What is intermittent fasting?

You may have heard of this health and fitness trend, but intermittent fasting is really quite simple. It’s cycling periods of eating with periods of fasting. There are several different intermittent fasting methods, but the most common seems to be 16/8 where you fast for 16 hours and eat for 8 hours. For example, you may skip breakfast and limit your eating to 11 AM-7 PM. Other forms of intermittent fasting include a complete fast for 24 hours 1-2 days a week or significantly restricting your calories to 500-600 calories (on the fasting days).

I have had several clients like intermittent fasting because it is not a restrictive diet and it offers flexibility depending on what works best with your lifestyle. However, what does the research say?

Glance at the Research

  • This eight-week study of young males (with resistance training experience) showed that those who ate for 8 hours and fasted for 16 hours lost 16.4 percent of their fat mass, compared to less than 3 percent for a group who ate the same calories over a longer period.
  • A very small pilot study examined 10 participants on a short-term intermittent fasting protocol and they found it to be safe and possibly effective for reducing body weight and fasting blood sugar.
  • Intermittent fasting may prevent neuron damage in the brain
  • Animal studies have found an association between fasting and reduced risk of lymphoma
  • Correlation between fasting and reduced symptoms of arthritis
  • Fasting may promote longevity.
  • This study is a good review of literature on “alternate day fasting” or intermittent fasting. Both human and animal studies found alternate day fasting may be effective at reducing cardiovascular disease. Animal studies found alternate day fasting to be protective and reduce cancer risk.
  • This study on mice found that calorie restriction or intermittent fasting can help ameliorate age-related deficits in cognitive function.
  • Back in 2007, this study looked at 40 healthy adults during Ramadan (12 hour fast per day, aka intermittent fasting for 1 month) to evaluate improvements in inflammatory markers.  They found significant improvements in IL-6, CRP, and homocysteine (all markers of inflammation).
  • In 2012, another study validated that intermittent fasting (with Ramadan) reduces inflammation, blood pressure, body weight, and body fat percentage.

Why does it work?

For several reasons.

For one, when someone intermittently fasts they typically eat fewer calories throughout the day. When you limit the time you can eat, you are less likely to have late night snacking or overeating.

People are often successful because it is an easy to follow structure and intermittent fasting offers a lot of flexibility. For example, if you are someone that hates breakfast, you can start eating later in the day.

Finally, fasting triggers a process called autophagy where the body essentially kills off old or diseased cells.

Who is it not good for?

People who struggle or who have previously struggled with binge eating. I have had several patients who significantly overeat after their fasting period because they are simply starved. So instead of eating a small handful of trail mix they eat the entire bag. Also, if you have a history of anorexia it may trigger restrictive eating patterns again.

Those with significant adrenal dysfunction or poor stress response may not do well with intermittent fasting. When you fast, your blood sugar is lowered. When hypoglycemia occurs (or too low of blood sugar), your body produces cortisol (the stress hormone). High cortisol can cause weight gain, high blood pressure, anxiety, nervousness, and sleep disturbances.

If you are pregnant or breastfeeding. I don’t think I need to explain this one…. not the best time to restrict your calories.

Athletes. If you are training at a high intensity, intermittent fasting may not be the best option for you because your body needs fuel. It needs an adequate balance of protein and carbs to help with energy and muscle recovery.

Or if  you don’t feel good when your fasting!


If you want additional resources, consider reading Delay, Don’t Deny, The Complete Guide to Fasting, or The Scientific Approach to Intermittent Fasting.

Have you tried intermittent fasting? What was your experience with it? I would love to hear from you!

Kristin Oja, DNP, FNP-C, CPT

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