February 17, 2026
Your brain’s lazy; your legs pay
Thinking Hard Burns Almost No Calories–But Destroys Your Next Workout
Brains barely burn calories, but your workout taps out—cue caffeine, creatine, and chaos
TLDR: Thinking adds only a tiny calorie bump, but mental fatigue can make you quit workouts about 15% earlier, according to research. Commenters split between caffeine shock, creatine hype, morning-workout bragging, and a nerd fight over why our brains are so efficient compared to power-hungry AI.
The internet is spiraling after a new piece claims thinking hard barely burns extra calories—maybe a banana’s worth—yet leaves your next workout wrecked. The kicker? A study says people quit endurance tests 15% sooner after mentally draining tasks, not because their bodies failed, but because their brains screamed “nope” earlier.
Cue the comments. One camp clutched pearls at the suggested caffeine dose—“3–6 mg per kilo?!”—with users doing the math and realizing that’s multiple coffees before spin class. Another camp swore by supplements: one user evangelized creatine as a brain-power booster, citing research and personal wins, while critics rolled eyes at the idea of turning the office into a pre-workout aisle. Meanwhile, the chaos brigade showed up with humor: “Quadruple espresso and deathcore” as a cure for mental fatigue became an instant meme.
There was practical advice too: early birds flexed that morning workouts dodge the brain-drain, while skeptics joked the article’s calorie calculator should “just assume an Apple Watch” and call it a day. The nerdiest brawl? Someone asked why human brains do complex stuff so efficiently while AI slurps electricity—sparking a mini flame war on biology vs. server farms. Verdict: thinking won’t burn your pizza, but it might steal your PR.
Key Points
- •The brain uses about 20–25% of resting energy and ~120 grams of glucose per day, mostly for baseline maintenance.
- •Demanding cognitive tasks add only ~5% to brain energy use, equating to roughly 100–200 extra calories over a day.
- •Chess grandmasters show ~10% higher energy expenditure while playing (1.67 vs 1.53 kcal/min), indicating thinking’s modest incremental cost.
- •A 2009 study found 90 minutes of a demanding attention task led to 15% shorter time to exhaustion in a cycling test at 80% peak power.
- •Physiological markers were unchanged between conditions; higher perceived exertion accounted for reduced performance after mental fatigue.