A new Harvard study shows that the more obese friends you have, the more likely you are to become obese.

This confirms previous research that gaining weight may be socially contagious.

The research also shows that if nothing changes significantly in the environment and culture in the USA, about 42% of adults will be obese in about 40 years and then the obesity rate will level off.

About a third of Americans are obese -- that is, roughly 30 or more pounds over a healthy weight.

Those extra pounds of body fat produce inflammation that increases their risk of developing type 2 diabetes, heart disease and many types of cancer.

The Harvard study showed that having four obese friends doubled people's chance of becoming obese compared to people with no obese friends.

The study also confirmed that people have gotten better at gaining weight in recent years, but not at losing it.

David Rand, a Harvard research scientist who also worked on the study, says that the more obese people you have contact with, the more likely you are to become obese.

Researchers aren't sure why this is true. It may be that if you have a lot of friends with unhealthy eating habits, you wind up with similar eating habits, Rand says.

Perhaps among obese friends the obesity becomes socially acceptable.

Of course, other lifestyle factors, such as diet and physical activity, have a huge impact on weight gain, Rand says, but the lesson of this research is "it's in your best interest to help your friends lose weight."

This latest research confirms a 2007 study by Harvard researchers and others that showed that one person's obesity can significantly increase the chance that his or her friends, siblings and spouse also will become heavy, suggesting that weight gain does spread through social networks.

The question remains- Does weight loss spread through social networks?

In other words, if all of your friends are trying to be healthy, lose excess body fat and improve their health- is this behavior contagious as well?

Although no studies have been shown to prove this, I believe that this is true from what I have observed in my clinical practice.

Healthy people who wish to remain healthy by maintaining an ideal weight tend to choose friends that support their goals and motivate them to eat healthy and exercise regularly.Making the best choices when interacting socially with people who do not support your healthy goals is much more difficult.

Birds of a feather flock together!