The research: More than 2,000 people surveyed were asked to guess the sugar content of soft drinks, fruit juice, and fruit smoothies. When it came to fruit juice and smoothies, the average respondent underestimated the drinks’ sugar content by 48%, the study data shows.  The biggest errors occurred when people guessed the amount of sugar in pomegranate juice: The average person estimated .5 teaspoons of sugar per 3.5 ounces. In reality, pomegranate juice packs nearly 1 teaspoon of sugar into every fluid ounce, the study authors say—meaning people miscalculated by 550%. Apple juice and soda have nearly identical sugar and calorie amounts—roughly 5.5 teaspoons per 8.5 ounces. And orange juice is similarly sugar-heavy, the study data shows.  What it means: “Sugar is sugar whether it comes in lumps or in fruit,” says study coauthor Naveed Sattar, PhD, a professor of metabolic medicine at University of Glasgow in the UK. He says it’s not that fruit juice is bad for you; the problem lies in how people consume fruit juice. While one whole orange contains about 45 calories, just 8.5 ounces of OJ packs in 120 calories. And while eating a whole orange involves chewing—an action that signals to your brain that you should feel full—swallowing liquid is so quick and effortless that your brain doesn’t realize your body is consuming lots of calories, Dr. Sattar adds. Roughly 25% of people’s calories come from fruit juice and sugar-sweetened beverages like soda, his study found. And because the number of calories you consume is arguably the greatest contributor to your body weight, cutting back on fruit juice can help you stay slim, Dr. Sattar says. The bottom line: “You’ve really got to be a sugar detective when you are shopping: Read the label and watch out for words ending in ‘-ose’,” says Anne Alexander, editorial director of Prevention and author of The Sugar Smart Diet. “And for foods like fruit juice, just use a splash to flavor seltzer water. Even better—enjoy the whole fruit!” Simply because it looks healthy doesn’t mean it isn’t making you fat, Dr. Sattar adds. More from Prevention: The 57 Names Sugar Goes By