Foodie Friday – A Registered Dietitian’s Guide to Intermittent Fasting

Welcome to another guest post by our fabulous resident R.D – Serena. Today, she’ll break Intermittent Fasting down for us. Being a huge fan myself, the topic is very near Take it away, Serena! 

Today we are talking about one of the latest and greatest diet crazes: intermittent fasting (IF)! As a dietitian, I get asked about IF all the time.

What the heck is it?? Basically its just a fancy way of saying sometimes you intentionally skip meals. IF is the practice of intentionally abstaining from food, a practice for religious purposes, but was found to have numerous health benefits and consequently has gained popularity.

The way you intermittent fast is entirely up to you. You can choose to fast for entire days, consuming only non-caloric beverages, while consuming whatever you want the other days of the week. Alternatively, you can choose to eat a very low calorie diet twice a week (such as 500 calories) with consumption of whatever you want the other days of the week. Lastly, you can choose to partake in daily fasts ranging anywhere from 12-18 hours a day. The options are endless, but the research suggests that IF can help you lose 3-24% body weight in as little as 6 months.

Research also suggests that intermittent fasting also may decrease inflammation, improve blood markers which indicate good health, regulate sleep and potentially decrease the risk of cancer. Athletes should remember that lifting and cardio both generate pro-inflammatory “oxidative species” and diet is a prime way to decrease inflammation.

It is worth mentioning, that research suggests the weight loss results from IF are similar to simple daily calorie restriction. However, intermittent fasting offers the additional benefits listed above.

Okay, so let’s forget about research. Now that we know science suggests that its safe and effective, let’s talk about who can benefit from IF and how to implement it.

Good news! IF is for anyone! And while studies have mostly been done on the obese and overweight, many athletes have found that regularly occurring, fasted workouts help prolong that hitting-the-wall-feeling from happening during endurance activity. Be cautious however if you have a history of disordered eating or anorexia. Intermittent fasting is the practice of abstaining from food and restricting intake and could be “triggering” for those with a history.

If you are new to IF, I highly recommend trying a “time restricted feeding” window to start. Simply, set a rule not to snack after dinner, and a rule as to what time you can break your fast the next day. I find it fairly easy to stop eating after 8pm and resume eating at 12pm the next day, resulting in a 16 hour fast. Studies have shown that a fast as small as 12 hours can have major benefits, so even a fast as minimal as 8pm-8am may help you reach your goals.

When you first start IF, you may find it difficult to skip breakfast. Caffeine is a fabulous appetite suppressant and 8-24 ounces of black coffee or tea are helpful in aiding a fast. Green powders with less than 30 calories per scoop (such as Amazing Grass’s Green Powders) are a satiating, great way to replace the lost micronutrients you lose by skipping breakfast.

You may need to adjust your workout schedule to accommodate your fast. Unfortunately, there’s limited research on the subject, but I personally find that fasting after a high intensity workout can be really difficult, while fasting after endurance-based workouts or heavy lifting sessions is more doable. Its important to note that fasting pre- and post- workout may be detrimental if your goal is to gain muscle mass, since you’re missing out on the anabolic hormone insulin which is stimulated by eating carbohydrate.

Ultimately, IF is a really powerful tool and can be really helpful for those with significant weight to lose as well as those with “vanity” pounds to shed. Playing around with a fast as little as 12 hours a day can provide a powerful benefit to your blood markers and your waistline.


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2. Arumugam TV, Phillips TM, Cheng A, Morrell CH, Mattson MP, Wan R. Age and energy intake interact to modify cell stress pathways and stroke outcome. Ann Neurol. 2010;67(1):41-52.

3. Harvie M, Wright C, Pegington M, et al. The effect of intermittent energy and carbohydrate restriction v. daily energy restriction on weight loss and metabolic disease risk markers in overweight women. Br J Nutr. 2013;110(8):1534-1547.

4. Siervo M, Faber P, Lara J, et al. Imposed rate and extent of weight loss in obese men and adaptive changes in resting and total energy expenditure. Metabolism. 2015;64(8):896-904.

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