Sugar and the Brain: How Blood Glucose Shapes Cognition
The brain runs on glucose, but sugar spikes hurt focus and working memory. Here's how to keep blood sugar stable before an IQ test and long-term.
The brain is 2% of body weight but uses 20% of its energy – almost entirely as glucose. Yet the worst strategy before an IQ test is to grab something sweet right before.
The brain's fuel
Neurons need constant glucose. Both too little (hypoglycaemia) and too much impair performance. See also nutrition and intelligence.
Sugar spikes and cognition
Fast carbs cause a glucose peak followed by an insulin overshoot. Reactive hypoglycaemia 60–90 minutes later measurably impairs working memory.
Long-term effects
Chronic high sugar intake raises the risk of brain insulin resistance – sometimes called "type 3 diabetes" – linked to faster cognitive decline.
What to eat before a test
Combine complex carbs with protein and fat 60–90 minutes ahead: oatmeal, eggs and nuts. Avoid soda, sweets and large juice servings.
Test yourself
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FAQ
- Should I eat something sweet before an IQ test?
- No. A sugar spike triggers an insulin response that often overshoots, causing reactive hypoglycaemia 60–90 minutes later that impairs working memory. Complex carbs with protein and fat are far better.
- Does sugar cause long-term cognitive decline?
- Chronic high sugar intake raises the risk of brain insulin resistance – sometimes called "type 3 diabetes" – which is linked to faster cognitive decline.
- What should I eat before a test?
- Complex carbs plus protein and fat 60–90 minutes before: oatmeal, eggs and nuts. Avoid soda, sweets and large amounts of juice.