An unbalanced diet can cause malnutrition, a condition that develops when the body does not get enough nutrients, according to the National Institutes of Health. Most cases of malnutrition can be corrected, but in extreme cases, malnutrition can lead to the development of certain medical conditions, mental disabilities, physical disabilities and possibly death.
The World Health Organization explains that having a balanced diet is an essential part of preventing nutrition-related chronic diseases, such as cardiovascular disease, osteoporosis, diabetes, oral diseases and cancer. Eating a balanced diet also prevents obesity, which is common in those who overconsume high-fat and high-sugar foods with minimal nutrition. A diet that is unbalanced can be too low or too high in calories. It can be rich in certain nutrients and completely void of others.
The Harvard School of Public Health suggests eating whole grains, fruits, vegetables, healthy fats and proteins to maintain a balanced diet. Processed foods, sugary beverages and any food with little or no nutritional value should be avoided.
According to the Institute of Medicine, between 45 to 65 percent of an adult's diet should come from healthy carbohydrates, and 20 to 35 percent should come from healthy fats. Between 10 and 35 percent of an adult's diet should consist of lean proteins, and adults should consume a minimum of 21 grams of fiber per day.