Research has shown that people who are overweight or obese are more likely to suffer from asthma and that losing weight can sometimes improve their symptoms and lung function measurements, said the team.
"We hope this study will throw some light on whether this improvement is a result of changes in the mechanics of breathing, or changes in immune function that are also known to improve with weight loss," said Dr John Wilding from the university's medicine faculty.
The doctors will put obese asthma patients on an intensive weight loss regime, including meal replacement drinks. Alternative treatment is a six-month, standard dietary advice programme.
Lung function measurements plus sputum and blood samples - to assess changes in immune function - will be taken before, during and after weight loss.
The study has been awarded a grant of over £98,000 by the charity Asthma UK.