Before practising Yoga first understand what obesity is?
The first signs of obesity are weight gain; your body loses shape, due to buildup of fats in different parts of your body often, the body balance is affected. Obese people have to expend extra energy to move even. This results in decline of overall movements. Further, this fall in overall activity raises weight even more; also enthusiasm for any work goes down. For a regular healthy life the weight has to be in certain limits, there is standard chart, which relates height and weight. If the difference is more than 10 % as mentioned in table then we may say that the person is obese. One can get a brief idea from this chart but not totally correct figures.
Weight gain can be owing to of digestive problems. During digestion useful ingredients of food are absorbed by the blood. If there any problems arise in the process it could result in buildup of fats. If your digestive problem gets cured, obesity will reduce, automatically. Oftentimes even problems in the nervous system, causes weight gain; in which case the problem in the nervous system should be treated to cure obesity. The mind and body have complex relations between them. As a result of of mental and emotional imbalances, the endocrine gland systems get affected; this could also result in obesity.


Yoga for obesity
Exercise like running, swimming etc on a regular basis
Yogasanas such as Paschimottanasana, Bhujangasana, Sarvangasana, Halasana, Dhanurasana, Veerasana, Trikonasana, Ardha Matsyendrasana etc
Together with Yogasanas also do Sun salutation (Surya Namaskar).
Also do Pranayamas such as Kapalabhatti, Anuloma-Viloma and Bhastrika.
Cleansing kriyas such as Vaman Dhauti, and Shanka Prakshalana also help.
Yoga diet for Obesity
You should have fixed timings for lunch and dinner
You should maintain a time difference of 4 hours any two meals
Always on low fat meals that are fiber rich. Have vegetables and fruits regularly.
Reduce your fat intake, sweets, milk, butter, cheese etc in meals.

Other useful habits
Don’t sleep for over 6 or 7 hours a day
Try giving up addictions like cigarettes, alcohol and drugs.
Consult a dietician.
Whenever possible, get a massage and steam bath.

Practising Yoga regularly will certainly reduce your obesity and weight gain problems. However you will have to learn specific Yoga Techniques that are more effective in weight reduction.