We sent three people each to Weight Watchers, Jenny Craig and Light n' Easy and a control group to a dietician.

We can now report our dieters, who weighed on average 115 kilograms each before the challenge, have all shed weight.

The dieters have lost 120kg in 12 weeks.

"That represents a raise in self-esteem, energy levels. That means far more than a mass of fat," Merrick* said.

Sandy, who was on the Weight Watchers program, lost the most - an amazing 19kg in three months at a rate of more than 1.5kg a week.

"I've just stuck to it and exercised - something I've never done - just walked and walked and walked," Sandy said.

Sisters Wilma, Marja, and Carla, on the Lite n' Easy program, all weighed more than a 100kg each when they started the challenge.

Now they have crashed through that elusive 100kg barrier.

"I'm ectatic. I'm really happy for all of us, all three of us," Marja said.

The group lost a total of 36kg, making the Lite n' Easy program the winner of our challenge.

The Weight Watchers trio came a close second.

Sandy weighed 136kg when we started and is now down to 117kg.

Merrick is now down from 101kg to 92kg and Lorraine is down from 83 kg to 77kg.

Altogether the Weight Watchers group lost 34kg.

The Jenny Craig group came third.

Sisters Michelle and Deborah lost 6kg each and their brother Richard lost 13kg for a total group weight loss of 25kg.

The control group who saw a dietician came in last.

Roslyn, who weighed 168kg at the start of the challenge, put on weight in the last half of the challenge. She lost just 3kg.

"That's a lot for me. I think that is fantastic for me. In three months it's been an uphill battle," she said.

Pauline is down from 117.2 kg to 106kg and Belinda shed 8kg, bringing the dietician group's total weight loss to 22kg.

Nutritionist Catherine Saxelby monitored the diets.

"There is no magic bullet. There is no pill you can pop to melt the weight away. It's going to take a long time and if you lose the weight slowly it's probably going to stay off," she said.

"The end result from all your programs is that pretty well everybody has lost some weight, which is what you'd expect when those four programs are offering low-fat, balanced, healthy diets and encouraging exercise."

But the challenge is not over yet.

The ANA Harbour Grand Hotel treated our dieters to a well-deserved lunch with plenty of healthy food.

"I'm having a pig out today but I'll go back on to it tomorrow," Belinda said.

The test was to resist temptation and continue losing weight.

"I hope they've learnt new eating habits and I hope they've changed their lifestyle a little bit and they can continue on that," Ms Saxelby said.

"Particularly people who need to lose a lot of weight, it's going to take them three months, six months, some of them a year to get to a goal weight that they are comfortable with."

But our dieters are determined to keep the weight off.

We will catch up with them again in another three months and then after a year to give their diets more of a chance to work.

• The participants in our weight-loss challenge did not provide their surnames.