#11 - AMA #2: the Nothingburger — results from Peter's week-long fast between two weeks of nutritional ketosis — and answering questions on all things fasting
Peter Attia, MD, hosts an AMA and show-and-tell, detailing his personal 3-week 'KFK sandwich' fasting experiment (ketogenic diet, water-only fast, ketogenic diet). He discusses rationale, methods, lab results, and subjective experiences, including surprising changes in sleep and joint pain.
Deep Dive Analysis
12 Topic Outline
Introduction to the KFK Fasting Experiment
Rationale: Autophagy and Optimal Fasting Protocols
Peter's Baseline Lifestyle and Health Metrics
Baseline Lab Markers and Interpretation
Results After Week 1: Ketogenic Diet
Results After Week 2: Water-Only Fast
Subjective Experiences and Surprises During Fasting
Re-feeding and Results After Week 3: Ketogenic Diet
Discussion on Optimal Fasting Frequency and Duration
Best Practices for Breaking a Fast
Defining 'Breaking the Fast' with Various Inputs
Uric Acid as a Potential Autophagy Marker
7 Key Concepts
Autophagy
A process where the body 'eats itself' during nutrient deprivation, conserving energy and recycling suboptimal cellular machinery. It is believed to be a key mechanism for longevity benefits from fasting.
Nutritional vs. Starvation Ketosis
Nutritional ketosis is a metabolic state achieved through a very low-carbohydrate diet, while starvation ketosis is achieved through complete nutrient restriction, such as a water-only fast.
Keto Flu
A colloquial term for the subjective feeling of lightheadedness or orthostatic symptoms experienced when first transitioning into ketosis, often due to electrolyte imbalances.
Total vs. Free Cortisol
Total cortisol measures all cortisol in the plasma, but only the free cortisol (which is unbound to proteins) is metabolically relevant and endocrinologically active. Total cortisol levels alone are often uninformative.
Adrenal Fatigue (Misnomer)
The term 'adrenal fatigue' is largely a misnomer, as clinical adrenal fatigue (requiring corticosteroid treatment) is extremely rare. To accurately measure adrenal output, one must look at cortisol metabolites, not just cortisol, as cortisol represents only a fraction of total output.
Thyroid Axis (T3/rT3 Ratio)
The balance of thyroid hormone conversion, specifically the ratio of active free T3 to inactive reverse T3. A ratio below 0.2 generally suggests peripheral hypothyroidism, where the body is downregulating metabolism, often in response to stress, infection, inflammation, or significant weight loss.
Selective mTOR Inhibition
An ideal longevity strategy that involves selectively inhibiting mTOR (mammalian target of rapamycin) in certain tissues like the liver and fat cells, while maintaining or even stimulating it in skeletal muscle through activities like weight training to preserve lean mass, especially during periods of nutrient restriction.
11 Questions Answered
The primary objective was to save money while in New York by not eating for seven days, as food there is expensive.
The scientific rationale was to develop a protocol to study and identify a 'signature of autophagy' in humans, aiming to better understand and potentially customize optimal fasting protocols for longevity.
He chose the 'KFK sandwich' (ketosis-fasting-ketosis) for self-preservation, knowing that entering a fast from a high-carb state is more painful, and to guard against overeating ('going ape shit') during refeeding.
He consistently practiced time-restricted feeding (14-22 hours daily), avoiding junk food, sucrose, and high-fructose corn syrup, but not explicitly restricting non-junk carbohydrates like rice and potatoes. He lifted weights three days a week and did aerobic/anaerobic exercise on the other four days.
Despite going to bed hungry, his sleep quality significantly improved, with stage 3/4 (deep) sleep numbers being two to three times higher than normal, which persisted throughout the fast and abated upon refeeding.
He experienced no deterioration in strength during weightlifting, feeling 'like a beast' on heavy days, but found it 'impossible to move his legs quickly,' struggling with walking and maintaining cadence on the Peloton, indicating a reduction in power output.
He experienced a profound sense of calmness and mindfulness, meditating more deeply and being more present in his surroundings. He also noted a complete resolution of chronic right wrist pain and significant improvement in left elbow pain.
He subjectively felt he lost no measurable amount of lean tissue, estimating a loss of 1-2 pounds of muscle, 5-6 pounds of fat, and the rest as water mass, which was a pleasant surprise.
There is no known concrete answer, as it depends on the individual and their metabolic state. Peter speculates that nutrient cycling is key for longevity, and the frequency of fasting might depend on the 'damage' done when not fasting.
Peter did not experience GI distress but noted that overfeeding with too much volume after a fast can lead to hiccups, suggesting a cautious re-entry volume strategy with smaller meals initially.
It depends on the goal of the fast. For weight loss (caloric restriction), non-caloric items might not matter. For nutrient sensing/autophagy, it's best to consume 'as much nothing as possible,' as caffeine might artificially create a fed state and artificial sweeteners could re-sensitize appetite.
28 Actionable Insights
1. Implement Nutrient Cycling for Longevity
Incorporate regular periods of fasting and feeding into your lifestyle to promote longevity by cycling autophagy, anabolism, and catabolism, as well as mTOR activity.
2. Maintain Exercise During Fasting
Continue your regular exercise routine, especially weight training, during fasting periods to help preserve muscle mass and send a signal to the muscle to prevent shrinking. While strength may be preserved, high-cadence cardio might be more difficult.
3. Prepare for Fasting with Ketosis
Enter a fasting period from a state of nutritional ketosis to ease the transition and reduce discomfort, as the body will have already ramped up ketone production.
4. Refeed with Ketosis to Prevent Overeating
Exit a prolonged fast by re-entering a ketogenic diet to guard against overeating junk food and maintain reasonable eating habits during the refeeding period.
5. Reintroduce Food Gradually After Fast
Be cautious with the volume of food consumed immediately after a fast to avoid gastrointestinal discomfort, such as hiccups, due to the stomach being decompressed. Start with small, light meals.
6. Adopt Time-Restricted Feeding
Consistently practice time-restricted feeding, aiming for a daily eating window of 2-10 hours (14-22 hours of restriction), most days of the week.
7. Avoid Junk Food and Processed Carbs
Limit or avoid abject junk food, sucrose, high fructose corn syrup, and processed carbohydrates like potato chips to maintain a healthier diet.
8. Individualize Supplement Regimen
Recognize that supplement needs are highly individual; consult with a professional to determine a personalized regimen rather than blindly following what others take.
9. Increase Fasting Frequency if Metabolically Unhealthy
If in a metabolically poor state (e.g., diabetic, hyperinsulinemic, metabolic syndrome), consider increasing the frequency of fasting periods like Fasting Mimicking Diets (FMDs), and potentially reduce frequency as metabolic health improves.
10. Adjust Fasting Frequency Based on Diet Quality
Tailor your fasting frequency to your regular dietary habits; if you tend to eat less healthily, more frequent fasting may be necessary to mitigate damage, whereas a consistently clean diet might require less frequent fasting.
11. Practice Consistent Mindfulness Meditation
Maintain a regular routine of mindfulness meditation, as it can foster a unique sense of calmness and presence, especially during periods like fasting.
12. Track Sleep Consistently
Use a wearable device like an Oura ring to consistently track sleep duration, efficiency, and sleep stages (light, deep, REM) to gain insights into sleep quality.
13. Increase Electrolytes During Ketosis/Fasting
Supplement with increased magnesium and sodium (e.g., via bouillon) during ketosis and fasting periods to counteract electrolyte wasting by the kidneys, which can prevent lightheadedness and cramping.
14. Define Fasting Goals
Clearly understand your specific reasons for fasting (e.g., weight loss, autophagy, metabolic health) to guide decisions about what, if anything, you consume during the fast.
15. Avoid Artificial Sweeteners During Fast
Refrain from consuming artificial sweeteners or chewing gum during a fast, as they can potentially stimulate appetite and disrupt the benefits of the fasted state.
16. Consider Morning Main Meal for Circadian Rhythm
Experiment with shifting your largest meal to the morning and tapering food intake throughout the day to align with circadian rhythm and potentially optimize glucose disposal and insulin sensitivity.
17. Use DEXA Scans for Body Composition
Utilize DEXA scans to track body composition changes, ideally using the same machine and operator for consistent and accurate results over time.
18. Consume FMD Calories in One Meal
When following a Fasting Mimicking Diet (FMD), consume all allowed calories in a single meal, preferably dinner, to satisfy social needs and potentially enhance the feeling of satiety.
19. Prefer High-Carb FMD for Volume
For Fasting Mimicking Diets, a high-carb, low-protein, low-fat approach (e.g., salad and rice) can offer greater volumetric satisfaction compared to a low-carb, high-fat FMD.
20. Track Blood Glucose with CGM
Use a Continuous Glucose Monitor (CGM) like the Dexcom G6 for highly accurate and continuous tracking of blood glucose levels, which is more insightful than finger sticks and doesn’t require calibration.
21. Aim for Optimal Blood Glucose
Strive for an average blood glucose level between 85-90 mg/dL for optimal metabolic health.
22. Aim for Optimal Lipid Markers
Target specific lipid markers for cardiovascular health: LDL-P below 800 nanomole/liter, C-reactive protein below 1 mg/L (ideally below 0.5 mg/L), oxidized LDL below 40 U/L, uric acid below 5 mg/dL, and homocysteine below 9 µmol/L.
23. Aim for Optimal Thyroid Markers
Monitor thyroid function by aiming for TSH below 2 µIU/mL and a free T3 to reverse T3 ratio above 0.2, as these indicate healthy thyroid activity.
24. Consider Dutch Test for Adrenal Health
Use a Dutch test (dried urine test) to measure cortisol and cortisol metabolites, providing a comprehensive assessment of total adrenal output and free cortisol levels, which are more indicative than plasma cortisol.
25. Use Photos for Muscle Mass Assessment
Take sequential photos (e.g., seven days apart) as a simple, zeroth-order method to visually assess changes in muscle mass during dietary experiments.
26. Increase Dental Hygiene During Fasting
During prolonged fasting, increase dental hygiene (e.g., brushing teeth multiple times a day and savoring the toothpaste) to combat taste monotony and enjoy the sensation.
27. Review Podcast Show Notes
Always review the show notes for podcasts, especially those discussing experiments or data, as they often contain detailed information and metrics not fully covered in the audio.
28. Use AMA Page for Questions
Utilize the upcoming AMA page on the website to submit questions, allowing for more efficient aggregation and tabulation of popular topics.
5 Key Quotes
The secondary objective was actually to try to work out the kinks on a protocol that I would like to study later on to see if I can, in collaboration with a number of scientists, figure out what a signature of autophagy looks like.
Peter Attia
I think most people realize both scientifically and practically that to just take an individual and constitutively restrict their calories by say 30% or more, one, it's not clear that that actually produces a longevity phenotype in humans in the wild. And two, even if it did, it's not clear you'd want to do it.
Peter Attia
I felt like I'd slept 10 hours, even though I'd probably slept, I'd have to go back and look, but it might've been six and a half or something like that or seven. But my stage three, stage four numbers, which are typically the lowest numbers were surprisingly high.
Peter Attia
I don't think that doing a seven-day fast once a year and for the other 51 weeks of the year just eating like shit is going to do that much. It's probably better than just eating like shit 52 weeks a year, but I don't know if it's enough to move the needle.
Peter Attia
The thing that fits that description the most for me is actually the uric acid of eight after the fast. So even though the thyroid numbers are comical and the testosterone story is interesting, I can, I think I can generate reasonable hypotheses around them, especially the thyroid stuff.
Peter Attia
2 Protocols
Peter Attia's KFK (Ketosis-Fasting-Ketosis) Sandwich Experiment
Peter Attia- **Week 1 (Ketogenic Diet):** Consumed a boring, repetitive ketogenic diet (estimated 30-40g carbs/day, 110-120g protein/day), usually skipping breakfast or having a small one, with coffee and MCT powder. Lunch included macadamia nuts, avocado, olives. Dinner was salad and modest protein.
- **Supplementation during Ketosis Week:** Doubled magnesium intake to 800mg magnesium oxide and four Slow-Mag tablets daily, and used bouillon as needed to prevent lightheadedness and cramping.
- **Exercise during Ketosis Week:** Maintained regular exercise routine (weightlifting Monday/Wednesday/Friday, aerobic/anaerobic on other days).
- **Week 2 (Water-Only Fast):** Consumed only water and bouillon (sodium only, no fat or calories). Strictly avoided coffee, caffeinated tea, artificial sweeteners, and chewing gum.
- **Exercise during Fasting Week:** Maintained regular exercise routine, noting that power output on the bike was significantly reduced, while strength during weightlifting was maintained.
- **Week 3 (Ketogenic Diet Refeed):** Broke the fast with a small salad and chili, followed a few hours later by a larger meal (Atiyah curry stir fry). Then returned to a ketogenic diet, consuming a lot of dairy (heavy cream).
- **Exercise during Refeed Week:** Maintained regular exercise routine.
Peter Attia's Preferred Fasting Mimicking Diet (FMD) Method
Peter Attia- Consume the entire daily caloric allowance (e.g., 750 kcal/day) in one sitting, typically at dinner, to satisfy social needs and provide a sense of eating.
- Focus on a very high-carb, low-protein, low-fat meal, such as salad and rice, to achieve volumetric satisfaction, which is often lacking in low-calorie ketogenic FMDs.