The Role of Metabolic Switching in Intermittent Fasting
It all started with rats. In the 1940’s, scientists at the University of Chicago observed life span increases of 15–20% in rodents following a 2:1 alternate-day intermittent fasting pattern.(1)
Since this discovery, researchers hoping to expand human life spans have sought to better understand intermittent fasting. Fasts have been observed in countless species, and scientists keep noticing the same, amazing phenomenon: metabolic switching.
Metabolism includes a very complex series of chemical reactions. But in the simplest of terms; food goes in and energy comes out. We eat, we live. But when we haven’t eaten in a few hours, a metabolic switch occurs and the body begins to draw energy from stored fat. In order to understand why intermittent fasting causes this switch, it’s important to understand both the fed and fasted states.
Fed State
The body enters the fed state right after a meal. Recently eaten fat molecules head to fat tissue for storage, and recently eaten glucose molecules move to the mitochondria, or “the powerhouse of the cell” as biology teachers like to say. Glucose is then converted to a usable form of energy, and our cells carry on business as usual.
Fasted State
After going several hours without eating, the human body then moves towards the fasted state. Cells have used up all available glucose, and the body begins to resurrect fatty acids from stored fat tissue. In the liver, fatty acids can be converted to ketones — the molecule the “keto diet” is named for. As a fast continues, more fatty acids are converted to ketones. In lab rats this takes 4–8 hours, but in humans the rising tide of ketones begins 8–12 hours after our most recent meal.(2)
The longer we fast, the more ketones accumulate in our bloodstream. Once ketone bodies reach a critical mass, a metabolic switch occurs and ketones become the primary energy source instead of glucose. Our cells are amazingly efficient at converting ketones into energy, and as observed in the lab rat study, spending one out of every three days in a fasted, ketone-rich metabolic state had pretty positive results.
In humans, some of the most researched fasting intervals are 5:2 (fasting twice a week) and daily time-restricted feeding (16:8 fasts are my personal favorite). There is growing evidence that both types of fasts can improve glucose regulation, blood pressure, and resting heart rate.(3)
Researchers still have many questions about intermittent fasting, but we do know that metabolic switching and increased blood concentrations of ketone bodies have wide-ranging effects. Ketones especially influence the expression of growth factors involved in the aging process and cellular stress resistance. More studies are needed, but ten out of ten lab rats recommend intermittent fasting — and I think they’re onto something.
