Can diet impact mental health? A new review takes a look at the evidence. Overall, the authors conclude that although nutrition certainly does appear to have an impact, there are still many gaps in our knowledge.
Nutrition is big business, and the public is growing increasingly interested in how food affects health. At the same time, mental health has become a huge focus for scientists and the general population alike.
It is no surprise, then, that interest in the impact of food on mental health, or "nutritional psychiatry," is also gathering momentum.
Supermarkets and advertisements inform us all, at great volume, about superfoods, probiotics, prebiotics, fad diets, and supplements. All of the above, they tell us, will boost our body and our mind.
Despite the confidence of marketing executives and food manufacturers, the evidence linking the food we eat to our state of mind is less clear-cut and nowhere near as definitive as some advertising slogans would have us believe.
At the same time, the authors of the new review explain, "neuropsychiatric disorders represent some of the most pressing societal challenges of our time." If it is possible to prevent or treat these conditions with simple dietary changes, it would be life changing for millions of people.
This topic is complex and convoluted, but trying to understand the nuances is vital work.
Recently, a group of researchers reviewed the existing research into nutrition and mental health. They have now published their findings in the journal European Neuropsychopharmacology.
The authors assessed the current evidence to gain a clearer understanding of the true influence of food on mental health. They also looked for holes in our knowledge, uncovering areas that need increased scientific attention.
It makes sense
That diet might affect mood makes good sense. First and foremost, our brains need nutrients to function. Also, the food we eat directly influences other factors that can impact mood and cognition, such as gut bacteria, hormones, neuropeptides, and neurotransmitters.
However, gleaning information about how specific types of diet influence specific mental health issues is incredibly challenging.
The reviewers found, for instance, that a number of large cross-sectional population studies demonstrate a relationship between certain nutrients and mental health. However, it is impossible, from this type of study, to determine whether or not food itself is driving these changes in mental health.
At the other end of the scale, well-controlled dietary intervention studies that are better at proving causation tend to recruit smaller numbers of participants and only run for a short period of time.
Lead author Prof. Suzanne Dickson, from the University of Gothenburg in Sweden, explains the overarching theme of the team's findings:
"We have found that there is increasing evidence of a link between a poor diet and the worsening of mood disorders, including anxiety and depression. However, many common beliefs about the health effects of certain foods are not supported by solid evidence."
One diet that has received a great deal of attention during the past few years is the Mediterranean diet. According to the recent review, there is some relatively strong evidence to suggest that the Mediterranean diet can benefit mental health.
In their review, the authors explain how "a systematic review combining a total of 20 longitudinal and 21 cross-sectional studies provided compelling evidence that a Mediterranean diet can confer a protective effect against depression."
They also found strong evidence to suggest that making some dietary changes can help people with certain conditions. For instance, children with drug resistant epilepsy have fewer seizures when they follow a ketogenic diet, which is high in fat and low in carbohydrates.
Also, people with vitamin B-12 deficiencies experience lethargy, fatigue, and memory problems. These deficiencies are also linked with psychosis and mania. For these people, vitamin B-12 supplementation can significantly improve mental well-being.
However, as the authors point out, it is not at all clear if vitamin B-12 would make a significant difference to people who are not clinically defined as deficient.
Much left to learn
For many of the questions the researchers explored in this review, it was not possible to reach firm conclusions. For instance, in the case of vitamin D, some research has concluded that supplementation improves working memory and attention in older adults. Other studies have found that using vitamin D supplements might reduce the risk of depression.
However, many of these studies were small, and other, similar studies have concluded that vitamin D does not have any impact on mental health.
As the review's authors point out, because "a substantial proportion of the general population has a vitamin D deficiency," understanding its role in mental health is important.
Similarly, the evidence for a nutritional role in attention deficit hyperactivity disorder (ADHD) was quite mixed.
As Prof. Dickson outlines: "[W]e can see [that] an increase in the quantity of refined sugar in the diet seems to increase ADHD and hyperactivity, whereas eating more fresh fruit and vegetables seems to protect against these conditions. But there are comparatively few studies, and many of them don't last long enough to show long-term effects."
"There is a general belief that dietary advice for mental health is based on solid scientific evidence. In reality, it is very difficult to prove that specific diets or specific dietary components contribute to mental health."
Prof. Suzanne Dickson
The authors go on to explain some of the inherent difficulties in studying the impact of diet on mental health, and they offer some ideas for the future. Overall, Prof. Dickson concludes:
"Nutritional psychiatry is a new field. The message of this paper is that the effects of diet on mental health are real, but that we need to be careful about jumping to conclusions on the base of provisional evidence. We need more studies on the long-term effects of everyday diets."