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Intermittent fasting may improve the diversity of the gut microbiome. Design by MNT; Photography by R A V E N/Stocksy & STEVE GSCHMEISSNER/SCIENCE PHOTO LIBRARY/Getty Images.
  • Intermittent fasting and calorie reduction both benefit diversity in the microbiome.
  • Gut bacteria in the microbiome are important to a range of health-related processes in the body, and a lack of diversity is tied to more diseases.
  • There are several so-called blue zones in the world — one in the United States — areas with extremely high rates of people who live past the age of 100 years.

Intermittent fasting and calorie reduction are both effective methods of supporting all-important microbiome diversity. A new study from the University of Colorado’s medical school highlights how changes in the gut microbiome, brought about through dietary interventions, can influence gene regulation and overall health.

Both intermittent fasting and calorie-reduction diets positively affect the microbiome, the community of bacteria living in a person’s digestive system and throughout the body.

Participants in the study, all of whom had either overweight or obesity, were either instructed to fast for 3 non-consecutive days each week for a year or, alternately, to reduce their regular caloric intake by around 34% over the same period.

An earlier analysis found that the diversity of gut bacteria in individuals’ microbiomes was significantly improved, even at only 3 months into the year-long study. Improvements were seen for both groups — those who fasted and those who focused on reducing their daily calorie intake.

The analysis suggested that a person can improve the diversity of their microbiome and potentially their overall health using the weight-reduction strategy of their choice.

The new study reinforces the idea that changes in gut bacteria occur during weight loss. The researchers observed several associations between the abundance of microbes associated with metabolism and obesity and DNA methylation, a process by which gene regulation is altered, potentially impacting our health.

The study appears in Nutrients.

Inside the human body are roughly 100 trillion symbiotic microbial cells. Most of these are bacteria, and most live in the upper and lower intestine. Our understanding of these tiny organisms is still somewhat in its infancy. However, it is clear that they are influential actors in our health.

Gastroenterologist Dr. Rudolph Bedford, who was not involved in the study, explained: “The gut microbiome mediates so many different things. It mediates any type of inflammatory process going on within your body.”

Inflammation in the body has been implicated in many medical issues, from cancer to diabetes, dementia, and heart disease.

In addition, the microbes in the microbiome influence other processes as well, including appetite and obesity.

Dr. Bedford said:

“You want a very diverse microbiome because the more diversity you have, the better variety of function in various aspects of your body you will have. You want a very diverse microbiome in order to decrease and regulate all the mechanisms within your body.”

Research bears out the value of a diverse microbiome. Dietician Kristin Kirkpatrick — also not involved in the study — addded that “microbial diversity has been associated with a better microbiome.”

Studies have shown that healthy individuals often have a more diverse gut microbiota. We also see in the data that the greater the beneficial microbes, the greater the change of beneficial health outcomes,” said Kirkpatrick.

The researchers, following their earlier analysis, had commented that the mechanism could be the benefits seen with changes in metabolism, weight loss, cardiometabolic factors, or even improvements in dietary patterns associated with the two arms of intervention.

Dr. Bedford suggested a simpler reason. “The microbiome is working full-time,” he said. So when you fast or eat less, “[y]ou’re resting it, allowing it to repopulate, just like sleep. That’s certainly one of the theories as to why you’re improving [diversity] with intermittent fasting, things of that sort.”

Nevertheless, Kirkpatrick cautioned that “[t]here is no one size fits all approach to diet, so each individual diet needs to be assessed with a health practitioner.”

In addition, she advised that “[p]regnant women, [those who are] breastfeeding, or someone struggling with a chronic condition should speak with their doctor or dietitian prior to altering their dietary pattern.“

The dietitian also expressed concern that fasting diets and calorie reduction could cause further harm to people with a history of disordered eating.

“Individuals with a history of eating disorders or current disordered eating should also not consider fasting or low-calorie approaches,” said Kirkpatrick.

Fasting can be performed in a variety of ways. While participants in the study fasted 3 days a week, fasting can also be done for a few hours, or for multiple days in a row.

Dr. Bedford noted that “[t]he problem with fasting is that unfortunately, as human beings, we fast, let’s say for 12 to 16 hours, we go home, and then we overeat.”

He cautioned that fasting is not a good idea for people with diabetes, since the prolonged lack of food causes fluctuations of blood sugar and insulin levels.

Previous research has found that calorie reduction, if it is too extreme, can cause an increase in pathogenic bacteria in the gut, and may otherwise disrupt the microbiome.

Dr. Bedford did not question the findings of this research. However, he suggested that extreme calorie reduction is an unlikely practice.

“I think it’s more theoretical: You’re telling a normal person to starve themselves. It takes an enormous amount of discipline to do that. So, unless you’re capable of going on a hunger strike, I don’t see that as much of an issue. In 30 years, I’ve never seen it,” he told us.

“In an industrialized society,” said Dr. Bedford, “there are probably in our food supply no more than five or six different animals. And in terms of plants, again, a very limited number of plant products that we also consume.”

“You throw in all the antibiotics that we’re using to deal with our animals, and all the pesticides we’re using on the plants. Those are things that tend to limit the diversity of your microbiome because you are what you eat and so are the bacteria,” he continued.

“As a gastroenterologist, we’re all seeing younger and younger people with colon cancers, and it’s a phenomenon that’s actually at epidemic proportions in first-world countries,” said Dr. Bedford.

He noted the existence of so-called blue zones, regions around the world in which people live exceptionally long lives. “There’s one in Loba Linda in the state of California, believe it or not,” he said.

There is a reason, he said, why people live longer in these areas: “It’s because it’s mostly a plant-based diet, a diversity of plant-based diets. And it changes the microbiome for the better, and therefore the less disease, fewer issues, and fewer problems.”