Last week we covered some common reasons people choose to fast and some methods for safely going without calories for between several hours and several days. This week we are going to share some of the scientific reasons why a 3-day fast will help you live longer.
Fasting removes the body’s access to glucose and forces the body to produce its own sugar for energy. The liver converts non-carbohydrate materials, including fat, into energy at the start of a fast. Later, the body goes into ketosis and burns stored fat for energy.
Fasting puts the body under some mild stress that forces cells to adapt and become stronger. If you lift weights to strengthen your muscles, consider fasting to strengthen your cells. As with exercise, your body needs time to recover and grow from the stress. That’s why an occasional 3-day fast may be optimal.
The science that studies the effectiveness of fasting in humans is emerging and ongoing. Unfortunately, there are very few commercial reasons to study fasting (i.e. companies don’t have ways to profit from people not eating) and it is impossible to have a blinded study when one group is eating and one group isn’t!
We are going to share our scientific research that led to eight scientific benefits of fasting:
1. Reset your immune system
Recent studies are demonstrating how fasting for two days or longer causes metabolic changes that “reset” components of the immune system.
One scientific study looked at both mice and humans and found that the caloric restriction triggered the immune system to start producing new white blood cells (lymphocytes), a key component of the body’s immune system. Both the enzyme PKA and hormone IGF-1 were reduced by the fast, but stem cells kicked back into gear to replenish the cells during refeeding following the fast. A key finding in this research is that you have to fully deplete your energy reserves (the body’s glycogen), and it takes your body 24-72 hours to do this.
2. Reduce insulin resistance
Decreasing insulin resistance can allow the body to transport glucose from your bloodstream to your cells more efficiently. This is especially useful for those at risk of diabetes. Both intermittent fasting and alternate-day fasting were effective at reducing insulin resistance in these studies.
3. Decrease levels of inflammation
Research shows inflammation is involved in the development of chronic conditions such as rheumatoid arthritis, heart disease, and cancer. Some studies have found that fasting can help decrease levels of inflammation and promote better health.
One study in 50 healthy adults showed that intermittent fasting for one month significantly decreased levels of inflammatory markers. Another study discovered the same effect occurred when fasting 12-hours a day for one month. An animal study found following a low-calorie diet (to mimic fasting) reduced levels of inflammation and was beneficial in the treatment of multiple sclerosis, a chronic inflammatory condition.
4. May boost brain function and have a role in preventing neurodegenerative disorders
Fasting has shown promise for improving brain function and health. A mouse study showed positive outcomes from intermittent fasting for 11 months while other studies (here and here) showed an increase in the generation of nerve cells to enhance cognitive function. The reduction in inflammation mentioned earlier should also aid in preventing neurogenerative disorders including Alzheimer’s and Parkinson’s.
5. Boosts metabolism (and reduces calories) to increase weight loss
Both intermittent fasting and multi-day fasts reduce caloric intake so you quickly drop a few pounds. A bigger effect on weight loss could be due to an increase in metabolism. Some research has found that short-term fasting increases levels of the neurotransmitter norepinephrine. These weight loss benefits lasted beyond the length of the fast.
This study on whole-day fasting showed decreased body fat 12-24 weeks post fast. Another review found intermittent fasting over 3-12 weeks was as effective in inducing weight loss as continuous calorie restriction and decreased body weight by up to 8% and fat mass by up to 16%.
6. Could delay aging
Emerging science on longevity is the primary reason I am going to try a 3-day fast. Rats that fasted every other day had delayed rates of aging and lived 83% longer. Short-term, repeated fasting in female mice led to longer life-spans in a different study. Unfortunately, it will be a while before human studies demonstrate any benefits.
Human growth hormone (HGH) is involved in growth, metabolism, weight loss, and muscle strength but naturally decreases in humans as we age. Several studies have found that fasting naturally increases HGH levels.
One study in nine men found that two-day fasts resulted in five times the production of HGH. Another study in 11 adults found a 24-hour fast significantly increased levels of HGH. It is currently unclear if or how HGH levels affect longevity, but if fasting naturally increases their levels it would appear to be a positive.
7. May aid in cancer prevention and treatment
One rat study found that alternative day fasting blocked tumor formation. A test-tube study on cancer cells showed that fasting was as effective as chemotherapy in delaying tumor growth. Fasting combined with chemotherapy was even more effective than either alone. This science is emerging but promising!
8. Appears to be beneficial to your heart
Heart disease is currently the leading cause of death worldwide. Studies have found fasting improves heart health and reduces the likelihood of heart disease.
One larger study in humans demonstrated a lower risk of both coronary artery disease and diabetes. Another study in obese adults who had a “fasting diet” for three weeks resulted in a significant decrease and normalization of blood pressure, total cholesterol, and LDL cholesterol.
Scientific Reasons for a 3-day fast
The overall science is still emerging, but it is more than enough for me to try out a modified 3-day fast. Check back next week for a review of how I prepared for a fast and my personal experience with fasting.