What breaks a fast?

The concept of what breaks a fast is quite complex and contextual. It's not as simple as saying food X or beverage X breaks a fast. Here are a few key points to consider:

1. Type of Food: The type of food you consume matters. For instance, if you consume mostly fats, it probably won't break your fast. This is because fats won't increase blood glucose and insulin as much as carbohydrates will. Protein will have an intermediate effect.

2. Activity Level: Your activity level also plays a role. If you've just run an ultra marathon and then drink a can of soda pop, you might not be breaking your fast. But under normal circumstances, consuming a can of soda pop or a piece of pizza would break your fast.

3. Timing: The timing of when you last ate and your activity levels since then also matter. If you've been strictly fasting for five hours or more, what might break your fast could be different than if you've just eaten.

4. Individual Differences: Everyone is different. What breaks a fast for one person might not break a fast for another. It's important to establish what's right for you.

In general, it's useful to be fairly strict about when you initiate your feeding window and when you stop your feeding window. As time evolves and you establish a more regular routine of eating certain kinds of foods and not others, you'll get a better sense of what breaks your fast.