In this week’s episode of the Sports Medicine Weekly Podcast, Dr. Brian Cole discusses intermittent fasting.

Chances are, you’ve heard about Intermittent Fasting (IF). It’s a popular weight loss method, and a trending health and wellness topic. IF is not a diet, but a patterned approach to eating that can result in weight loss. However, a growing body of research shows its benefits may extend beyond that. But is the hype justified? Is IF a fad, or a nutritional approach based on scientific fact?

The Science Behind IF

Science shows intermittent fasting can help weight loss. The food we eat is broken down by enzymes in our gut and eventually ends up as molecules in our bloodstream. Carbohydrates, particularly sugars and refined grains, like white flours and rice, are quickly broken down into sugar, which our cells use for energy. If our cells don’t use it all, we store it in our fat cells as fat. But sugar can only enter our cells with insulin, a hormone made in the pancreas. Insulin brings sugar into the fat cells and keeps it there.

Between meals, as long as we don’t snack, our insulin levels will go down and our fat cells can then release their stored sugar, to be used as energy. We lose weight if we let our insulin levels go down. The concept behind IF is that the fast allows insulin levels to go down far enough and for long enough that we burn off fat.

Why Does Timing Matter?

Why does simply changing the time of our meals make a difference in our body? A review of the science behind IF published in the New England Journal of Medicine sheds some light. Fasting is evolutionarily embedded within our physiology, triggering several essential cellular functions. Flipping the switch from a fed to fasting state does more than help us burn calories and lose weight. The researchers combed through dozens of animal and human studies to explain how simple fasting improves metabolism, lowers blood sugar levels; lessens inflammation, which improves a range of health issues from arthritic pain to asthma; and even helps clear out toxins and damaged cells, which lowers risk for cancer and enhances brain function.

Evidence-based Benefits 

There are a number of benefits to IF that are backed by animal and human studies, including:

  • IF helps you eat fewer calories while boosting metabolism to effectively lose weight and visceral fat.
  • IF reduces insulin resistance and lower blood sugar levels in men.
  • IF can reduce oxidative damage and inflammation in the body and potentially provide benefits against aging and development of numerous diseases.
  • IF can improve numerous risk factors for heart disease, such as blood pressure, cholesterol levels, triglycerides, and inflammatory markers.
Types of Intermittent Fasting

There are many different types of time-restricted fasting, but two of the most popular and nutritionally sound are the 16/8 and 5:2 methods.

16/8 Fasting

In this approach, people fast for 16 hours a day and consume all of their calories during the remaining 8 hours. Proponents of this method believe it supports the body’s circadian rhythm, or internal clock. The easiest way to follow the 16:8 diet is to choose a 16-hour fasting window that includes the time spent sleeping and try to consume a majority of daily calories during the middle of the day. Eating healthy foods and avoiding junk food leads to the best results, but there are really no restrictions on the types or amounts of food that a person can eat during the 8-hour window.

The 5:2 Method

This is another one of the better-known fasting plans. With this approach, you eat what you want for 5 days each week and then significantly limit calories on the remaining 2 days. The 5:2 diet restricts calories to just 500 a day for women and 600 a day for men on two fasting days. On the other five days, you eat normally, without overindulging. Eating normally means that you eat the number of calories your body needs to perform daily functions.

Potential Side Effects

Of course, there are side effects to consider. When fasting, some people experience digestive issues, such as nausea, diarrhea, constipation, and bloating. Headaches are also a potential side effect. In addition, intermittent fasting may result in low blood sugar and make you tired and weak. And finally, there are some groups of people who should not participate in intermittent fasting, including children, pregnant women, diabetics, people with a history of eating disorders, and those on certain medications. As always, it’s important to consult with your doctor or a nutrition expert before you starting an intermittent fasting plan to determine if it’s safe for you.

Authored by Zach Meeker, Research Assistant for Midwest Orthopaedics at Rush University Medical Center


De Cabo, R., Ph.D., Mattson, M., Ph.D., (2020). Effects of Intermittent Fasting on Health, Aging, and Disease. New England Journal of Medicine.

Teruya, T., Chaleckis, R., Takada, J. et al. Diverse metabolic reactions activated during 58-hr fasting are revealed by non-targeted metabolomic analysis of human blood. Sci Rep 9, 854 (2019).

Barnosky, A., Hoddy, K., Unterman, T., Varady, K., Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings, Translational Research, Volume 164, Issue 4, 2014, Pages 302-311, ISSN 1931-5244,

Dong TA, Sandesara PB, Dhindsa DS, et al. Intermittent Fasting: A Heart Healthy Dietary Pattern?. Am J Med. 2020;133(8):901-907. doi:10.1016/j.amjmed.2020.03.030

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