Today's post is a really popular topic. So I wanted to give you some facts and research on intermittent fasting (IF) so that you can make educated decisions for yourself and determine if this is a good method for weight loss and/or health!
To start, I want you to know that IF is not the only or best way to lose weight. It just may be a viable option for some people and there are studies proving that this method works for many people.
Let's start off by describing what IF is and what methods there are:
Intermittent fasting (IF) refers to regular periods with no or very limited calorie consumption. It commonly consists of a daily fast for 16 hours, a 24-hour fast on alternate days, or a fast 2 days per week on non-consecutive days.
IF can be used with unrestricted calorie intake when not fasting, or in conjunction with other dietary interventions, meaning there is no calorie restriction on feeding days or you can combine it with a certain calorie restricted method on feeding days.
Alternate‐day fasting (ADF) and time‐restricted feeding (TRF) are characterized by extending night-time fasting.
ADF incorporates a complete fast every other day, TRF, the more popular method we hear about simply shortens the daily feeding window. Both ADF and TRF may inadvertently restrict energy intake and, therefore, cause weight loss. And this is something I covered in episode 3 about diet myths. It’s not the method itself that causes fat loss, it’s just that the method helps to induce a calorie restriction and deficit which is the cause of fat loss.
The other IF strategies, alternate‐day modified fasting (ADMF) and 5:2 diet regimens use very low‐calorie diets occurring intermittently throughout a 7‐d period.
Alternate‐day fasting and alternate‐day modified fasting
So, let’s discuss the fasting that is maybe a little less popular. Both ADF and ADMF switch back‐and‐forth between days of fasting and eating. Fasting days can range from 75 to 100% caloric restriction depending on the fasting regimen, and eating days are usually "ad libitum" meaning individuals eat as needed or desired. Studies in this field utilized either a complete fast (ADF) or a 20‐hour fast every other day (ADMF).
Trial studies in humans typically resulted in significant weight loss either with or without the intention of losing weight. Even fasting for 1 day or with a 75% caloric restriction resulted in an overall calorie reduction of approx. 30% in the 3 days following the restriction.
Another study I read placed males samples on the ADF and AMDF regimen hoping to simply maintain weight. Participants of the study were asked to feed at nearly 200% of their daily energy need on the non-fasting days. Results showed significant and unintentional weight loss which tells us that ADF and AMDF may be a valuable option as an obesity or weigh loss treatment.
Here's the downside...
Studies reported more than a 20% of dropout rates when the duration of the fasting regimens lasted 12 weeks or more. So, the question is, how sustainable is this method for most people? If you start a regimen and can't adhere, then the diet doesn't actually work in my opinion. Most people will stop their regimen, go back to the way they were eating, and then gain all their weight back, if not more than before!
5:2 Fasting Diet
The 5:2 diet is a diet that shares some similarities with Sunnah fasting (a religious fast), as both regimens call for modified fasting to occur two times per week. Some regimens allow for a 25% calorie intake on fasting days and then "ad libitum" eating on the other 5 days.
I've said this before... it's just a method to get you in a calorie deficit state.
Studies/Interventions with this method that range from 4 to 24 weeks resulted in a 4-8% weight reduction in most participants.
Specifically, a decrease in fat mass (which is what we want to lose) ranged from 9-13% with a 1-4% drop in fat-free mass (muscle/water).
Here's a downside...
Weight regain after stopping a 5:2 fasting regimen is highly likely and comparable to simple calorie restriction diets. Research reports a 33% weight gain upon normal eating habits being followed.
For this reason, I urge my clients and podcast listeners to take diet breaks to avoid metabolic adaptation, whether you're doing a fasting regimen or counting macros with a calorie deficit.
Time‐restricted feeding (TRF) - (eating window) *** most popular
TRF simply extends the daily fasting period by restricting food intake to a reduced window of time.
It is thought that the fasting last more than 10 hours for optimal benefits.
So, most people adhere to at most an 8 hour feeding window... something like 11am-7pm for feeding.
Again, another method to put you in a calorie deficit since you have less time to eat your food.
In one study I read, 8 overweigh young adults did a fasting window of 14+ hours which resulted in significant decreases in daily calorie consumption and hence, weight loss occurred. Participants also reported better sleep, better satiety around bedtime, and elevated energy levels.
Additionally, recent studies have shown TRF not only reduces fat mass, but also lowers cholesterol, ectopic fat, improves inflammation, and shows improvement in heart health, cancer outcomes, and better mortality rates. Clearly there are some significant health benefits to TRF!
So let's hit the summary points:
Overall, evidence suggests that IF regimens are not harmful physically or mentally (i.e., in terms of mood) in healthy, normal weight, overweight, or obese adults.
It appears that almost any intermittent fasting regimen can result in some weight loss. Among the 16 intervention trials included in this review, 11 reported statistically significant weight loss.
Alternate-day fasting appeared to result in weight loss, as well as reductions in glucose and insulin concentrations, in the three studies evaluating this regimen. However, this fasting regimen may not be practical because it leads to intense hunger on fasting days. Modified alternate-day fasting regimens result in reduced weight, with reductions ranging from 3.2%, in comparison with a control group (10) during a 12-week period, to 8.0%, in a one-arm trial during an 8-week period (57). There was limited and mixed evidence for reductions in insulin concentrations, improvements in lipids, or reductions in inflammatory factors.
Research has not demonstrated that alternate-day fasting regimens produce superior weight loss in comparison to standard, continuous calorie restriction weight-loss plans.
So, I hope this gave you some helpful information and insight about IF. If it’s something you think you want to try let me know about it and I’d love to see how it works for you in terms of weight AND health. Just don’t forget that if you’re in a calorie deficit either through calorie restriction or IF, you will eventually need a diet break. You have to get your body back to homeostasis allowing it to burn energy consistently for a time. From what I see there is nothing harmful about IF or CR, but your body is not meant to live in a state of CR.
Alright guys, that’s what I have for you today. If you enjoyed today’s post I’d love to hear about it. So, please leave a review for me if you learned something new today.