding the actual causes of any specific health effect remains elusive.
It seems pretty clear that of the two major divisions of species in our guts, the bacteriodetes are good and the firmicutes are bad. The mechanisms are not all well understood, and perhaps a lot of the findings are correlation rather than causation. But whether the bacteria cause healthy weight maintenance, reduction of disease, and promotion of "youth" or are merely associated with such advantages, the take-away message is the same: eat well and you will get a good microbiome and all of the desirable benefits.
Fiber is the secretThe trick to gaining better microbiome balance is simple: starve the bad bacteria and feed the good ones. The bad ones thrive on fat and sugar. A diet high in fiber is essential for a blooming population of bacteriodetes.
The Institute of Medicine recommends 38 grams of fiber per day for men and 25 for women. Studies of hunter-gatherer tribes show that this "evolutionary diet" contains over 100 grams of fiber. Further studies in mice show that eating fiber every other day with a western-style diet in between does not achieve a good balance, so consistency does count.
Here's an interesting thing about trying to get 25 to 38 grams of fiber or more per day in your diet: if you eat to get fiber content, it is almost impossible to eat unhealthy. Satiating portions of beans and broccoli and other fiber-rich foods will fill your meal plans. Beans and legumes (peas, lentils, etc.) are the secret weapon in the fiber diet arsenal. With 15-20 grams of fiber per cooked cup, adding these to soups and salads, and eating bean-based dishes provides a quick and tasty boost to fiber intake.
Foods referred to as "prebiotic" are full of the kinds of fiber known to feed the healthy microbiome. You don't need to go on a quest for jerusalem artichokes or other exotic superfoods: lots of readily available beans, legumes, and vegetables are prebiotic.
What about probiotics?What if you try the healthy, high-fiber diet approach and don't seem to be getting the benefits of a good microbiome? The science suggests we will start to see generations of people who may not have the biodiversity in their own guts to recover a healthy microbiome. A necessary course of antibiotics may also take a toll. Scientists really don't understand whether we can restore our good bacteria by exposure to our foods or environment.
"Probiotics" may offer hope. These are pills or foods that intend to deliver good bacteria into our systems. Probiotics is now a $35 billion business. This could be a great deal for consumers: a couple doses of the "good" bacteria should be all you need to re-seed your gut-garden. Instead, our western diets turn this into a great deal for the probiotic industry: customers have to keep eating the "probiotic" pills and foods because they proceed to kill off all the benefits with a high-sugar, high-fat, and low fiber diet.
If a high-fiber diet alone isn't helping you to reach the weight and health goals you have set yourself, talk to your doctor. She or he can point out the prebiotic products that have been validated in clinical trials, so you don't waste your money on hype.
Remember that we are talking about a complex ecosystem here. So listen to you gut - when you eat right, and feel good, both you and your family of gut friends win.