How Does Intermittent Fasting Affect Your Body?
Intermittent fasting (IF), an increasingly popular wellness practice, is usually advertised as a weight-loss tool. But the benefits go far beyond caloric reduction. From gut health to metabolic support, the evidence behind IF continues to grow.
Fasting, or abstaining from foods or beverages with calories for an extended period, is considered a stressor to the body. Unlike chronic stress, short-term nutritional stress is associated with positive adaptations that can lead to cellular support and protection.
While weight loss may be an added value of intermittent fasting, looking a bit deeper below the surface into the cellular changes can provide the science behind why this is more than just the next fad diet.
What is intermittent fasting?
Simply put, intermittent fasting involves alternating periods of eating with predetermined periods of fasting. The fasting window is generally longer than the time spent eating. You can eat meals as you usually would during your eating window, although some people eat less simply because there isn’t time for three meals and snacks.
There are multiple ways to practice IF, but the most popular IF schedules are as follows:
This cycle includes a 16-hour fast with eight hours of eating. It can be repeated daily or only on certain days of the week, depending on your lifestyle and individual needs.
Here, you’d eat normally for one to two days and then fast for 24 hours the following day, repeating once or twice a week.
Also called the Warrior Diet, this cycle includes a short four-hour eating window with a 20-hour fast for the rest of the day.
Instead of completely fasting, this method includes one to two non-consecutive days of very low calories (500-600 total) and normal intake the rest of the week.
A review article published in the New England Journal of Medicine found that IF is associated with many health benefits, including:
· Cognitive health
· Weight management
· Blood sugar balance
· Improvements in oxidative stress and inflammation
While researchers are still attempting to understand precisely why fasting may be so helpful, many of these advantages are likely related to the cellular adaptations that occur when the body is in a fasted state.
What happens to your cells when you fast?
While nutrition research usually examines diet and how the body responds when you eat certain nutrients, the power of IF happens when there is a lack of nutrients, so the body is forced to adjust.
When you eat, your body is in a cycle of growth or anabolism. Nutrients from your diet are used to build molecules in the body. While this is an essential physiological process, your body also needs time to balance anabolism with periods of repair.
In these times of rest, the body can focus on clearing out cellular debris, waste, and free radicals that otherwise lead to oxidative stress and damage in the body. Many of these restorative and protective processes only happen during periods of nutrient scarcity (most commonly when you sleep as described in Nature Communications) or while fasting.
As research tells us that oxidative stress is intimately connected with chronic health conditions, especially those associated with aging, fasting may be a tool to help. Some of the known cellular adaptations that may protect your body against oxidative damage include:
Repair and waste removal through autophagy.
A well-studied cellular adaptation to fasting is autophagy. Autophagy is the body’s way of removing damaged cells, cellular debris, and waste products to make room for healthier, stronger cells. It’s like the body’s programmable robotic vacuum that turns on at night when you are sleeping, moving from room to room, cleaning up the dust and mess created during your daily activities.
The absence of nutrients during fasting and low insulin levels (also seen in ketogenic diets) drives autophagy. As seen in the journal Cell Death and Differentiation, autophagy has been well-studied as a protective measure against oxidative damage.
A review published in Frontiers in Cell and Developmental Biology also suggests that autophagy is a potential tool to fight back against the aging process.
Inflammation and immune response.
Acute inflammation is a normal part of the immune response, but chronic inflammation is associated with significant health concerns. Fasting may help downregulate inflammation by impacting the pro-inflammatory immune cells that communicate messages to turn on the inflammatory process.
Researchers from Mount Sinai discovered that IF may reduce the number of circulating monocytes (inflammatory immune cells) in your blood. Further, this study found that the monocytes found in blood from the IF group had less inflammatory activity than those found in fed subjects.
As researchers are interested in the association between monocytes and certain chronic health conditions, reductions through fasting could be a simple, non-invasive approach to drive down inflammation.
Mitochondria are often called the powerhouse of the cell because they generate energy throughout the body. When nutrients are converted to energy, they also create reactive oxygen species (free radicals) as a normal byproduct.
Mitochondrial health can also be negatively affected by various lifestyle factors or simply as a regular part of metabolism. Mitochondrial dysfunction is associated with accelerations in aging and many chronic health concerns, as described in the Journal of Integrative Medicine.
Fasting can support mitochondrial function, cleaning up free radical byproducts through autophagy. Research published in Molecular and Cellular Biochemistry found that fasting also increases NAD+ , which stimulates sirtuin activity.
Sirtuins are proteins associated with many healthy aging benefits, including the support of mitochondrial function and adaptations to stress. They may also play a role in the regulation of autophagy as documented in Experimental and Molecular Medicine.
Downregulates mTOR activity.
The mammalian target of rapamycin (mTOR) is a signaling pathway that helps with cellular growth and metabolism. Fasting turns off mTOR activity which is one autophagy, allowing for the growth of new, healthy cells.
Once nutrients are reintroduced during the feeding window, mTOR can turn back on and regenerate new healthy cells, but only after the body has had a chance to clear out any that are damaged.
Nrf2 is a protein that turns genes on or off, activated in response to oxidative stress to protect against free radical damage.
A review article published in Frontiers in Pharmacology found that while Nrf2 levels naturally decline with age, fasting activates Nrf2, contributing to the clean-up of reactive oxygen species in the body.
It also plays a vital role in healthy detoxification and is associated with neuroprotective benefits through its antioxidant activity, as seen in a review from ASN Neuro.
Intermittent fasting is a flexible wellness tool.
Intermittent fasting may be a simple way to support your health through the cellular adaptations that happen when the body is forced to go without nutrients. A conversation with your healthcare practitioner is always a good idea before starting, but IF provides a flexible framework to benefit from these changes without longer-term caloric deprivation.
While everyone responds differently, and some will benefit from shorter or less frequent fasts, IF can be a simple, effective tool to add to your wellness practice.