Bagels are likely to cause you to gain weight if you eat them in excess. Overconsumption of any food can be bad for the body especially one made with flour. Consuming excess bagels can cause belly fat and overall weight gain. It is best to have bagels eating in moderation and ensure to be cautious of many calories you are taking in. If you are a bagel lover then it's best to choose one made with 100 percent refined flour as that contains fewer calories.