What is Intermittent Fasting?
- The definition of Intermittent Fasting: taking intentional breaks from eating. What are ways to Intermittent Fast?
- 16:8 Method: Restrict intake for 8 hours, and fast for 16. Example: eat 11 am to 7 pm.
- Eat-Stop-Eat: Fasting for 24 hours, 1-2 times a week.
- 5:2. You consume 500-600 calories on two non-consecutive days of the week, and eat normally the other 5 days.
How does Human Metabolism work?
- Glucose (or sugar) is the primary energy source for most of your tissues/cells throughout the day
- Fatty acids represent an alternative fuel source for organs that are metabolically active like muscle, liver, brain, and rise overnight while you are sleeping (/fasting).
The Cycle Of Intermittent Fasting
EAT
FED STATE
- Hour 3
- In the fed state, your glucose (blood sugar rises), and your pancreas secretes insulin to accomodate for the blood sugar spike.
- In this state, your body stops breaking down fat to release fatty acids.
- It breaks down glucose, and this is where you get your energy from.
- If there is excess caloric intake, it is stored as fatty acid in the body
THE POST ABSORPTIVE STATE
- Hour 18
- AKA “early fasting state”
- The insulin secretion has decreased, leading to gluconeogenesis (instead of breaking down sugar from carbs, breaking down sugar from fat and protein).
- Increases the breakdown of fatty acids
THE FASTING STATE
- Hours 36-48
- Insulin secretion is down
- Metabolism shifts to breaking down Fatty acids and Ketones as fuel
- Lipolysis (breaking down of fats increase)
- Increase glucagon (counteracts insulin, by stimulating the liver to increase glucose production, and increase blood glucose levels).
> 48 HOURS OF FASTING
- Decreased insulin
- Releases Fatty Acids
So, what do we know?
- Nearly all IF studies have resulted in some degree of weight loss, ranging from 2.5-9.9% of fat loss
- Animal studies found a decrease in serum glucose or blood sugar and insulin
- The human trials showed stable or decreased fasting insulin, with no change in fasting blood sugar
- Animal models show IF to be beneficial for weight, body composition, cardiovascular biomarkers, and aging, decrease inflammation, and promote longevity
- The studies vary on their definition of IF, protocol, and duration of fasts.
Questions to ask yourself?
Take-Aways
- Research is not robust enough to suggest IF to patients as a standard of care
- Best recommended to people who are able to avoid overeating following a fasting period
- Americans prefer highly palatable, calorically dense foods!
- Trials ongoing on cancer, alzheimers, diabetes, and longevity
