A striking infographic recently went viral: "a high-fat diet drives anxiety through a brain circuit". The study behind it is real, published in Nature Communications in September 2026. But it was done in mice. Posts like this appear every week, so it is worth asking the question the other way round: what has diet actually been shown to do for mood in people?
Depression: Real Trials, Real but Modest Effects
This is where the human evidence is strongest.
- SMILES (Australia, 2017). Adults with moderate to severe depression received either seven sessions with a dietitian to move toward a Mediterranean-style diet, or the same number of social support sessions, on top of their usual care. After 12 weeks, 32 percent of the diet group were in remission, against 8 percent in the other group. The trial was small, with 56 people analysed at the end.
- AMMEND (Australia, 2022). 72 young men aged 18 to 25 with moderate to severe depression followed either a Mediterranean diet or befriending sessions for 12 weeks. Depression scores improved clearly more with the diet. Participants knew which group they were in, which can inflate results.
- The big picture (2019). A meta-analysis pooled 16 randomised trials and 45,826 people, most of them not clinically depressed. Improving diet reduced depressive symptoms, but the effect was small. The benefit was larger in studies of women.
Observational studies point in the same direction. People who follow a Mediterranean-style diet most closely had about a third lower risk of developing depression in four long-term studies. That is a link, not proof of cause: people who eat well also tend to sleep, move and earn differently.
Anxiety: No Clear Effect Yet
The same 2019 meta-analysis also looked at anxiety, in 11 trials and 2,270 people. Dietary changes did not reduce anxiety symptoms. The mouse study that went viral may point to a mechanism worth exploring, but for now there is no good human evidence that changing your diet will ease anxiety on its own.
Ultra-Processed Food: A Consistent Warning Sign
A large review of reviews published in the BMJ in 2024 found that eating more ultra-processed food was linked to a higher risk of depression, by about 22 percent, and to more sleep problems. These are associations, and the researchers rated most of the evidence as low quality. Still, the signal is consistent across many studies, and cutting back on these products rarely does harm.
Supplements: Weaker Than Advertised
- Omega-3 for depression: a 2021 Cochrane review found at most a small effect, too small to matter clinically, with low certainty.
- Omega-3 for ADHD in children: a 2023 Cochrane review found high-certainty evidence of no effect on ADHD symptoms rated by parents.
- Magnesium and other "7-day" cures: we looked at one of them in detail in our magnesium fact-check.
For ADHD specifically, the questions are different, such as food colourings and supervised elimination diets. We cover them in ADHD and nutrition and ultra-processed food and ADHD in children.
What About the Mouse Studies?
Animal research, like the high-fat diet study, is useful for finding possible mechanisms: which brain circuits, hormones or gut bacteria might connect food and mood. Our article on the gut-brain axis looks at some of them. But mice do not live human lives, and many findings in mice never hold up in people. A mouse study is a question, not an answer.
What This Means for You
A varied, mostly unprocessed diet, close to the Mediterranean pattern, is a reasonable support for mood, especially for depression and alongside other care. It is not a replacement for therapy or medication, and no single food or supplement has been shown to cure depression or anxiety. If your mood has been low or your worry constant for weeks, a short validated questionnaire can help you put words on it before talking to a professional: the PHQ-9 for depression or the GAD-7 for anxiety.
Sources: Jacka FN et al., SMILES trial, BMC Medicine 2017. Bayes J et al., AMMEND trial, American Journal of Clinical Nutrition 2022. Firth J et al., Psychosomatic Medicine 2019. Lassale C et al., Molecular Psychiatry 2019. Lane MM et al., BMJ 2024. Appleton KM et al., Cochrane Database of Systematic Reviews 2021. Gillies D et al., Cochrane Database of Systematic Reviews 2023. Animal study: Nature Communications, September 2026.