by Meghan Hockey
For many of us, we instinctively turn to chocolate when we are in a bad mood. Is it the taste or are we programmed to choose these foods because of their mood-boosting benefits? Chocolate, along with fruits, vegetables, spices, tea, coffee and red wine all contain nutritive compounds called polyphenols. Put simply, polyphenols are a broad category of micronutrients that have antioxidant properties. Research is now emerging, that these polyphenols may have a role in influencing our mood, so is it the case, that we all just need a little chocolate?
Polyphenols – a new prebiotic
Unlike our macro – and micronutrients, polyphenols are poorly absorbed in the body. In fact, only 5-10% are absorbed in our small intestine with the remaining polyphenols making its way to our large intestine or colon. Here, the polyphenols act as food for our gut bacteria, which is why they are described as having prebiotic-like effects; like polyphenols, prebiotics are non-digestible components of food, which are broken down by the gut bacteria. They then go on to alter the gut microbiota which may confer numerous health benefits.
In the colon, our gut microbiota breaks down the polyphenols to create new, smaller, compounds (called metabolites), which can then be absorbed into the blood stream. In fact, it is thought by many, that these metabolites are actually responsible for the health effects seen from polyphenols, rather than from the polyphenols themselves. But none of this would matter, if it weren’t for our gut. It is suggested that the health of our gut, moreover, the composition of our gut microbiota, is critical in determining the level of polyphenols our bodies absorb. This is explained by the reciprocal polyphenol-microbiota relationship; the polyphenols act as food and modulates the composition of the microbiota, and in turn, the microbiota determines the absorption of these polyphenols.
Compelling evidence has already acknowledged the role that the gut microbiota can play in mental-health related behaviours. Although these polyphenol-microbiota relationships have not yet been tested in humans, it sounds like a promising avenue for nutritional psychiatry.
Could polyphenols be used to treat depression?
Polyphenols have numerous health benefits. We know they are beneficial for conditions such as cardiovascular disease and obesity, however we are only beginning to understand their role in shaping our mood. Cocoa, a key ingredient in chocolate, is rich in the polyphenols called flavonoids. A recent review found that chocolate was mostly able to influence our mood, and attenuate negative mood states. However, it was unclear whether the effects of chocolate were due to the desirable taste or from specific components, such as the polyphenols themselves.
Curcumin found in tumeric, is one of the more widely studied polyphenols. A review on its effects found that it was shown to positively effect parts of the brain involved in mood regulation, known as the hippocampus. Curcumin was also shown to increase levels of serotonin, which is often termed as the “happy hormone”, although these effects have only been seen in animal studies.
Other polyphenols have been shown to exert anti-inflammatory benefits, however similar to before, we lack the studies to prove these benefits in humans. The literature currently suggests that, that by targeting inflammation we may be able to negate the risk and progression of depression. So, in theory, polyphenols through their anti-inflammatory effects may be useful for future adjuvant treatment of mood disorders.
What does this all mean?
Due to the lack of human studies we are not yet at a stage where we can recommend a prescriptive dose and frequency of polyphenols for depression. It is important to note that just because these substances are ‘natural’ does not mean they are safe; they may have side effects, just like medications, particularly when taking in high doses via supplements. Because of this, we require safety assessments and more human trials prior to recommending polyphenols as an adjuvant therapy for depressive disorders.
Until then, spice up your meals with turmeric, load up your plate with veggies and eat modest amounts of chocolate, to reap all the other health benefits from consuming polyphenols.
Meghan Hockey is an Accredited Practising Dietitian and a PhD candidate with the Food and Mood Centre