Insulin
Insulin is the master nutrient partitioning hormone—it decides where the energy from your food goes. Understanding insulin is essential for fasting protocols, body composition, and metabolic health.
What Insulin Does
| Function | Effect |
|---|---|
| Glucose uptake | Moves blood sugar into cells |
| Energy storage | Signals cells to store fuel (fat, glycogen) |
| Protein synthesis | Promotes muscle building |
| Lipolysis inhibition | Stops fat burning when elevated |
Key insight: When insulin is high, you’re in storage mode. When insulin is low, you’re in mobilization mode (including fat burning).
The Fed vs. Fasted State
When You Eat (High Insulin)
- Blood glucose rises from food
- Pancreas releases insulin
- Insulin signals cells to take up glucose
- Excess stored as glycogen and fat
- Fat burning is suppressed
When You Fast (Low Insulin)
- Blood glucose drops
- Insulin falls
- Glucagon rises (insulin’s opposite)
- Body mobilizes stored energy
- Fat burning is activated (lipolysis)
This is the foundation of why time-restricted eating works for fat loss.
What Raises Insulin
Different foods affect insulin differently:
| Food Type | Insulin Response |
|---|---|
| Simple sugars (glucose, fructose) | High, rapid |
| Refined carbs (white bread, pasta) | High |
| Complex carbs (whole grains) | Moderate |
| Protein | Moderate |
| Fat | Low |
| Fiber | Minimal |
The glycemic index and glycemic load attempt to capture these differences.
Insulin Sensitivity vs. Resistance
Insulin Sensitivity (Healthy)
- Cells respond well to insulin
- Small amounts of insulin move glucose effectively
- Blood sugar stays stable
- Body easily switches between fed and fasted states
Insulin Resistance (Problematic)
- Cells don’t respond well to insulin
- Pancreas must produce more insulin
- Blood sugar becomes harder to control
- Eventually leads to type 2 diabetes
- Associated with obesity, inflammation, metabolic syndrome
Improving Insulin Sensitivity
1. Exercise
Both resistance training and cardio improve sensitivity:
- Muscles take up glucose during exercise
- Post-exercise, muscles remain sensitive
- Regular exercise maintains long-term sensitivity
2. Time-Restricted Eating
Fasting windows improve insulin sensitivity:
- Gives pancreas a break
- Allows insulin to fall fully
- Restores sensitivity over time
3. Body Composition
Reducing excess body fat improves sensitivity:
- Fat tissue, especially visceral fat, promotes resistance
- Muscle tissue improves glucose disposal
4. Sleep
Poor sleep rapidly impairs insulin sensitivity:
- Even a few nights of poor sleep measurable effect
- Prioritize sleep for metabolic health
Insulin and Fat Loss
The practical application:
| Strategy | Why It Works |
|---|---|
| Eating window | Creates extended low-insulin periods |
| Avoiding snacking | Keeps insulin from constantly spiking |
| Morning fasting | Extends overnight low-insulin state |
| Exercise timing | Depletes glycogen, increases fat utilization |
When insulin is low for extended periods, fat mobilization (lipolysis) is enhanced.
GLP-1 and Satiety
GLP-1 (glucagon-like peptide-1) works alongside insulin:
- Released from gut after eating
- Slows gastric emptying (feel full longer)
- Enhances insulin release
- Targets of new weight loss drugs (Ozempic, etc.)
Natural GLP-1 release is enhanced by:
- Protein and fiber
- Slower eating
- Fermented foods
Related Pages
“Insulin is the switch between storage mode and mobilization mode. If it’s always high from constant eating, you’re always storing, never burning.” — Andrew Huberman