MSG is the sodium salt of glutamate. Glutamate is an amino acid, found in all foods with protein. Glutamate is found naturally in many foods we eat. Our bodies don't recognize the difference between naturally occurring glutamate and that which is added to foods in the form of MSG. From our bodies perspective, the glutamate present in a tomato is the same as the MSG added to foods. To put the amount of glutamate in a tomato and it's juice (or sauce) in perspective for you, here are some foods and their corresponding glutamate content:
Roquefort cheese 1280 mg/100g
Parmesan cheese 1200 mg/100g
Soy Sauce 1090 mg/100g
Walnuts 658mg/100g
***Fresh tomato juice 260 mg/100g
Grape juice 258 mg/100g
Peas 200 mg/100g
Mushrooms 180 mg/100g
Broccoli 176 mg/100g
***Tomatoes 140 mg/100g
Oysters 137 mg/100g
Corn 130 mg/100g
Potatoes 102 mg/100g
Chicken 44 mg/100g
Fish (Mackerel) 36 mg/100g
Beef 33 mg/100g
Eggs 23 mg/100g
Cow's Milk 2 mg/100g
So, I think my problem with tomatoes is that when I consume them, I eat a bunch of them...not just a slice. Since I am not often drinking mushroom juice (gross thought...I know) or broccoli juice (not quite as gross of a thought), the limited content I consume even though it may be a generous vegetable serving is not enough to trigger a headache. I have been known to eat a entire bowl of those yummy grape tomatoes and who doesn't like a nice big bowl of spaghetti? Apparently my migraine brain doesn't!
Because Pizza is a problem due to it's sauce, cheese, and freshly baked crust (as well as potential nitrates and nitrites in pepperoni etc.) I make my own delicious pizza with some migraine modifications.
I use a pesto base for the sauce by putting some basil, oregano, garlic cloves, salt, pepper, and olive oil in a food processor and pulsing them all up until it's a consistency I like.