Fasting and the Gut Microbiome

By Dr. Sean M Wells, DPT, PT, OCS, ATC/L, CSCS, NSCA-CPT, CNPT, Cert-DN

For many decades nutrition experts and researchers were aware that fasting could impact certain disease states. From rheumatoid arthritis (RA), osteoarthritis, and several metabolic diseases (e.g. gout), fasting could reduce symptoms, improve functioning, and/or improve metabolic profiles for a short period. This short period of improvement could help patients during flares or bouts but couldn't offer long lasting effect. Many physiotherapists in the United Kingdom are aware of the power of fasting and vegetarian diets for patients with RA.

The understanding of how symptomology would improve in light of fasting was not well understood. Some authors offered the notion of the soma vs metabolic tradeoff, where the body took its time to repair its systems vs channeling energy into digesting food. Other researchers suggested that certain foods promote inflammation, and thus, removing food could reduce inflammation. While this notion is valid, it doesn't explain how some less noxious or "lower inflammatory" type foods would still not confer the same benefit as fasting.

Recent research may be shedding light on a new, more plausible mechanism for symptom improvement with fasting: the gut microbiome. The microbiome are small fungi, archaea, bacteria, and yeast that inhabit the digestive tract, especially the large intestines. Living symbiotically with the human body, these small bugs can confer immune system benefits, modulate inflammation, and/or produce important chemical compounds like neurotransmitters (e.g. serotonin) and short-chain fatty acids (used for energy and to help improve lipid profiles).

Certain foods, drugs, supplements, and behaviors can influence the gut biome. A plant-based diet can offer a rich source of prebiotic material, which gut bacteria loves to consume. Some foods are rich in probiotics like yogurt, fermented tofu, miso, and kraut; these can help to add to the variety or replace certain bacterial species. Drugs can shift the biome in various ways, sometimes in a fashion that is still not well understood. Oral antibiotics categorically damage the gut biome, which can cause major shifts in certain species and types of bacteria, yeast, and fungi, creating dysbiosis. Dysbiosis may be related to certain disease states, like auto-immune, inflammatory, or metabolic diseases. Some authors have suggested that dysbiosis is markedly connected with Parkinson's Disease, suggesting a strong connection between the brain and gut, known as the gut-brain axis.

Recent Fasting Research

One amazing animal study demonstrated that fasting could improve the gut biome in rats, which further reduced the animal's blood pressure. Could the gut biome, and its associated dysbiosis, be a driver of hypertension? If so, perhaps fasting and dietary interventions aimed at improving the gut biome could be the future for treating hypertension. Obviously, physical therapists and physicians don't treat rats, so let's look at some human data...

Another study examining intermittent fasting demonstrated a clear connection between gut bile acids and their associated gut biome changes. Intermittent fasting is where a person may consume food one day and then subsequently fast the next. Alternatively a person may use an alternative form of intermittent fasting, like time restricted feeding, where a person limits food consumption to a specific time during the day (e.g. from 11am to 7pm only) while fasting the remaining time. This study really honed in on the impact that intermittent fasting has on bile acids released by the liver during food consumption. Such bile acids impact the gut biome and may shift it in such a way to promote dysbiosis and hypertension, according to the authors. Hypertension is a significant cardiovascular and renal issue; reducing hypertension can help those in cardiac rehab and many inpatient physical therapy settings.

Intermittent fasting has also shown promise in patients with inflammatory conditions in this systematic review and meta-analysis. Researchers found significant reductions in C-Reactive Protein (CRP) in those following intermittent fasting diets compared to ad libitum diets. Energy restricted diets also conferred some reductions in CRP, but it was less than those fasting. It's important to note the effects were strongest in those with obesity, suggesting those individuals already have a pronounced dysbiosis. Obesity has been strongly correlated with dysbiosis. It goes without saying that reducing inflammation can significantly improve many PT patients' conditions.

Another recent study examined the effects of fasting on bile acids and blood sugar maintenance. In brief, fasting can impact bile acid production, which in turn can positively impact the gut biome, and then produce improved glucose metabolism and regulation. Understanbly restricting a diabetic patient's food intake would reduce consumed sugars and carbohydrates, but this study actually examined extraneous pathways and signaling that would impact glucose metabolism. In other words, the improved glycemic control wasn't simply from removing consumed carbohydrates -- it was also mediated by gut biome changes. Improving glycemic control can help physical therapy patients have less diabetic neuropathic pain, reduced tendon pathologies, and/or better PT outcomes.

Conclusion

In the end, the gut microbiome offers an amazing avenue for clinicians to manipulate in practice. Simple recommendations like consuming a variety of unprocessed plant foods, limiting antibiotic use, consuming probiotic foods, and possibly fasting or limiting the available hours of when food is consumed may confer significant health benefits. Obviously more research is need to optimize dosing parameters on when, how long, and what type of fasting is best for each condition and person; however, doctors of physical therapy (DPT) can help make simple dietary changes today to impact their patients' health tomorrow.

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