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3 intermittent fasting mistakes that cancel fat loss and stop you seeing the benefits | Prof James Betts

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Apr 9, 2026

Guest

James Betts

Prof James Betts, a physiology professor at the University of Bath who researches meal timing and fasting. He explains what truly counts as a fast and why small calories can cancel benefits. He contrasts fasting styles like 5:2 and time-restricted eating. He discusses hunger dynamics, what you can drink during a fast, and why planning your first meal matters.

57:46

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ANECDOTE

James Betts Monday To Friday Fast Experience

James Betts personally fasted Monday to Friday and reported intense hunger day two that disappeared by day three, then felt energized by day four.
He monitored low blood glucose and rising ketones coinciding with regained energy and diminished hunger.

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ADVICE

Only Drink Water During A True Fast

During a physiological fast avoid macronutrients and alcohol; water is the only true fast-friendly drink according to Betts.
For controlled studies he even excludes caffeine because caffeine perturbs metabolism, though practical guidance allows coffee/tea.

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INSIGHT

Breakfast Isn't Universally Beneficial

Bath Breakfast Project randomized people to breakfast vs skipping until midday and found no clear overall metabolic advantage to breakfast.
Lean people lost weight when skipping breakfast; people with obesity tended to compensate later or gain weight with breakfast.

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What is nutrient timing and why it matters

01:41 • 7min

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Defining the fasted vs postprandial state

08:44 • 7min

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Types of intermittent fasting explained

15:31 • 2min

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Why small calories on 'fast' days can ruin fasting

17:01 • 3min

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Hunger paradox: stricter fasts can feel easier

19:40 • 3min

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What you can consume during a fast

22:11 • 3min

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Bath Breakfast Project: does breakfast matter?

25:26 • 4min

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What fuels your body use when fasting

29:49 • 3min

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Why fasting might improve metabolic health

32:40 • 2min

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Fasting, inflammation and autophagy evidence

34:17 • 2min

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How much weight people lose fasting

35:57 • 1min

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Practical fasting patterns for sustainability

37:25 • 5min

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Exercise while fasted: pros and cons

42:23 • 3min

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Eating time consistency and circadian cues

45:11 • 3min

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Does olive oil or small fats break a fast?

48:19 • 1min

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How to break a fast sensibly

49:37 • 2min

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Key takeaways: who benefits and final advice

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Intermittent fasting may help with blood sugar, appetite, fat loss, and energy. But many people do it wrong.

In this episode, Professor James Betts, one of the world’s leading experts on meal timing and its metabolic effects, explains what fasting actually is, how long you need to fast to see changes, and the key mistakes that can stop the benefits.

Today, we break down what happens in your body when you stop eating and explain why it may support weight loss and blood sugar control, but also why fasting doesn’t work for everyone. You will learn why breakfast may not matter, why the 5:2 diet often fails, and why eating even small amounts can stop a true fast.

By the end of this episode, you will understand what counts as a real fast, how long your eating window may need to be, why longer is not always better if you cannot stick to it, and why planning your first meal matters, because hunger can drive poor choices.

If fasting can work, but is not magic, what actually makes the difference: the timing, the consistency, or simply eating less?

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Timecodes

00:00 Intro

02:30 The answers that completely contradict fasting advice

09:10 What fasting really means (it’s not what you think)

12:10 Why most people never actually fast

14:25 Why “eat to fuel your day” may be wrong

16:00 The 3 types of fasting people confuse

17:30 Why 5:2 might not work the way you think