Don’t be fooled by the enormous portions at many restaurants. Recommended serving sizes are actually a lot smaller than what you probably think they are. One study found that portions sizes of many popular foods added an extra 50 to 150 calories a day. In the long run, that can easily lead to unexpected weight gain. So the next time you decide to “up-size” your fries or reach for a midday snack, keep in mind what constitutes one serving.