Junk food is bad because it typically has a high caloric content that consists of fat and sugar packed into small portions, according to WebMD. Additionally, junk food is formulated to taste very appealing to the senses, making it difficult to stop eating or addictive. Popular junk foods include potato chips, candy bars, cookies, soda, snack cakes and most fast food.
While the definition of junk food varies considerably, WebMD defines it as food that contributes lots of calories to the diet with little nutritional value. Most types of junk food fall into the two categories of snack foods and fast food. Due to lack of nutrients, the satiation value, or the level of fullness one feels after eating junk food, is minimal, leading to consuming significantly more calories than needed in a single sitting or meal. These foods and drinks then replace other items in the diet that contribute to good health, such as water, fruits, vegetables and whole grains.
A study from the Children's Hospital in Boston shows that due to both the lack of nutrients and good taste of fast food, children tend to take in more than half of the daily recommended caloric intake in one meal.