Animal studies exploring fasting-mimicking diets for IBD have produced promising results. But the research is still emerging, and fasting in general has yielded mixed results among people with IBD.

If you have an inflammatory bowel disease (IBD) — that is, ulcerative colitis (UC) or Crohn’s disease — you may be curious about the benefits of fasting for your condition.

There’s a lot of buzz around the many benefits of fasting for different health conditions. It’s been shown to be beneficial to blood sugar levels, obesity, psoriasis, rheumatoid arthritis, asthma, and other conditions where inflammation is at play.

But fasting and fasting-mimicking diets appear to have mixed results in IBD. A fasting-mimicking diet shows promise, whereas certain types of fasting, like alternate-day fasting and time-restricted fasting, may make symptoms worse.

Here’s what we know so far.

In 2019, a study from the University of Southern California (USC) found that a low calorie eating plan reduced inflammation in the intestine and reversed the pathology of IBD in mice.

Researchers said that the results could be significant in the treatment of IBD.

“We had shown that the fast-mimicking diet was effective against a multiple sclerosis (MS) mouse model and also provided initial evidence for its effect against MS in humans,” Valter Longo, PhD, study author and the director of the USC Longevity Institute at the USC Leonard Davis School of Gerontology, told Healthline.

“We suspected it could be effective against many autoimmune diseases, particularly those involving the gut. This is important because it addresses potential strategies to truly reverse, and not just keep under control, widespread illnesses such as Crohn’s disease and ulcerative colitis.”

In Longo’s study, one group of mice underwent a 4-day fast-mimicking diet in which they consumed roughly 50% of their normal calorie intake on day 1 and 10% of their normal intake on days 2, 3, and 4.

A second group of mice fasted only with water for 2 days (48 hours).

The researchers found that some IBD pathologies and associated symptoms reversed in mice who had the fasting-mimicking diet followed by their normal diet.

Interestingly, the mice in the water-fasting group didn’t experience the same benefit. The researchers suggested that this may have been because particular nutrients in the fasting-mimicking diet help promote a healthy microbiome and reduce inflammation in the gut.

The researchers explained that the fasting-mimicking diet encouraged an increase in intestinal stem cells by supporting a growth in healthy gut microbiota.

“Water-only fasting was effective mostly in promoting intestinal regeneration. The fast-mimicking diet instead was effective in reversing disease pathology by regulating microbiota, regeneration, and inflammation,” Longo said.

A 2021 study in mice found similar results. A fasting-mimicking diet led to reduced inflammation and promoted the repair of the intestinal wall.

On a fasting-mimicking diet, you eat a very low calorie diet for usually just a few days, but your eating isn’t time-restricted as in typical types of fasting, like intermittent fasting.

Experts recommend eating nutrient-dense foods during a fasting-mimicking diet so that you can get the essentials even though you’re restricting your calorie intake.

One popular prepackaged version of this diet is offered by a company called ProLon, founded by Longo, the author of the fasting-mimicking study in mice mentioned above. The diet is designed to last for just 5 days, and the meals deliver 34% to 54% of the calories you’d normally consume in a day.

The company website recommends going on this 5-day eating plan either once a month or twice a year, depending on your health needs.

It’s important to note that the study in fasting-mimicking above was conducted in mice, not humans, and that it was done by the same people who are promoting the ProLon diet. Therefore, it’s wise to be skeptical of the study results and Longo’s interpretation of them.

It’s also possible that the foods eaten during fasting-mimicking may be more beneficial than actual fasting, but it’s difficult to tell at this point what diet is best.

If you have IBD and you’re interested in the fasting-mimicking diet, you don’t necessarily need to follow the ProLon diet. If you’re interested, ask your doctor for a personalized recommendation.

Fasting-mimicking vs. fasting

A fasting-mimicking diet is different from a fasting diet, in which you don’t eat during certain periods of the day or week.

For example, if you practice the popular 16/8 intermittent fasting method, you only eat within an 8-hour interval of your choice every day, like between 10 a.m. and 6 p.m. Unlike with fasting-mimicking diets, some people practice intermittent fasting long-term.

IBD is an umbrella term to describe Crohn’s disease or ulcerative colitis (UC), two conditions characterized by chronic inflammation of the gastrointestinal tract.

Common symptoms include:

  • abdominal pain
  • rectal bleeding
  • weight loss
  • fatigue
  • persistent diarrhea

In 2015, about 3 million American adults reported having Crohn’s disease or UC.

The precise cause of IBD remains unknown. However, it’s believed the condition happens when the immune system attacks the gut.

In the body of the average person, the immune system attacks foreign invaders, such as viruses, to protect the body. With IBD, the immune system identifies beneficial gut bacteria as invaders and causes the gastrointestinal tract to become inflamed.

Various types of medication are available to treat IBD. In severe cases, surgery may be an option.

But according to Brigid Boland, MD, assistant professor of medicine at the University of California San Diego and a spokesperson for the American Gastroenterological Association, finding the right treatment can be difficult.

“The treatment of IBD is challenging. It’s a complicated disease that requires an underlying genetic predisposition, environmental and microbial triggers, leading to an overactive immune response,” Boland told Healthline.

“Treating IBD or reversing pathology is challenging. Even the most effective drugs for IBD don’t induce long-term remission in the majority of people with the disease. As a result, finding better therapies for IBD remains a priority and an ongoing research focus.”

Currently, no diet has consistently treated inflammation caused by IBD or put the disease into remission.

Some diets, such as the FODMAP diet, can assist with symptoms, but they must be combined with other treatments to adequately manage the disease and prevent complications.

“Finding a way to control this disease with diet would be an incredible achievement and could prevent lifelong medical therapy,” Jesse Stondell, MD, an assistant professor of gastroenterology and an IBD specialist at UC Davis Health, told Healthline. “There’s a strong desire within medical and patient communities to find this type of solution.”

“We know for sure that people with IBD have very different bacteria living in their bowels compared to people without the disease,” Stondell continued. “It’s not known if this is a cause or effect of the IBD, but many scientists have theorized that correcting the bacterial imbalance could lead to improvement in the disease. Unfortunately, this has proven to be very difficult to achieve.”

Should you fast if you have Crohn’s or UC? The effects of fasting in IBD aren’t fully known, and research on the topic is mixed, suggesting there may be several interacting factors. So, the answer isn’t straightforward.

It’s true that studies over the years have shown fasting can be very beneficial for many conditions.

In non-IBD populations, intermittent fasting improves gut microbiota composition and reduces inflammation in the gut and throughout the body. Plus, studies have found fasting has positive effects for people with other inflammatory conditions, including rheumatoid arthritis and psoriasis.

However, studies specifically on IBD suggest the story may be a bit different for Crohn’s and UC.

A 2022 observational study in 80 people investigated how intermittent fasting during Ramadan affected people with IBD. The researchers measured disease activity and levels of certain inflammatory markers that are involved in IBD in people who fasted for Ramadan.

Ramadan is a month-long Islamic practice in which people fast (including abstaining from water) during daylight hours, eating before dawn and after sunset.

The study found that people’s IBD symptoms actually increased by the end of the fasting month. Two participants with UC had to stop fasting because their condition got worse. In other words, fasting was associated with a negative effect in this study.

The authors suggested that fasting may have opposing effects in people with IBD compared with other autoimmune disorders because changes in eating may affect the gut differently than other parts of the body.

Moreover, some research has shown that these different types of fasting may have different effects in UC.

One 2020 study in mice with colitis found that time-restricted fasting and intermittent energy restriction stopped UC disease progression, reduced inflammation and oxidative stress, and increased gut microbiota diversity and beneficial microbial compounds in the gut.

But another type of fasting called alternate-day fasting did not have the same effects and caused colitis to worsen in the mice.

Further studies are needed to untangle the complex factors that affect inflammation and disease activity in IBD.

Many of the experts who spoke with Healthline advise against people with IBD trying a fasting-mimicking diet as the effectiveness of this in humans has yet to be determined.

The researchers say further study in the form of a randomized clinical trial is essential to determine the safety and efficacy of such a diet in humans.

Kian Keyashian, MD, a clinical assistant professor of medicine at the Stanford School of Medicine in California, said that the results of the study are promising but will require examination of more elements to determine success in humans.

“Studies for fast-mimicking diets in the general population have shown some health benefits,” Keyashian told Healthline. “However, the translation of such animal studies to humans requires consideration of additional factors. In addition, safety of these diets for people with IBD have not been studied.

“People with IBD are at increased risk of malnutrition, and any restriction in diet can further exacerbate this,” he added. “There needs to be good demonstration of efficacy and safety of any restricting diet in human trials before these diets can be recommended for people with IBD.”

Fasting-mimicking is different from fasting, in that you don’t abstain from food completely. Early studies in mice with colitis suggest that fasting-mimicking may help ease symptoms, but more research in humans is needed before we know with more certainty whether fasting-mimicking can help people with IBD.

Fasting practices, such as intermittent fasting, have piqued researchers’ interest as a potential treatment in people with IBD because of their known ability to reduce inflammation in the general population and in people with other inflammatory conditions.

However, fasting doesn’t seem to have a clearly positive effect on people with IBD, and some research among people who fasted during Ramadan suggests that intermittent fasting had a harmful effect on people with IBD.

Thus, the jury’s still out on whether fasting and fasting-mimicking might help people with IBD, and more research is needed.

If you’re interested in trying fasting-mimicking or fasting for IBD, ask your doctor for a recommendation. Care for patients with IBD can vary widely depending on your condition and needs.