Roberto Codella describes for SIIC his article published in Journal of Affective Disorders 224:76-86, December 2017

Milano, Italia (special for SIIC)
We conducted a comprehensive literature search to explore the putative exercise-mechanisms that may break the bond between sugar over-consumption and affective disorders. There is a direct link, in fact, between a variety of addictions and mood states for which exercise could be relieving. Particularly, we hypothesized that exercise is the missing puzzle-card in diverting one’s addictive behaviour: by increasing the dopaminergic function and the hippocampus volume via BDNF levels, i.e. by stimulating neuroplasticity, exercise may deflect sugar addiction from its legitimate reward pathways.

Differently from other drugs of abuse –such as heroin, cocaine or alcohol–sugar cannot be considered as a true addictive substance. However, because of its hedonistic and homeostatic components, sweet food may influence brain’s reward pathways, therefore mimicking a typical addiction-like phenotype. In several conditions, including drug addictions, aggressive behaviours, sexual arousal, food overconsumption, etc., a powerful neurotransmitter in the brain –dopamine– is activated and it is responsible for feelings of well-being. This occurs even during prolonged, sustained endurance exercise. In other words, when we feel tremendously happy, satisfied, a kind-of-high, then dopamine is likewise stimulated. Sadly, in diverse scenarios of addictions and substance-dependence, over-modulation of dopamine might disrupt brain reward circuits resulting in a vicious circle: a never-satisfying seeking of being satisfied. It is never enough.

Physical exercise has been prescribed as a viable therapeutic approach in a multitude of affective- and psychological stress-related disorders. In fact, exercise was shown to be a naturally reinforcing and rewarding activity. Beyond its anti-inflammatory effects, offering protection against all-cause mortality, exercise was demonstrated to favourably modulate mood states, gaining health benefits in clinical and community individuals. Both anaerobic (weight lifting) and aerobic exercise (running) are capable to ameliorate profiles of mood states. After having exercised, one might feel a sense of revitalization, euphoria, and achievement. On the other hand, exercise might distract people from negative and troublesome thoughts. This latter is more than a theory. In fact, physical activity, especially endurance running, boosts the release of hormones of happiness (endorphins) and stimulates the growth of nerve cells in the brain, more precisely in the hippocampus, through specific factors called BDNFs (brain-derived neurotrophic factors). The hippocampus is a curved, elongated ridge in the brain that controls learning and memory. When we exercise, we release BDNFs, which in turn are involved in protecting and producing neurons in the hippocampus. BDNFs strengthen synapses in the brain –the interconnectivity of the neurons– therefore augmenting the hippocampus volume. The more running, the more BDNFs. More neurons grow in the brain as well. This exercise-induced increase in nerve cells is called neurogenesis.

Not only neurogenesis but also neuromodulation, like the triggering of the dopaminergic system, can be driven by physical exercise. Dopamine modulates a spectrum of behavours, including motivation or expectation of a reward. Similarly, regular exercise has been shown to have rewarding effects by continuously stimulating these dopaminergic circuits, therefore leading, for istance, to a better resistance to negative stress. Being fit means also being more tolerant against stress of the daily living activities.

What does this have to do with sugar addiction? Tasty foods, particularly those high in sugar content, can induce reward and craving that are at least comparable with those induced by other addictive substances or exercise: they all activate the dopaminergic system. We thus speculated that exercise, by firin’ up neuroplasticity (embracing the above mentioned neurogenesis and neuromodulation), can massively compete with other addictions (sugar or other drugs) in knocking at the door of the rewards circuits. This brain explanation is reinforced by other parallel psychological interpretations. According to the theory of the distraction, exercise would constitute a relieving break that diverts from one’s daily troubles and negative thoughts. In other words, if we are so focused on running, we can't think of anything else. Our attention is diverted from those frustrations generating addictive behaviours, like the craving for sugar.

In conclusions, by increasing the amount of citoprotective molecules (BDNFs) and dopamine in certain regions of the brain, exercise can elicit a myriad of health benefits that contrast negative mental states. Exercise may pursue pathways competing with those travelled by other substances of dependence or abuse, like sugar.

In the future, we are willing to challenge the potentialities of exercise and physical activity against these multiform addictive behaviours. In particular, dose-response studies would be of assistance in understading the optimal exercise regimen, in terms of frequency and intensity, having clear-cut therapeutic effects at individual, personalized level.

There are plenty of reasons to put on our running shoes and go out for a run!