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Intermittent Fasting Explained

If you have been listening to the news or anywhere on social media recently, you may have heard of intermittent fasting.  Although it is very trendy at the moment, the concept of periodically limiting intake at meals or the time frame for eating is nothing new. If you like to read history, you may remember how in earlier times, our ancestors did not have the convenience of supermarkets or of eating whenever a craving hit.  They went through seasons of feast, such as during harvest time, and famine, for example, when crops failed. In fact, many cultures throughout the world continue to practice periodic fasting as part of their cultural practices or simply for spiritual purposes.

At Carolinas Weight Loss Institute, we have been using successfully the practice of intermittent fasting for many years. However, in order to make it successful, we need to be aware of a few critical factors that will be summarized in this article. 

What Exactly is Intermittent Fasting?

Intermittent fasting is defined as a calorie restriction of 60% or greater of estimated energy needs for 2-3 days per week.  The form of fasting that is perhaps the most popular is time-restricted eating. In this type of fasting, a person consumes all meals within an 8-10 hour time frame most days of the week, equating to a 14-16 hour fast each day.  Another type is referred to 5:2 fasting, where a person eats normally for 5 days a week and restricts energy intake to approximately 25% of estimated needs (about 500-600 Calories) for the remaining 2 days. For the purpose of this article, let’s explore the trendy time-restricted eating.  

One of the main reasons people choose to take up intermittent fasting is for weight loss purposes.  Studies in humans show that this type of eating pattern may be as effective at promoting weight loss as daily calorie restriction.  Other studies in animals reveal improvements not only in weight but also body composition and metabolism with time-restricted feeding, even in the absence of reduced daily caloric intake. 

While eating in a time-restricted pattern it is still important to ensure proper nutrition.  This means that during the hours of the day that you are eating, you must consume nutrient-dense foods rather than those that are considered empty calories, such as foods high in sugar, highly-processed starches, and unhealthy fats.

Intermittent Fast- Weight Loss Connection

So how does time-restricted eating work to promote weight loss?  The body has a limited capacity for storing glucose, one of the body’s main fuel sources.  The primary organs in the body that store glucose includes skeletal muscle and the liver, which is able to hold 100-120 grams of glucose in its storage form, glycogen, which although doesn’t seem like a lot, it is usually enough to provide energy to the body during a 24 hour fast.  

During a prolonged period without eating, the glycogen storage gets depleted; so now the body begins to use a new source of energy, via the breakdown of fat tissue.  Once your body burns through its storage of glucose, many of the cells in the body can rely on fat for energy, while the brain can utilize ketones, which are a byproduct of fat metabolism.  

Incorrect Fasting Technique Can Lead to Crash in the Energy Level and Possible Muscle Loss

Some of the body’s cells need glucose, such as red blood cells (RBC).  The RBCs are critical to proper health and survival. They carry oxygen to all body cells which is important for energy production. RBCs can’t use ketones as a form of energy source so they require glucose. This is one reason why some patients experience extreme fatigue during prolonged fasting. In order to provide the RBC with glucose, during fasting, the liver is responsible for taking other molecules and converting them into glucose.  Some of these molecules can include protein from muscle tissue. This can be why some people who do extended fasts can experience muscle loss and elevated fasting blood sugar, as the body ramps up carbohydrate production from protein sources. This is a crucial clinical component that we monitor closely with our patients. As muscle loss is extremely detrimental to health and can lead to serious renal complications and kidney damage. One way to prevent excessive muscle breakdown is to monitor blood sugar with a glucometer and break the fast once you notice an increase in blood sugar. This way, you ensure the maximum benefit of the fast without the side effect of lean tissue loss. The use of glucometer is a new clinical component that we are now introducing with our patient population in order to be as specific as we possibly can with the fasting period. Patients are instructed clearly about the specifics of the glucometer and what numbers to watch for. So that the fasting process would occur in a healthy way without detrimental side effects. 

Additional Health Benefits

Some studies have found additional benefits for fasting besides that of weight loss.  During a fast, the body’s machinery for “cleaning house” ramps up and is more efficient in clearing the body of waste and cellular debris.  This helps to keep the mitochondria, which are the cells’ powerhouses, in working order and reduces oxidative stress and free radical production.  More current research is showing that reductions in oxidative stress lead to preserved learning and memory capacity with aging, while some animal models even point to slower progression of tumors and increased survival rates with certain cancers.

Is intermittent fasting for you?  It depends. For those who are more sensitive to drops in blood sugar and tend to get headaches, light-headedness, fogginess, or dizziness when meals are skipped, intermittent fasting might not be ideal.  Patients with a history of eating disorders should also exercise caution with any type of dietary and/or caloric restriction. Others, such as those who are either pregnant or breastfeeding, or patients who take insulin or other blood glucose-lowering medications should check with their physicians prior to embarking on an intermittent-fasting diet.  Particularly, medications may need to be adjusted for diabetics, followed by close monitoring of blood sugar.

Caution- Don’t Slow Down Your Metabolism

Since prolonged fasting can cause the resting metabolic rate to decrease, slowing down your metabolism, it is important to ensure that you are consuming an adequate number of calories daily if you are considering time-restricted eating.  This means that if you regularly skip breakfast (we highly advise against it), you may want to consider eating it later in the morning or make up for the missed calories and protein later on in the day.  Some ways to do this would be to increase portion sizes with lunch and dinner or to add some healthy snacks (containing protein and fat) in between meals to make up the difference.

Dr Lidia Adkins, PKT, DC, CFMP
Suzanne Doad, MS, RD, LDN