There are so many videos, podcasts talking about fasting. But a lot of them are one-sided. So let’s talk about what are the pros and what are the cons of different types of fasting
First, let’s define the types of fasting. There are two broad categories: Intermittent and Periodic Fasting
- Alternate Day Fasting: essentially alternating 24-hour eating with 24-hour fasting.
- Modified Alternate Day Fasting: Eating roughly 25% of calorie intake on fasting days.
- 5:2 Fasting: This involves fasting for two non-consecutive days, with eating normally for the remaining five days. Some variations call for eating 500-700 kcal on fasting days.
- Time-Restricted Feeding: This involves reducing the eating window to 6-12 hours and fasting for the remainder of the time.
- Prolonged Water Fast: 3-21 consecutive days of water-only fast followed by ad-libitum eating. This should only be done under medical supervision due to the risk of electrolyte abnormalities.
- Fast Mimicking Diet: 4-7 consecutive days once per month or once every few months followed by ad-libitum eating.
Fasting and Longevity
The data on fasting and longevity in animal models is quite fascinating. For example, yeasts have a 3x increase in lifespan simply with caloric restriction. Mice experiments show a 30-50% increase in lifespan. We don’t have any data yet to see if fasting leads to longevity in humans. However, human trials support fasting improving risk factors for cancer, cardiovascular disease and preventing obesity, diabetes, and high blood pressure.
Interestingly, there may be some differences in benefits when fasting begins at a younger versus older age. In certain mice models (C57BL/6J), intermittent fasting started at 1.5 months increases longevity. However, starting intermittent fasting at ten months has no benefit or even reduction in longevity.
Fasting and High Blood Pressure
In an interesting study published in the Journal of Manipulative and Physiological Therapeutics, Dr. Goldhamer and colleagues did a medically supervised water-only fast lasting 10-11 days. It was followed by refeeding with a low-fat, low sodium vegan diet. The authors found an average reduction in blood pressure of 37mmHg systolic and 13mmHg diastolic. All of the participants who took blood pressure medications at the start of the study discontinued them. However, we don’t know what happened in the weeks and months that followed the study. Once the participants started going back to their regular lifestyles, did the results persist, or did their blood pressures go up again?
Fasting and Brain Health
In animal studies, fasting has demonstrated neuronal protection and improved cognitive impairment. In a study by Halagappa and colleagues, the authors’ tested fasting in a triple-transgenic mouse model for Alzheimer’s disease. Starting at three months of age, mice were either maintained on a control diet, caloric restriction, or intermittent fasting. At 17 months, the mice in the calorie restriction and intermittent fasting arm showed higher levels of exploratory behavior and did better in behavioral testing tasks. The authors concluded that calorie restriction and intermittent fasting might reduce the age-related declines in cognitive function.
Fasting and Immune System
Multiple Sclerosis is a devasting disease with demyelination, inflammation of the central nervous system, and damage to neurons. An experimental form of autoimmune encephalomyelitis is used to study the effects of Multiple Sclerosis.
Piccio and colleagues subjected mice with autoimmune encephalomyelitis to 66% calorie restriction. They showed that eight weeks of calorie restriction prevented autoimmune encephalomyelitis by modulating the immune response and regenerating oligodendrocyte precursor cells.
Fasting decreases the amount of circulating T cells and inflammatory cytokines and chemokines. An interesting question is whether it could play a protective role in other autoimmune conditions such as lupus, asthma, or other diseases.
Fasting and Cancer
Intermittent and periodic fasting has been shown to protect normal cells from chemotherapy’s toxic effects and sensitize cancer cells to treatment. Some of the mechanism by which it makes cancer treatment more effective is by:
- ↓ IGF-1
- ↓ Insulin
- ↓ Leptin
- ↓ Cytokines
Fasting and Diabetes
Intermittent and periodic fasting improve diabetes by decreasing weight, decreasing subcutaneous and visceral fat, improving lipids, and improving overall insulin sensitivity in humans.
If a little bit of something is good, a whole lot may not be better. In the Minnesota Starvation Experiment (1944-1945), male participants had 45% reduced calorie intake for 24 weeks. The results were:
- low blood counts
- muscle wasting
- neurological deficits
- leg swelling
In a study of 4730 women participating in the first National Health and Nutrition Examination Survey, the authors looked at the role of prolonged overnight fasting with the risk of gallstones. In women fasting 14 hours versus those who fasted for 8 hours, the risk of gallstone disease nearly doubled.
With extended fasting (intermittent or periodic), other commonly reported side effects include:
- Sleep Disturbance: 14.94%
- Fatigue: 13.70%
- Dry Mouth: 8.84%
- Back Pain: 7.43%
- Hunger: 6.81%
- Bad Breath: 5.39%
- Headache: 5.39%
- Muscle Pain: 4.33%
- Abdominal Bloating : 4.16%
- Diarrhea: 3.36%
Research is just beginning to show that fasting can be an essential part of our healthy lifestyle. Fasting allows the body to enter alternative metabolic modes and optimize survival. Both refeeding and fasting are important, and using an evidence-based dietary regimen like a whole-food, plant-based diet will optimize the fasting regimen. The key with fasting is not to do it to extremes as it can negatively impact health and longevity.