Does Your Diet Affect Your Mood? What the Studies Found

When people talk about eating well, they usually mean for their heart, their weight or their blood sugar. Mood rarely comes into it, even though plenty of us know the flat, foggy feeling at the end of a week of takeaways and vending-machine lunches.

In 2017 a small Australian trial tested the idea directly and got a lot of press. The larger analyses since then have been more cautious, though they lean the same way.

The Trial That Got the Attention

The SMILES trial recruited 67 adults with moderate to severe depression. For 12 weeks, one group got dietary support to move towards a modified Mediterranean diet. The comparison group got social support instead. At the end, 32% of the diet group were in remission, compared with 8% of the social support group.

Jacka, F.N. et al. (2017). “A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial).” BMC Medicine, 15, 23.

That’s an encouraging result from a very small study. It also wasn’t blinded. Everyone knew which group they were in, and people who expect a change to help them often report feeling better for that reason alone. On its own, the trial can’t tell you how much of the improvement came from the food.

What the Larger Studies Found

In 2019 a meta-analysis pooled 16 randomised trials of dietary improvement, with around 46,000 participants between them. Changing diet reduced symptoms of depression, and the difference held up statistically, though it was modest. There was no significant effect on anxiety. The effect also looked larger in women, which is interesting but the kind of subgroup finding that needs confirming.

Firth, J. et al. (2019). “The Effects of Dietary Improvement on Symptoms of Depression and Anxiety: A Meta-Analysis of Randomized Controlled Trials.” Psychosomatic Medicine, 81(3), 265-280.

Studies that follow people over years agree on the direction. A review of that research, also from 2019, found that people whose eating most closely matched a Mediterranean pattern had about a 33% lower risk of developing depression than people whose diets matched it least.

Lassale, C. et al. (2019). “Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies.” Molecular Psychiatry, 24(7), 965-986.

That figure is easy to overread. People who eat a lot of vegetables and fish tend to differ from those who don’t in income, exercise, drinking and a good deal else. The link also runs backwards. When you’re low, cooking feels like a chore and the biscuit tin is closer, so some of the connection between poor diet and depression is the depression shaping the diet.

What Eating for Mood Looks Like

There’s no special mood diet to buy. What SMILES used, and what the observational studies measured, is close to the ordinary Mediterranean way of eating: more vegetables, fruit, legumes, whole grains and nuts, more fish, olive oil as the main fat, and less ultra-processed food. If you want one change to try this week, add a portion of beans, lentils or vegetables to a meal you already eat most days, which is far easier to keep up than a new diet.

Two less glamorous habits are worth a look too. Eating at fairly regular times helps, if only because a skipped lunch so often ends in a 4 p.m. raid on whatever is nearest. And alcohol is a depressant: a few drinks can lift the evening and leave the next day flatter. If you’re dealing with depression, food can be part of looking after yourself, but it isn’t a substitute for treatment, and changing your diet shouldn’t mean stopping anything your doctor has prescribed.

Looking for Your Own Pattern

Population studies can’t tell you how food affects you in particular. A couple of weeks of notes can give you a rough idea, as long as you don’t ask too much of them. Write down what you eat and, once a day, how you feel, then look at the weeks rather than the days.

A grim afternoon after a heavy lunch might just as easily be down to a tense meeting or a bad night. A run of low days during a week of skipped meals and late takeaways is more worth noticing, and so is a stretch that felt better while you were cooking more. Keep the backwards link in mind, too: if you ate badly during a low week, the low mood may have come first.

In Lamplit you can log meals in the nutrition tracker and do the three-tap mood check-in in the journal, both on the free plan. Do both daily for two weeks, then compare the mood trends in the journal’s analytics with what you were eating. With Lamplit Max, Genie’s cross-domain insights can look across food, mood, sleep and training for links you might miss. Whatever turns up is best treated as a hunch, and the way to test a hunch is to change one thing for a fortnight and see what happens.

Log your next meal in Lamplit and add a mood check-in tonight. Both are free.