Coffee is the most common source of caffeine in the American diet. Tea and chocolate also contain some of this addictive substance that can provide boosts in energy and mood. Although some plants contain caffeine in their leaves, none of these is a plant you eat as a vegetable.
If you are trying to cut back on caffeine, you may be concerned about hidden sources. You also may be allergic to the substance and want to prevent an accidental intake. Pregnant women should also monitor their caffeine intake -- keeping it to just 150 to 300 milligrams daily, the American Pregnancy Organization says.
Coffee beans, tea leaves and cacao beans contain naturally occurring caffeine. Guarana is not a vegetable but a climbing plant related to maple trees. Its large leaves and berries, which are the size of coffee beans, contain about twice the amount of caffeine as coffee beans. The berries are considered a fruit, not a vegetable, and usually are included as an ingredient in juices, breads and sodas. Yaupon holly is another plant that produces a large amount of caffeine. You can make a drink from the leaves of this tree, but it is not common nor is it eaten like a vegetable.
While Brasicca vegetables do not contain caffeine, consuming them can affect absorption. A May 1992 study in the journal “Human and Experimental Toxicology” found that vegetables in the Brassica family can stimulate caffeine metabolism. Brassica family vegetables include cabbage, brussels sprouts and broccoli. Researchers guess that your intestines increase in permeability after consuming these vegetables, making them absorb caffeine at a faster rate.
Eating cabbage may heighten the effects of caffeine on your body, while consuming carrots or parsley may decrease these effects. A 2000 issue of “Carcinogenesis” confirmed the findings that suggest Brassica vegetables increase caffeine sensitivity, but also found that consuming vegetables from the apiaceous family decreased sensitivity. Celery, fennel, dill and parsnips are other vegetables in this family.