Dr. Peter Attia – Zero Fasting Q+A | Part I

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Key Takeaways

  • Whether or not black coffee “breaks the fast” depends on the reason you’re fasting
  • Aim to break longer fasts (anything more than 3 days) with:
    • A smaller meal (your stomach shrinks during a fast, and it’s best to slowly reintroduce food)
    • A meal limited in carbohydrates (a meal too high in carbohydrates will result in an unpleasant glucose crash)
  • Fish oil, vitamin D, and branched-chain amino acids all probably “break the fast” and are best to avoid while fasting
  • Autophagy probably starts occurring around day 3 of a prolonged fast
    • Autophagy is essentially the process by which your body breaks down damaged cells/cellular components


  • This is a Q&A with Dr. Peter Attia (@PeterAttiaMD) and Mike Maser, the CEO of Zero, a fasting app
    • Peter is The Peter Attia Drive Podcast – check out the Podcast Notes
  • Check out the Podcast Notes from the last Zero Fasting Q&A with Dr. Rhonda Patrick
  • “I don’t think anybody 100% knows the answer to any question we’re about to answer…my default is that everything we’re saying, we’re speculating on”

Does black coffee or herbal tea break a fast?

  • It depends on your objective
    • If you’re practicing time-restricted feeding for weight loss/calorie restriction:
      • Black coffee won’t affect this
      • Caffeine/black coffee can actually help mitigate hunger
    • If you’re practicing time-restricted feeding to help gastrointestinal issues/rest the gut:
      • In this situation, coffee would break the fast (it would be altering the gastric pH and lots of stuff related to it)
    • If you’re practicing time-restricted feeding (or doing a longer fast) for autophagy purposes (autophagy is essentially the process by which your body breaks down damaged cells/cellular components):
      • In short, we don’t know – we can’t measure autophagy in the body
  • For herbal tea, it’s a little different (it’s probably okay to consume during a fast – it’s not thought to affect autophagy)
    • When Peter does his longer 7-day fasts once per quarter, he consumes “flat water”, “bottled water”, herbal tea, and bouillon (which is basically sodium and water)

Time-Restricted Feeding vs. Fasting

  • Fasting = Going 3-7 days without food and only water
  • Going 12-18 hours without eating = time-restricted feeding
    • Where it gets gray is when people go 24 hours without eating

What’s the best type of food to break a fast with? What about entering a fast?

  • “The easiest way to enter a fast is through a state of nutritional ketosis”
    • (ketosis entered through a ketogenic diet)
  • “If you eat too much on the exit, especially for longer fasts, you’re gonna pay the fiddler”
    • During a fast, your stomach shrinks quite a bit and when you eat a ton afterwards, you’ll experience “gastric distention”
    • When you’re fasting (around the 3rd-5th day), your body goes into a physiological state of insulin resistance (aka transient insulin resistance)
      • Your muscles are doing a good job of making sure all of your circulating glucose is preserved for the brain (so your muscles are running on fatty acids and ketones)
        • Even with a very, very long fast – glucose is providing ~half the energy for your brain and the other half comes from ketones
        • As the fast goes on, the muscles rely less and less on glucose
      • So if you break a fast with a pizza, your blood glucose levels will skyrocket due to the state of insulin resistance you’re in
        • Thus, your body is going to do everything possible to normalize your glucose levels (it will most likely overshoot though, resulting in a glucose crash)
    • Peter likes to break his fast with a small meal limited in carbohydrates
      • His go-to is a small salad with a bowl of chili or scrambled eggs
    • In general, aim to break a fast with foods that are least likely to disrupt your glucose levels
      • Eat more complex carbs, both soluble + insoluble fiber, more fat/protein

Do supplements/medication/vitamins break the fast? Do they affect autophagy?

  • We don’t know the answer…
  • As a general rule, Peter himself (and his patients) stop taking most of their medications/supplements during a fast
    • This includes things like fish oil and vitamin D – they’re technically nutrients, so best to avoid
      • Same thing goes for branched-chain amino acids (BCAAs)

How long does it take for your body to undergo autophagy?

  • “For autophagy to reach the level it’s going to have a clinical impact, you have to be far enough away from nutrients that you’d probably start to see measurable changes”
    • As a random aside:
      • The body tends to preserve a normal level of leucine (an amino acid important for building muscle) during a fast
      • But methionine (another amino acid) levels tend to drop during a fast
  • Peter has noticed that during the first 1-2 days of a fast, his glucose levels don’t really change that much compared to when he’s eating (checked with his continuous glucose monitor)
    • This is probably due to short-term bursts in cortisol during the first few days of a fast (which causes glucose levels to rise)
    • But by day 3 of his fasts – his glucose level starts to drop to a constant (which for him, is around 60 mg/dL or ~3.5 mmol/L)
      • His thinks this is when autophagy starts occurring

Is it wise to train fasted when trying to build muscle?

  • Intermittent fasts (3-5 day fasts) done several times per year do not appear to impair muscle building
  • Time-restricted feeding also does not appear to impair the building of muscle
    • Ideally, you want to exercise at the end of your fasting window and eat immediately after exercise

Random But Useful

  • “Once you free yourself from the constant drip of food, you realize the mental clarity that comes from that…the ability to have regulated energy levels is remarkable”
  • “Your food environment informs so many of your choices” – Mike
  • During his fasts, Peter does a hard workout at least 1x/day
  • If you experience headaches while time-restricting your feeding, it’s probably due to a caffeine withdrawal
  • Peter does a 7-day fast 4x per year
    • He always begins his fasts on a Sunday (when he flies from San Diego to NY for work)

These notes were edited by RoRoPa Editing Services