Does intermittent fasting change your microbiome?

Most nutrition research is about what you eat. People, however, are complex biochemically and psychologically, we aren’t a simple engine using fuel, so what we eat is just part of the equation. We’re learning that the when and the how of food make a difference.  

Intermittent fasting is gaining popularity as a wellness regimen. People seeking weight loss, better sugar metabolism and heart health opt to limit their eating window to much less than their waking hours – 6 hours of eating and 18 with no food is one common regimen. 

There’s some evidence that it works.

Most diets work because they lead to a reduction in caloric intake – any plan that achieves a caloric deficit leads to weight loss. Is the intermittent fast just a trick to eat less, a way to reduce caloric intake without counting calories, or is there also a metabolic bonus that changes how our body treats the energy we consume according to some mysterious inner clock? 

Lessons from ritual fasting 

There are hints from research that intermittent fasting is actually more than just a trick for consuming less. The weight loss seen in some, but not other, studies is in excess of what you’d expect from just the caloric deficit. 

If people indeed lose more weight than expected through intermittent fasting what could explain that?

A proposed mechanism involves one of the most intriguing and promising subjects in current human metabolism: the microbiome. Our gut microbiome consists of trillions of microbial cells, outnumbering our own human cells nine to one. There’s growing evidence that specific gut bacteria regulate fat metabolism and affect obesity. Does intermittent fasting change the microbiome? 

Microbial allies

A new study in the American Journal of Clinical Nutrition utilizes a type of intermittent fasting practiced by a vast number of people around the world: the fast of Ramadan. Ramadan fasting is from sunrise to sunset, around 16 hours a day, for an entire month. Unlike the silicon valley intermittent fasters, who might be health seekers with multiple other confounding health related behaviors, religious fasters are a widely varied group. The cohort was recruited in China, and included healthy non-obese men.

In this group, eating only between sunset and sunrise resulted in weight loss. It also resulted in beneficial impacts on the gut microbial population. Fasting increased the diversity of gut microbes, and increases in populations of the butyric acid-producing Lachnospiraceae, which are microbes linked with health benefits.

What happens after Ramadan ends? The gut microbial population gradually returned to its baseline.

The authors propose that the beneficial microbes, and the molecules they excrete, may be responsible for the physiologic advantages of time-limited eating. 

This study’s results, if confirmed by other research, may offer yet another method to improve the population of the tiny helpers residing in our gut. Intermittent fasting research is still in its infancy though.

We know a lot more about how dietary and lifestyle habits, medications and the environment affect our microbiome, and the key dietary components to keep in mind when thinking about the health of your microbiome are whole plant foods (fruits, vegetables, grains, legumes, nuts), lots of fiber (whole plant foods take care of that), and reduction of refined and highly processed foods.

To be proactive in cultivating good bacteria choose the foods that we already know are good for us human hosts.

Dr. Ayala