The disadvantages of oats are few, but they do exist. One of the main issues is that oats can cause bloating, gas and abdominal pain - which is something you're likely far too familiar with already. As long as you're eating oats in moderation, this side effect should pass fairly quickly. Another issue is that it's very common for those with gluten intolerance to also be unable to tolerate oats - even gluten free oats. Unfortunately, I am one of those unlucky people!