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ADF (Alternate Day Fasting) Diet 101

ADF (Alternate Day Fasting) Diet 101

ADF (Alternate Day Fasting) Diet 101

Any diet that places you in a calorie deficit can work for weight loss, be it Zone, Paleo, Keto, IIFYM, or Intermittent Fasting.


The question is which of these diets are best suited to your dietary preferences and schedule.


After all, the single biggest determinant in the success or failure of a diet is an individual’s ability to adhere to.


What this means is that no matter how “perfect” or “ideal” a given diet may be, if you feel deprived or constantly hungry while following the diet, the chances of you sticking it out are slim and none.


Today, we look at one of the most off-the-beaten path diets you’re likely to encounter on your quest to get results -- alternate day fasting (ADF).


What is Alternate Day Fasting (ADF)?


As the name suggests, alternate day fasting (ADF) is a style of dieting where you alternate days of feeding and fasting.


It is a “riff” (variation) of intermittent fasting.


By fasting one day and eating the next, you’re effectively cutting your weekly calorie intake in half.


There is, however, a “modified” alternate-day fasting approach in which individuals are allowed to consume ~500 calories, around 20-25% of daily energy requirements.


In fact, some research indicates that a modified alternate day fasting approach, where individuals can consume 500 calories on “fasting” days may be more tolerable than complete fasts on fasting days.[1]


What Can I Eat & Drink on Fasting Days?


On fasting days, you may drink as many calorie-free beverages as you like.


Examples of calorie-free beverages include water, unsweetened, black coffee and unsweetened tea.


If you are following a modified alternate-day fasting diet, you may consume up to 500 calories worth of food.


In the interest of preserving muscle tissue on a diet, it is recommended that these 500 calories should come mostly from dietary protein (chicken, fish, whey protein, etc.).


Most individuals following and ADF diet plan find it best to eat one "big" 500-calorie meal late in the day as opposed to 2-3 150-200 calorie snacks.


Still, you should use whichever method works best for your lifestyle and dietary preferences.


If eating a few low-calorie snacks on your fasting days helps you feel fuller and less hunger, go for it. If not, feel free to fast the whole day or just have one giant snack at the end of your fasting day.


Remember, calories are king when it comes to weight loss.


However you go about creating that calorie deficit is second to actually creating and adhering to the deficit.


Is Fasting More Effective Than Conventional Dieting for Weight Loss?


Similar to intermittent fasting, alternate-day fasting is no more effective for weight loss than any other reduced-calorie diet.


As we’ve mentioned several times, any diet can work for weight loss, and the diet that best suits your lifestyle and dietary preferences is the one you should follow.


That being said, if you have tried conventional dieting (where you maintain a consistent calorie deficit each day) and haven’t experienced much success (i.e. constant feelings of hunger or deprivation), then alternate-day fasting may be a dieting method worth trying to help you stick to your calorie deficit.

In fact, some animal research indicates that modified alternate-day fasting may lead to lower concentrations of hunger hormones (ghrelin) and increased amounts of satiety hormones (leptin) than other diets.[4,5]


This isn’t all that surprising since you’re “fasting” days aren’t entirely devoid of nutrition.


Additionally, other research suggests that alternate-day fasting may preserve more muscle mass than conventional dieting.[2]


However, when you read the full studies, you’ll see that subjects in these studies are not consuming nearly enough dietary protein each day.


In fact, subjects were only consuming around 15% of their daily calories from dietary protein[2] -- hardly enough to satisfy the requirements for retaining lean muscle mass during a diet.


FYI, current recommendations for dietary protein intake during a diet are between 1-1.25 grams per pound of bodyweight.[3]


Other studies note that alternate-day fasting is as effective as daily calorie restriction in terms of reducing body fat and body composition as well as improving metrics associated with metabolic syndrome, such as high blood sugar levels and insulin resistance.[6,7,8]




Alternate-day fasting is a viable dietary approach to lose weight where you alternate between days of fasting and days of feasting.


Traditional alternate-day fasting days do NOT allow for any calories to be consumed while “modified” alternate-day fasting allows for up to 500 calories to be ingested (~20-25% of normal calorie intake).


The reason that alternate-day fasting helps people lose weight is that it creates an energy deficit, where individuals consume fewer calories than required to maintain weight.


Alternate-day fasting has been shown to be as effective (not more effective) than conventional diets (such as IIFYM) for losing weight and improving markers of metabolic health.


With this is mind, if alternate-day fasting allows you to experience greater satiety or fewer feelings of hunger, then feel free to try it. But, if you’d prefer to follow more conventional diets (continuous calorie restriction), understand that you can have just as good results.


Remember, the diet you can stick to consistently is the one that is the “best” for weight loss.



  1. Heilbronn, L. K., Smith, S. R., Martin, C. K., Anton, S. D., & Ravussin, E. (2005). Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. The American Journal of Clinical Nutrition , 81(1), 69–73. Retrieved from
  2. Catenacci VA, Pan Z, Ostendorf D, et al. A randomized pilot study comparing zero-calorie alternate-day fasting to daily caloric restriction in adults with obesity. Obesity (Silver Spring). 2016;24(9):1874–1883. doi:10.1002/oby.21581
  3. Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr. 2014;11:20. Published 2014 May 12. doi:10.1186/1550-2783-11-20
  4. Varady, K. A., Hudak, C. S., & Hellerstein, M. K. (2009). Modified alternate-day fasting and cardioprotection: relation to adipose tissue dynamics and dietary fat intake. Metabolism: Clinical and Experimental, 58(6), 803–811.
  5. Varady, K. A., Roohk, D. J., Loe, Y. C., McEvoy-Hein, B. K., & Hellerstein, M. K. (2007). Effects of modified alternate-day fasting regimens on adipocyte size, triglyceride metabolism, and plasma adiponectin levels in mice. Journal of Lipid Research, 48(10), 2212–2219.
  6. Melanson, K.J., Summers, A., Nguyen, V. et al. Body composition, dietary composition, and components of metabolic syndrome in overweight and obese adults after a 12-week trial on dietary treatments focused on portion control, energy density, or glycemic index. Nutr J 11, 57 (2012) doi:10.1186/1475-2891-11-57
  7. Alhamdan BA, Garcia-Alvarez A, Alzahrnai AH, et al. Alternate-day versus daily energy restriction diets: which is more effective for weight loss? A systematic review and meta-analysis. Obes Sci Pract. 2016;2(3):293–302. doi:10.1002/osp4.52
  8. Barnosky, A. R., Hoddy, K. K., Unterman, T. G., & Varady, K. A. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational Research, 164(4), 302–311.

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