Calories

What is a calorie?

A calorie is a unit of energy. In the scientific world, a calorie is the amount of energy needed to raise 1 gram of water by 1 degree Celsius, which is sometimes called a small calorie. In the nutrition world, a calorie indicates the amount of energy in foods. Since a food calorie is equal to 1,000 small calories, it is sometimes called a large calorie or a kilocalorie (kcal).

Food calories come from four sources: carbohydrates, proteins, fats, and alcohol.

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How does the body use calories?

While the body uses calories (energy) to perform all of its functions, most people are primarily concerned with how excess calories affect our body weight. In a nutshell, if we consume more calories than we burn, our bodies can store the excess energy as body fat. Historically, the extra fat often meant the difference between life and death during severe food shortages. Today, however, this lifesaving bodily feature has become a problem for many of us. In fact, storing too much body fat (obesity) has become a leading risk factor for premature death.¹

Weight loss can occur when we consume fewer calories than our bodies need. Our bodies can adapt to the food shortage by using body fat as an energy source. If the calorie deficit continues for an extended period, our bodies can consume large amounts of body fat.

How many calories do I need in my diet?

Each person has unique energy needs depending on factors such as age, gender, height, weight, body composition, and goals. You can calculate the number of calories needed to maintain your weight by using a Basal Metabolic Rate (BMR) equation such as the Harris-Benedict Equation.

If you would like to lose weight, you can eat fewer calories than your calculated BMR and/or increase your activity level. To lose one pound per week, you would need to create a calorie shortage of 3,500 calories per week — or 500 calories per day.

What are good sources of calories?

You should consume a variety of foods that contain a high quantity of nutrients per calorie (nutrient-dense foods) such as fruits, vegetables, nuts, and minimally-processed products. Avoid high-calorie, low-nutrient foods (empty calories) like soft drinks, alcohol, and desserts.

Which foods are high in calories?

The following foods have a high calorie-to-weight ratio (calorie-dense foods):

Additional Resources

• How many calories should I eat a day?
• MedlinePlus: Nutrition