Taxi driver Kenny Forbes, 43, won Male Slimmer Of The Year at his local class in 2012 after going from 22 stones to 14st.
His class leader believed he shed the pounds sticking to the club's healthy eating plan. But his solicitor has told a court how father of four Forbes, whose son died last year of a drugs overdose, had used amphetamines to help him lose the weight.
Amphetamines, commonly known as speed, are an appetite repressant that increases the heart rate and leave people taking it severely dehydrated, leading to weight loss.
Defence agent Kenneth Pringle revealed his client's secret after Forbes was found to be in possession of 172 grammes of amphetamines.
He said his client had used the drugs, found hidden in his home during a police raid, for personal use and that they had helped him lose eight stones.
However, he admitted the amount of drugs found made it look bad for his client.
Dumbarton Sheriff Court heard Forbes, of Second Avenue, Clydebank, was also found with three mobile phones and £1,000 in his car when stopped by police.
Later, during a police raid, a further £2,000 in mixed notes was found hidden in a sock and a set of digital scales was also found stashed in a cupboard.
The court heard how it all began to go wrong for Forbes when he was stopped by police last September 25.
Fiscal depute Claire Martin said police were on patrol in Dalmuir, Clydebank, and saw a parked car.
She said: "Police had cause to attend the vehicle and speak to the driver. Once they had spoken to him they had cause to search Mr Forbes and found £955 in mixed notes and a further £55 in a box in the driver's door.
"They also found three mobile phones on the dashboard ."
Ms Martin said police then applied for a search warrant and carried out a raid at his home later that evening. She said: "They found 7.5 grammes of white powder and two solid lumps of white paste in a drawer in the fridge.
"They also found a set of digital scales in a bag in a cupboard and found almost £2,000 in mixed notes hidden in a sock in a drawer in a bedroom."
She said Forbes was taken to the police station and tests on the substances found in the flat showed they were amphetamines.
She said their total weight was 172.5 grammes, with a street value of £430.
She said: "Mr Forbes said he had a habit and the amphetamines belonged to him and that the £3010 in mixed notes found by police belonged to him.
"He denied being involved in the supply of any drugs. He claimed the mobiles belonged to him."
Defence agent Mr Pringle said his client had the cash in his car to pay for a garage bill for work done on his vehicle.
He said: "In relation to money recovered from his home, he is adamant they were savings."
Mr Pringle told the court his client had a speed addiction.
He said: "He does have a habit and he used amphetamines to help lose weight.
"However he accepts the quantity of drugs involved was deemed to be excessive for personal use."
Forbes pleaded guilty to being concerned in the supply of amphetamine in September last year and was jailed for eight months.
Marilyn Mackie, who runs the Slimming World class in Clydebank that Forbes attended, said: "As far as I knew he had lost the weight using our healthy eating plan.
"He came into the class to lose weight and got weighed every week like everyone else. He did really well in the class and that is why he won the award.
"I have never seen him since."