Does Diet Influence Mental Health? Assessing The Evidence

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.

This topic is complex and convoluted, but trying to understand the nuances is vital work.

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.

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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.

“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.”

Some specifics

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.

Much left to learn

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

“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.”

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