Losing weight. Quitting smoking. Becoming a better person. Good intentions are rarely enough to get the job done. That's why people are encouraged to have a plan to help guide them to their goal. According to a study from the University of Leeds, having both a plan and a partner works even better.

The study looked at people who wanted to increase their amount of physical activity. Over six months, people who had both a partner and a plan exercised more often and for a longer period of time than people who had only a plan or a partner alone. And as an added bonus, they also lost more weight and trimmed more inches off their waistlines in those six months.

People who made and carried out plans on their own lost only one-third as much weight as the people who added a partner to the mix.

There have been few studies done on the effects of planning or partnership on exercise or weight loss. Most have been short-term studies done with college students. The Leeds study used employees from 15 British councils, government organizations of social workers whose employees are socially and economically diverse. Because the study group was broad-based, it makes it more likely that the study's results are generalizable, results a typical person could expect to achieve.

The study was of 258 council employees who had expressed interest in increasing their physical activity. They were randomly assigned to one of four groups. Members of one group were asked to plan with another person, such as a friend or family member, when and where they would perform physical activity. Members of a second group formed these plans by themselves but had no partner. A third group was asked to recruit a partner, but no mention was made of any planning. And the fourth group, the control group had neither a plan nor a partner.

Both the frequency and duration of exercise was self-reported at the start of the study and one, three and six months into it, using the Self-report Walking and Exercise Tables (SWET). Weight and waist size were also self-reported, at the study's start and six months later.

All groups were given material explaining how lack of exercise can lead to heart disease, to help motivate them.

Because a bad plan can be worse than no plan at all, participants were encouraged to formulate their plans as if-then statements. For an individual, this might be along the lines of "If I miss an exercise session this week, then I'll do an extra one next week." For two partners, it might be "If it's raining and we can't play tennis, then we'll play racquetball indoors." Other studies have shown that if-then plans tend to be more effective than less specific plans are.

But as the Leeds study results point out, just having a plan isn't enough if you don't stick to it. People who made and carried out plans on their own lost only one-third as much weight as the people who added a partner to the mix.

The study authors aren't sure why the combination of if-then plans and a partner works better than either do singly. It could simply be that two heads are better than one when it comes to planning. Or it could be that partners help each other from straying from their plans.

Having a partner might not work so well for people with a strong individualistic streak. They usually like to go it alone. But for everyone else, the study suggests that, like the rest of life, it's easier to stick to a plan and reach your goal when you have a friend on your side.

An article on the study is scheduled to appear in a future edition of Health Psychology.