As someone who was recently diagnosed as being both gluten- and dairy-intolerant, I have a new awareness of foods that are common in our everyday diets (and I've been doing a heck of a lot of reading about them). Apparently, tomatoes, potatoes, bell peppers, and eggplants are all part of a family of vegetables called Nightshades. If it sounds creepy, it's because some nightshades like belladonna have long been associated with poisons and witchcraft. All nightshades contain nicotine in some form, yes, even your mild-manner potato (it's called "solanine" in potatoes).
For some people this isn't a big deal, but there are others who are intolerant to these mainstays and can develop a number of mental, emotional, and physical problems from eating them. So, bottom line: if you're having trouble with heartburn or acid reflux, eliminating tomatoes, potatoes, and eggplants from your diet may help.
For more information, check out this article: Nightshade Foods