3.6 Serotonin

BreakThrough! Serotonin Mental and Metabolic Health

Dopamine activity affects our motivation and desire, but not our experience of pleasure. In our brain-body connections serotonin is the neurotransmitter that regulates our moods and sense of contentment. Most don’t realize that over 90% of the human body’s total serotonin is in our digestive tract [32]. So how does this work? The amino acid tryptophan is a gut derived metabolite that’s required for the development of serotonin and melatonin, the sleep hormone [32, 33]. High levels of tryptophan are found in certain protein rich foods and beverages, such as canned tuna, milk, and turkey. Interestingly though, it’s difficult for naturally occurring tryptophan in these food groups, to compete with other food substances and amino acids [32].

Ultra-processed foods or comfort substances high in carbohydrates, (chips, cookies, cake, cereal, and more, reach the brain faster creating the serotonin “high”. Some processed foods are engineered (coated with chemicals) to start working almost immediately in the gut-brain pathway. Increasing serotonin levels can alleviate depression but it’s temporary. The insulin that allows tryptophan to enter the brain, subsequently causes an abrupt drop in blood glucose levels resulting in fatigue, irritability, and cravings for “more”.


This process explains why we crave and cave, often increasing our consumption of carbohydrates during periods of depression. Serotonin levels play an important role in the regulation of appetite, sleep, and impulse control.

Dysregulation of any of these three factors can contribute to weight gain. Carb cravings are often observed in people trying to give up smoking. This is because nicotine rapidly increases serotonin secretion in the brain. Conversely, withdrawal often results in depression and irritability.

We tend to develop “addictions” or “preferences” for substances that act most rapidly in the brain.

For patients with premenstrual syndrome (PMS), premenstrual dysphoric disorder (PMDD), and seasonal affective disorder (SAD), excessive carbohydrate intake temporarily relieves depressive symptoms by increasing serotonergic activity [34, 35].

For women with PCOS, food cravings associated with higher insulin levels present a significant challenge and an increased likelihood of developing binge eating disorder [34, 35].. The interventions for these disorders are numerous and exceed the scope of this course. They include pharmaceutical and medical treatment, nutrition and dietary considerations, sleep hygiene, exercise, stress reduction strategies, mindfulness, and much more.

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