Intermittent fasting provides many health benefits, and most of them can be enhanced with long fasts. Research suggests that long fasts are beneficial for weight loss, promote autophagy, stimulate growth hormones and improve blood sugar control. But long fasts also have some downsides.
Throughout history, people have fasted for multiple days, for religious reasons, due to famine, or not being able to find food. As intermittent fasting has gained popularity in recent years, the effects of fasting for longer periods have been studied more closely.
Most people who do intermittent fasting refrain from eating for 12-18 hours daily. However, some will fast longer, up to 48 hours, to give their body more time to reap the benefits.
A fast longer than 48 hours is referred to as a prolonged fast, also called an extended fast or water fast. Most people who do prolonged fasts go 3-7 days without food. It is recommended that such a fast be done under medical supervision.
This article will focus on the 24 to 48-hour intermittent fasting long fast.
Although it isn’t required to do longer fasts to enjoy the benefits of intermittent fasting, some experts recommend a 24-48 hour fast a few times a month to boost weight loss results. You could also try 24h fast once a week.
If you’re new to intermittent fasting, first sit back and get comfortable with the daily 16-ish hour fasts for at least a month. Let your body and mind adjust.
If you’re a more seasoned faster who has hit a weight plateau, wants to boost results, or gain the additional health benefits, a periodic long fast of up to 48 hours might be a great fit. Start with a goal of 24-36 hours the first time and build to a 36-48 hour fast.
The most important thing is to honor your body. There’s a difference between low energy because you haven’t eaten in a day and a half and actually feeling ill. Pay attention to what your body is experiencing and adjust as needed. Don’t push yourself to a dangerous place for the sake of a few additional hours of fat burning.
While the benefits of periodic long fasting are many, there are some drawbacks to fasting for more than a day, including hunger, dizziness, sluggishness, and exhaustion. Long fasts can also make social situations uncomfortable.
The following people should either avoid or be extra cautious if fasting over 24 hours:
Mix up your intermittent fasting routine with a 24-48 hour fast periodically to boost your long-term results.
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3. Hartman ML, Veldhuis JD, Johnson ML, et al. Augmented growth hormone (GH) secretory burst frequency and amplitude mediate enhanced GH secretion during a two-day fast in normal men. J Clin Endocrinol Metab. Apr 1992;74(4):757-65. doi:10.1210/jcem.74.4.1548337
4. James LJ, Shirreffs SM. Effect of electrolyte addition to rehydration drinks consumed after severe fluid and energy restriction. J Strength Cond Res. Feb 2015;29(2):521-7. doi:10.1519/JSC.0000000000000657
5. Chung HR. Iodine and thyroid function. Ann Pediatr Endocrinol Metab. Mar 2014;19(1):8-12. doi:10.6065/apem.2014.19.1.8
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