A Dietitian’s Review: Intermittent Fasting

Blog, Food

by Melinda D. Maryniuk, MEd, RD, CDE 

We review several different eating approaches in our “Dietitian’s Review” series with the goal of helping people who are looking to evolve their eating style towards better health. It’s important to emphasize that “going on a diet” is very rarely associated with long-term success with weight. We provide these reviews for anyone who wants to improve their health and is looking for an eating approach that will best fit their lifestyle and preferences.

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An intermittent fast is choosing to go without food for a specific period of time.  It can be confusing as there are many different ways to fast… and, know there is no one best way.  Choose the one that you think you’d have the best chance of following.  The popular choices of fasting diets include:

16:8 fast:  No food for 16 hours and eat only during an 8 hour window (such as between 11 am – 7pm).

20:4 fast: Food can only be eating during a 4 hour window each day (a meal and one to two snacks)

5:2 day fast:  For 5 days in the week you eat normally (aiming for smart, healthy choices) and for 2 days you fast (not consecutive days). During those fast days, you might allow yourself up to 500 calories.

What do I eat?

This meal planning approach is not about counting calories, restricting certain food groups or even weighing and measuring serving sizes.  Its only focus is on restricting the times when you can eat.  After that, you eat what you want.  However, this can also be its downfall, as you are not learning healthy habits and once the fasting phase stops, you are more likely to regain the weight you lost.  During fasting periods – drink plenty of water or other non-caloric fluids to stay hydrated.

Is it effective?

There is a growing body of research looking into the benefits of fasting.  There is evidence that fasting helps with weight loss, decreases insulin resistance and inflammation, increases energy levels and increases the loss of body fat.  However, it is common for people in the research studies to tire of the fast after a short period of time, and drop out of the study.  So for those who stick with it, it seems have some benefits – but many find they just can’t do it. Note:  Fasting is not recommended for children under age 18, pregnant or lactating women or those taking prescription medications (such as for diabetes) without consulting with your doctor.

What are some pros and cons?

Pros:  Easier for those who do not want to think about calories or portion sizes

Cons: In addition to hunger, many experience side effects including constipation, headaches and dizziness.  High drop-out rate.  Does not help establish long-term healthy eating patterns.

How do I learn more?

Note: There are many approaches to weight loss that can be successful for people.  My Weight– What to Know does not recommend a particular diet, but is happy to share facts about a variety of approaches. As with all meal planning approaches, regular exercise is recommended.

Eating a healthy diet and being active are both really important for being healthy, but for many people diet and exercise alone aren’t enough to help them reach their weight-loss goals. If this sounds familiar, read this fascinating article about what to do when diet and exercise aren’t getting you to where you want to be.

UPDATE: A recent study from the NIH suggests that a diet high in ultra-processed foods led to overeating and weight gain. Watch a Facebook Live episode that covers what to know about ultra-processed foods here:

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