Paul Betts served in the Australia army for more than a decade until 1990, when he was discharged with service-related injuries to his back, knees, ankles and left arm.

He weighed 87 kilograms when he enlisted in 1979 and 108kg upon discharge 11 years later.

But that figure ballooned to 145kg in 2000 and continued to increase because chronic pain from his injuries restricted his exercise.

In 2009, he weighed 212kg and, two years later, his weight could not be determined because the scales did not exceed 200kg.

In 2011, his body mass index reached 53. An index of 30 or more is usually regarded as obese.

Mr Betts told the tribunal that the diet introduced to him while in the military changed his eating habits and led to a lifetime of over-eating and his morbid obesity.

He said, as a recruit, he was served three meals and morning and afternoon tea each day.

He also bought cordial and soft drinks from the dry canteen.

But Mr Betts found the diet more limited when he was transferred to Holsworthy army base, so began to supplement his diet with food from off-base takeaway outlets.

He kept his weight gain under control during his service by running five kilometres every morning, taking part in group exercises before work and playing team sports in the afternoon.

Mr Betts argued that, despite being aware of his increasing weight, the army failed in its duty of care by not offering him support to lose weight, and that this failure contributed to his morbid obesity.

Mr Betts recently applied for a special rate of pension, but the request was rejected by the Veterans' Review Board, which found his bulk was unrelated to his service.

But the Administrative Appeals Tribunal overturned that decision.

In a judgment published earlier this month, the tribunal found there was no evidence Mr Betts was given any real, practical support to lose weight while in the service.

It also found Mr Betts' service-related injuries curtailed his ability to exercise.

''We are satisfied that the injury he sustained in 1989 and his resulting conditions was the most significant factor in his inability to exercise after his discharge,'' the tribunal ruled.

''Over time, his increasing obesity has itself limited his ability to exercise, but that does not change the contribution in a material degree by his accepted conditions at the relevant time, and since.

''We are satisfied that, on the balance of probabilities, Mr Betts' accepted conditions contributed in a material degree to his morbid obesity and, therefore, that it was caused by his service.''

The tribunal set aside the original decision and remitted the matter to the Repatriation Commission for assessment.