Run by Linda Agoudjil, Arriba! Weight Loss Challenge, a non-profit community weight-loss group, has helped dozens of people lose weight this year.
Unlike many weight-loss groups, the participants are not restricted by an imposed diet.
The community classes offer cash prizes for those who lose the biggest percentage of their body weight over 12 weeks from £300 to £100.
Miss Agoudjil says the latest Fishponds group to start has been an "exceptional success", and has attracted 21 people, who have all lost weight and body fat.
Miss Agoudjil, 34, said: "This weight-loss challenge has been successful and rewarding.
"The group lost a total of 147 pounds and 30 per cent of internal body fat, and they completely changed their eating habits.
"They feel happy and proud about it. We had a lot of fun together, the group was curious, determined to implement long-term changes.
"It was more than a slimming class, we mostly talked about nutrition and health, as weight loss is a result of those two things.
"We all underestimated the benefits of this challenge.
"Some of the participants have already signed up to the next challenge so I am definitely looking forward to starting all over again."
Two years ago, Miss Agoudjil, an aerospace engineer at Filton, piled on the pounds after being diagnosed with breast cancer and a benign tumour on her uterus.
The normally sporty woman was unable to do her usual street dancing and cycling and in just a year she put on two-and-a-half stone.
This weight gain put 5ft 6ins Miss Agoudjil into the overweight category. Today, Miss Agoudjil, who lives with her partner in Downend, runs the weight-loss business after getting back to a healthy weight.
Arriba! Weight Loss Challenge classes will start at All Saints Church, in Fishponds, on Wednesday, May 19, at 7pm, and at the Unified Reformed Church, in Mangotsfield, on Thursday, June 17, at 7.15pm.
There is a joining fee of £39 to cover the cost of the venue and the cash prizes. Each class can take a maximum of 40 people.
Any who is interested in joining the group, call 07545 046096 or 908 1025, or email linda@bristolweightlosschall enge.com.