Iceberg lettuce contains carbohydrates that cause gas, according to Mayo Clinic, and this may cause stomach discomfort, such as cramps. Salad greens also are frequently contaminated with harmful pathogens due to poor handling and lack of washing, according to NBCNews.com.
The Center for Science in the Public Interest lists leafy greens as the riskiest of all FDA-regulated foods due to the numerous outbreaks discovered in relation to salad greens, notes NBCNews.com. Leafy greens often carry pathogens, which are ingested if the greens are not prepared in a proper manner. Nearly a quarter of the instances of foodborne illness occur when people consume iceberg, romaine, leaf, butter and baby leaf lettuce; spinach, cabbage; chard; arugula; endive; kale and spring mix. Norovirus is the pathogen most frequently found on leafy greens, but salmonella is another culprit. Leafy greens can become contaminated during processing and production or through improper handling.
Stomach discomfort may also be due to ingesting the carbohydrates contained in the lettuce. Mayo Clinic lists lettuce as a gas-producing food and recommends avoiding or limiting the amount of gas-producing foods to keep bloating to a minimum. Consumption of milk and milk products, onions, whole grain foods, fruits, carbonated drinks can also cause gas that leads to gas and bloating.