Restaurant meals typically deliver more calories than homemade ones. And dining out even just once a week could hinder your slim-down efforts. Women who ate lunch out at least once a week lost an average of five pounds less over the course of a year than those who ate out less frequently, according to a study in the Journal of the Academy of Nutrition and Dietetics. (Eating breakfast and dinner out, by the way, had a similar effect.) Although researchers can’t say that dining out definitively caused weight gain, knowing how many calories you’re getting "can be more challenging when you eat out because you’re not in control of ingredients, how food is prepared and portion sizes," says Angela Kong, Ph.D., R.D., M.P.H., lead author and research scientist at the University of Illinois at Chicago. If you do dine out, check the restaurant’s menu for nutritional information, ask for healthy modifications (for instance, requesting salad dressing on the side) and eat smaller portions.