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

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? 🌱 Try our science-backed and tasty wholefood supplement Daily 30 Get our brand-new app and Gut Health Test designed by world-leading gut health and nutrition scientists to build healthy eating habits 👉 Join ZOE Follow ZOE on Instagram. 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 18:15 The tiny mistake that ruins a fast 19:45 Why stricter fasting can feel easier 20:20 Why hunger disappears after a few days 21:20 What happened when he fasted for 5 days 22:35 What you can actually have during a fast 24:25 Do coffee and tea break your fast? 26:20 The truth about breakfast (finally tested) 28:15 The breakfast result no one expected 29:15 The hidden downside of fasting 32:20 What your body switches to when you stop eating 34:25 What really happens on day two of fasting 35:30 Why fasting might improve your health 37:05 Does fasting reduce inflammation? 38:25 What fasting actually helps with 39:20 How much weight people really lose 40:00 The most effective way to fast 41:00 The minimum fasting window that works 42:30 Who benefits most from fasting 44:30 Should you exercise before eating? 47:20 Do your eating times need to be consistent? 50:25 Does olive oil secretly break a fast? 51:45 The one rule for breaking a fast 53:40 The biggest takeaway about fasting 58:15 Should you actually try fasting? 📚Books by our ZOE Scientists The Food For Life Cookbook Every Body Should Know This by Dr Federica Amati Food For Life by Prof. Tim Spector Ferment by Prof. Tim Spector Good Mood Food (preorder) by Prof. Tim Spector Free resources from ZOE The Hormone Harmony Guide: Tuning Your Body’s Internal Orchestra Eating for Better Brain Health: Your brain-gut blueprint How to eat in 2026 - Discover ZOE’s 8 nutrition principles for long-term health Live Healthier: Top 10 Tips From ZOE Science & Nutrition Gut Guide - For a Healthier Microbiome in Weeks Better Breakfast Guide Mentioned in today's episode Effect of the 5:2 Diet on Weight Loss and Cardiovascular Disease Risk, The International Journal of Endocrinology (2025) Intermittent fasting ‘no magic bullet for weight loss’, Science Translational Medicine (2021) Bath Breakfast Project, Springer (2011) The role of intermittent fasting and meal timing in weight management and metabolic health. Proceedings of the Nutrition Society, (2020) The causal role of breakfast in energy balance and health: a randomized controlled trial in lean adults. American Journal of Clinical Nutrition, (2014) Nutrient timing and metabolic regulation. The Journal of Physiology, (2022) Calorie counting vs. minute counting; does nutrient timing matter for weight-loss? Current Opinion on Clinical Nutrition and Metabolic Care, (2025) Have feedback or a topic you'd like us to cover? Let us know here.Episode transcripts are available here.