Yoga may burn calories during the performance of the physical exercises, but it can also help a person lose weight in other ways. Growing a yoga practice can assist a student in becoming more aware of their physical body and how it is feeling. (Many students come to yoga with poor proprioception and other forms of self-knowledge about their own bodies.) Learning to pay attention to the feelings–physical and otherwise–in a post can assist with paying attention off the mat. This may translate to improved skills in determining whether I am actually hungry, and therefore need to eat, or whether I am really just bored, or sad, or something else. Further, a yoga practice may encourage people to examine the specific foods they choose to eat, and the quantities in which they choose to eat them, as they learn to recognize the cause and effect connection between food and how they feel after eating it.
Heat by itself does NOT cause you to burn more calories or up the intensity of any exercise, yoga included. If it did, the most popular way of losing weight would be to lounge around in the sauna! Because heat makes you sweat more, participants in heated exercises often feel like they had a more intense workout, even though this is not necessarily the case.
Heated yoga practice is also not appropriate for all students. It may be inappropriate for people with heart conditions, cardiovascular disease, or uncontrolled blood pressure, among other health conditions. A heated room can lead to heat-related injuries for some individuals, including dehydration. Without air circulation, sweating is a less effective means for the body to cool itself, and some bodies are unable to maintain a proper body temperature in a heated and humid environment. If you are going to teach heated yoga, it is important to give your students information on how to practice safely in the heat and educate them on the signs of heat-related health problems. There is an excellent article on heated yoga and the specific physiological effects on the body available in the electronic library of the International Association of Yoga Therapists, written in plain language that is easily understandable.
A steady practice and muscular engagement during the physical practice will aid a yoga practitioner in losing weight. Standing poses in particular can help build and work muscles when they are performed engaging the muscles. It takes an experienced, well-trained teacher to help newer students learn how to perform asanas this way. There isn’t anything “wrong” with doing asanas a different way–for example in a purely flowing, aerobic style–but a combination of aerobic and anaerobic exercise has consistently been shown to be most effective in weight loss. It isn’t any different with the physical practices of yoga.