Body shapers give the illusion of a smaller figure, flattening the stomach and bringing in the waist line, and it's only natural to want those changes to be permanent. Since body shapers make it more difficult to breathe, it might seem like you would burn more calories during exercise due to the increased stress on your body. But in reality, wearing a body shaper during a workout can do more harm than good.
Body shapers compress the stomach and push down on the diaphragm, preventing you from taking a full breath. Aerobics and strength-training increase your respiratory rate, and if you're unable to breathe effectively, you'll find yourself tiring more quickly than usual. A less productive workout means fewer calories burned, undermining your weight loss efforts.
Sucking in your stomach utilizes the transversus abdominis muscle, the innermost muscle of the abdomen. This muscle stabilizes the core, improving posture and protecting the spine. An exercise technique known as the "stomach vacuum" can strengthen the transversus abdominis, helping to flatten your stomach. (However, most body shapers only compress fat or push it to another location, and therefore don't effectively work the deepest abdominal muscles.
Body shapers restrict diaphragmatic breathing, resulting in shallower breaths. During intense exercise, the body requires sufficient oxygen to perform; without it, you can end up feeling dizzy and weak. Wearing a body shaper is fine if you intend to remain mostly stationary, but if you're doing cardio, yoga or weightlifting to lose weight, you could end up fainting due to a lack of oxygen. Furthermore, the fabrics used in some body shapers aren't very breathable and prevent sweat from escaping. Sweat regulates your body temperature and helps to keep you cool during exercise.
It's always a good idea to wear comfortable, loose-fitting clothes while working out. If you're working out in a hot climate, opt for light-weight fabrics with light colors; in the winter, wear multiple thin layers, and choose dark colored clothing. You should also avoid wearing plastic, leather or rubberized clothing when exercising.