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Jason Fung

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Jason Fung
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Fung is one of the worst charlatans out there. Fear mongering money hungry charlatan. His claims have been debunked numerous times. He uses fear to spread misinformation to sell his stuff.
—Nutritional scientist Layne Norton on Jason Fung[1]
Low carbohydrate high fat breakfast

Jason Fung (1973–) is a Canadian nephrologist, cholesterol denialist, and low-carbohydrate diet advocate who promotes pseudoscientific views about nutrition. Fung advocates intermittent fasting and a low-carbohydrate high-fat diet to prevent and treat practically every disease, including cancer, heart disease, and obesity.[2][3][4] Fung advertises himself as a "world expert" on intermittent fasting.[2]

Fung is a functional medicine proponent (a type of alternative medicine pseudoscience) who works with naturopaths.[5] He has authored many low-carbohydrate books and cookbooks and chooses to avoid publishing his ideas in peer-reviewed medical journals.[6][7] His book The PCOS Plan: Prevent and Reverse Polycystic Ovary Syndrome Through Diet and Fasting was co-authored with naturopath quack Nadia Brito Pateguana.[8] Similar to Eric Berg, Fung promotes his low-carb dietary views on YouTube.[9]

Fung has been criticized for bullying academics who disagree with his low-carb dietary views and fat-shaming physicians.[10][11]



Fung argues that intermittent fasting (IF) and a ketogenic diet can prevent and treat cancer and wrote a book, The Cancer Code[12] making far-fetched claims.[13][14] As of 2022, there is no reliable evidence that intermittent fasting and a ketogenic diet can prevent or treat cancer.[15] A recent review concluded that although some limited preliminary studies have reported positive results "the effects of IF on human cancer incidence and prognosis remain unknown because of a lack of high-quality randomized clinical trials".[16] The American Cancer Society does not recommend fasting to prevent cancer.[17] Fung has claimed:

The people who live traditionally in Africa get no cancer, no colon cancer, but the minute they transitioned to a Western-style civilization with their foods … they actually start to get cancer.[14]

Fung's claim that native Africans never get cancer is not supported by any evidence. However, it has been reported that there is a reduced incidence of colorectal cancer among natives of West Africa because such populations have little meat in their diet and instead eat a lot of fibre from fruits, grains, and vegetables. Many West African nations traditionally consume a high-carbohydrate, high-fiber diet that is low in animal protein with grains such as boiled maize-meal content.[18][19] This diet is the complete opposite to Fung's, as he recommends a low-carbohydrate high-fat diet with lots of animal protein.


Fung sells The Fasting Method Coaching Program™ which costs $1199. A 30-minute session with one of his fasting coaches including naturopaths costs a whopping $199.[20] He says he can reverse type 2 diabetes "naturally" with intermittent fasting.[21]

Fung is a big proponent of "detoxing" and formulated the product "Ginger Fasting Green Tea" with the company Pique[22] He is a fan of tea fasting and says green tea helps fasting.[23][24] He also controversially promotes water fasting which has been described as dangerous for those with pre-existing medical conditions.[25]

Dr Alastair McAlpine has noted that:

When Fung is not fat-shaming respected colleagues, he is appearing on the blog of some of the world’s biggest quacks. When he’s not spouting nonsense about cancer (and falsely claiming cancer deaths are going up, ignoring the last 30 years of data which show they’re coming down), he’s promoting dubious green tea products (which he is paid for). This despite a comprehensive Cochrane Collaboration meta-analysis that shows they have no statistical effect on weight loss.[2]

In a 2022 interview on fasting with his friend Vinnie Tortorich, Fung stated that weight loss isn’t about calories, its about insulin and allowing your cells to work.[26]

Fung spends most of his life promoting intermittent fasting but there is no good evidence that it has any health benefits as most of the studies that have been done are based on animal models.[27][28] Animal model findings are not considered strong evidence in clinical medicine, nor do they translate consistently into clinical effects in human beings but Fung does not understand this.

Bullying and fat-shaming[edit]

Fung has been accused of "fat-shaming" physicians in general and bullying those who have criticized his low-carb dietary views.[10] In 2016, Fung "fat-shamed" two obesity researchers on Twitter for being fat themselves. Both researchers were keynote speakers at the 2016 Obesity Week.[11] In response, Dr Yoni FreedhoffWikipedia took issue with Fung's behaviour on Twitter. Fung then filed a complaint to Dr Freedhoff's department in an attempt to get him fired. However, the opposite happened and Dr Freedhoff was promoted to Associate Professor.[29] He tried to get Dr Alastair McAlpine fired from his job after he wrote an article questioning Fung's cancer statistics and green tea promotion.[30] Fung also tried to get Layne Norton fired from his job after he criticized Fung's pseudoscientific dietary views, but Norton is self-employed.[31]


  1. Layne Norton. Twitter.
  2. 2.0 2.1 2.2 Intermittent fasting: From Pythagoras to Fung.
  3. How to Reverse Fatty Liver Disease Naturally.
  4. The Science of Intermittent Fasting (Foods to Live Longer & Reverse Type 2 Diabetes.
  5. Jason Fung, MD.
  6. Dr. Jason Fung, MD.
  7. Books.
  8. Meet the authors of “The PCOS Plan”
  9. Jason Fung.
  10. 10.0 10.1 It’s Not Calories… It’s Hormones: A Response to Dr. Jason Fung
  11. 11.0 11.1 Fat shaming, explained in one terrible tweet
  12. The Cancer Code: A Revolutionary New Understanding of a Medical Mystery by Jason Fung (2020) Thorsons. ISBN 0008436207.
  13. The Cancer Code with Dr. Jason Fung – Diet Doctor Podcast
  14. 14.0 14.1 Can We Prevent Cancer Just By Fasting?.
  15. Römer M, Dörfler J, Huebner J. (2021). "The use of ketogenic diets in cancer patients: a systematic review". Clin Exp Med 21 (4): 501–536. doiWikipedia:10.1007/s10238-021-00710-2. PMC 8505380. PMID 33813635. 
  17. American Cancer Society Guideline for Diet and Physical Activity for Cancer Prevention
  20. Weight Loss Coaching.
  21. Dr. Jason Fung.
  22. Ginger Fasting Green Tea
  23. Do NOT miss this! Fasting Tea Challenge with Dr. Jason Fung
  24. Green Tea Helps Fasting.
  25. Is this the most dangerous diet ever?.
  26. Your Fasting Questions Answered with Dr. Jason Fung – Episode 2241
  27. Intermittent fasting may not be all it’s cracked up to be, study finds
  28. Intermittent fasting leads to weight loss, not improved health
  29. Yoni Freedhoff. Twitter.
  30. Alastair McAlpine. Twitter.
  31. Layne Norton. Twitter.