DEAR DR. BLONZ: Calories are listed on the Nutrition Facts panel of foods, so are they considered nutrients? What's the best way of figuring out how many calories we need? And is there an explanation for why nuts and seeds have so many calories? -- F.P., Sunrise, Arizona
DEAR F.P.: Calories are not nutrients; they are a unit of energy. The calorie is the basic unit of food energy in the U.S., but other common energy units are the joule and the British Thermal Unit (BTU).
The nutritional calorie is defined as the amount of energy (heat) necessary to raise the temperature of one kilogram of water by one degree centigrade.
Fats, proteins, carbohydrates and even alcohol are complex compounds that each have caloric values because, when absorbed and metabolized, they can release energy for use by the body. On a weight basis, fats contain the most calories: 1 gram contains approximately 9 calories; 1 gram of protein or carbohydrate contains 4 calories; 1 gram of alcohol contains 7 calories. Vitamins and minerals do not provide calories.
The amount of energy your body needs depends on your age, size, body composition and how much physical work you do. It is difficult to generalize what any one individual might require. A first step is to get an estimate of your basal metabolic rate (BMR), which is the amount of energy your body requires at rest.
Your BMR changes throughout your life, being highest during times of rapid growth. After age 30, it tends to gradually decrease through the rest of one's life. One contributor to the decline is the decrease in muscle mass in relation to body weight, muscles being metabolically active tissue. As an analogy, think of how an eight-cylinder car will burn more gas at idle than a four-cylinder car.
The slowdown contributes to the tendency to gain weight as we age, particularly for those who continue to eat the same way they did when they were young. For an average adult, BMR accounts for the burning of 1,200 to 1,800 calories per day. To this number, we then add the caloric requirements for your daily activities, which for a 150-pound adult might include 1.4 calories per minute for sitting still, 5 calories per minute while walking at 3.5 mph, or 15 calories per minute during a vigorous game of soccer. The total of your BMR plus your activities is the number of calories you would need to take in every day to maintain your body weight. Online calorie calculators provide an estimate of daily calorie needs based on your height, weight, age and activity level (check goo.gl/zTLXE3).
The human body is not designed to waste resources. Calories not needed at the moment get stored for later use. Humans, like other mobile creatures, store excess energy as fat -- the most concentrated form. Plants, by contrast, don't need to be mobile, and they produce their own energy from the sun. The energy in plants is stored as carbohydrates, which allows them to get more growth "bang" for their calorie "buck."
All this changes when the plant makes its seeds: With a seed, the need is for a light, concentrated source of energy -- one sufficient to fuel the plant's growth until it can sprout its own leaves and produce its own energy. This explains why we find fats and oils in the nuts and seeds of plants.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to firstname.lastname@example.org. Due to the volume of mail, personal replies cannot be provided.