Rangan Chatterjee (doctor, former nhs gp) and Jason Fung (physician, kidney specialist) side by side: how they train, eat, supplement and sleep, how strong the evidence is, and how to build a plan from either or both.
Training splits are our estimates from each expert’s published routine. Following checked October 2026.
The key differences
Fung puts more of the week into strength: about 45% against 30%.
Chatterjee puts more of the week into aerobic base (zone 2): about 50% against 35%.
In plans in their style, Chatterjee's hard sessions are 1-minute intervals; Fung's are 4-minute intervals (Norwegian 4 × 4).
We rate the evidence behind Chatterjee's protocol higher: solid, against mostly weak for Fung.
Supplements that go into a plan: Chatterjee, none (food first); Fung, none (food first). Prescription items and personal stacks stay out of every plan.
Only Chatterjee has a mobility or movement routine of their own.
Protocols side by side
Each line is rated for the evidence behind it. “Doctor only” items never go into a plan.
Training
Rangan Chatterjee
Walk at least 10,000 steps a daySome evidence
Strength training twice a weekStrong evidence
Short daily glute exercises (e.g. hip extensions), a couple of minutesPersonal habit
Five-minute home workout: five moves back to back, 20 s on / 40 s off for beginners or 40 s on / 20 s off for advanced, five roundsSome evidence
Swap any move that is too hard, painful or unsafeNote
Jason Fung
No specific guidance in what we reviewed.
Eating
Rangan Chatterjee
Eat within a 12-hour window (for example 8am to 8pm), leaving about 12 hours a day without foodSome evidence
Five portions of different vegetables every dayStrong evidence
Around eight glasses of water a dayPersonal habit
Eat at least one meal a day at a table, with no phone or device nearbyPersonal habit
No fixed protein target in the sources we checkedNote
Jason Fung
Cut added sugar and refined grains; eat whole foods with natural fats.Some evidence
Stop snacking: three meals a day, then skip one meal a day.Personal habit
Eat within a shorter window of the day (time-restricted eating).Some evidence
Fasts of 24 hours (skipping two meals in a row) two or three times a week, as used in his clinic's programme.Personal habit
Longer fasts of several days; in 2016 he said fasts of up to a month were fine.Doctor only
For type 2 diabetes: no sugary drinks, fructose or processed food, and more natural fats.Doctor only
Sleep & recovery
Rangan Chatterjee
A tech-free wind-down before bed, ideally about 90 minutesSome evidence
Set a cut-off for work email in the evening (e.g. 8–8:30pm)Personal habit
Avoid emotionally charged topics, such as money worries, late in the eveningPersonal habit
Get daylight or time in nature in the morning, even five minutes, to help set the body clockSome evidence
Jason Fung
No specific guidance in what we reviewed.
Stress & mind
Rangan Chatterjee
A daily stillness practice, starting with two minutes of meditationSome evidence
3-4-5 breathing: in for 3, hold for 4, out for 5, for about five minutesSome evidence
One full screen-free day a weekPersonal habit
Before bed, write down three things that went well and whySome evidence
Five minutes a day enjoying natureSome evidence
Jason Fung
No specific guidance in what we reviewed.
Weak spots to know
Rangan Chatterjee
The 4 pillar approach is broad, sensible lifestyle advice, but the evidence behind specific claims is mixed; for example, a large trial found a daily eating window added no significant weight loss on top of cutting calories.
Some targets are round rules of thumb rather than research-based numbers: the 10,000-step goal is higher than where the benefit levels off for people over 60 (about 6,000–8,000), and eight glasses of water a day is a convention, not a tested target.
He has commercial ties alongside his health advice: books, an app and a paid community, and since 2023 an advisory role with Levels, a glucose-monitoring company.
Jason Fung
Red Pen Reviews scored The Obesity Code at 31% for scientific accuracy, and The Diabetes Code at 33%.
His central claim that calories do not matter is contradicted by controlled studies.
Much of his support comes from case reports, small older studies and his own clinic.
Build a plan from Chatterjee, Fung or both
Your free plan shows a week of gym sessions, cardio, a day of eating, supplements and mobility, fitted to your age, time and health.
What is the main difference between Rangan Chatterjee and Jason Fung?
Their training split differs most in strength: Chatterjee about 30%, Fung about 45% (our estimate from their published routines). Chatterjee's signature habit is Relax · eat · move · sleep; Fung's is Fasting, less sugar.
How much protein do Chatterjee and Fung recommend?
Chatterjee: No fixed target. Fung: No fixed target.
Whose advice has stronger evidence?
We rate the evidence behind Chatterjee's protocol higher: solid, against mostly weak for Fung.
Do Chatterjee and Fung disagree?
Not directly in what we reviewed. Their differences are in emphasis: fung puts more of the week into strength: about 45% against 30%.
Can I combine Chatterjee and Fung?
Yes. In Build my mix you choose one expert per area, for example one for strength and another for eating. Your free plan shows the result straight away.