Depression
Junk food may lead to depression in teenagers, according to Andrew F. Smith, author of the book "Fast Food and Junk Food: An Encyclopedia of What We Love to Eat." Hormonal changes at puberty make teens more susceptible to mood and behavioral swings. A healthy diet plays a part in keeping hormone levels on an even keel, while a diet high in junk food falls short of these requirements. Consuming trans fats, saturated fats and processed food is associated with up to 58 percent increase in risk of depression.
Nutrient Deficiencies
Processing that removes vitamins, minerals and fiber makes junk foods into the sources of empty calories that nutritionists disparage. Children who eat a lot of junk foods may develop nutritional deficiencies that lead to low energy, mood swings, sleep disturbance and poor academic achievement, among other health conditions, according to the University of New Hampshire Cooperative Extension.
Sodium
High sodium levels are a defining characteristic of many junk foods and one of the contributing factors to the overconsumption of salt that typifies the Western diet and contributes to high blood pressure and heart, liver and kidney diseases, according to Harvard Health Publications. The average American eats five to 10 times more salt than the 2,300 milligrams per day recommended by the U.S. Dietary Guidelines for Americans. Considering the high rates of high blood pressure among Americans, that level should be even lower -- about 1,500 milligrams per day -- for 70 percent of adults. However, the trend since 1988 shows that fewer people with hypertension adhere to a low-sodium diet now than did then.