Burgers, fries, pizzas: "only once" is not enough

People occasionally treat themselves to a cheat day, a day of indulging in unhealthy food and drink. But even infrequent consumption leaves a mark.

The effects of cheat days

What are cheat days?

You know the feeling: although you eat a mostly healthy diet and make sure you get enough exercise, you sometimes get a craving for sweets, fast food or other high-calorie delicacies. If you give in to these cravings and treat yourself to a day of feasting (or a few, during holidays), it´s often referred to as a "cheat day". In short, a day to deviate from normal eating habits.  

Indulging every now and then is ok... right?

A cheat day here and there usually has no significant impact on weight; that is if the feast is followed by a healthy diet. On a molecular level, however, things look different, as a recent study has shown. Using an animal model, researchers investigated the effects of a short-term change in diet on the immune system.

What happens to the immune system during a short-term high-calorie diet?

The study authors were able to show that even a short-term change in the regular diet to high-calorie foods with less fibre had consequences for the immune system. The risk of certain infections, for example with some strains of salmonella, increased. This is due to the change in CD4+ cells, which negatively affects the immune system, both systemically and by changes in the intestinal mucosa.

The good news is that if more fibre is added to the diet, cell function returns to normal. 

Conclusions for medical practice

Cheat days are seen as an acceptable limited period of dietary indulgance for most people. However, the current study shows that they may not be as harmless as often assumed. The data suggests that the immune system could be compromised by this change in normal eating habits, potentially opening the door to infections. However, these effects do not appear to be long-lasting. When more fibre was added, the cell functions in the animal model were regulated. It could be useful to educate people who are already immunocompromised about the potentially harmful effects of short-term indulgence outside of their routine diets.

  1. Siracusa, F., Schaltenberg, N., Kumar, Y. et al. Short-term dietary changes can result in mucosal and systemic immune depression. Nat Immunol 24, 1473–1486 (2023). https://doi.org/10.1038/s41590-023-01587-x