A healthy diet is one that provides adequate levels of vitamins, minerals, protein, carbohydrate and healthy fats from a variety of foods. An unhealthy diet, in contrast, is one that contains too much saturated and trans fats, cholesterol, sodium, added sugars and processed ingredients or contains too few nutrients. Unhealthy diets result in a poor nutrient-to-calorie ratio, which can lead to weight gain and malnutrition as well as related health problems.