IIf you spend a lot of time on the internet, you may have noticed that parts of the internet have caught fasting fever. Online message boards are rife with posts touting the benefits of time-restricted eating and other intermittent fasting approaches that involve not eating calorie-dense foods or drinks for an extended period of time — anywhere from 12 hours to several days. These online testimonies have helped promote intermittent fasting, and often feature two rationales: first, that humans evolved in environments where food was scarce and meals were sporadic. And second, that the relatively recent switch to round-the-clock eating has been disastrous for gut health and metabolism.
Digging the internet for accurate information, especially when it comes to dieting, can be like searching for gold. You have to scavenge a lot of junk to find anything of value. But this is one case where gold nuggets can be easy to find. Plenty of published peer-reviewed research on intermittent fasting makes the same claims you’ll find on these Reddit message boards. The authors of the 2021 review paper wrote in The American Journal of Physiology. “Early knowledge of human evolution and data from recent studies of hunter-gatherer societies suggest that humans evolved in environments with intermittent periods of food scarcity.” They say fasting regimens may provide a period of “intestinal rest” that can lead to many meaningful health benefits, including improved gut microbiome diversity, gut barrier function, and immune function.
The past decade has seen an explosion of research into fasting. (According to Google Scholar, the past five years alone contain nearly 150,000 articles examining or mentioning fasting.) While this work has helped establish links between intermittent fasting and weight loss, as well as other benefits, it is not yet clear when (or whether Fasting can help treat a diseased gut. “I still consider the evidence to be moderate,” says Dr. Emeran Mayer, MD, professor of medicine and founding director of the Goodman Luskin Center for the Microbiome at the University of California, Los Angeles. “[Fasting] It appears to be a wise way to maintain metabolic health or restore metabolic health, but it is not a magic cure.”
When it comes to bowel diseases such as inflammatory bowel disease (IBD), he says the research is either absent or inconclusive. In his view, the researchers found that Ramadan fasting — a month-long religious period in which people don’t eat or drink between sunrise and sunset — can “reshape” communities of bacteria in the gut in beneficial and healthy ways. However, among people with IBD, studies of Ramadan fasting have also found that a person’s gut symptoms may get worse.
While it’s too early to promote fasting plans as a panacea for bowel-related disorders, experts say there’s still reason to hope that these approaches will emerge as a form of treatment. Obviously some drastic, and possibly radically beneficial, things happen when you give your body breaks from food.
How fasting can repair the gut
In a recent series of studies, a team of researchers in the Netherlands and China examined the effects of Ramadan-style intermittent fasting on the gut microbiome — the billions of bacteria found in the human digestive system. (Ramadan comes up a lot in published research because it provides a real opportunity for experts to examine the effects of 12 or 16-hour fasting, which is what many popular intermittent fasting regimes espouse.) “We really wanted to know what Dr. Michael Pipplinbusch, a member of the research team and professor of gastroenterology, says. at Erasmus University Medical Center in the Netherlands: “Intermittent fasting affects the body.” “In general, we have seen that intermittent fasting changes the microbiome very clearly, and we view some of the changes as beneficial. If you look at fasting in general, not just Ramadan, you will see that certain types of bacteria are increasing.”
For example, he says, intermittent fasting pumps into the gut a group of bacteria called . Lachnospiraceae. “In the gut, bacteria are constantly fighting for environmental space,” he explains. Unlike some other gut microorganisms, Lachnospiraceae It can live happily in an empty digestive system. “They can live on the sticky that the intestines make, so they can overwhelm other bacteria in the fasted state.” Lachnospiraceae It produces a short-chain fatty acid called butyrate, which appears to be extremely important for gut health. Butyrate sends anti-inflammatory signals to the immune system, which may help reduce pain and other symptoms of intestinal dysfunction. Butyrate also improves barrier function in the intestines, says Pipplinbusch. This is likely a very big deal. Impaired barrier function (sometimes referred to as “leaky gut”) is a hallmark of common gastrointestinal conditions, including inflammatory bowel disease. If intermittent fasting can reduce inflammation and also help normalize the walls of the digestive tract, these changes could have significant therapeutic implications.
Lachnospiraceae It is just one of several types of beneficial bacteria that research has linked to fasting plans. But at this point, there are still a lot of gaps in the science. Peppelenbosch says the guts of people with gut disorders don’t seem to respond to fasting in quite the same way as the guts of people without these health issues. “In patients, we see the same changes in the microbiome, but it’s not as pronounced as in healthy volunteers,” he says. “So now we’re actually trying to figure out what’s going on there.”
Healthy shifts in the microbiome aren’t the only potential benefits researchers have linked to intermittent fasting. Meyer of the University of California, Los Angeles, mentions a phenomenon called migratory complex. “This is rarely mentioned in fasting articles today, but when I was on the faculty, it was one of the most important discoveries in gastroenterology research,” he says. The migratory kinetochore refers to repeated cycles of strong contractions that sweep across the contents of the intestine, including bacteria, all the way to the colon. “It’s a 90-minute repetitive wave of contraction that flips over the intestines, and its strength is comparable to a nutcracker,” he says. Essentially, this motor complex acts like a street cleaning crew that cleans up after the show. It ensures that the intestines are cleaned and cleaned between meals, through repeated 90-minute cycles that fasting allows to become more frequent. It also helps in rebalancing the microbial populations in the gut so that more of them live in the colon and lower areas of the digestive system. “But it stops the moment you take a bite — it goes off instantly,” he says.
Meyer says that modern eating habits–so-called “grazing,” or eating steadily throughout the day–leave little time for the migratory motor complex to do its job. “This function has been deprecated to the time we sleep, but even that has been disrupted because a lot of people get up in the middle of the night and eat lightly,” he says. “So it’s those longer periods of time that we’re repurifying and rebalancing our gut so that we have normal distributions of bacteria and normal population densities — which have been severely disrupted by these lifestyle changes.”
Ideally, Mayer says, people can (for the most part) stick to the type of time-restricted eating program that allows a full 12 to 14 hours each day for the motor complex to function. “If you don’t snack, this kinetic complex will happen between meals, and you also get that 12 to 14 hour window at night where your digestive system is empty,” he explains. In other words, sticking to three meals a day and avoiding bites between meals (or nighttime snacks) may be enough. But again, it’s not clear if this type of eating schedule can undo intestinal damage or treat existing dysfunction.
Read more: The truth about fasting and type 2 diabetes
More potential benefits
Another potential benefit of fasting is a biological process called “autophagy.” During autophagy, old or damaged cells die and the body gets rid of them. Described by some researchers as a useful housekeeping mechanism, it occurs naturally when the body has been short of energy (calories) for an extended period of time. There has been some expert speculation, based on evidence in laboratory and animal studies, that autophagy could help fortify the gut or counter the kinds of barrier problems seen in people with IBD. But these improvements have yet to be seen in real-world clinical trials involving people.
Meanwhile, some experts have found that fasting may help reset the metabolic rhythms in the gut in beneficial ways. “By changing the timing of the diet, this will actually change the activity of
microbiome, which may have negative health effects,” says Dr. Eran Elinav, principal investigator in the host-microbiome interaction research group at the Weizmann Institute of Science in Israel.
Some of Elinav’s work, including an influential 2016 research paper published in the journal cell, that the gut microbiome undergoes changes day and night that are influenced by a person’s food intake schedule, altering patterns of metabolite production, gene expression, and other important components of gut health. “If you change the timing of the diet, you can flip the daily activity of the microbiome,” he says. This likely has health implications, although what, exactly, they are, remains a mystery.
Read more: What we know about leaky gut syndrome
Fasting is not going anywhere
Obviously, when you eat, including how often you eat, is important to the health of your gut. But the devil is in the details. At this point, it’s not clear how intermittent fasting can be used to help people with bowel-related disorders or metabolic diseases.
“For a condition like inflammatory bowel disease, it’s important to differentiate between what you do during a flare and what you do to prevent the next flare,” Meyer points out. Research in people who celebrate Ramadan, at least during a flare, suggests that fasting may make a person’s IBD symptoms worse. Finding out whether fasting can also lead to long-term improvements is just one of the many questions that need to be answered.
While there are still many unknowns, experts say that common methods of fasting appear to be safe for most people. Time-restricted eating, for example, involves crawling all of the calories in your day into a single six- to eight-hour window for eating. Even among people with metabolic diseases such as type 2 diabetes, research indicates that this form of fasting is safe, provided the person does not take blood glucose medications.
However, there is not much work on intermittent fasting as a treatment for bowel problems. Also, there is very little research on more extreme forms of fasting, such as plans that include not eating calories for several days in a row. These diets may be therapeutic, but they can also be dangerous. If you’re considering any of these approaches, talk with your healthcare provider first.
“We really need much better studies to compare all the different fasting protocols,” says Bipplinbusch. “But in general, increasing the distance between consuming calories is good for you. The body is not made to eat all day.”
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