Blood Sugar And Reaction Time
Your brain runs on glucose — and runs poorly when supply dips.
TL;DR — Blood glucose below ~70 mg/dL (3.9 mmol/L) slows RT by 15–40 ms. Eating a low-glycemic snack 30–60 minutes before play stabilises the curve and avoids the post-meal crash.
Skipping a meal and then playing is roughly as costly as missing two hours of sleep.
The threshold and the curve
Owens et al. (2014) and Benton (1996) consistently found that mild hypoglycemia (60–70 mg/dL) increases mean RT by 15–25 ms and triples error rates on choice tasks. Severe hypoglycemia below 55 mg/dL slows RT by 40+ ms.
What to eat — and when
| Snack type | Effect on RT 60 min later |
|---|---|
| High-sugar (candy) | brief boost then -20 ms crash |
| Low-glycemic (oats, banana) | +5 ms sustained 2–3 h |
| Protein + complex carb | most stable, +5–10 ms for 3 h |
| Heavy meal (>700 cal) | -20 ms post-prandial dip 1–2 h |
Why the post-meal dip exists
Large meals trigger insulin spikes and divert blood flow to digestion. Both reduce prefrontal arousal for 60–120 minutes. Avoid scheduling competitive play in this window.
Practical session timing
- Light snack 30–60 min before play (banana + nuts is a classic).
- Avoid heavy meals 2 hours pre-session.
- Sip water or low-cal drink during play — sugar drinks crash you in 60–90 min.
Frequently Asked Questions
Should diabetics test before playing?
Yes if managing insulin — RT impairment is one of the earliest cognitive signs of low blood sugar.
Is fasting bad for reaction time?
In adapted fasters, mostly neutral. In non-adapted fasters, mildly negative after 12+ hours.
Does sugar give a real boost?
Briefly (~20 min) then equal-or-worse crash. Net often negative.
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