Fasting Flexibility: An Interview With Dr. Jason Fung

Intermittent and long-term fasting both have a range of health benefits. IFM Director of Medical Education Dan Lukaczer, ND, IFMCP, recently spoke with Jason Fung, MD, to discuss the challenges, benefits, and misconceptions involved. Dr. Fung explains that there are a “huge number of diseases, chronic diseases that potentially could benefit from the application of intermittent fasting.”

Dr. Fung is a nephrologist and expert on the use of fasting as a clinical tool to promote patient health. He is the author of The Obesity Code, The Complete Guide to Fasting, and The Diabetes Code, and he founded a clinically applicable health program that provides fasting strategies to promote weight loss, enhance cellular rejuvenation, and manage blood sugars.

What we are describing is an entire rejuvenation process.

– Dr. Fung

In this interview, Dr. Fung shares his knowledge and clinical insights on the downstream benefits of fasting as well as the mechanisms involved. He also expands on the flexibility of fasting strategies and on balancing the feeding and fasting periods for each patient to create the most effective therapeutic treatment. Dr. Fung believes that many chronic conditions may benefit from fasting, “which is fascinating,” he notes, “because it’s an entirely free and natural treatment, yet it seems to be incredibly powerful.”

*Please note that Dr. Fung was at the airport when this interview was recorded which may have impacted the audio quality.

One important topic covered in Dr. Fung’s interview is autophagy, which can be described as a cellular recycling system that occurs when cells clean out any unnecessary or damaged components. Autophagy also acts as an immune effector that mediates pathogen clearance.1 Fasting is a potential trigger of autophagy, and recent research has highlighted its potential therapeutic role in some inflammatory diseases.2 “The oldest and sort of junkiest organelles get thrown into the furnace,” explains Dr. Fung. “They get burned for energy, and when you start to eat again, because growth hormone is high, what you do is that you use the amino acids to rebuild the protein where you need it.”

The following text gives a bulleted breakdown of some of the topics discussed during the interview.

Challenges for those new to fasting:
  • Expectations regarding cravings and feeling hungry
  • Understanding metabolism and how the body chemically responds to fasting
Addressing muscle-loss concerns:
  • The effects of calorie restriction versus fasting strategies
  • Retaining lean mass and an active metabolic rate
  • A changing hormonal profile and accessing fat stores
  • Heightened growth hormone levels
Advising clinicians on appropriate fasting durations:
  • Personalized treatment strategy
  • Medical conditions to consider
Downstream benefits of fasting and mechanisms:
  • Weight loss and managing type 2 diabetes
  • Lowering obesity-related cancer risk
  • Autophagy and cellular rejuvenation
  • Developing research on anti-aging and disease prevention
Ketosis and intermittent fasting:
  • General overlaps with ketogenic diet
  • Ketone production and brain health
  • Fasting impacts and benefits distinguished from ketogenic diet
Chronobiology and optimization of fasting:
  • Timing impacts hunger and insulin response
  • Balancing lifestyle and social routines with fasting
  • Fasting flexibility with dynamic schedules, vacations, and holidays
Groups with potential fasting cautions or required monitoring:
  • The balance of feeding periods and fasting periods
  • Women who are pregnant, children, patients on different medications
  • Fasting as a clinical tool
Professional training opportunities for clinicians on fasting strategies:
  • Advanced lecture courses through fastingmethods.com

IFM’s Intermittent Fasting: Therapeutic Mechanisms & Clinical Applications course provides an evidence-based overview of several of the fasting methods listed above and outlines potential contraindications and points of personalization for each patient’s unique health needs and goals.



  1. Kuballa P, Nolte WM, Castoreno AB, Xavier RJ. Autophagy and the immune system. Annu Rev Immunol. 2012;30:611-646. doi:10.1146/annurev-immunol-020711-074948
  2. Qian M, Fang X, Wang X. Autophagy and inflammation. Clin Transl Med. 2017;6(1):24. doi:10.1186/s40169-017-0154-5

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