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Mayo Clinic: Mental Clarity or Energy? What Your Brain Really Needs to Stay Sharp

January 22, 2026 • Brent Bauer, M.D., Mayo Clinic


In a culture that rewards constant hustle, busyness is often mistaken for productivity. When the afternoon slump hits, stimulants like coffee or sweets feel like an obvious solution – more energy must mean better work, right?

But this assumption hides a fundamental misunderstanding about how the brain works. Energy and mental clarity are not the same thing. And confusing the two can quietly make thinking, decision-making, and emotional control worse rather than better.


Arousal vs. mental clarity

From a neuroscience perspective, arousal refers to how activated the nervous system is. It includes wakefulness, alertness, and stimulation.1

Mental clarity, by contrast, reflects how efficiently the brain can use its resources. It supports functions like filtering distractions, weighing options, sustaining attention, and regulating emotions.

These are not opposites; they are separate dimensions of brain function. You can feel wired and unfocused at the same time. You can also feel calm and mentally sharp. Productivity depends far more on clarity than on raw activation.


A familiar mid-afternoon scenario

It’s 3:15 p.m. and the day has already taken more out of you than expected. You rushed across town for an appointment, answered a steady stream of messages, and skipped a proper lunch in favor of something quick. You’re foggy and irritable, but you need to troubleshoot a work problem.

So you do what most people do. You grab a coffee and a cookie and get to work. Ten minutes later, you feel more awake. Your heart rate increases. Your thoughts speed up. You’re suddenly confident you’ll finish before five.

But the tradeoffs arrive quickly.


Why coffee and sugar feel effective

Caffeine and sugar work because they temporarily increase arousal.

Caffeine blocks adenosine, a chemical that signals sleep pressure. This makes the brain feel less groggy and more alert.2 In moderate doses, caffeine can also improve short-term vigilance, including reaction time and attention.3-5

Sugar provides rapidly available glucose, which can briefly improve perceived energy, memory, and attention – especially after a skipped meal.6 Many processed sweets combine sugar with fat, making them energy-dense and fast-acting.7

Together, caffeine and sugar can create a short-lived boost that feels like clarity. But what they primarily provide is stimulation, not improved cognitive control.


Why stimulation isn’t a long-term solution

Caffeine follows an inverted-U relationship with performance. Beyond a moderate dose, accuracy, impulse control, and executive functioning begin to decline.3

At higher doses – or in people who are sensitive to stimulants – caffeine increases jitteriness, emotional reactivity, and mental noise. The brain becomes faster, but less precise.4,8

There’s also the rebound effect. Caffeine-driven alertness borrows from future sleep. Even afternoon consumption can reduce total sleep time by nearly an hour – often the difference between adequate rest and chronic sleep debt.9 As stimulant effects wear off, fluctuations in adenosine, cortisol, and blood glucose can leave the brain more fatigued than before.10

Sugar adds another layer. As blood glucose falls later in the afternoon, fatigue and irritability increase. Many people respond by consuming more stimulants, reinforcing an unstable energy cycle.

By evening, the crash sets in. Ironically, the caffeine that helped at 3:00 p.m. may still be active at bedtime, delaying sleep and reducing deep restorative stages.9 The next day begins with more fatigue, and the cycle repeats.


Mental clarity: A different approach

Mental clarity is best supported not by pushing the brain harder, but by removing constraints on how it functions. The brain performs best when it has what it needs: quality sleep, steady fuel, and manageable demands. Clarity emerges from a nervous system that is regulated, not overstimulated.

The ingredients are surprisingly simple:

  • Balanced neurotransmitter activity (including dopamine and serotonin)

  • Adequate and stable glucose

  • Healthy blood flow and oxygenation

  • Flexibility between activation and recovery

Fortunately, this is not a hard-to-source recipe: The conditions that support these ingredients are built from ordinary, repeatable behaviors.


Honor the power of sleep

Sleep is the single most powerful driver of mental clarity.

Adequate sleep restores prefrontal cortex function, improves working memory, and stabilizes emotional responses. Even modest sleep restriction shifts the brain toward more reactive, less reflective processing.11,12 Over time, poor sleep quality is linked to attention lapses, memory errors, and cognitive decline.13

To support high-quality sleep:

  • Aim for 7-9 hours of uninterrupted sleep in a dark, cool, quiet room.

  • Avoid screens and bright light for at least an hour before bed.

  • Exercise early in the day, rather than in the evening.

  • Don't drink alcohol, which can disrupt sleep.

  • Cut off caffeine at least nine hours before bedtime.9


Move your body

Physical exercise consistently increases activity in a key brain region called the precuneus, which acts as a central “hub” connecting major brain networks involved in thinking and self-control.14  

The mental benefits of exercise can appear after a single session and increase cognitive aptitude across the board, including attention, memory, and processing speed.15,16 These benefits are strongest immediately after movement, so go for a brisk walk before a task that requires you to be at your clearest.16

No time to leave your desk? Even standing at your workstation can improve thinking and reasoning, in addition to increasing alertness and energy.17


Outsource your brain with cognitive offloading

Mental fog often reflects overloaded working memory rather than low energy. Unfinished tasks and decision overload can quietly eat away at your cognitive bandwidth.

Cognitive offloading restores clarity by freeing mental resources. Try the following:

  • Create lists and reminders. These can free up "brain space" and improve memory.18

  • Work in focused blocks of 25-50 minutes. Minimize notifications and multitasking.19-21

  • Batch emails and messages. This reduces context switching, which slows thinking and increases errors.19-21

  • Break vague goals into concrete steps. Clear endpoints reduce mental fog and feeling overwhelmed.22

  • Simplify your workspace. Visual clutter competes for attention, even when ignored.23


Eat for brain health

Overall dietary patterns matter more than quick fixes. The MIND diet in particular – which combines Mediterranean and DASH principles – is associated with better memory, brain health, and sleep quality.24-26

These diets emphasize vegetables, fruits, whole grains, and healthy fats while minimizing ultra-processed foods. (Think salmon, spinach, and berries instead of pizza and chips.) Higher intake of green leafy vegetables, in particular, is linked to more resilient brain aging.24

Experts generally recommend food-first approaches over supplementation.26 But there's some evidence that creatine supplements can enhance memory in healthy individuals.*27, 28 Note that any improvement in mental clarity caused by creatine is going to be cumulative – it's not something you take an hour before a big meeting and expect a quick hit.28


Watch the stress load

Chronic stress keeps the nervous system in a high-arousal state that favors urgency over insight. While fast-acting strategies – like deep breaths or cold exposure – can help during sudden stress spikes, it’s equally important to build a lifestyle that minimizes stress overall.

Effective stress regulation includes:29

  • Spending time outdoors daily.

  • Making time for relaxing activities like listening to music or taking a bath.

  • Noticing small positives in the present moment, like sunny weather or the smell of dinner cooking.

  • Developing a daily mind-body practice like meditation, guided imagery, or yoga.

  • Supporting physical health through sleep, nutrition, and movement.

  • Connecting regularly with friends and loved ones.

Remember that calm is not the enemy of productivity. It's often a prerequisite for good thinking.  


A final word on that coffee and cookie

Caffeine and sugar are not inherently bad. They are tools. Used sparingly and intentionally, they can be helpful. But mental clarity is not something you stimulate into existence; it’s something you build. People who think most clearly over time are rarely the most stimulated – they're the most balanced.


A word from Thorne

In addition to creatine, other non-caffeine containing supplements can support mental focus and clarity. Thorne Brain Factors contains whole coffee fruit, which, unlike the coffee bean, is virtually caffeine free. Instead, the whole coffee fruit in Brain Factors increases the body’s production of brain-derived neurotropic factor (BDNF). Benefits of enhancing BDNF include promotion of memory and focus by improving the communication between brain cells and enhancement of attention and learning by supporting growth and development of new brain cells.*


References 

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