The cause-and-effect relationship between food and mental health

‘You are what you eat” might sound like a cliché, but when it comes to mental health there is growing evidence that what we consume – and what we don’t – could have a significant impact on the way we feel about ourselves and life in general.

Dr Asad Sadiq, a consultant psychiatrist at The LightHouse clinic in Dubai, says it is well understood that a “western” diet of red or processed meats, fast food and sugary foods is a major factor in the rise of diabetes, heart attacks, strokes and cancer. But, he says, there is also “a wealth of evidence that poor physical health also causes poor mental health, especially depression and anxiety”.

Poor diet is “both a cause and symptom of mental illness”, says Sadiq, a former clinical director of psychiatry in the United Kingdom’s National Health Service. Having a mental illness makes you likely to eat unhealthily, which in turn worsens your mental illness.

“It’s a vicious cycle,” he says. “For example, depression results in isolation and a sedentary lifestyle, which in turn leads to reduced exercise and eating food that is easily available.” The ensuing weight gain “results in low self-esteem, avoidance of social contacts and physical illness”. This in turn “worsens the depression and so on. Another vicious cycle is set up”.

According to the Mental Health Foundation, which works to promote mental well-being in the UK, there is also mounting evidence of a physical cause-and-effect relationship between food and mood.

“Nutrition is one of the most obvious, yet under-recognised factors in the development of major trends in mental health,” says Dr Antonis Kousoulis, deputy director at the Mental Health Foundation.

“As well as its impact on short- and long-term mental health, the evidence indicates that food plays an important contributing role in the development, management and prevention of specific mental health problems, such as depression, schizophrenia, attention deficit hyperactivity disorder, and Alzheimer’s disease.”

Research shows that nearly two-thirds of people who do not report daily mental health problems consume fresh fruit or fruit juice every day, compared with less than half of those who do report daily mental health problems.

“This pattern is similar for fresh vegetables and salad,” says Kousoulis. “Those who report some level of mental health problem also eat fewer healthy foods and more unhealthy food.”

Other studies, says Sadiq, have shown that, “for example, vitamin D deficiency contributes to cognitive impairment, depression, bipolar affective disorder and schizophrenia” and there are “three dietary products with proven benefit for mental well-being” – benefits that are “greater for children and younger adults as the brain is developing”.

Omega-3 fatty acids, found in fish and fish oil, have been shown to prevent psychosis – in which sufferers experience hallucinations or delusions – in high-risk people between the ages of 13 and 25. As a bonus, “they also improve cognitive function, improve learning and prevent heart disease”. The UK’s Royal College of Psychiatrists recommends at least two portions of fish a week.

Vitamin D has also been found to help prevent and contribute to improvements in mental illness. Though found in milk, yogurt, orange juice, salmon, tuna and mackerel, the body’s natural production of vitamin D is most important and generated through exposure to sunlight – which can be a problem for those who cover up for cultural or religious reasons.

For the rest, of course, it’s important that adequate production of vitamin D doesn’t come at the expense of sunburn.

Fruit and vegetables also improve mental health outcomes, says Sadiq. A “rainbow” diet of at least five pieces a day of multicoloured fruit and vegetables is recommended.

More controversial is the role of “probiotics”, live bacteria and yeasts found in yogurt products or taken as tablets, and promoted as having various physical and mental health benefits. In many countries, including Europe, they can be marketed only as foods, as the evidence that they have any medical benefits is considered too weak.

However, in a random-controlled study of 124 patients reported in the European Journal of Clinical Nutrition, it was found that after three weeks, improvements in mood and cognition were significantly greater among people who had consumed a daily milk drink containing probiotics than those who had been given a placebo.

Ultimately, body weight is one of the key indicators that all is well with our psychological relationship with food.

“A normal and stable weight that doesn’t fluctuate too much is the ideal,” says Sadiq.

The standard definition of “normal” is based on the Body Mass Index, or BMI. Any doctor can calculate this, but you can also easily work out your BMI: it’s your weight in kilograms divided by your height in metres squared, and anything between 18 and 25 is considered ideal.

A BMI over 30 is considered obese, “which can result in an increased likelihood of mental illness”, while eating too little can lead to anorexia (a BMI less than 17.5 is one criteria).

But a key sign of a mentally healthy diet, says Sadiq, is that “food should be an enjoyable experience and not an anxiety-ridden one”.

“Our relationship with food is lifelong and therefore parental education is essential to the setting of lifelong healthy habits.”

The key ingredients of a healthy diet are regular, balanced meals, starting with breakfast. And it all begins by making sure the kitchen is stocked with the right foods.

“Meals should be enjoyable and preferably at the table, with the family together, undistracted by phones and tablets,” says Sadiq.

It is, he concludes, “better to live to eat than to eat to live, for food is truly a great blessing and should be enjoyed”.