Intermittent fasting may reduce risk for severe COVID-19

Intermittent fasting was associated with a lower risk for COVID-19 hospitalization and mortality and could be used as a complementary therapy to vaccination, according to researchers.

Existing evidence indicates that repeated fasting can boost parameters of inflammation control and host defense against infections, Benjamin D. Horne, PhD, the director of cardiovascular and genetic epidemiology at the Intermountain Heart Institute in Utah, and colleagues wrote in BMJ Nutrition, Prevention & Health. In previous studies, routine periodic fasting reduced the risk for coronary artery disease (CAD), type 2 diabetes and incident heart failure (HF).

“Such risk reductions by fasting of diagnoses that exacerbate the severity of COVID-19 (eg, diabetes, CAD and HF) may indirectly reduce COVID-19 severity, providing a possible ... biological mechanism for fasting-induced protection from severe COVID-19 outcomes,” they wrote. “Due to these direct and indirect impacts of fasting on infectious disease outcomes, it is hypothesized that periodic fasting is associated with lower COVID-19 severity in people infected by SARS-CoV-2.”

Horne and colleagues conducted a prospective, longitudinal, observational cohort study to better understand any associations of periodic fasting with initial infection and COVID-19 severity.

The researchers analyzed data from 205 people — 132 who did not fast and 73 who engaged in periodic fasting for approximately more than 40 years. The primary outcome was a composite of hospitalization or mortality.

They found that the composite outcome occurred in 28.8% of non-fasters and 11% of periodic fasters (HR = 0.61; 95% CI 0.42-0.9). Multivariable analyses, they wrote, confirmed the association.

In a secondary analysis, the researchers found that COVID-19 was diagnosed at similar rates for both groups: 14.3% of fasters and 13% of non-fasters.

Horne told Healio that “it is best to view fasting as a potential complementary therapy ... that provides secondary support to the other preventive and treatment options that we have available” because “fasting is not more powerful than medications and other treatments.”

“We suspect that fasting will support immunity to SARS-CoV-2, bolstering the immune response when vaccine-induced immunity is strongest but also helping to support immunity during periods when the vaccine-related immunity has waned,” Horne said. “For people in areas where vaccines are not available or are too expensive, fasting may be helpful to provide some support to those who cannot obtain vaccines, but further research is needed on this.”

Mechanisms of action

According to Horne and colleagues, intermittent fasting can modulate the inflammatory response and boost defense mechanisms.

“We continue to discover the potential mechanisms that are likely being triggered by fasting that may reduce the severity of COVID-19,” Horne said. “These mechanisms appear to strengthen and support the immune system, reduce hyperinflammation, and counteract adverse effects of SARS-CoV-2 on various systems of the body, including that fasting may prevent or reverse adverse effects of the virus on the gut microbiome, on energy production in cells and on the cellular recycling mechanism called autophagy.”

Horne noted that “one of the most intriguing potential mechanistic aspects” to the phenomena is that “fasting is well known to induce ketosis, in which fatty acids are extracted from adipose tissue and converted into ketones.”

“A group in England has described a pocket on the surface of the SARS-CoV-2 spike protein into which one or more of the fatty acids (primarily linoleic acid) fits as a receptor-ligand pairing,” he said. “When linoleic acid is attached to the spike protein’s fatty acid pocket, the spike becomes locked in a shape that makes it difficult for the virus to attach to the ACE2 protein on the surface of human cells and, thus, this limits the severity of COVID-19. Both fasting and ketogenic diets should cause this misshapen spike protein to occur.”

Messages for PCPs

Horne said there are multiple take-home messages for primary care providers.

“One is that in addition to the vaccine and antiviral options that are available now, fasting is a no-cost, low-risk dietary behavior that most adults should be able to use safely in addition to vaccines (I encourage people to get vaccinated) to improve their health and protect against severe COVID-19,” he said.

Additionally, Horne noted that the research team studied periodic fasting in those who had been following their approximately once-per-month 24-hour fast for more than 40 years, “which should have conditioned their body to respond quickly to any fasting and may have over the years and decades reduced the risk of coronary disease, diabetes, heart failure, and other chronic diseases.”

“Since fasting is generally safe and available without prescription, though, most adults may benefit from it,” he said. “Because people do not have 40 years to build up their fasting, it is likely that an intermittent fasting regimen of 1, 2 or up to 3.5 days per week of fasting or the fasting regimen called time-restricted eating should also trigger the same mechanisms as periodic fasting and provide more immediate benefits since people do not have the time to wait for 40 years to use a 1-day-per-month periodic fasting regimen to obtain the immediate need for relief from COVID-19.”

Horne also mentioned the “numerous safety precautions that should be considered regarding intermittent fasting.”

“There are groups of people who need more caution, some who need enhanced health monitoring, and others who simply may not be candidates for fasting, but these are small proportions of the general population,” he said. “But there are some people who may be harmed more by fasting than they are benefitted if precautions are not taken, and this is important because people can engage in fasting without a prescription or without consulting a health professional.”

For example, Horne said people with diabetes who are taking medications that lower blood sugar could have an adverse reaction to fasting because it “acutely reduces blood sugar while food is being withheld.”

“Also, children generally should not fast for health purposes unless their health professional has prescribed it for them because it can blunt physical and cognitive development when used inappropriately,” he said. “People with eating disorders or malnutrition also should not fast.”