In addition to protecting our hearts from cardiovascular disease and our brains from dementia, reducing sugar intake may also protect us from depression. Specifically, sugar has been shown to suppress growth of brain-derived neurotrophic hormone (BDNF) which plays a role in memory (which is why having a lot of it is linked to low levels of dementia), but also in depression and schizophrenia, possibly even acting as a trigger.
A 2004 study showed that diets higher in refined sugar and dairy products predicted a worse 2-year outcome for schizophrenia and that, overall, dietary predictors for schizophrenia and depression were similar to those predicting heart disease and diabetes. A follow up study released last year showed that men were particularly vulnerable to this relationship. Those men with the highest intake of sugar were, after five years, more likely to suffer a common mental disorder. It’s unclear whether the stronger results for men were because women were underrepresented in the study or because men actually consume more sugar than women, but the results did establish that anxiety and depression were caused by sugar and not the converse (that people who feel down eat more sugar).
Indeed, depression often comes anxiety—many people suffer from both. Other studies bear out the correlation between sugar and anxiety: high sugar diets can exacerbate anxiety symptoms— even replicating panic attacks— and the ability to cope with stress. Researchers also believe that in addition to sugar decreasing BDNF levels, it can exaggerate insulin response and thus hormone levels that affect one’s moods, and that inflammation caused by high-carb diets also results in depression. Another dimension to high sugar intake is that eating added sugars depletes nutrients from other foods, with your body diverting important nutrients like B-complex vitamins— thiamine, riboflavin and niacin—and magnesium in order to metabolize the sugar, when we need these nutrients to stabilize our moods.
While I cannot speak to schizophrenia or chronic depression, I can speak to feeling calmer since I reduced my sugar intake by probably 90%. Though I don’t know how much of this had to do with feeling I was more in control of my health via my diet, a reduction in caffeine, an increase in exercise (which improves mood dramatically) or determination to tell chronic stress to shove off. While I initially tried to figure out which of these variables had the most impact, they are in fact so interdependent and mutually supportive, that it really doesn’t really matter. On a more basic level, when I think back to the many years I used sugar as a means of quick energy (sugar high) and also fell into a post bagel energy slump (sugar coma), I’m relieved not to experience such extremes anymore.