The Science of Human Sleep
Sleep is active maintenance, not shutdown. The stages of sleep, what the brain and body do overnight, and why rest is…
4.6
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Anatomy Category
Health & Lifestyle
The everyday biology of feeling well — sleep, nutrition, hydration, movement and how the body changes as it ages.
Guides
Guides in Health & Lifestyle
Start with any guide below — each one is written for beginners and builds on the last.
Nutrition Basics
What macronutrients and micronutrients actually do inside the body. A calm, evidence-based map of how food becomes…
4.9
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Vitamins and Minerals
Tiny amounts, huge jobs. What the key vitamins and minerals do, where they come from in food, and why balance matters…
4.7
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Water in the Human Body
You are roughly 60% water, and every system depends on it. What water does inside cells, and how the body keeps its…
4.6
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Exercise Physiology
What happens inside the body when you move. How muscles, heart and lungs adapt to training, and why recovery is part of…
4.8
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The Aging Process
Why bodies change over time at the level of cells and systems. The biology of aging, explained without hype or fear.
4.9
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Practice
Related tools
Reinforce what you learn with these interactive tools.
Calculator
Sleep Duration Calculator
Work backwards from your wake time through 90-minute sleep cycles to find sensible bedtimes.
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Tracker
Daily Health Journal
A private, browser-only journal for logging sleep, water and movement to spot your own patterns.
4.7
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Planner
Nutrition Planner
Build a simple, balanced day of meals and see an educational breakdown of macronutrients.
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Related articles
Deeper dives and fascinating facts from the blog.
Why We Sleep: What the Brain and Body Do Overnight
Sleep is when the body repairs and the brain files the day away. A tour of the sleep cycle and why rest is non-negotiable.
The Science of Exercise: What Movement Does to You
From the first minute of movement to weeks of training, here is how exercise reshapes muscle, heart and mind.
Hydration Facts: How Much Water Do You Really Need?
The "eight glasses a day" rule is a myth with a kernel of truth. Here is what the science says about staying hydrated.
Explore another body system
Every part of the body connects to the rest. Browse all nine categories and keep exploring.