Insulin

Insulin is the hormone that moves glucose out of the bloodstream and into muscle, liver, and fat tissue. The same hormone keeps blood sugar steady and decides where the calories from any meal end up.

In the lean context, insulin sensitivity is the trait that matters. When muscles are sensitive to insulin, calories from food go into muscle glycogen and protein repair. When muscles are insulin-resistant (after short sleep, after sedentary days, after a high-sugar meal pattern), the same calories tilt toward fat storage and the deficit feels heavier than it should.

Insulin spikes with carbs are normal. The body handles them. The problem is the chronic pattern: a daily background of sweetened drinks, sugary snacks, and disrupted sleep keeps insulin running higher than it has to and dulls the muscles' response over time.

What raises sensitivity

• Strength training. Lifted muscles pull glucose out of the bloodstream more readily for hours after a session.
• Sleeping. One night of short sleep makes muscles roughly 20 percent less responsive to insulin the next day. Restoring sleep restores sensitivity.

What lowers it

• Sugary drinks. Liquid sugar with no fiber or protein spikes insulin sharply and routes the calories toward storage rather than muscle repair.