Fasting and muscle
From our Jason Fung profile
Fung uses long fasts; Attia moved away from them after losing muscle, and Lyon and Sims caution against fasting for active people in midlife.
Compare experts › Gabrielle Lyon vs Jason Fung
Gabrielle Lyon vs Jason Fung
Gabrielle Lyon (physician (do)) 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.
Words explained (7)
- Zone 2
- Steady cardio at a pace where you can still talk in full sentences, but not sing.
- Intervals
- Short hard efforts with easy recovery in between, such as 30 seconds fast, 90 seconds slow.
- 4 × 4
- Four rounds of 4 minutes hard with 3 minutes easy in between. Also called Norwegian intervals.
- Mobility
- Moving your joints freely through their full range.
- Leucine
- A building block of protein that helps switch on muscle building. Meat, fish, eggs, dairy and soy are rich in it.
- Creatine
- A well-studied supplement that supports strength and muscle.
- Time-restricted eating
- Eating all your meals within a set window of the day, for example 8am to 6pm.
At a glance
| Measure | Gabrielle Lyon | Jason Fung |
|---|---|---|
| Background | Physician (DO) | Physician, kidney specialist |
| Training split | 60% strength · 20% aerobic · 15% intervals · 5% mobility | 45% strength · 35% aerobic · 12% intervals · 8% mobility |
| Signature habit | 30–50 g protein a meal | Fasting, less sugar |
| Protein | ~2.2 g per kg ideal weight | No fixed target |
| Training style | Muscle-first | Fasting |
| Overall evidence | Strong | Mostly weak |
| Following | Instagram 1.2M · YouTube 288K | YouTube 1.5M |
Training splits are our estimates from each expert’s published routine. Following checked October 2026.
The key differences
- Lyon puts more of the week into strength: about 60% against 45%.
- Fung puts more of the week into aerobic base (zone 2): about 35% against 20%.
- In plans in their style, Lyon's hard sessions are 1-minute intervals; Fung's are 4-minute intervals (Norwegian 4 × 4).
- We rate the evidence behind Lyon's protocol higher: strong, against mostly weak for Fung.
- Supplements that go into a plan: Lyon, creatine monohydrate; Fung, none (food first). Prescription items and personal stacks stay out of every plan.
- Only Lyon has a mobility or movement routine of their own.
Where they disagree
Protocols side by side
Each line is rated for the evidence behind it. “Doctor only” items never go into a plan.
Training
Gabrielle Lyon
- Resistance training 3–4 days a week, done with focusStrong evidence
- 1–2 days a week of short, higher-intensity intervalsSome evidence
- Steady aerobic work, such as a 30-minute session or a brisk walkStrong evidence
- Move after meals: a walk, some air squats or a short bodyweight circuitSome evidence
- For older adults who do nothing yet, any regular resistance training is the priorityStrong evidence
Jason Fung
No specific guidance in what we reviewed.
Eating
Gabrielle Lyon
- About 2.2 g per kg of ideal body weight a day (she also gives 1.2–1.6 g per kg, sometimes up to 1.8 g per kg)Some evidence
- 30–50 g of high-quality protein at the first meal, and a similar large dose at the last mealSome evidence
- About 2.5 g of leucine (roughly 30 g of quality protein) per meal, and about 9 g of leucine across the daySome evidence
- People eating mainly plants may need more total protein, around 1.6 g per kg, because plant protein is lower quality per gramSome evidence
- For inactive people, about 130 g of carbohydrate a day, roughly 40–50 g per meal, with more after exercisePersonal habit
- Older adults should avoid long fasts, which can speed muscle lossSome evidence
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
Supplements
Gabrielle Lyon
- Creatine supports muscle; she mentions possible brain benefits at higher dosesSome evidence
- Prefer complete protein foods over leucine alone; amino acid supplements make most sense when a meal is low in proteinNote
- She regards the official leucine allowance (about 2.7 g a day) as too low because it was based on young menNote
Jason Fung
No specific guidance in what we reviewed.
Weak spots to know
Gabrielle Lyon
- Her daily target of about 2.2 g per kg of ideal body weight is well above the official allowance of 0.8 g per kg and the 1.0–1.2 g per kg that an expert group recommends for over-65s; whether intakes that high add further benefit for most older adults is still debated.
- The 'leucine threshold' idea behind her per-meal targets and her food rankings is contested; critics such as Simon Hill argue that total protein matters more and that well-chosen plant proteins can meet needs.
- Some of the foundational research she draws on, such as Layman's 2005 study, was partly funded by beef and food industry groups.
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 Lyon, 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.
Questions
What is the main difference between Gabrielle Lyon and Jason Fung?
Their training split differs most in strength: Lyon about 60%, Fung about 45% (our estimate from their published routines). Lyon's signature habit is 30–50 g protein a meal; Fung's is Fasting, less sugar.
How much protein do Lyon and Fung recommend?
Lyon: ~2.2 g per kg ideal weight. Fung: No fixed target.
Whose advice has stronger evidence?
We rate the evidence behind Lyon's protocol higher: strong, against mostly weak for Fung.
Do Lyon and Fung disagree?
Yes, on fasting and muscle. See "Where they disagree" on this page.
Can I combine Lyon 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.
More comparisons
Peter Attia vs Gabrielle LyonAndrew Huberman vs Gabrielle LyonAndy Galpin vs Gabrielle LyonGabrielle Lyon vs Rhonda PatrickGabrielle Lyon vs Layne NortonGabrielle Lyon vs Stacy SimsPeter Attia vs Jason FungAndrew Huberman vs Jason FungAndy Galpin vs Jason FungRhonda Patrick vs Jason FungLayne Norton vs Jason FungStacy Sims vs Jason FungAll comparisons →
Full sources are on each profile: Gabrielle Lyon · Jason Fung. Reviewed October 2026.