A study published in Cell Reports conducted on mice revealed an unexpected association between diet and the ability of the immune system to respond to seasonal flu: while the rodents that ate cereal-based feed recovered quite quickly from the disease, those that ate ultraprocessed (i.e. industrially processed) and low in some micronutrients, they were dead within two weeks. If confirmed, the results of this study would have important implications for research on laboratory animals, which are normally fed with either ultraprocessed or cereal-based feed.
The study involved two groups of mice, one fed with ultraprocessed feed and the other with “simple” feed based on cereals: under normal conditions, there were no differences in the metabolic response of the two groups. But when they were infected with the influenza A virus, something changed.
The image illustrates the process that led to the death of the rodents that fed on the ultraprocessed feed: after contracting the flu virus, these (on the right) lost their appetite and died, unlike their similar ones that had been fed grain-based food, they started eating again and eventually recovered.
© Cootes et al. | Cell Reports
All dead. After ten days all the rodents fed with the simple diet began to recover by gaining weight; on the contrary, after fourteen days all the mice fed with ultraprocessed feed died of the infection. The analyzes showed that this incredible difference in the reactions of the two groups was not due to a lack of immune response of the organism to the virus, but rather to the fact that the mice subjected to an ultraprocessed diet showed a poor appetite and this, in turn, prevented them from returning to a situation of “self-regulated equilibrium”. Compared to those consuming a simple diet, the rodents that ate processed foods ate less during the first nine days of infection, had a much lower core temperature after one week, and showed reduced glucose uptake by the ninth day.
The role of interferon gamma. To understand more, the scholars looked at the role of interferon-gamma (IFN-γ), a protein released by infected cells and already associated with hypothermia in mice: by analyzing a group of modified rodents − deprived of this protein − it emerged that these they regained weight and temperature in a similar way to those who ate raw food, while subsisting on ultra-processed feed. This means that IFN-γ affects the outcome triggered by the ultraprocessed diet, but the details of this mediation are still unknown.
Some doubts. However, not all experts are convinced that the ultraprocessed diet is the real culprit of the death of the mice: “These results do not demonstrate that the ultraprocessed feed is responsible for the adverse effects found in the mice,” emphasizes Philip Calder, a nutritional immunologist who did not participate to search. Many of the micronutrients present in smaller quantities in this type of feed, he explains, are vital for the immune system, and therefore their absence could be an alternative explanation for the mice’s lack of response.
Carl Feng himself, one of the authors of the research, acknowledges that at the moment the differences between the two groups of rodents cannot be traced with certainty to the type of diet. The expert also points out that these results are not automatically valid for humans as well but, as Yale immunologist Ruslan Medzhitov points out, “this study confirms that diet has an important impact on the immune system”.