Intermittent fasting (IF) is an eating pattern where you cycle between periods of eating and fasting.
Also known as intermediate fasting, it is not a diet but rather a style of eating.
You already fast every day while you sleep. Intermittent fasting simply extends that fast a little bit longer.
For example, if you eat your last meal at 8 pm, skip breakfast and then ate your first meal at noon, you fasted for 16 hours and restricted eating to an 8-hour eating window. The 16/8 method is the most popular form of intermittent fasting.
Intermittent fasting is very easy to do and most people actually report feeling better and having more energy during the fast.
Hunger is usually not an issue, although it can be a problem in the beginning while your body is getting used to not eating for extended periods of time.
The Benefits of Intermittent Fasting
The main benefit to intermediate fasting is lowered insulin levels. This allows for optimal fat loss and detoxification.
Related: 3 Things You Can Learn From Intermittent Fasting
Now don’t make the mistake of thinking that insulin is all bad. Insulin is an essential hormone that is needed by the body to absorb and utilize the food you eat. The tricky thing about insulin is that insulin is a storage hormone. Fat loss and detoxification are opposite bodily processes. Your body cannot burn fat and detoxify itself optimally when insulin is present.
The benefits of intermittent fasting go far beyond weight loss. Intermediate fasting has also been shown to improve heart health, reduce cancer risk, prevent type 2 diabetes, reduce inflammation and improve metabolic features important for brain health.
- Heart Health: Intermittent fasting has been shown to improve cardiovascular disease risk factors including blood pressure, total and LDL cholesterol, blood triglycerides, inflammatory markers and fasting blood sugar1.
- Cancer Prevention: Fasting has several beneficial effects on metabolism that may lead to a reduced risk of developing cancer. There is also evidence on human cancer patients showing that fasting reduced side effects of chemotherapy2.
- Diabetes Prevention: The main feature of type 2 diabetes is high blood sugar levels caused by insulin resistance. Anything that reduces insulin resistance and helps lower blood sugar levels protects against developing type 2 diabetes. Human studies found that intermediate fasting reduced fasting blood sugar levels by 3-6% and reduced fasting insulin levels by 20-31%3.
- Reduced Inflammation: Several studies show that intermittent fasting enhances the body's resistance to oxidative stress and helps fight inflammation4.
- Improved Brain Health: Several studies show that intermediate fasting increases levels of the brain hormone brain-derived neurotrophic factor (BDNF), which deficiencies have been linked to depression and various other brain problems5. Animal studies have also shown that intermittent fasting protects against neurodegenerative disease such as Alzheimer’s6.
What Can I Consume While Fasting?
No food is allowed during the fasting period, but you can drink water, coffee, tea and non-caloric beverages.
Most forms of intermittent fasting allow small amounts of low-calorie foods such as greens powders and amino acid supplements during the fasting period. Although they contain calories, the calorie content is so small that it won’t break you out of the fast.
Similarly, taking supplements is generally allowed while fasting as long as they are non-caloric.
Safety and Side Effects of Intermittent Fasting
Hunger and irritability are the main side effects people experience while intermittent fasting. These side effects are usually only temporary as it takes time for your body to adapt to the new meal schedule.
Related: 5 Things "Diet Gurus" Don’t Want You to Know
If you have a medical condition, you should consult with your doctor before trying intermittent fasting. This is particularly important if you:
- Have diabetes.
- Have problems with blood sugar regulation.
- Have low blood pressure.
- Are underweight.
- Have a history of eating disorders.
- Are a woman who is trying to conceive, pregnant or breastfeeding.
All that being said, intermittent fasting has an outstanding safety profile. There is nothing dangerous about fasting if you’re healthy and overall well-nourished.
Frequently Asked Questions about Intermittent Fasting
1. Can I Drink Liquids During the Fast?
Yes. Water, coffee, tea and other non-caloric beverages are fine. However, do not add sugar.
2. Isn't It Unhealthy to Skip Breakfast?
No. Most stereotypical breakfast skippers have unhealthy lifestyles. Skipping breakfast in itself is not unhealthy.
3. Can I Take Supplements While Fasting?
Yes. However, some supplements like fat-soluble vitamins may work better when taken with meals.
4. Can I Work out While Fasted?
Yes. However, it is recommended to consume essential amino acids (EAAs) during a workout while fasting to prevent muscle loss.
5. Will Fasting Cause Muscle Loss?
All weight loss methods can cause muscle loss which is why it’s important to lift weights and keep dietary protein intake high. Generally speaking, muscle loss during fasting isn’t a concern unless you are fasting for periods greater than 24 hours.
6. Will Fasting Slow Down My Metabolism?
No. Studies show that short-term fasts actually boost metabolism. However, long duration fasts of 3 or more days can suppress metabolism.
7. Should Kids Fast?
Intermediate fasting is generally not recommended to anyone younger than 18 years of age.
- Varady, K. A., Bhutani, S., Church, E. C., & Klempel, M. C. (2009, November). Short-term modified alternate-day fasting: A novel dietary strategy for weight loss and cardioprotection in obese adults. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/19793855
- Safdie, F. M., Dorff, T., Quinn, D., Fontana, L., Wei, M., Lee, C., . . . Longo, V. D. (2009). Fasting and cancer treatment in humans: A case series report. Aging,1(12), 988-1007. doi:10.18632/aging.100114
- Barnosky, A. R., Hoddy, K. K., Unterman, T. G., & Varady, K. A. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: A review of human findings. Translational Research,164(4), 302-311. doi:10.1016/j.trsl.2014.05.013
- Bruno, A. (2007). Faculty of 1000 evaluation for Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma. F1000 - Post-publication Peer Review of the Biomedical Literature. doi:10.3410/f.1071147.524148
- Lee, B., & Kim, Y. (2010). The Roles of BDNF in the Pathophysiology of Major Depression and in Antidepressant Treatment. Psychiatry Investigation,7(4), 231. doi:10.4306/pi.2010.7.4.231
- Arumugam, T. V., Phillips, T. M., Cheng, A., Morrell, C. H., Mattson, M. P., & Wan, R. (2010). Age and energy intake interact to modify cell stress pathways and stroke outcome. Annals of Neurology,67(1), 41-52. doi:10.1002/ana.21798
Hi Trevor. Any suggestions on how to prevent hair loss while fasting? Thanks
Hi, Kim. Will keep this up so Trevor can answer if he sees it, but my suggestion would be to stop fasting and seek medical attention. Not long how long you've noticed hair loss, but I would get medical advice to be safe.