What Are The Pros And Cons Of Fasting?

Whenever the topic of fasting comes up with my clients, they usually ask one of three questions: 

"Is that healthy?"

"Doesn't that slow down your metabolism?" 

"Don't you get hungry?." 

Dr. Rhonda Patrick speaks with Dr. Valter Longo, a professor of gerontology and biological sciences and director of the longevity institute at the University of Southern California. Dr. Longo has made huge contributions to the field of aging, including the role of fasting and diet in longevity and healthspan in humans as well as metabolic fasting therapies for the treatment of human diseases.

So I decided to do some research and put together a simple guide that will help clear things up. If you are interested in more information then the video on the right is a great resource to learn more. 

Fasting 101

  • Consume 0 calories for an extended period of time

  • Start by consuming only coffee, water, tea but eventually just do water

  • Start at 16 hours and work your way up to 72 hours

  • Increase your fast by 8 hours per week or month

  • Most fasts last 1 to 7 days

  • Intermittent fasting lasts 16 to 24 hours

  • The longest fast ever was 382 days (1)

  • Fasting has been a common practice in humans for thousands of years 



  • Impacts one’s social life

  • It can be very challenging for some people

  • Mood swings or lack of energy in the first 24 hours

  • Decreases caloric intake which could lead to a decrease in muscle mass






  • Increases calorie expenditure during the fast (1)

  • Increases growth hormone levels up to 500% (48 hour fast)  (2)

  • Improves cognitive function, decreased risk of brain disease (3)

  • Decreases risk of cancer (4)

  • Decreases your risk for type II diabetes  by decreasing insulin levels (5)

  • Decreases inflammation (6)

  • Decreases risk of depression by increasing BDNF (7) (8)

Fasting And Exercise

  • Perform strength training, but keep the duration/ volume low 

  • Strength Training: 1-3 sets by 1-5 reps 

  • Perform steady state cardio and keep the intensity low

  • Steady State Cardio: 20-30 minutes, heart rate:120-150 (50-65%)

  • If you are doing high intensity interval training then consume a large amount of carbohydrates (150 - 200 grams) the day before you start your fast

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