Drinking black coffee may not break a fast, but adding milk or sugar might. The Big IF study aims to understand how intermittent fasting affects hunger levels, mood, and energy.

Tim Spector, a top scientist and regular faster, discusses the debate between 'clean fasters' and 'dirty fasters' regarding what can be consumed during fasting windows.

Some believe up to 50 calories won't break a fast, while others adhere strictly to water. Tea and coffee contain fiber, but it's believed not to significantly impact fasting and eating periods.

Adding sugar to your coffee or tea will definitely break your fast, as it sends signals to your brain and gut to expect food, shifting your body from a repairing resting state to sudden alertness.

We never have to break a fast again. Sometimes we make mistakes. Tim says that's okay, especially if you intend to make fasting a part of your life going forward.

Tim Spector emphasizes the importance of finding a balance between practicality and perfection when it comes to intermittent fasting. He suggests not beating yourself up if you can't adhere to it every single day due to social circumstances or different lifestyles.

Jonathan Wolff advises not to give up morning tea or coffee to stay in a fasted state and suggests adding a splash of milk if it helps adhere to the plan. He also highlights the significance of not adding anything beyond that to avoid breaking the fast.

The episode is part of a limited series celebrating the launch of The Big If Study, the world's biggest clinical study on intermittent fasting. To participate for free, one can visit joinzoe.com/thebigif or the link in the show notes.