Intermittent Fasting
What I learned this week
This week we’re taking a deep dive into all things fasting!
Recently, fasting patterns have become popular because of an upswing of research that suggest fasting can be an effective means of losing weight, entering ketosis, and my personal favorite, for encouraging cellular repair.
***Disclaimer: this information is not intended to be taken as dietary or medical advice. Please, please, please consult a medical professional before beginning a diet or weight loss program.
Stages of Fasting
Stage 1: Fed State (hour 0 to 12)
Most people don’t consider labeling anything less than 12 hours as a fast. Between your last meal and hour 6, your stomach and small intestine are busy receiving and absorbing most of the nutrients from that meal. It’ll take up to four hours for food to leave your stomach, depending on the fat content of the meal. The body is in a “fed” state for most of this period. Glucose is the primary energy source being burned. When all the glucose from the last meal is has been burned, the glycogen (glucose) stores will be used from the liver and muscles.
Stage II: Metabolic Switch (Hours 12 to 18)
12 hours is the lower end of the “normal” window for fecal transit time. In other words, after 12 hours some people might experience a bowel movement, but this is highly dependent on the individual. Others may take up to 24 or even 36 hours.
Somewhere between hours 12 and 18, the body will run out of glycogen stores to supply a steady supply of glucose. When these stores are depleted, the body will burn fatty acids instead. This adjustment in energy source is known as the “metabolic switch” and reaching this transition is often the target of a fasting regimen.
Stage III: Ketosis (Hours 18 to 36)
After 18 hours without food, the rate of fatty acid oxidation will steadily increase. When fatty acids are burned, ketones are created as byproducts of the oxidative reaction. Ketones are used as an alternative source of fuel when glucose levels are depleted. Manipulating the diet to enter state of ketosis was actually first developed as a treatment for people with epilepsy.
Benefits of Fasting
BDNF
BDNF stands for brain-derived neurotrophic factor – this is a molecule that has recently gained a lot of attention due to its impacts on mood, memory and cognitive function. After 12 hours of fasting, levels of BDNF increase, which could be why those who fast experience improvements in their cognitive function and in their depression symptoms.
Weight management
Multiple human trials have demonstrated the potential of intermittent fasting (time-restricted eating) for weight loss. If you have weight to lose, fasting may very well be the way to lose it. Many find this schedule less restrictive than a typical diet because no foods are off-limits.
Resting Heart Rate
Fasting can lead to a lower resting heart rate, which is often considered an indicator for heart health and endothelial function.
IGF-1
IGF-1 is a human growth hormone that functions as a signal to cells to replicate. It is particularly relevant in the context of cancer prevention, because elevated IGF-1 encourages tumor cells to grow. Certain fasting regimes have been shown to lower IGF-1 levels in humans. It’s definitely worth looking into the research on fasting and cancer prevention and treatment – the literature is dense and growing rapidly!
Mood
Many people who try extended fasting (longer than 36 hours) report feelings of euphoria and mental clarity. I cannot say I learned about the biochemistry of this, but it’s an interesting side effect to note nonetheless!
