5 Common Mistakes People Make with Intermittent Fasting

Intermittent fasting is a hot topic these days. This type of eating pattern involves an “eating window” and a “fasting window,” rather than a style of eating that pertains to food groups or macronutrients. The length of each window can differ depending on the style you choose to adopt.

Fasting, documented throughout history for its benefits, has been adopted all around the world and is now accepted as a way to support human health. Some published data reports benefits of intermittent fasting such as weight loss, improved mental clarity, improved metabolism, better glucose regulation, and the potential to slow natural aging conditions, among others.1

The most common forms of intermittent fasting are:

Daily intermittent fasting: eating within a 4-10-hour window and fasting for 14-20 hours

24-hour fast: fasting for 24 hours, typically 1-2 times a week  

5:2 protocol: restricting calories to 20-25% of your usual intake for two nonconsecutive days in a 7-day time frame and consuming calories as per usual for the other 5 days

Regardless of the intermittent fasting form people choose, they tend to make the same five common mistakes:

1. Not eating the suggested foods

This is by far the biggest mistake you can make when trying to implement an intermittent fasting schedule into your life. In order to fast successfully, you generally need to be able to control your appetite for a long stretch of time (~12-24 hours). Food choices will make this practice easy or hard, and you don’t want this to be hard! Metabolism works like a hybrid car: For fuel you can either burn glucose or fats and the byproducts of fat metabolism, ketones.

A carbohydrate reliance can make fasting difficult because our blood glucose is constantly fluctuating, and in turn our appetite is constantly fluctuating. An easy way to fast is to follow a low-carbohydrate diet where the focus is on quality proteins and fats. This way you are satiated for longer periods of time and allow for the metabolic flexibility to tap into fat stores for fuel during the fasting window. You may even end up going in and out of ketosis without even trying, just by virtue of the diet and the long periods of time between meals. The satiety factor of a low-carbohydrate diet can work in your favor during the fasting window.    

2. Not being prepared

Intermittent fasting goes against society’s “normal” eating patterns. If you participate in daily intermittent fasting, you are probably eating at odd times of the day, breakfast at 11 AM or dinner at 4 PM, for example. If you work a standard 9-5 job, this can be challenging, but all it takes is a little preparation. Instead of eating breakfast at home, pack your meal to eat later, and the same goes for trying to eat dinner earlier. When you fail to prepare for your eating window, you might end up gravitating toward poor food choices when it’s “time to eat” or get stuck eating late into the evening.

3. Not eating enough calories

Although intermittent fasting is typically used as a strategy to inadvertently reduce overall caloric intake, restricting calories too much could have certain negative consequences. This is most pronounced in athletes and women. For athletes, activity level and goals should be taken into consideration when choosing an intermittent fasting protocol to support and enhance performance, muscle growth, and recovery. If you struggle to consume enough calories in your allotted “eating window,” consider extending your window to support your goals and optimize your health.

4. Restricting all day and binging at night

Have you ever gone an entire day without eating, only to come home later and clean out the entire pantry, fridge, and everything in between? Waiting until the end of the day to consume all, or the majority, of daily calories can work for some people but in others may trigger binge eating. This could lead to consuming more food than you normally would have, had you spread your meals throughout the day. In addition, overeating in the evening, and too close to bedtime, can result in poor sleep and disruption of circadian rhythms. You may wake up not feeling your best by eating in this way, and the whole reason for intermittent fasting is to feel better! Shifting the eating window to earlier hours of the day, for example 11 AM to 7 PM, may prevent overeating or binging into the late hours of the night.          

5. Making exceptions for what you consume outside your “eating window”  

This is a very common mistake and is actually quite controversial. To make things simple, anything with calories, and therefore energy, “breaks a fast.” This means no butter in your coffee and no glass of wine before bed. We hate to break it to you, but a true fast includes water only. With that said, if you are intermittently fasting for weight loss, herbal tea and black coffee are okay to consume outside your eating window, as they do not contribute to overall calorie intake. It is in your best interest to avoid zero-calorie sweetened beverages as well, since certain sweeteners, calorie-free or not, can actually trigger an insulin response and negate many of the benefits of fasting.2    

For more information on intermittent fasting, please visit the Metagenics blog.

Before starting any diet or making changes to your diet, please consult your healthcare practitioner.


  1. Mattson MP et al. Impact of intermittent fasting on health and disease processes. Ageing Res Rev. 2017;39:46–58.
  2. Pepino MY et al. Sucralose affects glycemic and hormonal responses to an oral glucose load. Diabetes Care. 2013;36(9):2530-2535.

Submitted by the Metagenics Marketing Team

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