Why small calories on 'fast' days can ruin fasting

James argues that even small calorie intakes on fasting days can interrupt fasting physiology and reduce benefits.

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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