The study from Yale University, published November 15 in the journal Science Immunology, discovered that mice fed a ketogenic diet (low in carbohydrates but high in fat with moderate protein) were better able to fight off the flu compared with mice given foods that were high in carbs. “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,” said the co-senior author Vishwa Deep Dixit, PhD, a doctor of veterinary medicine and a professor of comparative medicine and immunology at Yale, in New Haven, Connecticut, in a statement.
How the Keto Diet Works
A ketogenic eating plan helps people shed pounds by drastically limiting the intake of carbohydrates (such as breads, pastas, and sweets), while increasing the consumption of meats, dairy, fats, and nonstarchy vegetables. The diet puts the body into a metabolic state called ketosis, in which the liver breaks down fat into an energy source called ketones, which fuel the body in the absence of glucose. This type of eating plan has been shown to help maintain blood sugar levels in people with type 2 diabetes. There is also some evidence, such as a study in Federal Practitioner from February 2017, that a keto diet may improve tumor response in cancer patients. Another study, out of the University of California in Davis in 2017, found that mice on a high-fat diet had a 13 percent longer life span compared with mice on a high-carb diet.
Understanding How Keto May Affect the Flu Virus
In the latest study, Dr. Dixit and his collaborators observed that the ketogenic diet blocked the formation of inflammasomes, which are immune system activators that can cause harmful immune system responses. Seeing this response, the scientists set out to test how the diet might affect the flu virus. The researchers fed a group of mice infected with influenza a keto diet containing less than 1 percent carbs. Another group of infected mice received a standard diet with 58 percent carbs. The ketogenic diet spurred the release of gamma delta T cells, immune system cells that produce mucus in the cell linings of the lung; but the high-carbohydrate diet did not. An increase in mucus helps capture and eliminate the flu virus from the system, according to researchers. The researchers also found that the keto diet provided no protection against the influenza virus in mice specially bred without these gamma delta T cells. This confirmed that these cells play a critical role in warding off flu. “We have no idea yet why the gamma delta T cells appear to become activated by the keto diet. This is something we’ll be pursuing in the future,” says Emily Goldberg, PhD, a postdoctoral associate at the Yale School of Medicine who collaborated on the research. “A high-carb diet tends to stimulate inflammatory markers which inhibit immune function,” says Jan Rystrom, RD, a certified diabetes educator at the Swedish Medical Center in Seattle, who was not involved in the Yale study. “This could be the mechanism that the low-carb diet addresses.” On the other hand, some dietitians and medical experts believe that a low-carb diet can compromise the immune system. A lack of carbs may lead to a lack of energy and weaken a person’s health overall. There is also evidence that a keto diet can be harmful to the gut microbiome, which is essential to overall well-being. Rystrom points out that keto diets can have a lot of variation, and ones that are more “plant-forward” are likely to promote a healthier gut microbiota. “Generally speaking, it is true that the immune system should require increased glucose utilization to mount an effective immune response against infection,” says Dr. Goldberg. “It’s important to keep in mind that there is still glucose availability, albeit very limited, even during a keto diet.”
Flu Shot Remains the Best Protection
Although Rystrom suggests that the Yale study supports the anti-inflammatory effect of nutritional ketosis, she adds that a keto diet “certainly would not be a first line treatment [for flu].” William Schaffner, MD, an infectious-disease specialist at Vanderbilt University in Nashville, Tennessee, has not seen significant data connecting diet with flu protection. “It’s a very intriguing study,” says Dr. Schaffner. “If we can learn more about how the body fights flu, we can get smarter about how to treat influenza and perhaps prevent it.” He notes that there is some evidence that obesity may lead to a weaker response to flu vaccine, so that may be an indication of how diet could affect flu protection. Research is needed in humans, however, to validate that the keto diet can effectively protect against the flu. “People are not the same as mice. Thirty thousand to 40,000 people die in the United States each year from influenza,” says Len Horovitz, MD, a pulmonary specialist at Lenox Hill Hospital in New York City. “There’s no substitute for protection better than a flu shot!”
