Intermittent fasting provides many health benefits, and longer fasting times are more effective. A 24-hour fast once a week boosts ketosis and autophagy–two processes responsible for many of the health benefits of intermittent fasting.
Intermittent fasting provides many health benefits. For example, it lowers the risk of cardiovascular disease, improves insulin sensitivity, reduces inflammation in the body, and provides powerful anti-aging effects.
All intermittent fasting methods provide these benefits to some degree, even the beginner-friendly 16/8 method. Do occasional longer fasts, such as a 24-hour fast once a week, provide any additional benefits?
Being metabolically flexible means that your body can use sugar (and other carbohydrates) and fat as fuel and can easily switch between these two energy sources. With modern eating habits, without considerable fasting times, we mainly rely on sugar as fuel.
Why is that?
Our body can store carbs in the form of glycogen in muscles and the liver. When fasting, the body first accesses glycogen storage. Once they are depleted, we start to burn fat as fuel–this is also the point at which ketosis starts.
Once we can no longer satisfy our energy needs with carbs, the liver turns fat into ketone bodies–an excellent energy source that even our brain can use.
We can store around 2000 kcal in our glycogen storage (1). For the average person, that’s the calorie requirement for one day or 24 hours. This means that 24-hour fasting is the sweet spot at which fat burning is ramped up. It may start a few hours earlier, but at 24 hours, it becomes more efficient.
So, by regularly fasting for at least 24 hours, you train your metabolic flexibility or your fat-burning ability. This does not only facilitate weight (or fat) loss, but it is also responsible for the many health benefits of intermittent fasting (2).
We all learned that we just have to eat fewer calories than we burn to lose weight. This holds some truth, but there is one big problem: the less we eat, the hungrier we get.
Because standing hunger for the long-term is very difficult, consistent hunger is why diets fail.
Here is where intermittent fasting comes in. It allows us to access our energy storage. Because we all have plenty of energy stored, there is no shortage as soon as we effectively use our stored energy. As a result, hunger decreases (3).
You just learned that the carbohydrate storages comprise only around 2000 kcal. But our fat storages are nearly endless (4). Once your body learns to access fat storage, hunger wanes, and you’re less focused on your next meal–that’s the key to efficient weight loss!
For this reason, longer fasts (at least 24 hours) are more effective at getting hunger under control than shorter fasts.
Autophagy is an essential recycling process that you can compare to spring cleaning. It provides many health benefits and is also known as the fountain of youth (5). Fasting is the most potent stimulator of autophagy (6). When no fresh proteins come in, the cells are forced to recycle old ones. They are broken down and the building blocks are used to build new proteins (7).
There is not much research about when autophagy starts in humans, but for the average person, it seems to start after 18 hours of fasting, and it increases with time (8). So, a 24-hour fast is a great way to boost autophagy.
With all the benefits of longer fasts, wouldn’t it be good to do a (nearly) 24-hour fast every day?
Not necessarily. One Meal a Day (OMAD) is a popular intermittent fasting method that involves fasting for nearly 24 hours per day–ideally for around 23 hours. However, some people extend their meals to four hours so that they end up with a 20/4 fasting schedule.
One problem is that it is challenging to get sufficient nutrients (vitamins, minerals, and protein) with one meal per day (9). For this reason, it is not sustainable long-term for many people.
Therefore, an occasional 24-hour fast, once or twice per week, combines the benefits of both worlds: it provides the benefits of longer fasts, but it makes it easy to get sufficient nutrients.
A 24-hour fast provides many health benefits. It boosts ketosis and autophagy and helps to get hunger under control. However, fasting every day for 24-hours is not ideal as it makes it difficult to meet all nutrient requirements. A 24-hour fast once per week provides the benefits of longer fasts and makes it easy to get sufficient essential nutrients.
If you want to learn more about intermittent fasting, we invite you to join our intermittent fasting community for women only.
1. Knuiman P, Hopman MT, Mensink M. Glycogen availability and skeletal muscle adaptations with endurance and resistance exercise. Nutr Metab (Lond). 2015;12:59. doi:10.1186/s12986-015-0055-9
2. Anton SD, Moehl K, Donahoo WT, et al. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring). Feb 2018;26(2):254-268. doi:10.1002/oby.22065
3. Hoddy KK, Gibbons C, Kroeger CM, et al. Changes in hunger and fullness in relation to gut peptides before and after 8 weeks of alternate day fasting. Clin Nutr. Dec 2016;35(6):1380-1385. doi:10.1016/j.clnu.2016.03.011
4. Weiss R. Fat distribution and storage: how much, where, and how? Eur J Endocrinol. Aug 2007;157 Suppl 1:S39-45. doi:10.1530/EJE-07-0125
5. Martinez-Lopez N, Tarabra E, Toledo M, et al. System-wide Benefits of Intermeal Fasting by Autophagy. Cell Metab. Dec 5 2017;26(6):856-871 e5. doi:10.1016/j.cmet.2017.09.020
6. Bagherniya M, Butler AE, Barreto GE, Sahebkar A. The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing Res Rev. Nov 2018;47:183-197. doi:10.1016/j.arr.2018.08.004
7. Glick D, Barth S, Macleod KF. Autophagy: cellular and molecular mechanisms. J Pathol. May 2010;221(1):3-12. doi:10.1002/path.2697
8. Jamshed H, Beyl RA, Della Manna DL, Yang ES, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients. May 30 2019;11(6)doi:10.3390/nu11061234
9. Damms-Machado A, Weser G, Bischoff SC. Micronutrient deficiency in obese subjects undergoing low calorie diet. Nutr J. Jun 1 2012;11:34. doi:10.1186/1475-2891-11-34
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