This post was written by Danielle Heuseveldt

Intermittent fasting (IF) is an eating pattern that has been gaining popularity for everything from weight loss, improving metabolic blood work to even extending life. Those are some bold claims! Given my affinity for self-experimentation, I decided to dive in and give it a try for a full month. In this post, I’ll go through what IF is, what the research tells us and share with you my experience.

What is Intermittent Fasting?
We probably all know what fasting means, abstaining from food and drink. Fasting intermittently means abstaining at recurrent periods and is not a new concept. For millennia, it has been used as part of many religious practices. For example, during Ramadan, Muslims fast from sunrise to sunset. Growing up Catholic, I experienced fasting every Ash Wednesday and Good Friday. And guess what? We all intermittently fast every day…it’s called sleeping!

IF started gaining traction a few years back as a weight loss tool when the book The Fast Diet was published (1). The authors suggest a 5:2 eating pattern – fasting two days per week and eating normally 5 days per week. In this case, fasting means taking less than 500-600 calories (1). This is considered a modified fasting regimen as opposed to a complete alternate day fast where you consume no food or energy containing drinks on alternate days (2). The authors claimed you could lose weight but also improve many of the metabolic factors that influence risk for diabetes and cardiovascular disease (1).

Another method of IF is a time-restricted regimen. Here, the daily feeding window is abbreviated and the fasting period is extended between 12-16 hours per day (2).

What Does the Research Tell Us?
While the research is certainly building for the positive effects of IF, it needs to be noted that most is based on animal studies and only a few human studies. While much more research is needed, a statistically significant decrease in weight was seen in most human intervention studies (2). Why is that? Most likely, because energy (calorie) consumption is lower through the week regardless of method (time restricted eating, alternate day fast or modified fast) thereby producing weight loss (1). It should be noted that alternate day fasting did not produce better weight loss results than daily calorie restriction but the time restricted regimen when aligned with our normal circadian rhythms might be helpful in maintaining optimal metabolic function (2). Finally, there may be some benefit on body composition when combined with a resistance-training regimen (3).

What about improving lab results which could be indicators for chronic disease? The research is even further divided with some studies showing a reduction in glucose, triglycerides, LDL (bad cholesterol) or inflammatory markers but most human interventions showing no statistical significance (2).

My Experience
When I told my husband I wanted to try IF, I was surprised that he a) had heard about it and b) wanted to try it with me. We decided on the time-restricted regimen as it would be the easiest for us to implement and to save the people around me from the hangry rage that would almost positively happen if I was restricted to 500 calories per day. We decided to fast for 16 hours per day, restricting our eating to an 8 hour window from 11:00a to 7:00p. I wanted to see if just the fasting part would produce any benefits so I kept my food intake identical to how I was eating previously. Hubs decided to just shorten his eating window and let the caloric chips fall where they may. Spoiler alert, his experience was way better than mine.

I had a few factors working against me. I am 100% a morning person. I wake up much like a Disney princess, smiling with the sun at 5:00a. I love lattes and all things breakfast…oh and I also workout early morning. Not eating until 11a really cramped my style if you know what I mean. I could have black coffee (insert sarcastic yay) and water (genuine yay) but that’s about it for the 6 hours between when I wake up and the eating window opens. My husband, on the other hand, would be fine not eating until lunch and though he also works out in the morning, it is later and therefore closer to the start of the eating window.

The hunger was terrible for about a week for both of us, I just happened to mind it more than he did. It was really distracting. Fortunately, after a week it subsided along with the low energy and fogginess I experienced before 11a. It was replaced for me, however, with a sort of high strung anxiety (similar to the feeling you get when you drink too many espresso shots). My husband didn’t experience this and might be one example how IF can affect men and women differently (4). My body may have perceived skipping my usual meals as a life threatening stressor. The anxiety would resolve after I ate and interestingly, I didn’t experience the dip in energy I sometimes would mid-afternoon pre-IF. I also found my usual painful menstrual symptoms subsided for the month and while I enjoyed that, it might have been coincidental or might be another reason why IF would not be so great for some women. IF may affect woman’s reproductive hormones which could affect fertility (4).

My workout performance did not suffer. In fact, I actually PR’d on one of my lifts and made it through our hours long weekend sessions of stand up paddle surfing without any perceived decrease in energy or strength.

We both noticed a substantial increase in satiety at meal times, getting fuller faster (which is the opposite of what you think would happen). We noticed less bloating by the end of the day and a substantial increase in water intake (to help alleviate the hunger). Given the shortened eating time period and decreased appetite, I can see where IF could set you up for nutrient deficiencies unless you plan your meals carefully.

As far as weight loss, my weight didn’t change at all but, per my Fit Bit scale, I lost 2% body fat and did notice a visual difference. I have since transitioned back to my normal eating patterns as the benefits did not outweigh the drawbacks. While my husband’s weight changed only modestly through the first month, he has decided to keep up with IF, and to date (2 months) has lost 14 lbs.

Much more human research is needed before we can call this an evidenced based approach or before I would recommend IF to my clients for weight loss or disease prevention. For some (like my husband), however, it might be as effective as daily calorie restriction but more palatable promoting better adherence. It is not without risk, maybe more so for women than men so if you’re considering trying it, you’ll definitely want to consult with a Registered Dietitian.

Be well!

(1) Orenstein, B. (2014) Intermittent Fasting: The Key to Long-Term Weight Loss? Today’s Dietitian, Volume 26, No. 12, page 40

(2) Patterson, R. E., Laughlin, G. A., Sears, D. D., LaCroix, A. Z., Marinac, C., Gallo, L. C., … Villaseñor, A. (2015). INTERMITTENT FASTING AND HUMAN METABOLIC HEALTH. Journal of the Academy of Nutrition and Dietetics, 115(8), 1203–1212.

(3) Hayward, S., Outlaw, J., Urbina, S., Burks, B., Holt, J., Stone, M., … Wilborn, C. (2014). Effects of intermittent fasting on markers of body composition and mood state. Journal of the International Society of Sports Nutrition, 11(Suppl 1), P25.

(4) Kollias, H. Intermittent Fasting for Women: Important Information You Need To Know.

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