DEAR DR. BLONZ: I have a math issue regarding body weight and body fat. If a pound contains 454 grams, and there are nine calories per gram of fat, please explain how a pound of body fat is said to contain only 3,500 calories. You and many others use this figure but the math does not add up. -- D.L., Poway, Calif.
DEAR D.L.: There are indeed 454 grams in a pound, as you point out. So how do we come up with 3,500 calories from a pound of body fat when 454 x 9 = 4,086 calories? To start with, consider that fat is our most calorie-dense substance and it is capable of providing an energy equivalent to nine calories per gram. It is utilized as the primary form of energy storage because humans, like other animals, need to be mobile. Imagine the image of a human with energy stores in the form of carbohydrate or even protein; if such were the case our bodies would need to take up over twice the space they do now.
Getting back to the math problem, the answer rests with the fact that adipose tissue in the body is not 100 percent pure fat. This tissue contains a small amount of water and some structural material, accounting for close to 15 percent of tissue weight. It is this nonfat portion that helps explain why a pound of body fat is said to contain approximately 3,500 calories worth of stored energy.
DEAR DR. BLONZ: I was wondering what your thoughts were regarding the use of sports drinks as a beverage for active children. -- E.F., Oakland, Calif.
DEAR E.F.: I would not consider a sport drink to be a universal go-to beverage for children; water fits that description. Next might be a nutrient-rich 100 percent fruit juice, ideally one from any of a variety of berries. Sports drinks can be helpful for those involved with hour-plus workouts or athletic events, in that they can help replace the sodium and potassium lost through perspiration. A small amount of sweetener helps make the drink more palatable, and it provides a small boost of the type of fuel that is in short supply during an extended workout. You don't want too much sugar as that can work at cross purposes by slowing absorption. I also advise against giving exercising children any drinks that contain stimulants, such as caffeine.
The journal Pediatrics found that an effective beverage contained, per 8-ounce serving, 14 grams of sugar (6 percent carbohydrate) and 110 milligrams of sodium (18 mmol/l sodium). See tinyurl.com/h9nne for more information. This is the same formula found in Gatorade and some other sport drinks. Check the Nutrition Facts label on any products before you buy.
I recommend that you make your own sports drink from fresh juices. Such a beverage provides the same nutrients as store-bought sports drinks, but contains genuine flavors and the added benefits of the fruit's phytochemicals. My recipe can be found at tinyurl.com/krkj8mx. You know your child best, so you should adjust the recipe accordingly.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to email@example.com. Due to the volume of mail, personal replies cannot be provided.