An unhealthy diet can significantly contribute to chronic illness by providing excessive amounts of added sugars, unhealthy fats, and processed foods that promote weight gain and metabolic disturbances. Such a diet increases the risk of conditions like type 2 diabetes, heart disease, and certain types of cancer. Nutrient deficiencies may also arise from inadequate consumption of fruits, vegetables, and whole foods, leading to a weakened immune system and poor overall health. Prioritizing a balanced diet rich in whole foods can mitigate these risks and provide essential nutrients necessary for disease prevention.