Kristi Storoschuk, BSc (Hons.) is a science communicator with a research focus on ketogenic diets, metabolic therapies, and fasting for health optimization. She currently works alongside the world’s leading ketogenic researchers providing scientific education for the mainstream audience. Outside of her research, you will find her traveling the world, doing CrossFit, and optimizing her health through diet and lifestyle.

"All other things being equal, does age enter into the calculation of the length and frequency of prolonged fasting? For example, should a 30 year old and a 60 year old with the same health and fasting experience approach prolonged fasting differently?"

Yes, age is one of many factors that you should take into consideration when deciding the length and frequency of prolonged fasting (fasts longer than 48-hours). Here at Zero, we do not recommend extended fasting for anyone under the age of 18 unless doing so under the care of a medical provider. For seniors, we don’t have any explicit age cut-offs around certain fasting lengths, instead, we have some frameworks for you to consider. Also, keep in mind that Zero’s upper limit to prolonged fasts is 7-days unless medically supervised.

Because fasting can lead to weight loss, the older you are, the more you should consider how fasting may affect your body composition, and specifically muscle mass. Muscle size and strength gradually decline beginning around the age of 30, without active inputs (strength training and daily protein intake of at least 1.2g/kg). This is particularly concerning due to muscle’s profound benefits for human health and longevity (better glucose control, mobility, bone health, quality of life, etc.). 

Losing muscle during a prolonged fast is not inevitable; the body actually tends to preserve muscle during multi-day fasts, but fasting is still catabolic by nature and therefore does present a potential risk for muscle loss. This risk seems to increase the further you are advance in age. 

In Dirk’s example (assuming healthy weight), someone who is 60-years old will want to consider shorter and less frequent prolonged fasts, compared to someone who is 30-years old. Pay attention to any changes to your body, specifically body weight, and adjust your fasts as needed if you’re losing too much weight too quickly. Over the age of 65, if you have a healthy body weight, you may want to consider infrequent extended fasts (24-36-hours) or daily time-restricted feeding (TRF) rather than prolonged multi-day fasting.

All this said, muscle wasting with age is also dependent on one’s current health status. Carrying excess weight from body fat can also contribute to muscle wasting with age due to systemic inflammation and disuse (inactivity). If weight loss is your goal, prolonged fasting is likely to have more metabolic benefits than detriments. The same age considerations still apply if you are using prolonged fasting for weight loss: the older you are the more conscious you should be about protecting lean mass, and many people find success losing weight with TRF or infrequent extended fasts rather than long fasts. So, those concerned about any potential muscle loss with prolonged fasting may opt for shorter daily fasting as a means of achieving their weight loss goals. In a study of overweight women over the age of 60, six weeks of 16:8 TRF (daily 16-hour fast) led to fat loss without changes to muscle mass. These results suggest TRF is a safe practice for older overweight individuals and can result in health improvements.  

Luckily, older individuals may not need to fast as long to achieve certain benefits of fasting. For example, a popular reason to fast is to leverage the potential metabolic benefits of ketosis. Bood ketones appear to increase more rapidly in healthy older adults compared to younger adults while fasting.

Altogether, it is important to consider the context in which you are fasting. There are scenarios where fasting can improve your health and scenarios where shorter fasts might be a better choice to balance fat loss with muscle preservation, the latter of which becomes more critical with more advanced age.

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How Does Age Affect Fasting Length and Duration?

How Does Age Affect Fasting Length and Duration?

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