Caution: Eating with friends who overindulge

You might feel pressure to splurge when you're with buddies who overeat. And being overweight can be socially contagious, according to research from Harvard Medical School. Researchers there found that having a friend who becomes obese will increase by 57 percent your chances of gaining weight. Experts suspect the reason for this is that you mirror your friend's eating habits when you're together, or you choose activities for the two of you that involve eating rather than exercising.

The fix: Avoid bonding over food. Instead, get manicures, go to a museum, bowl or play tennis. When you do eat together, be careful to not match your friend bite for bite. Stick to your dietary resolve by going slowly and putting your fork down between mouthfuls.

NextCaution: Relaxing the rules on the weekends