Intermittent fasting. A phrase with so much confusion, misinformation, and questions! I often get asked about intermittent fasting, so I wrote this blog post to provide some information as well as my professional opinion based upon the research.
For simplicities sake, fasting can be defined as abstaining from food for a specific period of time. Intermittent fasting (IF) can be executed in many different ways, and you will find conflicting information on the internet about what strategy is most effective. This is why intermittent fasting can be misunderstood because there is no strict definition of what it actually is. There are many different ways that people implement IF.
Forms of Intermittent Fasting
Fast Days
A popular form of intermittent fasting is having “Fast Days” and “Non-Fast Days.” On fasting days, a person will restrict their calories significantly (sometimes as low as 500 calories or less.) Usually, these calories are consumed in one sitting. On non-fasting days, the person will eat normally, with no calorie restrictions. People who follow this form of IF will typically have 1-3 “fast days” per week. They might implement this on a weekly basis OR a monthly basis. This is an extreme form of fasting that I do not use with clients.
Fasting Window
Another common way to implement fasting involves what is called a “fasting window.” This form of IF requires consuming all of your food within an 8-12 hour window of time. For example, if your last meal finishes at 7pm, then your next meal would not be until 7-11am the next day. You are fasting for 12-16 hours. There are some individuals who extend the fast out even longer (as long as 20 hours.)
Metabolic Benefits of Intermittent Fasting
Most people would assume that intermittent fasting results in weight loss due to the caloric restriction that occurs, but a clinical trial from 2017 following 100 obese adults proved that intermittent fasting was no more successful in weight loss compared to a daily caloric restricted diet.
What research is finding is that intermittent fasting has beneficial effects on certain metabolic markers (leptin, insulin, and glucose), which are all involved in a person’s ability to lose weight. These markers are also involved in certain chronic disease states, most notably type II diabetes and metabolic syndrome. According to the CDC, over 100 million Americans have been diagnosed with diabetes or prediabetes.
Leptin, Insulin, and Glucose
To give you a brief synopsis, insulin is a hormone that is released after we have consumed food, specifically glucose. When we are in the “fed” state, our bodies are producing insulin. Insulin is not “bad,” rather TOO MUCH insulin. Insulin is an anabolic hormone, which means that it is responsible for tissue growth, especially “adipose tissue” or fat tissue. You might hear insulin termed the “fat storage hormone.” During the fasted state, the pancreas makes a hormone called glucagon, which works in opposition to insulin. Glucagon is the bodies main “catabolic” hormone and is responsible for breaking down fat. Basically, glucagon taps into our energy stores to provide fuel for our bodies when we are not eating. During the sleeping/fasting state, our bodies increase the production of leptin, a hormone that decreases hunger and glucagon which breaks down stored fat. Certain forms of intermittent fasting have also shown to decrease LDL cholesterol and improve HDL cholesterol, which can be protective against heart disease.
This table explains the physiological changes that are occurring during the waking/fed state and the sleeping/fasted state. (Disclaimer: lots of big science words!)
In summary: Intermittent fasting has been shown to be beneficial for weight loss and improvements in certain metabolic markers due mainly to the decrease in insulin production during the fasted state.
Intermittent Fasting and Digestion
The migrating motor complex (MMC) is responsible for moving undigested food into the colon. It is the “intestinal housekeeper,” making sure that undigested food and bacteria move through the intestines and out of the body. If food is allowed to sit in the gut, bacteria will feed off of it, producing gas. I often tell clients that it is as if you are brewing beer in your gut! This is what can lead to uncomfortable bloating a lot of people experience. The MMC is most active during the fasted state (in between meals and when we sleep.)
Although there have not been many studies conducted on the effects of intermittent fasting and digestion, in my own experience, I have seen improvements with digestion simply by implementing a 12-14 hour overnight fast. This allows ample time for the MMC to complete the task of moving waste through the entire digestive tract.
So if you struggle with bloating, constipation, or incomplete elimination, you MIGHT benefit from a 12-14 hour fasting window.
What to Eat During Eating Window
What you eat during the non-fasting window is just as important, if not more than fasting itself. Fasting is not going to make up for unhealthy food choices! It is very important that a person consumes adequate healthy fat, protein, and complex carbohydrates during their eating window.
When you break your fast, your blood sugar will be more sensitive since you have been fasting all night, so it is important that your meal is balanced, not filled with high sugar carbohydrates that will spike your blood sugar.
Who Should Use Caution with Intermittent Fasting
- Individuals who are taking blood sugar lowering medications
- Pregnant or breastfeeding mothers. (Avoid altogether!)
- Women with hypothalamic amenorrhea or women who are trying to optimize their fertility.
- Individuals who are currently battling or who have previously battled an eating disorder.
- Individuals with type I diabetes
Intermittent Fasting and Weight Loss
As I mentioned earlier, the research just does not support that intermittent fasting is more advantageous for weight loss compared to a typical calorie restricted diet. Intermittent fasting will shorten the eating window, which makes a caloric deficit a little bit easier to achieve. If a client is dealing with insulin-resistance, high cholesterol, or high blood sugar, intermittent fasting might be a potential strategy to be considered.
My Recommendation for Intermittent Fasting
Just like everything else that I share through this blog, remember that I am not giving you medical advice. Always speak with a medical professional about your personal health choices. This is simply my opinion, not medical advice.
Is intermittent fasting right for you? If it isn’t your jam, then don’t stress! Ultimately, you need to do what works best for YOUR body.
Have you tried intermittent fasting in any form? I would love to hear about your experience in the comments below! As always, if this post resonated with you or if you know someone who might benefit from reading, please share!
