Do you recognise this pattern? Mid afternoon of a busy day you find yourself reaching for something sweet or salty. Maybe it’s something you hadn’t planned to eat, and maybe it’s even something you had planned NOT to eat and you feel down about that. That night, sleep is harder to come by than it should be, and you wake up the next day tired.
This isn’t a willpower problem. There’s some genuinely interesting neuroscience behind it, and once you understand it this pattern might begin to make a lot more sense.
Our beautiful brains are not passive organs. Even when we’re sitting still and doing nothing very much the brain is constantly active — regulating, monitoring, processing. That activity all by itself takes a lot of energy, and it relies heavily on a neurotransmitter called glutamate.
Glutamate is the brain’s primary ‘excitatory neurotransmitter’ — that is, the chemical signal that tells neurons to fire. When you’re engaged in high-level thinking (like problem-solving, making decisions, managing emotions, or just concentrating hard on something) glutamate is being released in large quantities. This is normal and necessary. But research suggests that with sustained cognitive effort (whether that’s work, family demands, or physical effort), glutamate builds up in parts of the brain involved in high-level thinking — particularly the prefrontal cortex. This accumulation is one of the reasons we experience mental fatigue (Wiehler et al., 2022).
The prefrontal cortex is the part of the brain responsible for things like planning, decision-making, impulse regulation, and considering our options – all the things which guide how we make choices about everything from what to say, to what to eat, to what colour we should paint the walls. When glutamate levels rise to the point of impairing brain function, those capacities become noticeably less reliable. This is not because we’ve “run out” of brainpower in some vague motivational sense, but because there’s an actual neurochemical shift happening that affects how our brain processes choices.
When the prefrontal cortex is not functioning at full capacity, our brain’s reward circuitry — which is evolutionarily older, works faster, and much more impulsive — tends to have a greater influence. Research by Alonso-Alonso and colleagues (2007) described how diminished prefrontal activity is associated with relaxed control over our eating behaviours, meaning we are more likely to eat so-called “high-reward” foods because they seem to fulfill an immediate need, eat when we are not hungry, and eat beyond satiety if we are.
And as with most things there’s also a hormonal dimension. Sleep deprivation and mental exhaustion are associated with elevated levels of ghrelin (the hunger hormone) and reduced levels of leptin (which signals to our brain that we’ve had enough), creating a biological push toward seeking out kilojoule-dense foods (Spiegel et al., 2004). The brain perceives that we’re in a state of depletion, and drives us toward the quickest available energy source.
So the afternoon bakery treat, the takeaway snack on the way home after a hard day, or the mindless handful of something from the kitchen cupboard are not simply failures of our resolve! This is, at least in part, the predictable behaviour driven by our tired brain doing exactly what tired brains do to look after us.
Here’s where it gets particularly important: the way the brain clears glutamate is fairly dependent on how well we sleep.
During sleep, and particularly during the deeper stages of non-REM sleep, the brain undergoes what researchers have described as a kind of neural reset. The brain’s waste-clearance network becomes substantially more active, flushing out metabolic byproducts including excess glutamate (Xie et al., 2013). This is one of the reasons that one of the best pieces of advice you’ll ever get when faced with making a big decision is “sleep on it”. A good night’s sleep doesn’t just feel restorative — it literally is. The neural environment is being reset.
When our sleep is poor, shortened, or disrupted, this clearance process is incomplete. We wake up carrying more glutamate burden than we should, our prefrontal cortex is already compromised before the day has begun, and our capacity for deliberate, regulated decision-making is reduced from the get-go. Then on top of that the day’s demands (and the people around us!) add their own load, and by mid-afternoon we’re making food choices from a neurological position quite different from the choices we know are better for us.
Poor sleep also disrupts glucose regulation, compounding the problem further. Our brains are a glucose-hungry organ, and when blood sugar becomes less stable due to sleep disruption, the drive to seek quick energy — sugar, refined carbohydrates — increases (Knutson et al., 2007).
What we’ve just described is a feedback loop. Mental tiredness drives poor food choices. Poor food choices, particularly those high in sugar and refined carbohydrates, produce blood sugar spikes and crashes that disturb not only our energy throughout the day, but also our sleep. Disrupted sleep means that glutamate isn’t properly cleared from the brain, impairs prefrontal function, and the whole thing begins again the next day.
Understanding this doesn’t mean you’re trapped in it. But it does suggest that tackling any one element of the cycle in isolation — trying harder to eat well, or just “going to bed earlier” — may be less effective than addressing the underlying patterns that maintain the loop.
This is where hypnotherapy is fabulously useful. The patterns that drive these behaviours are not purely conscious ones. The associations between stress and reward, between tiredness and the pull toward certain foods, between anxious wakefulness and the inability to sleep — these are often deeply embedded in the way the mind has learned to regulate itself. Hypnotherapy works at the level where those patterns live, helping to shift responses that haven’t responded well to conscious effort alone.
If you find yourself caught in this kind of loop — always tired, reaching for foods you know aren’t the best way to support your health, struggling to sleep — it’s worth knowing that there’s more going on than a simple lack of discipline.
We’re happy to talk about whether hypnotherapy might be useful for you. Get in touch, or book a session at our Everton Park clinic or via Zoom.
References
Alonso-Alonso, M., & Pascual-Leone, A. (2007). The right brain hypothesis for obesity. JAMA, 297(16), 1819–1822. https://doi.org/10.1001/jama.297.16.1819
Knutson, K. L., Spiegel, K., Penev, P., & Van Cauter, E. (2007). The metabolic consequences of sleep deprivation. Sleep Medicine Reviews, 11(3), 163–178. https://doi.org/10.1016/j.smrv.2007.01.002
Spiegel, K., Tasali, E., Penev, P., & Van Cauter, E. (2004). Brief communication: Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Annals of Internal Medicine, 141(11), 846–850. https://doi.org/10.7326/0003-4819-141-11-200412070-00008
Wiehler, A., Branzoli, F., Adanyeguh, I., Mochel, F., & Pessiglione, M. (2022). A neuro-metabolic account of why daylong cognitive work alters the control of economic decisions. Current Biology, 32(16), 3564–3575. https://doi.org/10.1016/j.cub.2022.07.010
Xie, L., Kang, H., Xu, Q., Chen, M. J., Liao, Y., Thiyagarajan, M., O’Donnell, J., Christensen, D. J., Nicholson, C., Iliff, J. J., Takano, T., Deane, R., & Nedergaard, M. (2013). Sleep drives metabolite clearance from the adult brain. Science, 342(6156), 373–377. https://doi.org/10.1126/science.1241224
Brisbane Hypnosis Centre has been helping people in Brisbane with sleep, habits, and wellbeing since 1997. Located in Everton Park | 07 3354 4555