Want to lose weight, particularly body fat?  Choose the right gut bacteria.

They’ve already chosen you.

But can you select them?

A recent study in Copenhagen checked gut bacteria before starting  some overweight people on a half year diet.  Using a crude measure of different bacteria populations (high Prevotella to Bacteroides ratio,) the high ratio group who ate a “New Nordic Diet” with lots of fruits and vegetables lost lots of body fat and weight, a total of 10.9 pounds. But that was three and a half pounds more than those eating the same diet, but sporting a low bacterial ratio.

Diet type mattered.   Those trying to lose weight on the on the “Average Danish Diet” lost about half as much body fat. Their bacterial population ratios did not differentiate who lost more or less.

Why Should Gut Bacteria Affect Weight?

Because they affect so many other things we know about, and far more we don’t.  Our gut bacteria help digest food,  prepare vitamins, and shift mood and our susceptibility to disease while possessing striking immunologic effects that may affect heart disease and stroke.  That’s the little that’s known.

Why Is So Little Understood?

Recently the bacterial census was downgraded from 100 trillion to a 40 trillion cells.  There are perhaps 10 trillion human cells.  That’s still a lot of bacteria in the four to six pounds they take up in our guts.

One complicating factor is that little is understood of how the many thousands of bacterial colonies interact with each other.  We also don’t know a whole lot about how they respond to other microbes, like viruses. We don’t know how they pass information to our gut lining cells and other cells in the body. It is often said the gut has so many neural connections it is a “second brain.” Some of those connections may create the little understood pathways of  biological intelligence, determining  how gut bacteria get their messages to the brain.

What Changes Gut Bacteria Populations?

Who your mother was and her lifelong personal microbiological history. Whether you were born through Caesarean section.  Where you live.  How you move and exercise.  How and what you eat.  And perhaps probiotics – additions of bacteria to your bacteria.  Direct transference of large bacterial populations – loop to loop into the gut “transplants” – are proving an effective treatment of bacterium clostridium difficile infections, which kills thousands each year.  C diff, as it’s commonly called, generally occurs when immunocompromised patients get antibiotics that cause that single bacterial population, among many thousands, to proliferate wildly.

What Are the  Best Gut Bacteria to Have?

There’s the rub.  What may matter most is not your total “population numbers” but how those thousands of populations interact with each other – and with human immune and nervous function.  Trying to get one or another bacterial population up in number to make you “healthy” may be like trying to estimate the strength of the American economy by knowing how many Toyotas were sold in Michigan last March.  Useful information, perhaps.  But such information requires context. Still, it’s clear that overall health and eating patterns affect the bacterial guys you live with.

What Can You Do to Get  “Healthier” Gut Bacteria?

Expect thousands of ads for probiotics, yogurts, varied “superfoods” and fermented products to tell you in detail just what you should believe.  Though you may not want to believe them.

Nonetheless, eating lots of very varied foods, especially whole plant foods, is correlated with gut bacteria types seen in healthier, generally leaner people.  Which is “chicken and egg”?  Like most biological phenomena, it probably does not involve standard linear causality,  A leading to B leading to C, but innumerable interactions in many varied  directions.    What you can know is that nutritional variety is related to long lived, healthy populations throughout the planet.

Bottom Line

Gut bacteria matter.  They will have impacts on weight, immunity, disease, longevity, and the pleasures of  life.  Too little is presently known about which populations are related to better health or how to effectively change them.  Yet doing the same stuff that teaches the body to be healthy, eating many different whole foods and moving around a lot, are at least correlated with bacterial populations which make it easier to control your weight.

Someday we may learn what works best for us from the bacteria themselves.  They  clearly have their own agenda.  It’s going to take new research, and new paradigms for understanding information processing in the body, to figure out what they really want – and how they might help us.