What exactly should we eat? You would think that after thousands of studies we would have the answer. Actually already.

Food for thought – in the truest sense of the word

“When all the studies are put together, a pattern emerges. It’s an emphasis on plant-based foods…which even extends (suggested) to the quality of mental health.’

What exactly should we eat? One would think that after literally thousands upon thousands of studies published on all aspects of nutrition, we would have an answer to this question. Actually already. Maybe not “exactly” considering there are so many different nutrition studies out there, some of which can be classified as good, some as bad and most as mediocre. Still, with a little scientific detective work, you can separate the wheat from the chaff. While separating the wheat from the chaff is a good idiom for separating information from misinformation, it’s not so great when it comes to nutrition. We’ve learned that eating whole grains is preferable to eating refined grains in many ways. And what else have we learned?

Along with replacing refined grains with whole grains, we should increase our intake of legumes, eat five to seven servings a day from the fruit, berries and vegetable group, prioritize fish and poultry over red meat, limit sugar intake, and ignore the talk of “superfoods.” . It’s difficult to know much more detail because nutritional studies that would provide definitive answers are impossible to conduct. That would require an experiment in which an experimental group and a control group are followed for decades, with the only difference being the subjects’ diets. They would only receive food provided by the study’s designers, who would also monitor their health status over the years.

Given the financial and logistical barriers to such a study, most studies are “observational”. Groups of volunteers fill out detailed food frequency questionnaires and, years later, are asked to report any health problems they encounter. Often the questionnaire is completed at a single point in time and it is assumed, somewhat precariously, that the same diet will be followed throughout the trial period. Another complication is that people have a hard time remembering exactly what they’ve eaten and judging the amounts. Sometimes they also report what they think they should have eaten instead of what they actually ate.

Another type of study, called a case control, asks patients suffering from a specific disease to describe the dietary pattern they followed. It’s notoriously difficult to remember details of what foods and how much of each have been consumed over the years. Another problem is determining whether a particular effect is due to what is eaten or what is not eaten. For example, the disadvantages of a diet high in red meat are meat or low consumption of fruits and vegetables. There is also the problem that people do not react uniformly to dieting. With the same amount of sugar, blood insulin levels can vary greatly.

However, when you look at all the studies together, be it on cardiovascular disease, cancer or diabetes, a pattern emerges. There is an emphasis on plant foods. And it seems this is even extending to mental health, a condition that’s getting more attention amid an increased risk of depression being linked to COVID-19. Admittedly, the data on the relationship between diet and mental health is weak, but there is evidence of a link from observational studies. Some of these have linked the Mediterranean diet to lower rates of depression compared to the traditional “Western” diet. After all, although there is no specific Mediterranean diet, Italians don’t eat exactly like Greeks, we can generally think of the Mediterranean diet as being based on fruits, vegetables, whole grains, fish, olive oil, nuts and little red meat and processed foods. The Western diet, on the other hand, is high in red meat and processed foods, refined grains, potatoes, dairy, and low consumption of fruits and vegetables.

Of course, observational studies can show a connection, but cannot prove a cause-and-effect relationship. It may be that other aspects of a Mediterranean lifestyle, perhaps reduced calorie intake, higher levels of social interaction, a more cohesive family structure, better sleeping habits, or higher activity levels, contribute to a reduced rate of depression. A cause-and-effect relationship can only be established through randomized controlled trials. As mentioned, these are difficult to implement, but some attempts have been made with promising results. In one study, people diagnosed with depression were divided into two groups, one following a Mediterranean diet and the other following a Western diet. After three months, 8% of people in the Western group achieved remission compared to 32% of people in the Mediterranean group. But the study was small and not replicated by others.

The question then arises as to why diet should have an impact on mental health. Is it due to too much of one nutrient, perhaps saturated fat or sugar? These can break down dopamine in the brain, a neurotransmitter associated with a good mood. Or could the problem be a lack of some minerals or vitamins like magnesium, iron, zinc, vitamin B6, B12 or D? Depressed people can also have reduced levels of the neurotransmitter serotonin, much of which is produced by bacteria in the gut, and the ratio of “good” to “bad” bacteria that make up the “microbiome” depends on diet. Perhaps the Mediterranean diet, rich in pre- and probiotics that favor beneficial bacteria, is a factor. There is also the topic of omega-3 fatty acids, which are important for brain development and also have an anti-inflammatory effect. Some studies have linked depression to inflammation based on higher blood levels of inflammatory markers.

Finally, when depression is caused by low levels of some nutrients, the question of treatment with supplements arises. There are no convincing studies to prove its effectiveness. Perhaps supplements with vitamins, minerals, or omega-3 fatty acids can help some people who eat extremely poor diets, but not those who already have adequate intakes. There are also a variety of “natural” products that are usually advertised vigorously as being effective for reducing depression or anxiety. St. John’s Wort, S-adenosylmethionine (SAMe), 5-hydroxytryptophan (5-HTP), dehydroepiandrosterone (DHEA), saffron, turmeric, lavender, tyrosine, folic acid, and inositol fall into this category. Although there are some studies that have shown benefits, the evidence is less than convincing.

What is the bottom line, then, when it comes to some sort of advice on nutrition and mental health? Same as already discussed for other conditions. Look askance at supplements, reduce your consumption of red and processed meats in favor of fish and poultry, replace refined grains with whole grains, increase legumes, and eat at least 5 servings of fruits and vegetables a day. So that’s the connection between diet and health in a nutshell. And when you shell these nuts, you eat what’s inside, just like the Mediterranean nuts.