Fasting Glossary: Top Terms Explained for Beginners
Keywords: intermittent fasting terms, fasting glossary, autophagy, ketosis, insulin sensitivity, benefits of fasting, fasting for weight loss
If you’re exploring intermittent fasting for weight loss, improved energy, or better health, you’ve likely run into terms like autophagy, ketosis, or metabolic switching. These scientific terms describe the powerful changes happening inside your body during a fast—and understanding them can supercharge your results.
This beginner-friendly glossary will help you decode the most common fasting terms, complete with real-life examples. Bookmark this page and refer back often as you explore different fasting styles!
| Term | Definition | Example in Fasting |
|---|---|---|
| Autophagy | Cellular self-cleaning: your body recycles damaged cells to improve health and longevity. | Begins around 18–24 hours into a fast, especially in longer fasts. |
| Ketosis | A fat-burning state where your body uses ketones (from fat) as energy instead of carbs. | Starts after ~12–36 hours of fasting or through a keto diet. |
| Insulin Sensitivity | How effectively your body responds to insulin, crucial for blood sugar balance. | Improves with regular fasting like 16:8 or 5:2. |
| Gluconeogenesis | Creating glucose from fat or protein when carbohydrates are low. | Occurs during extended fasts after glycogen is depleted. |
| Glycogen Depletion | Using stored sugar in your liver and muscles before switching to fat-burning. | Happens in the first 12–24 hours of a fast. |
| Growth Hormone (GH) | Supports muscle maintenance and fat loss; naturally increases during fasting. | Can spike 4–5x after a 24-hour fast. |
| Time-Restricted Eating (TRE) | Eating all meals within a specific daily window. | The 16:8 method: eat from 12 PM–8 PM and fast the remaining 16 hours. |
| Intermittent Fasting (IF) | Alternating periods of eating and fasting on a regular schedule. | Includes methods like 16:8, 5:2, and OMAD (One Meal a Day). |
| Metabolic Switching | The body’s shift from using glucose to using fat/ketones as fuel. | Begins around 12–16 hours into a fast. |
| Leptin | The hormone that signals fullness and helps regulate appetite. | Fasting may restore leptin sensitivity, reducing cravings. |
| Ghrelin | The hormone that signals hunger. | Spikes at expected mealtimes but adapts with fasting practice. |
| Refeeding Syndrome | A rare but serious condition from reintroducing food too quickly after long fasts. | Prevented by breaking extended fasts (48+ hours) with light, nutrient-rich meals. |
| Circadian Rhythm | The body’s internal 24-hour clock that controls eating, sleeping, and hormone cycles. | Fasting in alignment with daylight may boost health outcomes. |
| Basal Metabolic Rate (BMR) | The calories your body burns at rest to maintain life functions. | Fasting does not lower BMR when done responsibly and with proper nutrition. |
| Hyperinsulinemia | Chronically high insulin levels, often from frequent eating and sugar intake. | Fasting helps lower insulin and reduce disease risk. |
You can find more information about the terms on our Blog page:
A more detailed term page is here: https://livewellfasted.com/uncategorized/fasting-glossary-top-terms-explained-for-beginners/