This Is Your Brain on Glucose: Why You’re Foggy, Snappy, and Craving Toast
- Jacs Scheinman
- Jul 21
- 4 min read
Welcome to Snack on This, a blog powered by Food 4 Thought Nutrition, PLLC—where science meets sarcasm and snacks are sacred.
I’m Jacs, a registered dietitian, neurodivergent human, and co-founder of this fully virtual practice based in Highland Park, IL.
Today, we’re diving into a question I get asked all the time:
“Why do I get foggy, impulsive, or emotionally fried when I skip a meal?”“Why does my brain feel like it’s buffering at 3 p.m.?”
Here's the blunt truth: Your brain is out of fuel.
The Brain: Tiny but Insatiable
The brain makes up only ~2% of body weight, yet consumes ~20% of your resting energy, mostly from glucose.
That’s about 5.6 mg of glucose per 100 g of brain tissue every minute.
Even when you're resting, your brain is buzzing: regulating hormones, heartbeat, digestion, sensory processing, social prediction—all powered by your metabolic budget.
Neuroscientists even call it a “prediction engine,” using resources to constantly forecast what’s coming next.
Glucose: Your Brain's Favorite Fuel
The brain depends heavily on glucose (derived from carbs) to generate ATP—a molecule essential for neuronal communication, synaptic activity, and maintenance.
When glucose dips—due to skipped meals, chronic dieting, or executive-function challenges—your brain starts to glitch.
Research shows that cognitive functions falter when blood glucose drops below ~3.0 mmol/L (~54 mg/dL)
Common symptoms include:
Brain fog
Irritability & mood swings
Trouble concentrating & memory slips
Physical signs like shakiness, dizziness, and hunger
One large meta-analysis in Frontiers in Neurology found a 47% increase in risk of cognitive dysfunction in people who experienced hypoglycemia—even just once.
The 3 PM Crash: Your Brain Going on Low Battery
This is not laziness or lack of willpower—it’s biology.
When glucose availability drops, your brain cuts energy to sophisticated systems (like emotional regulation or focus) and prioritizes basic survival.
Evolutionarily, your brain holds a metabolic line: even a 5% cognitive activity increase is significant—enough to trigger fatigue for resource conservation.
The Regulations Behind Hunger & Cravings
Cravings are your brain's alarm system, signaling that fuel is low—not moral failure.
Hunger is physiological intelligence saying, “Hey, I need energy!”
Eating regularly stabilizes:
Cognitive clarity
Mood and emotional regulation
Sleep quality & digestive health
Plus, stable glucose means less crash post-meal and fewer energy dips throughout the day.
Blood Sugar: A Delicate Tightrope
Both hypo‑ and hyper‑glycemia (low and high blood sugar) can impair cognition:
Hypertension: Chronic high blood sugar damages brain vessels, increasing risk for memory loss and dementia.
Hypoglycemia: Acute drops quickly cause confusion, irritability, and cognitive decline.
A recent NIH digital medicine study reveals that even short-term glucose fluctuations correlate with mood and memory changes—especially in neurodivergent or chronically ill individuals.
Food = Regulation, Not Just Fuel
Here’s what I see every day working with ADHD, chronic illness, and disordered eating:
People feel guilty snacking.
They believe carbs make them weak.
They ignore hunger signals out of fear.
Reality check: Your body knows what it’s doing.
Fueling regularly:
Keeps your brain running
Calms your emotions
Supports sleep & immune function
Helps you engage with others
Helps your digestion behave (less IBS drama!)
How I Can Help
If this resonates, you're not alone. Here’s how we tackle it together:
Virtual, values-aligned counseling for:
ADHD & autistic clients
Disordered eating, ARFID, BED, EDNOS
Digestive & autonomic disorders (IBS, POTS, EDS)
LGBTQIA+ affirming care
Caregivers navigating feeding complexity
How it works:
1. Understand your current fuel habits
2. Normalize flexible, hunger-attuned eating
3. Build snack strategies that fit your brain and life
A Thought to Snack On
Your brain isn’t asking for perfection—it’s asking for enough.
If you’re foggy, snappy, or scatterbrained… you’re not broken. You’re human. And your glucose-hungry brain deserves to be fed—with science, sass, and zero guilt.
References
1. Hypoglycemia and Alzheimer Disease RiskMeta-analysis shows both mild and severe hypoglycemia can impair executive brain function—highlighting how low blood sugar damages cognition
2. Impact of Hypoglycemic Events on Cognitive Dysfunction in T2DM (2023)Systematic review found a ~47% increased risk of cognitive impairment per hypoglycemic event, with each recurrence raising that risk by ~18%
3. Cognitive Vulnerability to Glucose Fluctuations (2025)Study using continuous glucose monitoring found significant dips in both low and high glucose ranges, confirming the brain's sensitivity to glucose swings
4. Consistent Effects of Hypoglycemia on Cognitive Function (2022)Clinical research showing that acute episodes of hypoglycemia lead to immediate declines in executive functioning
5. Brain Glucose ‘Microsystem’ & Cognitive Outcomes (2024)Recent papers describe a unique cerebral glucose regulatory system and link systemic glucose dysregulation to cognitive decline and dementia risk
6. Glycemic Variability and Cognitive Impairment Study Protocol (2022)The "Sugar Swing" study explores how glucose swings impact cognition, eating behaviors, and executive function in type 1 diabetics
7. Impact of Glucose Metabolism on the Developing Brain (2022)Shows how both hypo- and hyperglycemia disrupt structural development and cognition in children—spotlighting importance of stable glucose across the lifespan
8. Glucose Fluctuations Slowing Cognition in Type 1 Diabetes (2024)Medical News Today covers a lab and real-world study revealing that both low and high glucose episodes impair processing speed
9. Glycemic Control Normalizes Teen Brains (2022)Stanford study shows improving glucose control in teens reverses brain structure and function deficits in Type 1 diabetes
10. Impact of Blood Glucose on Cognition in Insulin Resistance (2024)Found that even individuals without diagnosed diabetes suffer cognitive risks from average glucose spikes and variability
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