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Alternate-Day Fasting: Fasting Every Other Day

"Andrea is a copywriter and editor specializing in holistic nutrition, health, and wellness. She holds a Bachelor of Arts in Communication Studies from McMaster University, is a certified personal trainer with the National Academy of Sports Medicine (NASM), and Certified Nutritional Practitioner (CNP) with the Institute of Holistic Nutrition."

The practice of intermittent fasting is something that’s been floating around the health and wellness space for some time now. It’s been touted for eliciting all sorts of health benefits from weight loss and fat loss, to clearer skin, more energy, better digestion, and even helping you live longer! 

In fact, fasting has been practiced for centuries and starting with something a bit simpler like alternate-day fasting, which still reaps all the benefits this eating pattern has to offer.

So, while you may have been convinced that skipping meals was a bad thing, it turns out that eating every other day could actually be more beneficial in the long run. 

In this article, we’re breaking down what you need to know about alternate-day fasting — what is it, what are the benefits, and is it safe.

What is Alternate Day Fasting?

Alternate-day fasting (ADF) is one of the many different methods of intermittent fasting. Unlike other methods where you have a specific eating window within a 24-hour period, ADF is as simple as it sounds — you alternate between days where no calories are consumed, and days where food and beverages are consumed as desired [1].

For example, here’s what a typical alternate day fasting schedule could look like:

Monday: Eat
Tuesday: Fast
Wednesday: Eat
Thursday: Fast
Friday: Eat
Saturday: Fast
Sunday: Eat

However, some people may choose to do a “modified” version of alternate-day fasting where calories are kept below a certain threshold, usually around 500 calories or 20-25% of energy requirements, on fasting days, which ultimately still provides the same results with some energy intake [2, 3]. 

Alternate-day fasting and weight loss

For a lot of people, fasting is an easy and super effective way to lose weight that doesn’t involve strict calorie counting, and we see that supported in the evidence. It can lead to weight loss and improved body composition. That’s because alternate-day fasting not only reduces energy intake by limiting total number of hours available for eating, but it may also alter appetite-regulating hormones like leptin, ghrelin, and xenin, which, when imbalanced may lead to increases in total energy intake and thus weight gain [3].

A 2005 study looked at the effects of alternate-day fasting in non-obese subjects participating in a 22-day experiment of eating every other day. Participants lost, on average, 2.5% of their initial body weight and roughly 4% of initial fat mass, and also saw an increase in fat oxidation and reduced fasting insulin levels [4].

Another study of 16 obese subjects using modified alternate-day fasting (consuming 25% of normal food intake) to facilitate weight loss and improve vascular health found an average of 5.6kg decrease in body weight after following the diet for 8 weeks, along with a reduction in body fat percentage from 45% to 42% [2]. 

However, it’s important to note that studies do suggest that where weight loss is concerned, not fat loss, alternate-day fasting may not be more effective than a conventional calorie-restricted diet [5, 6]. 

Alternate-day fasting and hunger

Hunger is a huge reason why calorie restriction doesn’t work. You reduce food intake, your hunger kicks up, and you end up eating more than you planned… it’s the path a lot of people fall trap to.

Appetite is regulated by a complex interaction between several hormones—leptin, ghrelin, cortisol, PYY, to name a few. Leptin is a hormone that is produced by fat cells and signals to your brain that you are full, whereas ghrelin is a hormone that exhibits stimulatory effects on food intake, fat deposition, and growth hormone release, and signals to your brain that you are hungry [7].

While it’s logical to assume that fasting may regulate appetite, studies are inconsistent. Some research shows that ADF causes weight loss by altering energy intake and expenditure and hormone balance, while other studies suggest that appetite remains unchanged during the duration of the fasting protocol [4, 8]. However, there is research to support the fact that modified ADF may be a more effective method for regulating hunger and achieving weight loss compared to full-day fasts [4]. 

Studies also suggest that a prolonged schedule of fasting and feasting (i.e. alternate-day fasting) leads to state of hunger and irritability, which would likely interfere with an individuals ability to sustain this style of eating long-term [4].

Health benefits of Every Other Day Diet

When it comes to the health benefits achieved with alternate-day fasting, there’s really no shortage of them. Research consistently shows that both ADF and modified ADF can [9]:

  • Improve insulin sensitivity
  • Reduce the risk of obesity
  • Improve cardiometabolic risk factors
  • Promote weight loss and fat loss
  • Improve cardiovascular health (blood pressure, resting heart rate, HDL and LDL cholesterol levels, triglycerides, glucose, insulin, and insulin resistance)
  • Reduce the risk of cancer
  • Reduce the risk of neurodegenerative diseases
  • Decrease oxidative stress and inflammation
  • Reduce tissue damage
  • Improve cell resiliency and resistance to stress
  • Promote longevity
  • Improve endurance, balance, and coordination

Overall, there’s a lot of potential for alternate-day fasting to improve several markers of health, but in terms of actually planning and implementing it, full-day fasts may be challenging, so some people may find similar benefits doing a modified version of ADF. 

Every Other Day Fasting and other health outcomes

In addition to what we just mentioned, there are some other major health benefits linked to fasting every other day. 

Cardiovascular Health

Cardiovascular diseases are the leading cause of mortality worldwide being responsible for over 30% of human deaths annually [10]. While the causes are multifaceted, studies show that alternate-day fasting protocols may offer cardioprotective effects by altering adipose tissue physiology (body fat distribution, triglyceride metabolism, adipokines) in such a way that may protect against various cardiovascular conditions, as well as reduce blood pressure, triglycerides, and cholesterol levels to enhance vascular function [2, 11].

Reduces oxidative stress and inflammation 

Chronic low-grade inflammation and elevated oxidative stress are major risk factors in the pathology of several chronic diseases [12], but regular periods of fasting may mitigate levels of oxidative stress and help curb inflammation. 

A study of ten participants with a BMI >30 were put on a modified alternate-day fasting regimen (<20% calories on fasting days) for 8 weeks to determine the effects on oxidative stress and inflammation [13]. Results showed a significant decrease in serum triglycerides and cholesterol, as well as several markers of oxidative stress, increased levels of the antioxidant uric acid, and decreased markers of inflammation (TNF-alpha, BDNF), suggesting that ADF can improve pulmonary function and decrease oxidative stress and inflammation.

Autophagy

If you’ve never heard of autophagy before, you can think of it like your body’s cellular clean up crew. During periods of fasting, the body stimulates this process to help rid the body of old, worn out, or dysfunctional proteins. Studies suggest that a disruption to the process of autophagy is an underlying factor involved in neurodegeneration, along with various metabolic diseases [14, 15]. 

Essentially, stimulating autophagy helps the body remove debris and self-regulate; it hits the reset button on your body to promote greater functional efficiency, as well as stronger survival and adaptation responses to stressors and toxins that enter the body.

Metabolic flexibility

When glucose is in short supply, like during a fast for example, the body must adapt to using other resources for fuel; this is what we call ‘metabolic flexibility’. It’s defined as your body’s preferential shift from using glucose via glycogenolysis to fatty acids and fatty acid-derived ketones for energy [16]. There’s a growing body of evidence to suggest that during prolonged periods of fasting or strenuous exercise, the body’s preferred source of fuel is actually ketones derived from fatty acids as opposed to what we’ve always thought—glucose. 

And for anyone looking to alter body composition, this can be really beneficial because it represents the switch from lipid synthesis and fat storage to fat mobilization, which is why research supports the role of IF for the treatment of obesity and other metabolic conditions. For most people, the metabolic switch is flipped on somewhere between 12 and 36 hours after food consumption has stopped [16].

Is Eating Every Other Day safe?

It’s pretty clear that alternate-day fasting benefits run a long list, but is it actually safe to do? Studies suggest that for most people it is. However, some research shows minor mood or behavioral side effects in response to fasting, including feeling cold, irritable, low energy, difficulty concentrating, or hungry, but symptoms tend to subside after about one month [3, 9].

For people who struggle to do full day fasting every other day, some health experts will recommend the 5:2 fasting diet, with approximately 1000 calories consumed one day per week, then gradually reducing it until 500 calories can be consumed 2 days per week. This may help reduce some of the unpleasant side effects and allow the body to adjust more effectively.

People that are pregnant/nursing, are elderly, have struggled with disordered eating, or have an underlying medical condition should always consult with their healthcare professional before embarking on a fasting protocol as it may not be recommended.

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