When Intermittent Fasting Do Calories and Food Choices Matter?

Intermittent Fasting

When Intermittent Fasting Do Calories and Food Choices Matter?

Intermittent fasting is an effective tool for weight loss, but if your mindset is to starve yourself now so you can eat whatever you want during your eating window, you’ll be disappointed with your results.

When Intermittent Fasting…Does It Matter What Foods I Eat? [Video]

In this video, I share research that shows that intermittent fasting protects against weight gain even when calorie intake matches that of all-day-grazers.

However, I explain why that research does not give you a license to eat any foods with abandon during your eating window.

Do Calories Matter When Intermittent Fasting?

The first study I read on intermittent fasting, also called time-restricted eating (which is the name we often see used in research), was an iso-caloric study (1).

Iso-caloric means the calories consumed by the test subjects were the same as those fed to the control group.

When Intermittent Fasting Salk

Despite being fed the same amount of calories, the rats who consumed those calories within a shortened eating window were protected against getting fat.

So this study and similar iso-caloric studies make it seem like as long as we abstain from eating for about 16 hours, we can chow down, throw caution to the wind, and eat whatever we want for the remaining eight hours without fear of weight gain…maybe even achieve weight loss!


This is not the message we should be taking from these types of studies.

Food Choices are Important When Intermittent Fasting

If you are looking at intermittent fasting as a license to eat a whole pizza and a whole cake every afternoon you’re not setting yourself up for success.

I’ll share three reasons why:

1) These studies are iso-caloric, but subjects were fed a reasonable amount of calories.

Intermittent fasting mouse

So intermittent fasting is a great tool to help you lose weight, but it is not a license to gorge yourself on junk food.
2) Food choices matter just as much (if not more) than calories when it comes to losing weight. 

Many people have trouble losing weight because they are insulin resistant. I’ve covered this topic in other blog posts like this one on Insulin Resistance And Weight Gain.

Essentially, the cells of someone who is insulin resistant no longer respond to insulin properly, so carbohydrates and sugars are more easily converted to fat.

If you’ve been overweight for a long time, have a long history of poor food choices, or just notice that your body has a hard time losing weight, then you will likely not find weight loss success by eating cookies, cakes, and candies during your eating window.

3) There is some wisdom to allowing fasting periods within your eating window. 

In other words, it’s best not to continually graze for the entire eight hours or so that your eating window is open.

Fasting provides a period of time for your body to complete digestion which is a major metabolic process. Once digestion is complete your body can switch gears, and take care of cleanup and build up.

This is called autophagy, which is the clearing out of old dead cells and cell products to dedicate energy to tissue growth and repair.

Bottom Line:

You’re smart to use intermittent fasting as part of your overall weight-loss strategy but eat sensibly during your eating window for the health and benefit of your body.


(1) Hatori, Megumi, et al. “Time-restricted feeding without reducing caloric intake prevents metabolic diseases in mice fed a high-fat diet.” Cell metabolism 15.6 (2012): 848-860.

About the Author

Dr. Becky Gillaspy, DC graduated Summa Cum Laude with research honors from Palmer College of Chiropractic in 1991.

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