If you know someone on a diet, or if you've been on one yourself, you know that losing weight can make you grumpy. So it may be no surprise that giving — or getting — advice about what to eat or not to eat while dieting can backfire.

A study of 400 people in Greece who lost 10% or more of their body weight tracked their efforts to keep it off for a full year. After a year 289 people had kept the weight off; 122 had regained some or all of it.

People with friends who've lost weight might want to think a bit more about what they say to them. The fact is that those who have lost 20 pounds are much more deserving of compliments than reminders that ice cream is fattening.

Next, researchers looked at the kind of social support dieters received from their friends and whether it tended to make them successful or less successful. People who had regained much or all of the weight they lost reported having had more social support than those who kept it off. This is not good news for those friends and family who try to help by cheerleading their loved ones to dieting success.

Why would receiving more help make regaining weight likelier?

The simplest explanation is that some types of help are a lot more helpful than others. Indeed, a closer look revealed that people who kept the weight off tended to receive more compliments on their eating habits. They also were more likely to report friends and family helping by example, that is, eating healthy foods with them rather than pepperoni pizza with extra cheese.

Those who regained weight, on the other hand, reported more frequent advice from friends and family, such as not to eat high-fat foods or on the importance of exercising.

If this is the type of help you've been giving friends who are trying to lose weight, it might make sense to gently remove foot from mouth and try a different approach.

“Family and friends of people trying to maintain weight loss could possibly be more helpful when offering their support in the form of compliments and active participation, rather than verbal instructions and reminders,” say the researchers. They also point to a previous study, where some women said that reminders to eat better or exercise more made them feel worse, because they were already struggling to make these changes.

Well-intentioned as these comments may be, they can be taken as criticism.

This isn't to say that these comments and instructions were actually responsible for people regaining weight. It could be that people didn't start making these comments until they noticed their friends regaining weight or eating with abandon.

It is also possible that people who had regained weight were understandably sensitive to such comments and likelier to remember them. Still, it suggests that people with friends who've lost weight might want to think a bit more about what they say to them. The fact is that those who have lost 20 pounds are much more deserving of compliments than reminders that ice cream is fattening.

The study appears in the Journal of Behavioral Medicine.