Brain chemistry and metabolic health

What is the connection between feeling good and feeling fit? 

Back when I was a practicing road cyclist in Scotland, I learned a crucial difference between the two. 

We were a pack of five "roadies" stopped briefly at a junction, fully kitted up in spandex astride our skinny bikes, when a comrade who hadn't been seen since last season suddenly appeared. There was a moment of sizing up, when at last our group's elder statesman offered to the newly arrived rider, "You're looking well." 

In cycling etiquette of the day, that was not a compliment.

You see, there are two states of appearance to others in cycling parlance. You can appear to be looking well, or you can be deemed as looking fit. Looking well basically means you're happy and fat.

Looking fit, well, that is the holy grail of endurance sports: half-starved and motivated.

So the connection between feeling good and feeling fit is as much a mental one as it is physical, and this little anecdote gets us into the relationship between dopamine, serotonin, and metabolism.

The primer:

Our bodies conduct an intricate chemical conversation every time we move, with dopamine and serotonin playing crucial roles not just in how we feel, but in how our bodies process energy. Recent research has revealed that these neurotransmitters influence everything from glucose regulation to fat metabolism (Li et al., 2024; Aslanoglou et al., 2021). 

The balance between dopamine and serotonin plays a significant role in health and fitness, particularly in relation to physical performance and fatigue management. Dopamine enhances effort and performance, while serotonin signals fatigue. Essentially, dopamine leads the charge on chasing (whether that's fitness or yogic asceticism or a deer or excellence of any kind).

With the onset of fatigue, serotonin dominates.

The serotonin-to-dopamine ratio is a key determinant of fatigue, and physical training can help modulate this balance to improve not only fitness outcomes, but craft a movement routine to harmonize with life's rhythms.

It can be helpful to consider the relationship in terms of athletics:

Dopamine and Serotonin in Physical Performance

• Dopamine's Role: Dopamine is crucial for effort-reward integration, influencing how effort is allocated based on potential rewards. Increased dopamine levels can enhance motor vigor and effort allocation, especially when high rewards are anticipated, thereby potentially improving physical performance (Michely et al., 2020).

• Serotonin's Role: Serotonin is associated with the onset of fatigue during prolonged physical activities. Increased serotonergic activity can lead to reduced performance, suggesting that serotonin may act as a mechanism to signal fatigue and regulate exercise intensity (Cordeiro et al., 2017).

Interaction and Balance

• Serotonin-to-Dopamine Ratio: The interaction between serotonin and dopamine is critical in determining fatigue levels. A higher serotonin-to-dopamine ratio is linked to increased fatigue, while a balanced or lower ratio may enhance performance. This balance is more influential than the levels of either neurotransmitter alone (Cordeiro et al., 2017).

• Neuroplasticity and Training: Regular physical training can induce neuroplastic changes that modulate the action of these neurotransmitters, potentially improving performance by optimizing the serotonin-to-dopamine balance (Cordeiro et al., 2017).

Aligning Fitness with Wellness using Routine

The Morning Metabolic Window

Morning movement takes advantage of a crucial metabolic window. Research shows that dopamine levels naturally peak in the morning, coinciding with optimal glucose sensitivity and heightened mental alertness. This natural surge in dopamine helps explain why many people* feel most productive and focused during early hours.

^{Except from when they don't. Yes, the ideal metabolic profile casts us all as eager beavers in the morning, but your experience might be different and that's something we need to understand too... stay tuned.} 

Whenever you feel it, the combination of elevated dopamine and increased glucose sensitivity creates an ideal window for cognitive tasks, decision-making, and creative work. Understanding this biological rhythm can help us optimize our daily schedules and make the most of our body's natural energy patterns (Mendoza & Challet, 2014).

This timing isn't just about feeling energized—it's when our bodies are most efficient at processing nutrients and regulating blood sugar (Gabriel & Zierath, 2019), which emphasizes the link between mind and body.

If you're a movement educator interested in understanding about these links as they relate to your teaching practice, head over to this post.

The Dopamine-Metabolism Connection

It is generally accepted that dopamine directly influences how our bodies handle glucose and lipids. This neurotransmitter, traditionally known for its role in pleasure and reward, has now been shown to play a crucial part in metabolism.

We now know that dopamine signaling affects insulin sensitivity and helps regulate blood sugar levels throughout the body. Additionally, dopamine appears to impact how our bodies store and process fats, suggesting a complex relationship between brain chemistry and metabolic health.

Through both central and peripheral pathways, dopamine affects:

• Insulin secretion and sensitivity

• Glucose uptake in muscle tissue

• Fat storage and utilization

• Overall metabolic rate (Tavares et al., 2021)

Serotonin's Regulatory Role

While dopamine drives motivation and reward, serotonin helps regulate energy balance and metabolic homeostasis. These two neurotransmitters work together in complex ways throughout the brain and body, each playing distinct yet complementary roles in our daily functioning.

Dopamine is often called the "feel-good" chemical, surging during pleasurable activities and pushing us toward goal-oriented behaviors. Meanwhile, serotonin acts as a crucial moderator of our physical and emotional well-being, influencing everything from our mood and appetite to our sleep patterns and digestive processes.

Understanding how these neurotransmitters interact helps explain why maintaining their proper balance is so essential for overall health. Research shows that serotonin levels influence:

• Appetite regulation

• Glucose uptake

• Energy expenditure

• Body temperature regulation (Namkung et al., 2018)

Movement's Impact on Both Systems

Physical activity, especially in natural settings, creates optimal conditions for neurotransmitter-metabolism interaction. When we exercise, our bodies respond with a complex cascade of biochemical reactions that enhance both mental and physical well-being. 

The combination of movement and exposure to nature triggers the release of key neurotransmitters like serotonin and dopamine, while simultaneously optimizing our metabolic processes. This synergistic effect is particularly pronounced during activities like hiking, trail running, or even a simple walk in the park, where the natural environment adds an extra dimension to the therapeutic benefits of exercise.

Studies show that exercise:

• Enhances dopamine receptor sensitivity

• Improves serotonin synthesis and regulation

• Optimizes glucose metabolism

• Supports healthy lipid processing (Lin & Kuo, 2013)

Head over here for more on the overlapping systems in terms of movement practice.

References

Aslanoglou, D., et al. (2021). "Dopamine regulates pancreatic glucagon and insulin secretion via adrenergic and dopaminergic receptors." Link: https://doi.org/10.1038/s41398-020-01171-z Summary: Details the direct effects of dopamine on pancreatic function and insulin regulation.

Cordeiro, L., Rabelo, P., Moraes, M., Teixeira-Coelho, F., Teixeira-Coelho, F., Coimbra, C., Wanner, S., & Soares, D. (2017). Physical exercise-induced fatigue: the role of serotonergic and dopaminergic systems. Brazilian Journal of Medical and Biological Research, 50. https://doi.org/10.1590/1414-431X20176432 

Gabriel, B. M., & Zierath, J. R. (2019). "Circadian Rhythms and Exercise - Re-Setting the Clock." Link: https://doi.org/10.1016/j.cmet.2019.03.013 Summary: Explores the relationship between exercise timing and metabolic health.

Li, Z., et al. (2024). "Dopamine in the regulation of glucose and lipid metabolism: a narrative review." Link: https://doi.org/10.1002/oby.24068 Summary: Comprehensive review of dopamine's role in metabolic regulation, examining both central and peripheral effects on glucose and lipid metabolism.

Lin, T. W., & Kuo, Y. M. (2013). "Exercise Benefits Brain Function: The Monoamine Connection." Link: https://doi.org/10.3390/brainsci3010039 Summary: Examines how exercise influences brain monoamines and their metabolic effects.

Mendoza, J., & Challet, E. (2014). "Circadian insights into dopamine mechanisms." Link: https://doi.org/10.1016/j.neuroscience.2014.07.081 Summary: Explores the relationship between circadian rhythms and dopamine function.

Michely, J., Viswanathan, S., Hauser, T., Delker, L., Dolan, R., & Grefkes, C. (2020). The role of dopamine in dynamic effort-reward integration. Neuropsychopharmacology, 45, 1448 - 1453. https://doi.org/10.1038/s41386-020-0669-0

Namkung, J., et al. (2018). "Peripheral Serotonin: a New Player in Systemic Energy Homeostasis." Link: https://doi.org/10.1016/j.molmet.2018.01.019 Summary: Details serotonin's role in energy balance and metabolic regulation.

Tavares, G., et al. (2021). "Peripheral Dopamine Directly Acts on Insulin-Sensitive Tissues." Link: https://doi.org/10.3389/fphar.2021.713418 Summary: Examines how dopamine influences insulin signaling and metabolic function in peripheral tissues.

Note: All references have been verified with active DOIs as of 2024. Each paper is available through academic databases or publisher websites.

Fascinated with Forest Bathing? Check out this post: Your Brain on Forest.

For the extra-nerdy, Tarpey's 20+ year old paper still offers more insight:

The Link Between Dopamine, Serotonin, and Metabolism

Dopamine and serotonin are neurotransmitters that play crucial roles in the brain's function and are linked to metabolism through their synthesis pathways. Tetrahydrobiopterin (BH4) is a critical cofactor involved in the synthesis of these neurotransmitters, as it is necessary for the activity of enzymes like phenylalanine, tryptophan, and tyrosine hydroxylases. These enzymes are responsible for the production of catecholamines (including dopamine) and serotonin (Tarpey, 2002).

Dopamine, Serotonin, and Metabolism in Conversation

• Role of BH4: BH4 is essential for the synthesis of dopamine and serotonin. It acts as a cofactor for the hydroxylase enzymes that convert amino acids into these neurotransmitters. A deficiency in BH4 can lead to reduced levels of dopamine and serotonin, impacting neurological function and potentially affecting metabolic processes (Tarpey, 2002).

• Enzyme Activity: The enzymes that require BH4 for dopamine and serotonin synthesis are involved in metabolic pathways. These enzymes include phenylalanine hydroxylase, tyrosine hydroxylase, and tryptophan hydroxylase, which are crucial for the metabolism of amino acids into neurotransmitters (Tarpey, 2002).

• Metabolic Homeostasis: BH4 also plays a role in maintaining cellular metabolic homeostasis. Its involvement in neurotransmitter synthesis links it indirectly to metabolic processes, as neurotransmitters like dopamine and serotonin can influence metabolic functions such as appetite, energy balance, and glucose metabolism (Tarpey, 2002).

Dopamine and serotonin are linked to metabolism through their synthesis pathways, which require the cofactor BH4. This cofactor is crucial for the enzymatic processes that produce these neurotransmitters, and its deficiency can lead to metabolic and neurological disturbances. Understanding this link highlights the interconnectedness of neurotransmitter synthesis and metabolic regulation.

Further nerdiness: