With its growing popularity, intermittent fasting is now a subject of interest among a wide range of individuals, not just health experts. Some claim it to be the key to fat loss, while others claim it is just another health fad. But what does the evidence say? And who can benefit from it?

Fasting Basics

Humans have practiced fasting since the beginning of time. From an evolutionary standpoint, our ancestors routinely went through periods of feast and famine, where food was abundant at certain periods and less available at other times. This conditioned the human body to burn stored fat as its primary source of energy when food was not always there. Also, many ancient religions considered fasting as a means of cleansing and creating mental alertness.

Intermittent fasting, otherwise known as Time- Restricted Eating (TRE), offers many general benefits for overall health and wellness, including weight management and reducing the risk of various diseases such as obesity, diabetes, cardiovascular disease, neurodegenerative conditions, and cancer, as noted in a meta-analysis of 85 studies published in the New England Journal of Medicine in December 2019. (1)

Timed Fasting

It can increase insulin sensitivity, reduce inflammation, improve mental clarity, improve gut health and digestion, promote weight loss, and increase autophagy. Autophagy is the process by which the body breaks down and recycles damaged cells, which can help to slow down the aging process and reduce the risk of diseases such as cancer.

Intermittent fasting can lead to metabolic switching from glucose to ketones, making the body more metabolically flexible—a key aspect of metabolic health. In a normal, healthy state, the human body uses glucose, which is derived from carbohydrates, as its primary energy source. However, during fasting or low carbohydrate intake, the liver produces ketones from stored fat, which can be used as an alternative energy source. Metabolic flexibility enables the body to quickly and efficiently switch between glucose and ketones as needed. This can result in cellular healing benefits such as mitochondrial stress resistance, antioxidant defense, autophagy, and DNA repair while decreasing glycogen, insulin, and protein synthesis. (2)

A lack of metabolic flexibility can lead to health issues, like insulin resistance, which can ultimately result in type 2 diabetes. Insulin resistance occurs when the body is unable to effectively use insulin to transport glucose from the bloodstream into cells for energy production. As a result, the body is forced to rely more on glucose as an energy source, which can further exacerbate insulin resistance and lead to a vicious cycle of impaired metabolic function. 

It is important to note that this is not a calorie-restriction diet, nor does it count macronutrients or portion sizes, but rather just limiting the window in which we consume food during the day. 

Fasting Strategies To Fit Your Lifestyle

There are several ways to go about intermittent fasting, depending on lifestyle factors and personal preference. The most common method used is the 16:8 method which consists of 16 hours of fasting and an 8-hour window for eating. Although sixteen hours of fasting may seem a bit much, keep in mind that sleep will take up between 7-9 hours already. 

Fasting 16/8

We naturally enter a fasting state each night when we sleep. During this time, our bodies do not receive any new energy from food, and this absence of nutrients triggers a series of metabolic processes. This natural fasting state allows our bodies to conserve energy and resources that would have otherwise been spent on digestion. This saved energy can then be redirected to other essential processes such as cellular repair, growth, and regeneration. 

You can take advantage of this natural fast by aiming to finish eating earlier in the day (at least 3 to 4 hours before bedtime) and avoid any late-night snacking. The following day, delay consuming breakfast (literally, break-fast) a little later than you normally eat. This is a simple way to extend the hours your body is in a fasting state and give your digestion a rest. You can then incrementally extend the hours of your fast.

During your fasting period, you can and should consume water, as well as unsweetened coffee, tea, or a similar beverage that does not contain calories or cause a significant rise in blood sugar. It’s also okay to take supplements during this time. Some people find that adding full-fat cream or MCT oil to their coffee does not break their fast, but it’s best to use a blood glucose tester or continuous blood glucose monitor to measure your glucose level and ensure this is the case. As long as your beverages and additives do not contain calories or significantly affect blood sugar levels, they are generally acceptable to consume during a fasting state.

How Long Should I Fast?

Different lengths of fasting can lead to different benefits, including the start of autophagy at 17 hours, gut reset at 24 hours, fat-burning at 36 hours, dopamine reset at 48 hours, and immune reset after 72 hours or more. (3)  

It is not advisable, however, to embark on these extended fasts until you have had some practice with time-restricted eating. Think of fasting sort of like a muscle that needs to be exercised—your body needs to ‘practice’ fasting before you just go all in. For the average person, both evidence and time constraints make an 8-hour feeding window optimal. (4) The feeding window could be 6-12 hours. Any less than that is difficult and may actually result in overeating, and longer makes the fasting period too short for benefit. As with all aspects of self-care, you will find what works best for you. 

Fasting Considerations For Women

It is important to note that certain considerations apply to women in regard to fasting. In her book, Fast Like A Girl: A Woman’s Guide to Using the Healing Power of Fasting to Burn Fat, Boost Energy, and Balance Hormones, Dr. Mindy Peltz recommends that women should fast differently than men due to hormonal differences. (5) In terms of hormonal balance, fasting can be helpful for declining hormones experienced during perimenopause and infertility. Cycling long autophagy fasts once or twice a week can maximize sex hormone production. However, fasting can affect hormones differently depending on the phase of the menstrual cycle.  

Dr. Peltz proposes a hormonal fasting schedule based on a woman’s menstrual cycle. During what she calls the power phase (Days 1-10 and Days 16-19) when estrogen levels are high, fasting can be done for 13-72 hours. During ovulation (Days 11-15), when testosterone levels are elevated, fasting should be limited to 13 to 15 hours. During the nurturing phase (Day 20 to bleed) when progesterone peaks, no fasting should be done. According to this recommendation, women going through menopause should begin their fasting routine based on the current phase of the moon, with the full moon marking the start of ovulation.

Breaking A Fast

Breaking a fast can be a delicate process, especially if you have been fasting for an extended amount of time. To ensure proper fast-breaking, recommendations for breaking a fast depend on individual goals such as resetting the gut, building muscle, or burning fat. Avoid breaking a fast with processed foods. Keep your portion small to start, and wait a few hours before eating again. Drink plenty of water, add a pinch of sea salt and a squeeze of lemon to replenish electrolytes and minerals. For breaking a fast of 48 hours or more, it is suggested to start with a cup of broth, followed by a probiotic-rich meal with fat, steamed vegetables, and animal protein.

Bone Broth

Factors to Consider Before Fasting

Intermittent fasting is not a one-size-fits-all approach and may not be for everyone; many people who are trying to lose larger amounts of weight or trying to stabilize insulin levels may find it to be beneficial. Those who have inflammatory diseases like arthritis, atherosclerosis, irritable bowel syndrome, asthma, etc., may also find great relief from practicing time-restricted eating. Here are a few factors to consider before embarking on a fast:

1. Which strategy works best for you? Which is most convenient for your daily schedule? It is also important to note that you can create your own intermittent fasting schedule; for example, you may begin with a twelve-hour eating window and twelve-hour fasting window and work your way down to a smaller eating window as your body slowly adapts to the change.

2. You MUST already have good eating habits. Intermittent fasting will not be of any benefit if the food being consumed is processed and high in refined sugars and carbohydrates. You MUST be consuming whole foods—fruits, vegetables, nuts, seeds, grass-fed/organic meats, and healthy fats. Intermittent fasting on a “junk food diet” is NOT the way to do it!

3. Sleep is crucial. If you aren’t sleeping well, intermittent fasting may not be the best option for you. This is a sign you most likely have disruptions in your circadian cycle, which is important to intermittent fasting.

4. Hypoglycemia or sugar imbalances. If you are hypoglycemic or have unbalanced blood sugar, you may want to avoid fasting for long periods as it can cause drops in blood sugar and induce feelings of lethargy.

Remember that the best way to understand what’s right for your health is to try things out for yourself. Everyone’s body is different, and what works for one person might not work for another. So, experiment, pay attention to how you feel, and trust your judgment. Finding what keeps you healthy and happy is a personal journey, and you’re the best person to lead it.

References

  1.  de Cabo, R., & Mattson, M. P. (n.d.). Effects of intermittent fasting on health, aging, and disease | nejm. New England Journal of Medicine. Retrieved February 8, 2023, from https://www.nejm.org/doi/full/10.1056/NEJMra1905136 
  2.  Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. Ageing Res Rev. 2017 Oct;39:46-58. doi: 10.1016/j.arr.2016.10.005. Epub 2016 Oct 22. PMID: 27770653.
  3. Panda, S. (2018). The circadian code: Lose weight, supercharge your energy, and tranform your health from morning to midnight. Rodale, an imprint of the Crown Publishing Group. 
  4. Gabel, K., Hoddy, K. K., Haggerty, N., Song, J., Kroeger, C. M., Trepanowski, J. F., Panda, S., & Varady, K. A. (2018). Effects of 8-hour time restricted feeding on body weight and metabolic disease risk factors in obese adults: A pilot study. Nutrition and Healthy Aging, 4(4), 345–353. https://doi.org/10.3233/nha-170036 
  5. Pelz, M. (2023). Fast like a girl: A woman’s guide to using the healing power of fasting to burn fat, boost energy, and balance hormones. Hay House.  
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