Medical experts recommend combining diet and fitness as the best possible path to good health. Choosing nutritious foods and exercising regularly helps you maintain a healthy weight, promotes weight loss, and provides the basis for cardiovascular fitness. So essential is this combination for good health that the American Heart Association and the American Diabetes Association recommend combined diet and fitness as the primary disease prevention and management tool.
Benefits of Combining Diet and Fitness

In the USDA's 2010 Dietary Guidelines, the agency suggests a combination of diet and exercise to achieve optimal health. It's a simple formula that's been around for decades: healthy diet plus regular exercise equals a healthier you. When you exercise and eat right, your body functions well because it receives the nutrients it needs to thrive, along with physical activity to improve strength, endurance, body composition, and cardiovascular health. What are the benefits of combining exercise and diet?

The ability to achieve or maintain a healthy body weight
A thinner appearance with better muscle tone
Increased vigor and energy
Reduced risk of many chronic diseases, including hypertension, heart disease, diabetes, and certain cancers
Increased insulin sensitivity, which can help stave off weight gain, metabolic syndrome, and type 2 diabetes
Improved blood lipid profiles including cholesterol and triglycerides
Improved immunity
Better sleep
Reduced stress
Diet and Exercise Synergy

For years, nutrition experts have recommended controlling calories for weight loss and maintenance. To do so, they recommend balancing calories in versus calories out. Food contains calories, which are units of energy your body derives from the things you eat. In the calorie model of weight control, when you eat more calories than you burn via your body's basic processes and activity levels, you gain weight. When you burn more calories than you consume, you lose it.

Adding regular exercise increases energy expenditure, which either increases the amount of food you can eat without gaining weight, or reduces the number of calories you need to reduce to lose it. At the same time, exercise helps generate an additional metabolic advantage, as well. When you exercise, you build muscle mass, which utilizes more fuel than fat. One caveat to this, however, is that people tend to overestimate the metabolic advantage and caloric burn gained from exercise, and they overcompensate by eating more. According to the caloric hypothesis, in order to lose weight successfully by combining diet and exercise, you need to avoid overcompensating for exercise energy expenditures with additional food intake.

Healthy Diet Defined
How do you know if you are eating a healthy diet? The USDA's food pyramid provides a tool for determining what constitutes a healthy diet for you based on your height, weight, age, and gender. In general, a healthy diet consists of:

Whole grains, nuts and legumes
A variety of fruits and vegetables across the spectrum of color
Lean proteins and low-fat dairy
Small amounts of healthy fats including omega-3, monounsaturated and polyunsaturated fats
Adequate water intake of at least 64 ounces per day
Limitation of sugar, artificial ingredients, and added sodium
Fitness Defined
Achieving fitness encompasses all five components of physical fitness, including muscular strength and endurance, cardiovascular endurance, healthy body composition, and flexibility. An effective fitness plan balances all of these, and should include:

Aerobic activity in your target heart rate zone at least 30 minutes per day most days per week
Strength training activity that works all of your major muscle groups two to three times per week
Stretching
Achieving Health

By putting both diet and exercise together, you can obtain good health. Many people try fad diets that bring about quick weight loss, and assume because they have lost the weight, they do not need to exercise. You can lose weight or be naturally thin without being fit. Likewise, you can be strong and have good cardiovascular health and maintain an unhealthy diet. It is the combination of the two, however, that propels you forward to overall better health, more energy, and disease prevention.