Extreme drowsiness brought on by foods (Dairy and Grain Groups), what could cause this?

People vary greatly in their response to different foods. You need to experiment and learn what works best for you. To maintain adequate levels of brain fuel glucose, it's important to eat often enough and at the same time trying to avoid eating heavy meals of certain foods. These sugar spikes combined with low sugar episodes can easily cause drowsiness and fatigue. So much of it has to do with what your body's condition before the meal and what and how much you eat during the meal. It's a combination of all. For some people, this means eating snacks as well as main meals. For others, it just means eating at least every five hours. One little known trick to help you is to combine eating some carbohydrates with protein foods and these spikes in sugar will be more balanced and you will be less likely to crash and burn after your meals. In a matter of no time your stomach will be full but yet you will still be energized as the Joecool person you are.

Food allergies could be the cause.