Eating a ketogenic or keto diet might stave off the flu, according to a new study published on 15 November in Science Immunology (1). Mice fed a high-fat keto diet, which seems to boost certain immune cells, were protected from a lethal strain of influenza.
The study was devised by Ryan Molony, at the time a graduate student working with Prof Akiko Iwasaki at Yale University and Dr Emily Goldberg, a postdoc in Prof Vishwa Dixit’s lab, also at Yale. The Dixit group previously showed that a ketogenic diet blocks an inflammation pathway triggered by a protein complex that plays a role in some autoimmune disorders (2). Then, a year later, Iwasaki’s group showed that the same protein complex drives a lethal influenza infection (3).
So together, the researchers posited whether diet could affect immune system response to pathogens such as the flu virus. To test their hypothesis, they placed one group of mice on the keto diet (90 per cent fat, 9 per cent protein, 1 per cent carbohydrate) and another group on standard feed (18 per cent fat, 58 per cent carbohydrate, 24 per cent protein) for 7 days before exposing them to a deadly strain of the flu virus.
Incredibly, mice on the keto diet had a much higher survival rate than those on the normal high-carb diet. In addition, they found that keto-fed mice lost less weight, maintained higher blood-oxygen saturation levels, and had lower levels of the virus in their blood.
The results were ‘totally unexpected’, said co-author Prof Waldemar Von Zedtwitz, an immunologist at the Howard Hughes Medical Institute.
The keto diet triggered the release of a subset of T cells in the lungs — specifically gamma delta T cells — resulting in enhanced mucus production by lung cells. The mucus can effectively trap the virus, the authors explain. This type of response has not previously been associated with the immune system’s response to influenza.
To prove the immune cells were indeed responsible for bestowing protection on the mice, the study was also performed on mice without the ability to produce gamma delta T cells. In this case, the ketogenic diet provided no protection against the influenza virus. Even more intriguing, regular mice fed a much simpler high-fat diet — but not a keto diet — also had more gamma delta T cells in the lungs but were not protected against the infection.
Could this controversial diet that ditches carbohydrates in favour of fats be the key to overcoming the flu? While the results are definitely interesting, experts urge caution. The study certainly highlights the important impact of diet on the immune system, unfortunately, the findings are of little practical use.
Animal results are not transferable to humans. For starters, mice have a totally different metabolism than people. Moreover, the strain of influenza used in the study does not cause illness in humans. Therefore, additional studies using a human strain of the virus are needed.
Furthermore, the study was short — just one week — and the researchers are not sure whether lung cells would continue to produce more gamma delta T cells over a longer period of time — and if that would have positive or negative effects.
Nonetheless, the 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 Dixit.
For humans, the keto diet consists of meat, fish, poultry, and non-starchy vegetables, which forces the body to burn fat for energy and is popular among people trying to lose weight. But scientists still don’t know the long-term consequences of adopting such a diet. So for now, it might be good to hold off on fighting the flu with the keto diet — at least, for this flu season.
(1) Goldberg, E.L. et al. Ketogenic diet activates protective γδ T cell responses against influenza virus infection. Science Immunology (2019). DOI: 10.1126/sciimmunol.aav2026
(2) Youm, Y-H. et al. The ketone metabolite β-hydroxybutyrate blocks NLRP3 inflammasome–mediated inflammatory disease. Nature (2015). DOI: 10.1038/nm.3804
(3) Pillai, P.S. et al. Mx1 reveals innate pathways to antiviral resistance and lethal influenza disease. Science (2016). DOI: 10.1126/science.aaf3926