Intermittent Fasting: Explained

7 Minute Read

Intermittent fasting is a HOT topic right now, and for good reason! Intermittent fasting is a great way to start setting a new pattern of eating into your daily routine if you are looking to become healthier on a cellular level. Feeling a bit confused? No worries, this blog post will give you all the info you need to get started AND to understand how this will change your health and body!

What is intermittent fasting?

Intermittent fasting is a pattern of HOW you eat food throughout the day. Although it isn’t a “diet” on its own, it certainly can be combined with diets such as ketogenic or paleo ways of consuming food. Keep in mind that intermittent fasting is a pattern of when you should be eating and will have many great benefits to the body (see below!). However, WHAT you are eating is just as or even MORE important than how you are eating. If you aren’t quite ready to make a big change to what you are eating, intermittent fasting certainly is a great way to start on your health journey.

Types of Intermittent Fasting

Intermittent fasting types differ in the length of your fasting and fed windows. As you will see below, the first number is the hours you are fasting and the second number indicates the hours you are fed (eating).

12:12 - Fast for 12 hours: Eat within 12 hours. A 12:12 fast is pretty common for people even when they aren’t trying to fast. Let’s say you eat breakfast at 7am and finished dinner/snacks by 7pm. You will end up fasting for 12 hours.

16:8 - Fast for 16 hours: Eat within 8 hours. A 16:8 fast is a great place to start if you want to dive into intermittent fasting. There are several options, but one common way is to push when you would normally have breakfast to 4 hours later. You can have water, herbal tea, and coffee in the mornings.

18:6 - Fast for 18 hours: Eat within 6 hours. A 18:6 fast can initially be more challenging, so I would suggest starting with a 12:12 or a 16:8 and build up to an 18 hour fast.

20:4 - Fast for 20 hours: Eat within 4 hours. A 20:4 fasting schedule is by far the most challenging, so again, start with a 12:12 or a 16:8 and build to this if you want to increase your fasting window.

What happens to my body while I am fasting?

First, let’s talk about what happens when you eat! Once you start consuming calories, your digestive system kicks into gear to break down that food so it can absorb nutrients, such as carbohydrates, fats, and proteins. One major hormonal response to consuming calories, especially carbohydrates is the release of insulin from your pancreas. Insulin will cause sugar (glucose) to enter into your cells to be used for energy. Think of insulin as the hormone that opens up your cell to allow sugar to enter.

We called this the fed state. When your body is in the fed state, it will use glucose for energy, and will NOT use fat for energy. In addition, if your body doesn’t need all of this glucose energy right now, it will start to store it in fat cells (aka adipocytes).

Once this food has gone through the digestive system, we move into the post-absorptive state (about 8-12 hours after your last meal). In this state, insulin levels become very low, meaning the body can now break down fat for energy. So, your body needs to be in a fasted state to burn fat.

What are the benefits of fasting?

Fasting has numerous benefits to the body that stem from hormonal changes as well as your body becoming more adapted to burning fat for energy. Weight loss is a common effect that people are looking for and this is supported by studies. Interestingly, fat loss due to fasting isn’t just due to a decrease in calories. The hormonal changes that occur during a fast are just as important as a reduction in calories.

When fasting, studies result in a decrease in fasting insulin, fasting glucose and a reduction in inflammatory markers. Before we go on, let’s talk about the importance of these known effects. We talked about how an increase in blood glucose will increase insulin, resulting in fat storage. Blood glucose increases can also increase inflammatory markers in the body. Chronic inflammation will lead to fat gain and ALL chronic diseases. Blood sugar regulation is probably the most important in fat loss and decreasing risk for chronic disease!

Studies also show improved insulin sensitivity, which is how well your cells will respond to insulin. If your cells do not respond well to insulin, your body has a hard time taking glucose from the blood and using it for energy (the door won’t open!). All of this “leftover” blood glucose will end up being converted to fat if it isn’t used. Therefore, we really want our cells to respond to insulin to decrease blood glucose levels.

Along with weight loss and decreased chronic disease risk, fasting has also been shown to have improved effects on aging and overall lifespan. One hypothesis behind an increased lifespan is that fasting decreases cellular exposure to free oxygen radicals, which damage our cells. Cumulative damage to free radicals over a lifetime causes more damage and inflammation.

During the fasting process, your body is able to remove damaged proteins and other damaged structures. Reducing damaged parts will increase overall health by reducing chronic conditions such as diabetes, cardiovascular disease, autoimmune diseases, cancer and neurodegenerative diseases.

Besides the beneficial hormonal changes and reduction in free radicals, your body will produce more ketones that have a variety of positive effects on your brain, physical abilities, and protection against disease. Ketones result when fat is broken down and are heavily used by the brain for energy.

In addition, ketones can actually affect what genes are turned on or off in your cells. So, they aren’t just used for energy, but can also act as a signaling molecule. Genes affected by ketones are thought to influence both health and the aging process.

Specifically, genes that increase antioxidant defenses will increase, which means the body can fight oxidative stress from environmental free radicals. DNA repair and proteins quality control will also be enhanced. Mitochondrial production also increases, which are responsible for producing energy in your cells. Increased mitochondrial function allows for more sugar and fat to be used for energy. Lastly, autophagy will be affected, which is the breakdown of old and damaged cells. Essentially, there is a “cleaning” out of both damaged proteins and cells.

How will I feel on intermittent fasting?

The first several days of intermittent fasting will be the hardest while your body adjusts your blood sugar balance and your brain starts to listen to what your body is doing! After about a week or so, you will start to reap the benefits of intermittent fasting. Common adjustments people will feel: weight loss, more energy, better memory, improved executive functioning, better endurance, improved balance and coordination, and a decrease in joint pain.

Other effects of intermittent fasting that people observe is lower blood pressure, lower cholesterol, decrease in visceral or belly fat, and a decrease in both blood sugar and insulin levels.

What should I eat during my eating window?

I always recommend eating REAL whole foods! Check out my blog post what to eat for recommendations. You should be focusing on proteins, vegetables, and healthy fats while staying away from added sugars and other processed ingredients. Your body will thrive best on real food!

What are the best foods to break a fast?

After you have completed your intermittent fast, your first meal is very important to gain the optimal benefits! Ideally, you want to break your fast with some protein first or bone broth. If this isn’t an option, you can break your fast with a combination of EITHER fat and protein OR fat and carbohydrates. It is best if you DO NOT mix fat and carbohydrates together.

What’s next?

Get started on your fast! You can use an app on your phone to help countdown and track your fasts. My favorite is the Zero app. Stay hydrated and let me know if you have any questions!

Sources for this post include:

De Cabo, R. and Mattson, M., 2019. Effects of Intermittent Fasting on Health, Aging, and Disease. New England Journal of Medicine, 381(26), pp.2541-2551.

Mattson, M., Longo, V. and Harvie, M., 2017. Impact of intermittent fasting on health and disease processes. Ageing Research Reviews, 39, pp.46-58.

Patterson, R. and Sears, D., 2017. Metabolic Effects of Intermittent Fasting. Annual Review of Nutrition, 37(1), pp.371-393.

Sutton, E., Beyl, R., Early, K., Cefalu, W., Ravussin, E. and Peterson, C., 2018. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metabolism, 27(6), pp.1212-1221.e3.

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