Alternate day fasting is a type of intermittent fasting where you fast every other day, and eat normally on the days between. This fasting schedule equates to roughly 36 hours of fasting, followed by 12 hours of eating, on a repeat cycle.
Alternate day fasting is one of the most studied methods of intermittent fasting, which confirms the many benefits and few drawbacks. Read on to see if fasting every other day is the best method for you.
Alternate Day Fasting and Weight Loss
While on an alternate day fasting plan, you’ll eat your regular meals on Day 1, eat nothing on Day 2, eat normally again on Day 3 and repeat. Because going a complete day without food can be challenging, some alternate day fasting rules allow for consumption of approximately 500 calories on fasting days. This equates to about 25% of most people’s daily caloric intake.
Consistent water consumption on fasting days is highly recommended, especially since many of us receive a good part of our hydration during meals. Drinking coffee or tea is also fine, as long as you avoid added sugars, sweeteners or creamers that would break your fast.
By pushing caloric restriction to alternate days, versus every day at every meal, alternate-day fasting can be effective for weight loss without the corresponding feeling of daily deprivation.
Because you can eat normally several days per week, and because there’s no need to count calories, many seeking to lose weight find the alternate-day fasting plan easier to maintain than daily calorie reduction. This leads to better rates of long term compliance and therefore greater weight loss for most people.
According to a 2019 study published in Cell Metabolism, alternate day fasting resulted in an average weight loss of up to eight pounds over four weeks. As an added benefit, alternate-day fasting weight loss tends to take place in the body’s fatty tissues, preserving lean muscle mass.
Hunger and Nutrition on Fasting Days
While some studies show there’s indeed a small tendency to make up for lost calories on non-fasting days, overall caloric reduction on an alternate day fasting plan still remains close to 35%. In fact, additional studies tell us that alternate-day fasting does not trigger binge-eating on ‘feast days’ as you might think it would, and in fact, leads to less overeating than daily caloric restriction.
Hunger is controlled during alternate day fasting thanks to the influence of intermittent fasting on your hormones. Aptly labeled ‘hunger hormones’ such as ghrelin decrease while satiety hormones such as leptin increase. With alternate day fasting in particular, participants in one study found their hunger decreased after week two, at which point they remained relatively free from hunger.
Not everyone responds the same way to hunger. Some may find it easier to consume something small on fasting days. If you’re opting for a meal or snack of 500 calories or less, it’s best to choose low-glycemic foods that won’t raise your blood sugar. This keeps you from entering a metabolic state that would break your fast and prevents the resulting hunger you’ll feel from a post-carbohydrate crash.
In general, as long as you eat healthy low-glycemic foods, you’ll feel great and reap the benefits of your alternate-day fasting plan. Ideally, meals on fasting days will be high in fat and low in sugars to maintain the effects of ketosis that are triggered by fasting. Suggestions include grass-fed meats and wild-caught fish, supplemented by healthy fats such as avocado or goat cheese, fermented vegetables or nuts and seeds.
If you’re fasting for health benefits other than weight loss, it’s possible to eat up to 1,000 calories on fasting days, yet most choose to stick with one meal under 500 so as to avoid a metabolic shift out of the fasting zone.
Only you know best how to avoid hunger, whether that’s splitting your small meal into several snacks throughout the fasting day, or avoiding food altogether to let your body adjust to its new alternate day fasting schedule.
Alternate Day Fasting Benefits and Drawbacks
Much of the scientific research on intermittent fasting, in both humans and animals, has been done using the alternate-day fasting method.
According to just a sample of those studies, the benefits of fasting every other day include:
- Lower levels of circulating blood sugars
- Lower heart rate and blood pressure
- Lower cholesterol and triglyceride levels
- Improved heart disease risk factors
- Increased cellular autophagy, the process of cell repair
- Increase in proteins associated with prolonged life
- Significant long-term weight loss
- Reduction in body fat
- Prevention of obesity and diabetes
- Reduced inflammation
With a fasting window that goes well past 24 hours and lasts throughout the day (as opposed to overnight only), alternate-day fasting is not recommended for the following groups of people:
- Anyone who is underweight or anemic
- Anyone with an eating disorder (although some disagree)
- Anyone with type 1 or type 2 diabetes (consult your doctor)
- Anyone on medications which affect blood glucose levels
- Women who are pregnant or trying to conceive
- Young children
- Elite athletes or others who rely on intense day time physical performance
For the best alternate day fasting results, it’s recommended to stay with the protocol for a minimum of eight weeks, while studies deem this style of intermittent fasting is safe for up to six months. How long you maintain compliance with the alternate-day fasting rules is up to you and your goals. As always, listen to your body, trust your intuition and seek advice from your doctor as needed.
Visit our guide to IF plans to see how other protocols work.