Alternate day fasting is considered a form of intermittent fasting in which you fast on an every other day basis.
This type of intermittent fasting was widely popularized by Dr. Krista Varady in her book The Every Other Day Diet.
If you’re wondering who she is, Dr. Varady is the leading researcher in alternate-day fasting diets and is a professor of nutrition at the University of Illinois. She’s published over 30 papers on the topic and even has been published in prestigious journals like The American Journal of Nutrition and Obesity.
How to do Alternate Day Fasting (aka ADF)
There isn’t just one approach to following this type of eating pattern, but they all have the same general idea – you only need to fast or restrict your calories every other day – instead of every day.
One of the widely popular ways to do this, outlined in The Every Other Day Diet, involves eating minimally (25% of your daily calorie needs, or around 500 calories) every other day.
Keep in mind this could be higher, depending on what your overall caloric needs are, but usually, this will fall somewhere between 500-800 calories.
Research shows that it’s also just as effective for weight loss, even when calories are consumed on “fast” days. This is because eating this way will still result in an overall calorie deficit if you follow it properly.
According to Dr. Varady, most people who follow this diet will naturally consume around 110% of their daily caloric needs on the normal eating days, which would still put them in a caloric deficit to lose weight when calculating the average of “feast” and “fast” days (overall about 1/3 calorie reduction).
In my opinion, this seems very close to a zig-zagging calorie-restricted diet. You’re still aiming for an overall deficit while only restricting yourself half the time.
A much stricter fasting approach could be followed on fast days, where you try to consume as close to zero calories as possible, although it’s not necessary if your goal is purely for weight loss.
What can you eat on fasting days while following an alternate-day fasting approach
There’s no absolute answer to this question nor an exact list of foods to eat and not eat, but there are some general rules/guidelines you can stick to.
You definitely want to make sure you drink plenty of water. Your body needs to be properly hydrated to function well, and it’s common to mistake thirst for hunger.
#2. Black coffee and tea, zero-calorie drinks
Most experts agree it’s OK to also consume zero-calorie drinks like black coffee and tea during your fasting days.
Coffee has been shown to be an appetite suppressant, so drinking it during a fast can help tremendously.
Artificially sweetened beverages like diet pop and other zero-calorie flavored drinks are fine. (Although there is some debate within the health/fasting community, I think it’s up to the individual to decide what works best for them).
#3. High protein, filling foods
Since you can only eat around 500 calories, it might be best to make sure what you do consume will keep your hunger at bay.
Here are some examples of foods that are high in protein and lower in calories:
- Lean meats
- Greek yogurt
#4. Foods with a low-calorie density
Low-calorie density means foods that contain a lot of bulk and fill you up without being high in calories.
- Soups (not cream-based)
- Plain broth
- Popcorn (without all the butter)
#5. Watch the condiments
Something important to consider is the calories in condiments – these can really add up if you’re not careful. Common condiments like ranch dressing and butter contain a ton of calories, so those would best be avoided on fasting days.
Pay attention to labels on any condiments you use. Here are examples of common condiments that are low in calorie:
- Hot sauce
You might find it easier to use a food tracking app, like MyFitnessPal, and weigh/measure all your food, to make sure you’re adhering to the 25% calorie rule.
How much can you eat on non-fasting days with ADF?
One mistake people make with dieting like this is they treat their non-fasting days like “feast” days and overeat.
But typically it’s recommended to still only consume somewhere between 110 % – 125% of your daily caloric needs on off-days.
As an example, if you take a standard 2,000 calorie per day diet – 110% – 125% would fall be between 2,200 – 2,500 calories. But it could be higher or lower, depending on your particular energy needs.
You can eat what you’d like provided it falls within calorie-range, but healthier options could give you better results and prevent you from over-eating.
Does ADF really work for weight loss?
Studies have found that alternate-day fasting is definitely is an effective weight-loss approach.
However, it’s not necessarily better than a more traditional, calorie-restricted diet.
The important thing to realize is that no method for weight loss is one-size-fits-all. Some people find fasting a much easier way to lose weight, others find it too difficult to stick with.
It followed 100 healthy obese adults over the course of a 1 year period and separated them into 3 groups.
- The first group participated in an alternate-day fasting approach where they ate 25% of their calorie needs on fast days, and 125% on other days.
- The second group restricted their calories on a daily basis to 75% of their needs.
- The third group was the control group, so they ate their regular diet.
The study ultimately found that alternate-day fasting worked just as well for weight loss as an everyday calorie-restricted diet.
However, the drop-out rate of the alternate-day fasting group was pretty high, at 38% (compared to a 29% dropout rate for calorie-restricted group, and a 26% dropout rate for the control group).
This could indicate that alternate-day fasting might be harder to stick with for certain people.
Despite these findings, another study found that while there was not a significant difference in overall body weight between participants who followed an ADF approach vs. low-calorie diet, there was a greater difference in fat mass loss among the ADF group.
Is ADF better than intermittent fasting?
Alternate-day fasting is just one way to follow an intermittent fasting style of eating. It’s not better or worse, just different.
Another less extreme version of ADF is a calorie zig-zagging approach (there’s a guide to that here), in which you vary your calories each day. You may find that better than traditional calorie restriction, but more tolerable than a fasting method.
If you find fasting just isn’t for you, I always recommend WW (Weight Watchers) as a great program to follow.