If you have been prescribed beta-blockers, your doctor may recommend that you limit your intake or consumption of bananas or other foods such as tomatoes, avocado, papaya and kale. This is because these are high in potassium and beta-blockers also contain potassium. A combination of this can lead to too much potassium in the body which can lead to erratic heart rhythm or kidney failure. Beta-blockers are primarily prescribed to treat heart-related problems and high blood pressure.