New Yale University-led research has unexpectedly found the ketogenic diet can protect from influenza infection in mice. Whilst experts are calling the study intriguing and significant, many are also cautioning these animal results are not transferable to humans and do not recommend people go on a ketogenic diet to battle the flu.
The high-fat/low-carbohydrate eating plan known as the ketogenic diet was originally developed in the early 20th century as a way to reduce seizures in patients with epilepsy. More recently the diet has become well-known in weight-loss circles and scientists are slowly discovering the effects of the eating strategy on a person’s health span and metabolism.
The new study followed on from a prior study finding the ketogenic diet was effective at suppressing the formation of inflammasomes, an immune system receptor known to trigger inflammation. The researchers wondered whether the dietary strategy would protect an organism from contracting influenza or make one more susceptible to the virus.
Two cohorts of mice were exposed to the influenza virus – one group was fed a keto diet (90 percent fat, 9 percent protein, 1 percent carbohydrate) for seven days prior to exposure, while the other group was raised on a standard chow diet (18 percent fat, 58 percent carbohydrate, 24 percent protein). The results suggested the animals on the keto diet were less susceptible to infection and demonstrated greater survival compared to the control group eating a normal diet.
Zooming in on the potential protective mechanism at play the researchers found higher levels of gamma delta T cells in the lungs of the keto diet mice. To confirm this was the protective mechanism the researchers bred a mouse without the ability to produce those particular T cells. When those animals were fed a keto diet and subsequently exposed to the influenza virus they demonstrated no additional viral resistance, validating the hypothesis that these particular immune cells may be the source of the protection.
Even more interesting was the finding that a third cohort of mice, fed a more simple high-fat but not ketogenic diet, showed increased gamma delta T cells in the lungs without the subsequent protective effects from viral infection. This suggests a broader metabolic process triggered by the ketogenic diet underpins the enhanced viral protection from increasing gamma delta T cells in the lungs.
“This study shows that the way the body burns fat to produce ketone bodies from the food we eat can fuel the immune system to fight flu infection,” says co-senior author Visha Deep Dixit.
A variety of experts reviewing the newly published study suggest that while the results are certainly academically interesting, they are not particularly transferable to humans. Michelle Tate, from the Hudson Institute of Medical Research, points out the metabolic differences between mice and humans mean these results don’t reveal a great deal for people looking to stave off the flu.
“It is important to note the study was performed in mice, which may not correlate to humans particularly as differences in metabolism exist,” says Tate. “In addition, the study was performed using genetically altered mice which differ to conventional laboratory mice, and a strain of influenza virus that causes disease in mice but not humans was used. Additional studies in humans and with human influenza viruses are warranted."
Nikolai Petrovsky, from Flinders University, is even more frank about the clinical significance of the study, suggesting the results are so marginal they are of no practical use. Petrovsky also notes the findings of increased inflammatory activity in the lungs relating to the ketogenic diet could increase the risk of triggering lung problems in susceptible individuals.
“Notably the effects shown here on influenza infection with the ketogenic diet were marginal at best, with most of the mice still dying of infection, and hence this finding is of academic rather than practical interest, particularly if such a diet might increase the risk of asthma and other lung problems due to the increased lung inflammation,” Petrovsky explains.
In the end the research offers a compelling insight into how diet can modulate immune system responses, but it certainly doesn’t imply people jump on a ketogenic diet to reduce the severity of an influenza infection. Rosemary Stanton, a Visiting Fellow at the University of New South Wales, notes even if further study reveals what mechanisms are at play the ultimate applicability to human health is minimal.
“Relating the results of these tests on mice to any comparable effect in humans would be drawing a very long bow,” says Stanton. “Even if the mechanisms in mice are solved, assuming the results might also apply to humans is another ball game."
The new research was published in the journal Science Immunology.
Source: Yale University
