Noted British psychiatric researcher Malcolm Peet has conducted a provocative cross-cultural analysis of the relationship between diet and mental illness. His primary finding may surprise you: a strong link between high sugar consumption and the risk of both depression and schizophrenia.
In fact, there are two potential mechanisms through which refined sugar intake could exert a toxic effect on mental health.
First, sugar actually suppresses activity of a key growth hormone in the brain called BDNF. This hormone promotes the health and maintenance of neurons in the brain, and it plays a vital role in memory function by triggering the growth of new connections between neurons. BDNF levels are critically low in both depression and schizophrenia, which explains why both syndromes often lead to shrinkage of key brain regions over time (yes, chronic depression actually leads to brain damage). There's also evidence from animal models that low BDNF can trigger depression.
Second, sugar consumption triggers a cascade of chemical reactions in the body that promote chronic inflammation. Now, under certain circumstances (like when your body needs to heal a bug bite), a little inflammation can be a good thing, since it can increase immune activity and blood flow to a wound. But in the long term, inflammation is a big problem. It disrupts the normal functioning of the immune system, and wreaks havoc on the brain.
Inflammation is associated with an increased risk of heart disease, diabetes, arthritis, and even some forms of cancer . . . it's also linked to a greater risk of depression and schizophrenia. And again, eating refined sugar triggers inflammation. So does eating heavily processed molecular cousins like 'high fructose corn syrup'.
If you think about it, it makes sense that our bodies don't handle refined sugar very well. After all, for the vast majority (99.9%) of our existence as a species, there simply was no such sugar. We were endowed with a sweet tooth so that we'd crave the highly nutritious fruits that were available - sometimes in short supply - in the ancestral environment. But with the advent of processed sugar cane a few centuries ago, the blessing of our formerly adaptive sweet tooth suddenly turned into a curse - causing us to crave foods that we were simply never designed to process.
As I've become increasingly convinced by these research data, I've begun gently encouraging my depressed patients to simply try cutting out sugars for a couple of weeks to see if they notice any effect. (I also ask them to cut out simple starches - like crackers and white bread - which the body converts directly to sugars). A few have had the courage and determination to given it a go: they're reported remarkable improvements in mood, energy, and mental clarity.