Alternate Day Fasting (ADF) calls for feasting on healthy foods for one day and then entirely fasting the next. In this guide, we’ll explore the benefits of an alternate day fasting schedule, while also highlighting some potential pitfalls and how to avoid them.
An alternate Day Fasting schedule is simple. You just eat to complete satisfaction one day, and then fast the next. The end result of this alternating schedule is that you eat roughly 50-60% of what you normally would.
Some adherents of Alternate Day Fasting have attempted to make it less challenging by allowing up 500 calories on fasting days. This form of ADF is referred to as ‘modified’ Alternate Day Fasting.
Whether your alternate day fasting schedule is modified or not, the one substance that’s permitted on fasting days is low-cal or calorie-free liquids.
You can enjoy coffee, tea, sparkling water, and other beverages and still stay in compliance with ADF.
The most popular modern version of Alternate Day Fasting is Dr. Krista Varady’s “Every Other Day Diet.”
Dr. Varady pioneered this way of eating after conducting numerous studies on the benefits of ADF. [2] She’s found that weight loss on ADF is predictably simple, regardless of whether adherents eat the bulk of their calories at breakfast, lunch, or dinner. [3]
Many people who try the Every Other Day Diet find that it’s surprisingly easy to stick to. One 12-month study found that participant adherence was the same for both ADF and the standard calorie-restricted model. [4]
The alternate day fasting schedule is considered a particularly extreme form of intermittent fasting.
When most people think of IF, they think of the 16:8 fasting schedule. It calls for fasting for 16 hours and then feasting for 8. But ADF takes this concept several iterations further. Alternate day fasters may go without food for up to 40 hours at a time!
Both types of fasting have pros and cons. Standard IF schedules, for one, are arguably more practical: those who follow them stick with the very same eating schedule every day. For more info on intermittent fasting, check out our Intermittent Fasting 101 article.
Research shows that both high-carb and low-carb diets can be effective for weight loss when one is alternate day fasting. [5] The only thing that’s truly non-negotiable with alternate day fasting is meal timing.
Strict ADF prohibits taking in any calories whatsoever on fasting days. While the most liberal forms of ADF don’t allow intake of more than 500 calories per fasting day. Even if you’re eating at all hours of the day on your feasting days, you’ll still be fasting for 36+ hours within each two-day (48 hour) cycle.
First things first: alternate day fasting requires your body to get used to not eating every once in a while.
This change requires several biochemical shifts. To fast without experiencing low blood sugar or intense hunger pangs, a person must: [6]
These strategies can help you make the transition to ADF:
Getting adapted to fasting is as simple as getting adapted to ketosis.
MCTs…LCT’s…ADF…IF…talk about acronym soup. We’ll do our best to keep this section simple.
Simply put, MCT sources like coconut oil or pure MCT oil could help you adapt to alternate day fasting by making it easier for your body to switch into a fat-burning metabolic state called ketosis.
MCT’s get turned into ketone bodies by your liver almost immediately after consumption. Once these ketones hit your bloodstream they’re an excellent fuel, keeping hunger at bay and blood sugar stable. [7]
ADF fasting possesses many potential health benefits — some central to any type of fasting, but others unique. Let’s take a closer look.
Alternate day fasting essentially makes your body recycle itself. Old cell membranes get recycled and swapped for new ones. Old fat cells get burned off as fuel. Old muscle cells are refreshed by human growth hormone. The macro-level result of all these micro-level changes is a fresher, fitter, leaner you. [8]
Studies in rodents, worms, flies, and isolated human cells all show that fasting can increase autophagy–the technical name for the cellular recycling process that rejuvenates cells.
Many people who begin ADF notice swift, significant weight loss. Part of this is a result of their body shedding its glycogen stores — each gram of glycogen is paired to four grams of water. But fasting’s weight loss benefit is far more profound than that.
Studies show that alternate day fasting may help a person lose 8% of their body weight after 2-12 weeks. To put those numbers into practice, a 200-pound individual could expect to lose 16 pounds in a few weeks to a few months. [9]
Other studies have found that ADF is no better than conventional calorie-restriction when it comes to weight loss, belly fat reduction, or inflammatory status. [10][11]
A study on ADF on nonobese subjects found that while “alternate-day fasting was feasible in nonobese subjects, […] hunger on fasting days did not decrease, perhaps indicating the unlikelihood of continuing this diet for extended periods of time.” [12]
The study suggested that nonobese fasters add in a small snack on fasting days.
Animal studies have been more insightful in helping us understand this topic. Several such studies suggest that modified ADF (<500 calories on fasting days) lowered hunger hormones and heightened satiety hormones compared to conventional calorie-restricted diets. [14]
Alternate day fasting may also reduce the compensatory hunger that usually comes when one’s body tries to ‘compensate’ for missing calories. [15]
Alternate day fasting trains your body to become metabolically flexible. With metabolic flexibility comes a number of benefits, namely an improved ability to regulate blood sugar.
More than a third of Americans have prediabetes, which is where blood sugar is much higher than usual but not yet clinically high. If their lives don’t change these Americans will likely go on to develop type 2 diabetes (this type currently accounts for up to 95% of all diabetes cases in the US). [16]
Though most types of diets lead to improved blood sugar regulation, this is yet another area where ADF really shines. ADF induces a cyclical ketogenic state that trains your body to efficiently burn fats, carbohydrates, and even amino acids for fuel. The better your body is at using fats for fuel, the more balanced your blood sugar will be. [17]
Fasting has long been associated with reduced risks of cancer.
One recent study, the first of its kind to analyze human serum, discovered that fasting’s anti-cancer effects come from its ability to restore normal circadian rhythm. Here’s what the study’s authors hypothesized:
“Time-restricted feeding can reset the disrupted clock rhythm, protect against cancer and metabolic syndrome. Based on these observations, we hypothesized that intermittent fasting for several consecutive days without calorie restriction in humans would induce an anticarcinogenic proteome and the key regulatory proteins of glucose and lipid metabolism.”
This hypothesis turned out to be correct. Here are some of the highlights among their findings: [18]
It’s likely that all or most types of intermittent fasting provide these benefits.
An alternate day fasting schedule can boost your body’s production of several different categories of hormones, including sex hormones, anabolic hormones, and mood-related hormones.
Short for brain-derived neurotrophic factor, BNDF-1 is essentially your brain’s version of Miracle-Gro.
BDNF-1 plays a vital role in memory, mood, and information processing. Boosting BNF-1 is almost a universally good thing — and fasting boosts BDNF-1 pretty powerfully.
BDNF-1 may even assist with weight loss. While BDNF doesn’t directly cause the pounds to come off, it may help you stay content and mentally occupied during your fasting periods. [19]
Other studies show that fasting can boost growth hormone levels. The title of a 1988 study says it all: “fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man” [20]
In practical terms, fasting’s ability to stimulate HGH production can lead to a variety of benefits:
Testosterone plays a vital role in muscle growth, intrinsic motivation, and stress regulation — in both men and women. Thankfully, alternate day fasting may be great for one’s testosterone levels.
One study found that, “Short-term fasting increased […] the corresponding testosterone response by 180% […]. These results imply that food deprivation affects the pituitary-testicular axis differently in obese and non-obese men.”[21]
To expound a little more on that last sentence, obese men didn’t exhibit the same fasting-driven testosterone boost that non-obese men did. Fear not, fasting, especially when combined with keto, can be an effective approach to weight loss.
Fasting’s ability to promote autophagy means it may also delay the aging process enough to increase lifespan.
So far this anti-aging effect has proven valid in mice, flies, yeast cultures, worms, and isolated human cells. [22]
Fasting may also increase your healthspan — the duration of time in which you’re vibrant, mobile, and disease-free.
The mechanisms through which fasting elicits these effects are quite diverse. Here are some of the highlights: [23]
An alternate day fasting schedule doesn’t have many inherent drawbacks. In fact, the best way to determine whether or not ADF has any drawbacks is to try it for yourself!
That being said, here are four potential drawbacks to be aware of before you begin a new ADF fasting routine.
Cortisol is the body’s primary stress hormone. One of cortisol’s secondary functions, however, is converting amino acids into carbohydrates. This type of conversion is exactly what happens when you begin fasting or eating keto for the first time. You might experience some extra cortisol-induced stress as your body becomes accustomed to ADF’s new meal timing. This is normal — so don’t sweat it! [24]
If you’re still experiencing the symptoms of hypercortisolemia after several cycles of ADF (these symptoms include trouble sleeping, anxiety, appetite loss, and mood swings), however, then it may not be for you. Consider opting for a gentler form of fasting like 16:8 IF, or circadian rhythm fasting.
ADF can also cause problems with high blood sugar if you’re eating more than normal on ‘feasting’ days.
To avoid this problem simply stick with a low-carb or ketogenic diet. If you do wish to eat fruit or vegetables opt for low carb options like keto friendly fruit or low-carb veggies.
Some people simply can’t consume as many calories as they need by eating every other day. Let’s say you’re a hard-training athlete, who normally eats around 4,500kcal/day. Even if you follow a modified ADF fasting schedule, you’ll still need to eat 8,500 calories on your ‘feasting’ days. That’s way more than most peoples’ stomachs can handle–unless you’re on keto and getting most of your calories from animal fats.
We’ve saved the biggest drawback of ADF for the end. It simply stems from the fact that it’s not yet known for certain if alternate day fasting is safe, let alone right, for everyone.
While “the health benefits of weight loss and energy restriction in these human clinical trials are supported by a century of laboratory research in rodents,” many of these benefits may not be related to weight loss or calorie restriction themselves. [25]
They might actually be due to the benefits that come with not eating junk food. In other words, fasting from low-quality lab food is indeed healthy. But so is eating a low-carb, animal-based diet centered on nutrient dense keto friendly foods.
If you have any of the following health goals, ADF fasting may be an effective approach for you:
While Alternate Day Fasting can be highly effective, it’s not for everybody. Some people do much better with milder forms of fasting. ADF is probably not for you if you:
Here’s a 7 day sample intermittent fasting meal plan that provides ample macro and micronutrients. Healthy intermittent fasting snacks to add in if needed include cottage cheese, full-fat yogurt, and other whole food snacks, along with fatty fish and seafood.
You can also insure you’re meeting your nutrient needs with beef liver and beef organ supplements.
Alternate Day Fasting (ADF) is a modern take on the eating patterns of our caveman ancestors. When a hunt was successful they’d feast on fresh food–mostly meat. In between successful hunts they’d have to fast.
ADF has several evolutionarily-based benefits, including:
However, alternate day fasting may not be for everyone. If you don’t have weight to lose or insulin sensitivity to restore, you may want to stick with a milder form of fasting. Nursing or pregnant women should also not practice ADF.
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