Alternate-day Fasting: Is It Practical for Sustained Dietary Changes?

If you decide to read up on fasting, specifically fasting for weight loss or health markers, you’re likely going to stumble upon an overwhelming amount of information (and misinformation – I mean… it’s the internet).

From a physique enhancement point of view (which will be the main focal point here), not only are there so many ways to employ fasting into one’s lifestyle, but there are also a lot of considerations that need to be taken before you jump into fasting as a means to lose weight or approach your nutrition as a whole.

Not all fasting is the same?

Not necessarily. Of course, the idea is the same with having a block of time spent without consuming any calories (and in certain cases, which we’ll discuss, involves consuming minimal calories), but there are a few different approaches in how these fasts are structured within one’s diet and lifestyle.

Here are some of the popular methods of fasting:

Intermittent fasting

Likely the most recognizable of the types; this involves cycling between blocks of time for fasting and eating each day. For example, a common approach is the “16/8” window, where 16 hours are spent fasting and 8 hours are given for mealtimes before fasting starts over again. It has become a popular setup for those dieting since it helps with feeling more satisfied between and after meals (less time to eat in the day, meals can be larger and closer together, etc.)

 Time-restricted feeding

This is a type of intermittent fasting. Here the individual would essentially follow a similar approach as IF, though the only difference is that this consistent window is maintained day to day in order to help with one’s sleep cycle, digestion, and even energy levels. Its main focus isn’t based on daily caloric restriction or weight regulation so much as it is based on improving and regulating those other important lifestyle factors. Ideally feeding windows would be between 8-12 hours depending on the person and their needs.

Alternate day fasting

This is another IF approach and the main focus of the study to be discussed. This name also does a good job of being pretty self-explanatory; this approach involves having alternating days of eating (to one’s liking) and fasting. It should be noted that the approach to these fasting days does seem to differ based on the person – some choose to eat nothing and consume only calorie-free beverages and water, while others may choose to eat an extremely low amount of calories these days (~500-600 calories).

Despite the red flags I’ve already seen in that small description, there is a lot more to discuss as far as alternate day fasting is concerned and the feasibility of even using this method as a catalyst for behavior change and weight loss.

The Study

Healthy, nonobese men and women (8 men and 8 women, specifically) were recruited. Nonobese is defined here as falling anywhere between a body mass index (BMI) of 20.0-30.0, or otherwise between normal and overweight bodyweight ranges. Physical activity differed among the subjects: 7 being completely sedentary, 3 moderately active (exercising 1-2 times/week), and 6 being pretty active (exercising 4-5 times/week). Competitive athletes were among those who were excluded from the study design.

Feast and Fasting Days

Subjects participated in a total of 3 weeks of alternate day fasting for the duration of the study period. This consists of subjects fasting from midnight to the following midnight on alternating days. On fasting days, the subjects were allowed to consume calorie-free drinks, tea, coffee sugar free gum. They were instructed to prioritize water intake and keep that high as well. On normal, or feasting days, participants were allowed to eat whatever foods they wanted. An interesting point was made to inform the subjects that doubling their usual caloric intake on these feast days would be needed in order to maintain their body weights.

Testing for this study was done on 2 consecutive days at baseline, before starting, and 2 consecutive days following that 3-week period (days 21 and 22) where their measurements were taken (body weight, RMR, body composition). A great addition to the initial assessments was starting out with the Eating Inventory questionnaire at baseline that evaluated the 3 identified eating behaviors: disinhibition, restraint, and hunger.

There’s an article all about these behaviors and how they impact our weight. Check it out here.

Intermittently during this study period, the participants were given questionnaires and visual analogue scales to answer on fasting days, specifically. These scales were used as a means of assessing the participants’ hunger, fullness, satisfaction, desire to eat, and approaching food consumption (for the feast day to follow).

Visual scales were used where subjects were asked to place a mark on a scale ranging from “not at all” to “extremely” in regard to their levels of hunger or satiety. Participants were also given an Eating Behaviors questionnaire, which essentially would determine whether the men and women considered themselves “dieters,” or those who actively watch what they eat, or “big eaters,” who gravitate towards 1-2 big meals per day. This helps us in sense that we can identify any additional trends between subsequent eating behaviors and weight change with the “types” of eaters they happen to be.

Key Findings

Following 3 weeks of alternate day fasting, subjects experienced significant drops in fat mass and fat free mass. While body weight was reduced on average for all subjects, it’s very important to keep in mind the varying activity levels among them, as it is unspecified how exactly these subjects were exercising. We don’t have knowledge of what mode their physical activity consisted of (i.e. resistance training, cardiovascular exercise, low intensity movement, etc.) so it’s a point worth considering when interpreting that decrease in fat free mass.

An interesting observation is how the subjects viewed themselves in the context of eating; men considered themselves to be “big eaters,” while more women reported they “watched what they ate.” Weight loss did not differ greatly between the men and women, but weight loss did appear to correlate negatively with considering oneself to be a big eater. This makes sense if you’re someone who is used to eating larger meals or portions – those feasting days would probably be taken advantage of even more after such a long fasting period. Not surprisingly, it was observed that feelings of hunger increased while feelings of fullness significantly decreased for subjects.

Now, correlation doesn’t equal causation, but this is a great observation when looking at how we behave under differing circumstances (prolonged hunger) and how we may individually approach meals day to day.

Considerations for Dieters

Regarding eating behaviors, restraint and disinhibition scales did not appear to predict weight loss. There were no real changes to the subjects’ perceptions of hunger, desire to eat, and satisfaction throughout the 3-week period either, but that still does not negate the possibility of negative consequences happening on a psychological level.

Many of the subjects reported feelings of irritability on their fasting days. Some reported issues with digestion and one even experienced some light-headedness. All normal and somewhat common side effects of undergoing long periods of fasting, but in the context of weight regulation and lifestyle change, these aren’t exactly great selling points. A strength of subjective data here is that we can get insight on the participants’ experiences to go alongside any inferences we make from the findings and interpret that information with a broader idea.

Fasting is already a concept (a fad, as of recently) that isn’t for everyone, and with that, alternate day fasting is taking this idea even farther. It’s apparent that weight dropped significantly using this approach and it can understandably be thought of as another means of dietary restriction, but there are still a lot of considerations to make moving forward on how practical of an approach this is for the average person.

Any benefit to physique enhancement and weight regulation is greatly weakened by the subjective states the subjects had found themselves in as a result of following this intense of a protocol (high hunger, high irritability). Not only that, but this can have some damaging implications on how individuals approach their meals or portions and the idea of dieting and lifestyle change as a whole (restrict-overindulgence-guilt cycles).

As we know the best diet is one that we can realistically see ourselves adhering to for the long term and one that we enjoy, at that. This not only applies to alternate day fasting, but to any dieting method/technique in which you find negatively impacts your day to day and is hard to mold to your lifestyle. Ultimately the principles remain the same, no matter how you slice it. The primary goal is to use those habit changes and fit them into your life in a realistic and sustainable manner.


Heilbronn, L.K., Smith, S.R., Martin, C.K., Anton, S.D., Ravussin, E. Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. Am J Clin Nutr. 2005; 81: 69-73

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