Scientists discovered that polyunsaturated fatty acids (PUFAs) - common fats found in many processed foods - might actually make you feel hungrier. In their study using mice, researchers found that these specific fats changed the gut bacteria, which then affected brain chemicals that control appetite. When they transplanted gut bacteria from PUFA-fed mice into germ-free mice, those mice also became hungrier. This suggests that some components of modern processed diets may literally rewire our appetite control system through changes in our gut microbiome, potentially explaining why it’s so hard to stop eating certain foods.

The Quick Take

  • What they studied: How different types of fats in processed foods affect hunger and appetite through gut bacteria
  • Who participated: Laboratory mice fed different types of diets, including some with no gut bacteria at all
  • Key finding: Polyunsaturated fatty acids increased appetite by changing gut bacteria, which then altered brain chemicals that control hunger
  • What it means for you: Certain fats in processed foods may make you hungrier by changing your gut bacteria, though more human research is needed to confirm this effect

The Research Details

Researchers fed mice different types of diets to compare how various components affected their appetite and brain chemistry. They tested Western-style diets against control diets, compared high-fat versus high-sugar diets, and specifically looked at saturated fats versus polyunsaturated fatty acids (PUFAs). The most interesting part involved taking gut bacteria from mice fed PUFA-rich diets and transplanting them into mice with no gut bacteria at all to see if the bacteria alone could transfer the appetite-increasing effects.

This approach allowed scientists to isolate exactly which diet components were causing changes in appetite, rather than just looking at overall diet patterns. The bacteria transplant experiment was particularly important because it proved that gut microbes were actually carrying the appetite-enhancing signal, not just responding to it.

This study used careful controls and multiple experimental approaches to test their hypothesis. However, it was conducted only in mice, and the sample sizes weren’t specified in the available information. The research appears to be a preprint, meaning it hasn’t yet undergone full peer review.

What the Results Show

The study found that polyunsaturated fatty acids had the strongest effect on increasing appetite compared to other dietary components tested. These fats increased levels of 5-HIAA, a breakdown product of serotonin, in the brain. Serotonin is a key chemical messenger that helps control appetite and mood. When researchers transplanted gut bacteria from PUFA-fed mice into germ-free mice, the recipient mice also showed increased appetite, proving that the gut microbiome was carrying this appetite-enhancing signal. This suggests that PUFAs don’t just directly affect the brain, but work through a complex pathway involving gut bacteria that then influence brain chemistry.

The researchers found that the overall Western diet pattern and high-fat versus high-sugar comparisons showed less dramatic effects than the specific PUFA comparison. This suggests that the type of fat matters more than just the amount of fat or overall diet quality when it comes to appetite regulation.

This research builds on existing knowledge about how industrialized diets contribute to eating disorders and metabolic problems, but provides a new mechanistic explanation focusing on specific dietary components rather than overall diet patterns. It adds to growing evidence that gut bacteria play important roles in appetite regulation.

This study was conducted only in mice, so we don’t know if the same effects occur in humans. The sample sizes weren’t provided, making it difficult to assess the statistical strength of the findings. As a preprint, it hasn’t undergone full peer review yet. Additionally, the study doesn’t address how long these effects last or whether they can be reversed.

The Bottom Line

Based on this early research, it may be worth paying attention to the types of fats in your diet, particularly limiting processed foods high in polyunsaturated fatty acids if you’re struggling with appetite control. However, since this research is preliminary and conducted in mice, these recommendations should be considered tentative.

People interested in appetite control and those struggling with overeating might find this relevant, but everyone should wait for human studies before making major dietary changes based solely on this research. People with eating disorders should consult healthcare providers before making any dietary modifications.

If these effects occur in humans, changes in gut bacteria typically happen within days to weeks of dietary changes, but we don’t know how quickly appetite effects might be noticed or how long they might take to reverse.

Want to Apply This Research?

Use the Gram app to:

  • Track your intake of processed foods high in polyunsaturated fatty acids (like certain vegetable oils, processed snacks, and fried foods) alongside your hunger levels throughout the day
  • Try reducing processed foods high in PUFAs for 2-3 weeks while monitoring your appetite and cravings to see if you notice any personal patterns
  • Log both your PUFA intake and hunger/satiety ratings over several weeks to identify potential personal correlations, while also tracking other factors that might influence appetite

This research was conducted in mice and has not yet been peer-reviewed or replicated in humans. Do not make significant dietary changes based solely on this preliminary research. Consult with a healthcare provider or registered dietitian before making major modifications to your diet, especially if you have existing health conditions or eating disorders.