Rishi Khatau was wearing large size adult T-shirts and 36 inch waist trousers before the gastrectomy, where doctors cut away three quarters of his stomach.
The child was suffering complications from his heavy weight, including sleep apnoea and he had difficulties walking.
Things got so bad that his mother Henna, 34, was forced to carry him to the school bus in the morning.
Rishi's weight rocketed because he suffers from Prader-Willi Syndrome, which means his body cannot burn calories properly.
But now that he has undergone the weight loss surgery - which is similar to a gastric band - Rishi has lost two stone in the six months since the operation.
He has also been eating a healthier diet of soup and juice, and exercising by playing cricket and cycling with friends.
His mother, from Kolkata, India said: 'I don't think we were to blame by giving him food.'
'He never felt satisfied with his meals, it baffled us.'
But happily, his father said that his son is now getting his life back - and despite craving sweets, his parents make sure he halves the portions to keep his weight down.
Prader-Willi syndrome causes sufferers to have a constant desire for food, reduced muscle tone, restricted growth and behavioural problems.
It is extremely rare, with only one in every 15,000 children in England being diagnosed with the condition.