Dr. Peter Attia – Zero Fasting Live Q+A

Watch the video here

Key Takeaways

  • Peter’s fasting routine:
    • Time-restricted feeding 4-5 days a week
    • A 36-48 hour water-only fast once a month
    • A 5-7 day water-only fast once a quarter sandwiched by a week of following a ketogenic diet on each end
      • During the water-only fasts, Peter doesn’t consume coffee and tries to strength train every day
  • Whether or not coffee breaks the fast depends on why you’re fasting in the first place
    • Artificial sweeteners belong in the same bucket
  • When breaking a prolonged fast, eat something small/low volume, low in glucose, and preferably higher in monounsaturated fats (as opposed to saturated or polyunsaturated fats)
  • Strength training during a fast is very important as it helps to preserve muscle mass
  • “Don’t try to trade your health for wealth then buy your health back” 

Products & Supplements Mentioned

  • During Peter’s water-only fasts, he supplements with:
    • Jarrow’s Phosphatidylserine (typically 300 mg) (which also makes it easier to fall asleep)
    • Magnesium – he steers clear of magnesium oxide (as it tends to act as a laxative) and instead prefers something like SlowMag
    • L-threonate (it’s a magnesium transporter that allows it to get across the blood-brain-barrier more effectively)
      • Peter says it’s helped his sleep, whether he’s fasting or not
  • Despite various claims, citrus bergamot probably doesn’t enhance autophagy 
  • You can measure your ketone levels with a Precision Xtra 


  • This is a Q&A with Dr. Peter Attia (@PeterAttiaMD) in partnership with the fasting app, Zero
    • Peter is The Peter Attia Drive Podcast – check out the Podcast Notes
    • Check out the Podcast Notes from Peter’s first Q&A
    • Also, check out the Podcast Notes from the Zero Fasting Q&A with Dr. Rhonda Patrick

Peter’s Fasting Routine

  • Time-restricted feeding 4-5 days a week
  • A 36-48 hour water-only fast once a month
  • A 5-7 day water-only fast once a quarter sandwiched by a week of following a ketogenic diet on each end

Where are we in the cause/effect chain of understanding the relationship between obesity and insulin resistance?

  • “I feel less knowledgeable today than I did in 2013… My absolute knowledge has grown, but my relative knowledge has shrunk.”

How has fasting improved Peter’s life?

  • Perhaps the biggest benefit of all is psychological
    • Having a regular fasting practice makes it 10x easier to avoid eating if he only has access to junk food (i.e. on a long travel day)

Advice for Younger People | Increasing Healthspan and Lifespan

  • “Longevity is a compounding sport”
  • Remember: Slow and steady wins the race
    • The more consistent you can be with the way you sleep, eat, and exercise, the greater the benefit you’ll experience much later on
  • “Don’t try to trade your health for wealth then buy your health back” 

How do you know if intermittent fasting is effectively addressing insulin resistance?

  • The short definition of insulin resistance: the body requires more insulin to get glucose out of circulation into the muscle
    • Signs include elevated levels of insulin and/or elevated levels of glucose following the ingestion of glucose
  • Average blood glucose and the standard deviation of blood glucose levels are good proxies for glucose disposal capability
    • Thus, you’d want to look for an improvement in these two numbers

Does coffee break a fast?

  • It depends why you’re fasting in the first place
    • If your fasting to lose weight…
      • No 
    • If you’re fasting to improve metabolic parameters often accompanied by weight loss (reductions in glucose/insulin)…
      • No
    • If you’re fasting to reduce inflammation…
      • No
    • If you’re fasting for gut rest…
      • Yes
    • If you’re fasting to increase autophagy (the process by which dysfunctional cells digest themselves)…
      • We don’t know the answer because we can’t measure autophagy in humans (yet)
      • During Peter’s water-only fasts, he chooses not to consume coffee – “But I don’t know definitively that I should not be consuming coffee. My intuition is the less I’m consuming, the better.”
  • In summary – “I don’t know the answer to this question and I don’t know anyone who does”

What about non-nutritive sweeteners like aspartame, saccharine, and sucralose?

  • “I think they probably belong in the same camp as coffee”

Major in the Major, Minor in the Minor

  • If you’re already fasting, you’re getting 97% of the benefit
    • Don’t worry about the 1-3% difference you’d obtain in your physiology by avoiding coffee/artificial sweeteners during a fast

More on Measuring Autophagy

  • As mentioned, it’s not currently measurable in humans
  • Ideally, in the future, we’d be able to look at a series of biomarkers and determine the extent to which you’re undergoing autophagy
    • We know what happens when we fast, so we’re not too far off:
      • Glucose decreases
      • Insulin decreases
      • Free fatty acids decrease
      • Some amino acids drop to 0 (like methionine)
      • Some amino acids drop and plateau (like leucine)
      • Uric acid increases
    • “My suspicion is that there are ~25 different biomarkers out there that would then get layered into an algorithm to give someone an autophagy meter if you will”

Sleep Supplements During a Fast

  • Many report trouble sleeping during a prolonged water-only fast
    • This isn’t solely due to hunger, but perhaps more so due to higher cortisol levels
      • There’s an evolutionary reason for this – our ancestors probably treated periods without access to food as a state of hyper-alarm 
  • During Peter’s water-only fasts, he supplements with:
  • Note – be careful with long-term melatonin supplementation (it downregulates your melatonin receptors)
    • And as a general rule, only use sleep supplements when you need them (i.e. to fight jet lag)

What else does Peter supplement with during a water-only fast?

  • Magnesium
    • In general, most people are magnesium deficient
    • Magnesium also tends to get depleted during a fast (or with general carbohydrate restriction)
    • Peter supplements with magnesium every day, but when fasting does so at a much higher level 
      • During a fast, he’ll stay clear of magnesium oxide as it tends to act as a laxative and instead prefers something like SlowMag
  • L-threonate (it’s a magnesium transporter that allows it to get across the blood-brain-barrier more effectively)
    • Peter says it’s helped his sleep, whether he’s fasting or not

What should you eat when breaking a prolonged water-only fast?

  • From a physiologic perspective, meals low in glucose will produce less of a glycemic spike (which you want to avoid)
  • Eat something small/low volume
    • Why? – During a long fast, your stomach contracts 
  • Eat something nutritious – you’re looking to refeed the cells that survived the fast and you want to provide them with the best nutrients possible
  • Eat monounsaturated fats as opposed to saturated fats which, especially if shorter chain, can lead to a very upset stomach
    • Also, avoid omega-6, polyunsaturated fats as well which are junky anyway

Should you exercise during a prolonged water-only fast?

  • Peter recalls a study:
    • Two groups of men were calorically restricted by 50%
    • Both groups were “exercised like crazy” (similar to ~2 hours of very intense exercise or ~3 hours of modest exercise)
    • Men that received testosterone supplementation gained muscle mass
      • The other group failed to lose muscle mass
  • Exercise is VERY important during a fast
    • For one, exercise should always be a part of a healthy day
    • Exercise seems to augment/amplify autophagy
    • Strength training preserves muscle mass
      • During a fast, mTOR activity is downregulated – strength training during a fast transiently activates mTOR (you’re sort of getting the best of both worlds)
  • On the cardio side, pick and choose your battles
    • Repeated bouts of extremely high-intensity exercise (like with a Tabata) are very difficult during a fast as your glycogen levels are depleted
      • For this reason, this type of exercise is off the table for Peter during a fast
    • A step just below the above in intensity (like the pace a runner or cyclist would use during a race) also becomes difficult during a water-only fast (Peter estimates even well-conditioned athletes are ~50%, if not more, dependent on glycogen during this phase of exercise)
      • This is known as the “functional threshold power” state
      • Peter doesn’t do much of this type of cardio, fasting or not – he much prefers shorter bouts of ultra-high power output or longer battles with zone 2 cardio (below)
    • Below the above, we have zone 2 cardio
      • Zone 2 is the highest level of output at which you can carry out a conversation (more accurately, your lactate levels must be < 2 mmol)
      • Peter typically does four zone 2 workouts a week
      • Zone 2 cardio is completely doable in the fasted state, but Peter much prefers to replace his typical zone 2 workouts with strength training sessions (he tries to lift every day during his fast)
  • The takeaways:
    • Er on the side of lifting more than doing cardio during a fast
    • If you do cardio, adjust your expectations in regards to your capacity to produce glycolytic power
    • Also, adjust your expectations when lifting
      • Strength typically doesn’t diminish during a fast, but your stamina and recovery time between sets will
    • Adjust your expectations in general:
      • “When I’m fasting, I’m only in the gym for about an hour as opposed to my normal 90 minutes”
    • In a sense, strength train during a fast only for as a physiologic stimulus for mTOR

Peter’s Workout Routine

  • Lift – Monday, Wednesday, and Friday
  • Zone 2 cardio – Tuesday, Thursday, and Saturday, and Sunday
  • Tabata workouts on his Peleton – sprinkled throughout

Fasting for Women

  • “I would say, based on my clinical experience, in general, it’s harder for women to fast than men. I don’t know why that is.”
    • Perhaps there’s an evolutionary reason – it’s much more difficult for women to ovulate or lactate while fasting
  • “For women who are trying to get pregnant, I don’t think fasting, I don’t think ketogenic diets, I don’t think anything that signals energy reduction makes sense”

Hot/Cold Therapy During a Prolonged Fast

  • “Few things feel better than a sauna during a water-only fast”
    • Why? – During a prolonged fast, people experience hypothyroidism 
      • Thus metabolism slows and you walk around at a lower body temperature (this is why Peter loves fasting during the summer)
  • Cold therapy tends to increases norepinephrine in the brain which enhances mood
    • There’s no reason you can’t take a cold shower or bath during a fast

Are there long-term negative effects on metabolism if you time-restrict your eating daily?

  • “I don’t think we know the answer yet”
  • As a precaution, Peter only time-restricts his eating 4-5 days a week
    • He recommends his patients do the same (and on the days they don’t time-restrict, he advises them to focus more on what they eat)
  • Peter spent 6 months in 2014 doing eating only 1 meal per day and didn’t notice any negative consequences

Fasting with Hashimoto’s Disease

  • Hashimoto’s is a form of hypothyroidism 
  • Peter’s advice – 100% speak with your endocrinologist or whoever’s managing your hormone medication before fasting

Does citrus bergamot activate autophagy?

  • Some people say it does
    • “I have never seen a credible piece of evidence to suggest that it could in any way, shape, or form increase autophagy”
  • It does have some efficacy at lowing cholesterol – “Though I’m not a fan at using it at all”
  • “I’m not a fan of this supplement in any way, shape, or form”

Are there benefits to fasting even if you don’t enter ketosis?

  • Definitely yes
  • Ketosis = having a blood ketone level of 0.5 mmol or greater
    • If you’re frequently eating carbs, your ketone levels are 0 mmol
    • When most people wake up in the morning, their blood ketone levels are ~0.1 – 0.2 mmol
    • During a prolonged water-only fast, you’ll enter starvation ketosis with a ketone level of 4-7 mmol
  • You can measure your ketone levels with a Precision Xtra 
  • At the end of the day – “It’s a huge mistake to turn fasting into a ketone contest. The idea that the success or failure of your fast is predicated on how high your ketone levels get is total nonsense.”

Additional Notes

  • Peter wears a Dexcom G6 continuous glucose monitor
  • Peter much prefers glass-bottled Topo Chico to plastic-bottled Topo Chico
  • Peter uses both the Lactate Plus and the Lactate Pro to measure his lactate levels during and after doing zone 2 cardio

More Notes on these topics