Be careful what you believe about nutrition and mental health. There is no shortage of dietary advice or supplements promoted to improve your mood, prevent cognitive decline, or treat disorders like autism spectrum disorders or attention deficit hyperactivity disorder (ADHD). And while diet can have a significant influence on mental health, the evidence for many of the diets or supplements commonly suggested for various mental disorders is pretty weak.
To clear things up and to create a current overview of the new field of Nutritional Psychiatry, European researchers reviewed the results of many past studies on the link between diet and mental health.
The connection between nutrition and mental health is firmly established in some instances. For example, a high fat, low carbohydrate diet, otherwise known as a ketogenic diet, does help control seizures in children with epilepsy. A deficiency of vitamin B12 can cause poor memory and depression, and treatment with the vitamin can alleviate those symptoms. The Mediterranean diet appears to provide a degree of protection against anxiety and depression.
Studies are few and they don’t last long enough to determine the long-term effects, if any, of dietary change.
People tend to believe that nutritional advice for mental health issues is based on scientific evidence, but it is difficult to prove that a certain diet or nutrient influences mental health. Even when studies do show that certain foods can be linked to a mental health condition, they don't show why the food causes the effect. Some foods have provable connections to mental health, particularly in relation to brain development and deficits in brain function later in life. It is more difficult to prove the effect of nutrition on mental health in the general population, however.
The impact of diet on mental health in healthy adults is small, subtle and often takes place over long periods of time, so the effects are hard to identify. Genetics may play a role in how a person responds to dietary changes, or differences in metabolism between people may make some people respond to dietary changes better than others. Dietary supplements may only work if there is a nutritional deficiency.
Practical difficulties in the research of diet and mental health also present challenges. Foods and drugs are tested differently. While a person can be given a dummy pill to test the placebo effect of a drug, there aren’t dummy foods.
A person’s diet can affect their mental health, but jumping to conclusions based on preliminary or inconclusive evidence is not a good idea. More studies are needed to determine the long-term effects of diets on mental health, behavior, mood and cognition.