Fasting, Hormones, & Health Part 1: Intermittent Fasting

Intermittent fasting is one of the many trends in the diet and exercise world that continues to gain momentum. As Intermittent fasting (IM) continues to grow in popularity, more research and data are rolling out that support intermittent fasting as more than just a fad.

In Part 1 of our series “Fasting, Hormones, & Health” we’ll guide you through the basics of what Intermittent Fasting is, how it works, and even how to practice it. Then, in Part 2 (coming soon), why optimal hormone levels are vital—not only for our overall health but also in achieving greater success with intermittent fasting (and weight loss in general).

Let’s first take a closer look at intermittent fasting: the types, health benefits, and how to practice it. That way you can decide if IM fasting is right for you and your health goals!

By: Alyssa, RDN, LD

What is Intermittent Fasting?

Intermittent fasting (IM) involves alternating between periods of fasting and eating. This type of eating is often called “cycles” or “patterns” of fasting. What is unique about it? Rather than a typical diet that focuses on WHAT to eat, intermittent fasting focuses on telling you WHEN to eat.

The idea of fasting isn’t about “starving” yourself. In fact, most of the time you should be consuming the exact number of calories when you are intermittent fasting as a normal day. The average person typically eats bigger meals during a shorter time frame. Intermittent fasting is a way of scheduling your meals and time of eating so that you get the most out of them.

Where Did Fasting Originate?

Even though it’s a popular trend right now, intermittent fasting isn’t new. The origins of the practice of fasting date back to ancient times where it was a common practice to fast to help heal the body. It’s also originates from our hunter-gatherer days, where we would go for longer periods of without eating due to the nature of acquiring food. Additionally, IM fasting also has been practiced in religion where it’s said to help deepen your connection to your faith.

More recently, this topic has gained interest because of its many health benefits.

How Does Intermittent Fasting Work? (The Science Behind IM Fasting)

One reason intermittent fasting is thought to be effective is because it increases your body’s responsiveness to insulin. Insulin, a hormone that is released when you eat food, causes your liver, muscle, and fat cells to store glucose.

During the fed state, your body is digesting and absorbing food. This state lasts for three to five hours after consuming food. This causes your insulin levels to rise, which makes it very hard for your body to burn fat. After that timespan, your body goes into what is known as the post-absorptive state where your body isn’t processing a meal. The post-absorptive state lasts 8-12 hours after your last meal, which is when you enter the fasted state.

In the fasted state (12 hours after your last meal), blood glucose levels drop. This leads to a decrease in insulin production, signaling your body to start burning stored energy (carbohydrates). After 12+ hours of fasting, your body runs out of stored energy and then begins burning stored body fat.

This is one of the reasons people will lose body fat without changing what they eat or how much they eat. Fasting puts your body in a fat burning state that you rarely can make it to during a normal eating schedule.

How do you practice intermittent fasting?

24-Hour Fast: Also known as the 5:2 method. Involves a 24 fast 1-2 days of the week and eating normally for the remaining 5-6 days.

Alternate Day Fasting: This type of fasting alternates between feeding and fasting days with the option for “modified” fasting days. Meaning you eat a normal diet one day and either completely fast or have one small meal (less than 500 calories) the next day.

Time-Restricted Eating: This is the most popular type of intermittent fasting. It involves fasting within a restricted time or “eating window” each day. 16/8 and 14/10 are common examples of time-restricted fasting

This means fasting for 16 hours and eating within an 8-hour time-frame. During the fasting hours, you’re “allowed” to drink water, tea, and black coffee. You can also take supplements during the fasting period, if they’re all non-caloric (AKA skip the cream and sugar).

If you are interested in trying to incorporate IM fasting, I advise a fast overnight. This is most natural for our bodies. A 12- to 14-hour fast (8 p.m. to about 8-10 a.m. for example) is a great place to start. After a few days of trying out a 12-14 hour fast, you can see if you are able to make it 16 hours. Know that some days might be easier than others, as it does take some time for the body to adjust.

Additional Fasting Tips:

It’s important to not reduce your calorie intake for the day. You should still be consuming the recommended amount of calories, but now in a shorter window.
Drink water! It’s okay to drink black coffee/tea during your fasting window, but also drink plenty of water to stay hydrated.
Practice mindful eating when consuming meals.
Exercise during the eating window, as exercise can trigger hunger.
Fasting is not recommended for:
- People with a history of eating disorders.
- Women who are pregnant or breastfeeding.
- Those under the age of 18.

Recommended Foods while Intermittent Fasting:

While the fasting methods do not specify which foods to eat and avoid, it is still encouraged to focus on healthy eating habits.

Healthy Eating guidelines encourage the following nutrient-dense food choices:

Vegetables, including a variety of dark green, red and orange. Also legumes (beans and peas), starchy and other vegetables.
Fruits, especially whole fruits
Grains, at least half of which are whole grains
Dairy, including fat-free or low-fat milk, yogurt, and cheese, and/or fortified soy beverages and yogurt
Protein foods, including seafood (8 or more ounces per week), lean meats and poultry. Also eggs, legumes (beans, peas, lentils), soy products, nuts, and seeds.
Oils, including those from plants, such as canola, corn, olive, peanut, safflower, soybean, and sunflower oils. Including those present in whole foods such as nuts, seeds, seafood, olives, and avocados.

Main Health Benefits of Intermittent Fasting:

Weight Loss: Several human studies have found that fasting has been associated with significant DECREASE in body weight, body fat, and waist circumference. A recent study in 2020 found that using intermittent fasting to treat obesity was highly effective, resulting in 8-13% decrease in body weight among participants.
Reduction of Body Fat: There have been studies that have protein intake and resistance training, IM fasting and exercise can help improve fat loss while maintaining fat free mass (aka muscle mass) compared to daily calorie restriction diets.
Reduce insulin resistance, lowering your risk for type 2 diabetes. IM fasting has been shown to have major benefits for insulin resistance and led to an impressive reduction in blood sugar levels. (10). In human studies, fasting blood sugar has been reduced by 3-6% over the course of 8-12 weeks in people with pre-diabetes. Fasting insulin has been reduced by 20-31%. (10)
Improve Inflammation: IM fasting has also been linked to a reduction of inflammation in the body, another key driver of many common disease. 17, 19).

Other Potential Health Benefits:

Brain Function and Memory: It may improve mental acuity and concentration. And there’s some early research to support that idea. A study published in November 2021 in MolecularPsychiatry found that fasting every other day may enhance memory
May help prevent Alzheimer’s disease. Recent studies in rats and mice show that IM fasting may delay the onset of Alzheimer’s or reduce its severity (29Trusted Source, 37Trusted Source). In addition, animal studies also suggest that fasting may protect against other neurodegenerative diseases. This includes Parkinson’s disease and Huntington’s disease (29Trusted Source, 39, 40Trusted Source).
Reduce blood pressure: The link between lower systolic blood pressure and IF appears in both animal and human studies, according to a review published in March 2019 in Nutrients. And a study published in September 2020 in the European Journal of Nutrition found that IF led to even greater reductions in systolic blood pressure than another diet that didn’t involve defined eating times.
May help to prevent cancer. Promising evidence from animal studies indicates that intermittent fasting or diets that mimic fasting may help prevent cancer. Research in humans has led to similar findings, although more studies are needed (26Trusted Source, 27, 28Trusted Source).

The Bottom Line with Fasting

Intermittent fasting is a very popular trend for weight-loss, but its benefits extend way beyond that. There are many to start practicing intermittent fasting. Approaches and results can vary. It’s important to try methods that make you happy and don’t cause your mind or body any harm.

If you are interested in learning more about intermittent fasting, consider speaking with a nutrition expert. We offer a nutrition guidance program to all our current patients to help you learn more about general nutrition topics, including intermittent fasting. Or, check out our weight loss program here. Just fill out our initial consultation form to get started with either process!

Now that you know how intermittent fasting works and how it can affect our hormone levels (namely, insulin)—be sure to check out Part 2: “Hormones & Weight Gain As We Age.” We’ll be publishing that in a couple weeks, so be on the lookout!

Related Research

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