As many employees spend longer hours on the job, they’re also having more meals, snacks and celebrations with colleagues — and that isn’t always great for the waistline.

Some coworkers pressure dieters to eat forbidden foods. Others pass home-baked snacks desk-to-desk. Some tease colleagues about their diets, or even order them restaurant foods they aren’t supposed to eat. All these pose a major hurdle for people who are trying to slim down, according to a survey of 325 dieters last January by Medi-Weightloss Clinics. An ongoing poll of thousands of dieters on the weight-loss website SparkPeople cites co-workers as the second biggest source of negative pressure for dieters — second only to spouses or partners.

And peers’ attitudes can make a difference. A study published in the journal Obesity last month says having teammates who exert positive influence is linked to greater weight loss among dieters. Being surrounded with peers who criticize or discourage a dieter has the opposite effect.

Colleagues often mean well.  Some see offering delicious food as a sign of friendship or affection, says Becky Hand, a registered dietician with SparkPeople. Many people don’t understand how hard it is for others to lose weight. They might feel guilty that they aren’t eating a healthier diet themselves. Some might be afraid of losing a friend who changes her life by losing a lot of weight.

Whatever their motivations, critical co-workers can make life tough for dieters. 

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