Caffeine mildly stimulates the nutrient sensing pathway called the PKA pathway (as well as some other pathways) that ProLon down-regulates. For this reason, it is best to avoid caffeine during the diet, although you may have up to 140mg of caffeine of caffeine each day, which is equivalent to approximately one 8-12 oz cup of black coffee, two cups of black or green caffeinated tea, OR 6 cups of decaffeinated coffee, all traditionally brewed.