In general, anything above 50 calories will break a fast.
Whether or not a particular food or beverage will break a fast depends on your goal for fasting. If you are using your fast as a way to bust past your weight loss plateau, then it is best to keep your calories as low as possible during your fasting period.
Conversely, if you are fasting to experience the benefits of autophagy and increased mental clarity (both of which you can learn about here), then it is best to consume no calories or beverages other than water. This will ensure that fat, protein, carbs, and caffeine don’t keep these advantageous processes from getting activated.
For more ideas on how you can use fasting to boost your health and weight loss results, check out these two fasting techniques: