The idea that what we eat and drink has direct impact on our mood is not a new one. Who can deny the salvation in a cup of tea after a rough day?
But the theory behind this intuition is now a central field of research, and there's growing evidence for the idea that our brains and our guts are intimately linked.
For writer and mental health campaigner Rachel Kelly, author of The Happy Kitchen: Good Mood Food, teaching people about this connection has become her life's mission.
Back in 1997, Kelly was working as a journalist at The Times in London, had three small children and a partner with an equally demanding job.
"Life was good, it was the job I wanted, but I was an anxious person and I had taken on a lot," she says.
"Basically, what happened was that one night I couldn't get to sleep, but with the insomnia came some quite alarming physical symptoms."
A racing heart, nausea and an uncontrollable stream of negative thoughts resulted in a serious depressive episode that lasted six months.
A few years later, Kelly had a similarly serious period of depression which lasted even longer.
While she treated the symptoms traditionally, with anti-depressants and cognitive behavioural therapy, she was left with a desire to explore the holistic side of mental health treatment.
"Actually I was just seeing my doctor for a regular check-up for my anxiety... and she said, 'Have you heard about happy foods?' And I said, 'No. Happy foods? Wow, tell me a little bit more.'"
She was referred to nutritional therapist Alice Macintosh, and a fruitful collaboration was born, eventually producing a book of 70 recipes based on 150 different nutritional studies
The second brain
While studies into nutritional therapy are still in their emergent stages, Kelly isolates two key areas of research she and Macintosh have found most compelling and useful.
"The first area would be around healthy fats, the omega-3s, and I'd say the second area would be the evidence around a healthy microbiome or our gut flora," she says.
Omega-3 fatty acids are widely believed to have a range of anti-inflammatory effects on our bodies and some studies that suggest this extends to parts of the brain that have been linked to depression.
Similarly, having healthy gut flora can improve your mood firstly by increasing your overall sense of well-being but also, crucially, because it has a direct effect on your immune system. And immune health is another factor that has a high level of crossover with mental health.
Some people, Kelly included, have gone as far as to call the stomach the "second brain".
Kelly also highlights the cultural shift that studies like the ones she's consulted are helping to bring about.
"I think as a backdrop to all this evidence is a really frontal shift in how I understood my brain really and how it operated," she says.
"When someone was suffering from anxiety and depression like me, people felt, 'OK, it's just about the brain.'
"I think now the shift is that we are looking at the whole system and the way that the brain links with other parts of our physical being."
The golden rules
Along with their healthy recipes, Kelly and Macintosh's work led them to devise a list of 10 rules to shape dietary behaviour and help with mental health:
1.Eat mostly plants. Veggies and legumes are nutrient and fibre rich.
2.Use plenty of herbs and spices. Particularly turmeric and saffron — the rules aren't called "golden" for nothing.
3.Go nuts! Kelly points to research that says nuts help with your mood. (And the play on words is irresistible.)
4.Eating for your gut. That is, managing the bacterial balance in your stomach and intestines — keep that second brain happy and healthy.
5.Fats are your friend. Healthy fats, like the aforementioned omega-3s, are thought to have a positive influence on parts of the brain linked to depression.
6.Getting the right balance of protein. Kelly suggests that we throw our lot in with good proteins like fish and lean meat and avoid highly processed meat products.
7.Avoid sweeteners and additives. Again, highly processed food has been linked to poor mental health.
8.Keep an eye on your blood sugar. This has all kinds of benefits and is never remiss.
9.Vary your diet. The average Western diet consists of around 20 ingredients, whereas ancestral humans probably ate more like 150.
10.Relax and enjoy. We can't forget the benefits of eating as a social and recreational activity — there's a reason pretty much every culture focuses their celebrations around food.
While the studies on nutritional therapy are preliminary, many nutritionists would argue that everything on this list is a good idea physically anyway.
"For those people who do not respond to medication, some of these other holistic approaches and using nutrition is just so exciting," says Kelly.
"This is going to be a huge area of growth in mental health in the next decade."
This article was written by Patrick Carey & originally appeared on All in the Mind.