Outside working hours, your weight-loss challenge can become a real social occasion.

Take turns hosting healthy dinner parties and enjoy a great chance for conversation as well. Challenge each other to create low-calorie, yummy feasts. The CalorieKing recipe archive is a good place to start, but most of your favorite recipes can be tweaked to be lower in calories too.

Take an hour a couple of times a week to exercise together.  Got babies and no sitter? A brisk walk with strollers can burn serious calories and tone your muscles. Some gyms offer discounts for group memberships, and since you’ll be encouraging each other, that membership is less likely to go unused.

If the thought of a gym session leaves you cold, go back to your childhood with activities like bike-riding or roller-skating.

Challenge each other to train for an event – it doesn’t have to be a marathon or ocean swim. Most cities hold walk-run charity events that don't require elite levels of fitness and draw crowds of like-minded people. If that’s not enough of a challenge, then set your sights on a half-marathon.

There are lots of ways to make your weight-loss challenge more interesting. Here are a few:

Agree on a dollar amount to contribute for every pound lost and put this money towards a reward when goals are reached. You might treat yourselves to a concert or book a day at a spa, for examples. If you can’t agree on a group treat, donate the money to a charity.

Create a progress chart for yourselves and  find a prominent place to display it. If you have a conference area or work lunch room, make it a work of art. Or even post it on the internet.

Hold a clothes-swap party. Since you’ll all be different sizes, chances are clothes that don’t fit you any longer will be perfect for a friend.

Take up a new hobby together – kickboxing, belly dancing, Pilates, or whatever you all agree on. Going in a group will make it more fun, and you’ll be much less likely to find excuses to put it off.