Why do we lose weight when we get infected?

Read our paper HERE

Or find it on the website of Nature Metabolism HERE

Why do we lose weight when we get a viral infection?

Is it just because we stop eating, or is it more? Our publication, now out in Nature Metabolism, shows that it is the latter: Our immune system stimulates fat cells to release lipids, which stimulates antiviral immune cells.

How does it work?

In our paper we show that upon a viral infection, stress signals are upregulated specifically in our fat (adipose) tissue. This causes immune cells to move into the tissue and produce immunological hormones, specifically IFNγ. This so-called cytokine tells fat cells to start releasing lipids into the blood. Why does this help us fight infection? Because activated immune cells, specifically B cells, use these lipids as a fuel and are better able to function. They seem to particularly like oleic acid, a fatty acid that is also highly present in olive oil. Most of our studies were done using mouse cells, but human B cells also use oleic acid, suggesting that this is a basic process happening during infection. When we blocked lipid production, the viral load strongly increased.

Why is this important?

Beyond infection, we believe that this process also may explain one of the most devastating symptoms of cancer: cachexia. In the final stages of cancer, patients start ‘eating’ their own body, first losing fat and after that muscle, which is followed by death. Why does this happen? We don’t know, but we believe that the process we discovered may play a role: during the final stages of cancer, the immune system may believe that it is infected with a virus and stimulate to start releasing lipids. Since there is no virus, this process spirals out of control. We are now investigating whether blocking these immunological processes may help in cancer.

Our Team:

The bulk of the work was carried out in Rijeka by our team members Mia Krapić and Inga Kavazović, with much support of Prof. Bojan Polić, while the clinical research was supervised by Assoc. Prof. Tamara Turk Wensveen. Also, our thanks to our national and international collaborators, including Sanja Mikašinović, Karlo Mladenić, Fran Krstanović, Gönül Seyhan, Sabine Helmrath, Elena Camerini, Ilija Brizić, Marc Schmidt-Supprian and Fleur Peters. Finally, many thanks to the Croatian Science Foundation, which partially funded this research.

You can find our research here: https://www.nature.com/articles/s42255-025-01273-2