Step 1: Understanding the Concept: 
A healthy diet is one that helps to maintain or improve overall health. It provides the body with essential nutrition: fluid, macronutrients, micronutrients, and adequate calories. 
Step 2: Detailed Explanation: 
- Spicy or Fried diets, if consumed excessively, can lead to health problems like indigestion, high blood pressure, and high cholesterol. They are not inherently healthy. 
- A Costly diet does not guarantee health. Simple, locally sourced foods can be very nutritious, while expensive processed foods can be unhealthy. 
- A diet that is Rich in nutrients (containing a balance of proteins, carbohydrates, fats, vitamins, and minerals) is the fundamental requirement for keeping a person healthy. This is the definition of a balanced and nutritious diet. 
Step 3: Final Answer: 
To keep a person healthy, a diet that is rich in nutrients is necessary.