Intermittent Fasting for Weight Loss

Learn about the benefits & different types of IF

By Pam Nisevich Bede, MS, RD, CSSD, LD
ZonePerfect Nutritionist

December 2019

Fasting, or intermittent fasting (IF), might be today’s new buzz term but in reality, people have been fasting for spiritual, medical, or other reasons for centuries. Let’s uncover some of the background and varieties of approaches out there!

What you need to know about Intermittent Fasting

In today’s world of food abundance and linked health conditions ranging from obesity to type 2 diabetes and the umbrella term of metabolic syndrome, the age-old approach of fasting just might -finally!- move you towards your goals. Proponents of IF assert that the approach to limiting food intake to a small window of time allows for the body’s digestive system to take a break and recover while preventing a multitude of insulin surges and dips across the day.

Intermittent Fasting

Common types of IF

There are various approaches to IF and in reality, there may be more approaches than there are clinical studies to support this way of eating! There have been several proposed protocols for intermittent fasting, from skipping one meal per day to eating only every other day. To date, despite IF being a buzz word, there are few well-controlled, scientific studies investigating the effects of intermittent fasting on health, body composition, or even performance in athletes. There are key differences (and quite a few similarities) across variations. Here’s what we know to be true about IF so you can make an informed decision about whether incorporating this habit into your day to day diet might move you towards your goals.

Common types


A common approach to IF, 16:8 appears to be more achievable than a more restrictive plan like 5:2 which calls for 2 days of extremely restrictive intake. 16:8 stands for 16 hours of fasting followed by an 8-hour window of “feeding” (you don’t have to “feed” the whole time!). 16:8 is a reasonable choice for many because if the kitchen is shut down after dinner, one needs simply sleep, skip breakfast, and fight hunger until lunch rolls around. This approach can work to promote weight loss as it eliminates mindless after-dinner snacking and forces one to recognize hunger signals before diving into lunch. Finally, for those incorporating early morning exercise into their routine, this plan allows for “training low” which may burn off additional calories and energy stores. Pro Tip: Training low should only be employed on occasion and on light workout days- never on race day and never before a crucial workout since hitting the (low glycogen) wall is a real possibility!


The Warrior Diet

This diet schedule is a variation of a 24 hour-long fast and promotes a single, healthy meal per day (typically dinner). The theory- just a theory- goes that this pattern of eating is in sync with humans’ circadian rhythm and will promote general health while “removing harmful toxins from the body”. Research on this approach is limited but, in an 8 week study comparing 3 meals a day versus 1, those fasting significantly reduced fat mass and lean mass tended to be greater. However, hunger steadily increased during the 8-week study period with only 1 meal per day, suggesting that appetite hormones did not acclimate.

The Warrior Diet

Alternate-day fasting

Alternate-day fasting is when food is consumed for 24 h, then restricted for 24 h (you can have all the water you’d like) for every 2-day cycle. It’s a common protocol for IF studies on animals but we don’t have much data on humans. One small study showed that across 21 days, alternate-day fasters improved select lab values and lost about 2.5 ± 0.5% of their body weight including 4 ± 1% of fat mass. In other words, depending on how much you have to lose, this practice might produce some significant results and other health benefits.


Making IF work for you

Remember that the “feeding” or eating window is not a free for all; focus on the nutritional quality of the meals that are consumed. Nutrients such as protein, fat, fiber, vitamins, and minerals are essential for good health and, since nutrients are not consumed while fasting, they are especially important when breaking the fast. In addition, drinking water and adding in electrolytes as needed is important in order to both stay hydrated and to alleviate hunger. And when you break that fast, try aiming for a moderate intake of carb so as not to overwhelm blood glucose levels. Instead, ease into eating with higher protein, higher fat, and lower carb choices.

It doesn’t happen overnight

It takes about 3-6 weeks for the body to transition or adapt to IF. During this time both the body and brain adapt to the new eating schedule. This period isn’t always easy; restricted eating has been anecdotally associated with extreme hunger, irritability, loss of strength, loss of libido, and other negative side effects. BUT once you’ve adapted, research shows that hunger levels may decrease and mood could become more positive compared to before the fasting program started.


Skip IF if the following applies to you….

IF is not typically recommended for athletes in heavy training and competition, not recommended for pregnant or breastfeeding women, not recommended for those who have a history of disordered eating or an eating disorder, not recommended for certain genetic metabolic conditions, and it hasn’t been studied exhaustively. Anecdotally, success with IF can occur for a plethora of reasons. Motives include a forced reduced calorie intake and therefore weight loss; a low energy state potentially leading lead to a state of ketosis; and, perhaps most importantly, a more thoughtful connection with food in which individuals become more mindful of intake.

IF and gender: what you need to know

Studies that exist on IF suggest that both genders respond to the effects of fasting and both genders have similar rates of weight loss. In regard to hormonal differences and disruption, certainly women who are malnourished should not fast as excessive weight loss and unhealthily low levels of body fat can lead to amenorrhea or menstrual dysfunction and the ill effects that follow. Across both genders it’s important to note that fasting is not necessarily easy. We humans are hardwired to seek food for survival and these innate signals are put in place to drive us to refuel. So long fasts are not always easy and if you experiment with IF and constantly feel poorly or ill, then seek advice from your health care provider and certainly reconsider this approach; IF is certainly not the only way to achieve the health or wellness benefits you may be seeking!

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