Fact: When something sounds too good to be true, well, it probably is. Take "negative-calorie foods" as an example. The notion is that digesting certain foods burns more calories than those foods provide. The faulty logic of this urban legend is based on the scientifically proven thermic effect of food (TEF), which simply means the amount of energy the body uses to digest a portion of food. The thinking goes, if you were to eat a very low-calorie food — common examples include celery, apples, and limes — then you'd actually create a calorie deficit. In other words, these foods would end up costing less than zero calories.
Sadly, there are no negative-calorie foods. The TEF generally ranges from 10 percent to 20 percent of the calories in a food. So let's say a celery stalk has seven calories. Even if you assume a 20 percent TEF, that means you're still left with about five and a half calories.
