Epictetus, a Greek Stoic philosopher who was born into slavery and died in 135 B.C., once said, "Other people's views and troubles can be contagious. Don't sabotage yourself by unwittingly adopting negative, unproductive attitudes through your associations with others."

More than 2,300 years later, researchers in the U.K. have come to the same conclusion. Their study on external challenges faced by people trying to lose weight reveals that you might find yourself derailed by friends and family whose behavior and comments may sabotage your hard-fought efforts.

Writing in the journal Current Obesity Reports, the researchers point out that when you successfully lose weight, it can change how you think about yourself, how you interact with the world, and how those close to you respond to your newfound self-confidence and strength.

Without being aware of what they're doing, your social circle may tempt you into weight-gaining behavior, discourage healthy eating, and put up barriers to attending support groups and getting physical activity.

You may also encounter people the study calls "feeders," who deliberately offer food to you between meals or urge you to eat more during meals, suggesting you shouldn't waste food or it's rude to refuse it, for example.

Knowing what's going on "out there," can help you stick to your weight-loss goals. But don't get mad at your sabotaging friends and family, instead talk with them. As Epictetus also said, "Any person capable of angering you becomes your master."