DEAR DR. BLONZ: Does the fact that muscle weighs more than fat explain the annoying fact that I tend to gain weight when I exercise? -- S.M., Hayward, California
DEAR S.M.: Let’s first acknowledge the obvious: that a pound of muscle weighs the same as a pound of fat. There are differences in caloric density, which is the number of calories (energy) per unit weight. A gram of fat contains nine calories, over twice the four calories in a gram of protein or a gram of carbohydrate. (A gram of alcohol, for what it’s worth, contains seven calories.) Using a monetary analogy, a $10 bill weighs the same as a $5 bill, but the 10 has twice the “spending energy” as the five.
The answer to your question lies with the fact that we are water-based organisms. Fat is the most concentrated form of energy in the human body, and adipose tissue, which is where fat is stored, contains very little water. By contrast, the protein that makes up our metabolically active muscles and organs is mostly water. The body prefers not to waste energy, so it will only have around the amount of muscle needed to maintain the status quo.
Whenever our routines become less active, the body will slowly reduce its muscular mass down to the basic level needed to keep the show going. When our routines or exercise habits involve an increased muscular demand, the body will respond by increasing its muscle mass. Other adaptations to regular increased muscular demand include an increased vasculature (blood vessels) and blood volume to carry the nutrients and waste products, and increased ventilatory capacity to deliver oxygen and remove carbon dioxide as needed.
Let’s assume you are eating a fixed number of calories when you begin an exercise program. As your body experiences the stress of exercise, it responds by making new muscles to handle the load. It also makes all the other supporting tissues and fluids -- all of which are primarily water. This means that the numbers on the scale can go up slightly, but realize that it is mostly water weight you are gaining. You are not getting fatter, but home scales do not provide that breakdown. (For this, you need to do a body composition test.)
If you were to stop exercising, you might lose weight. But again, it is water you are losing, and you might be getting fatter (increased percent body fat) at the same time.
Focusing solely on the scale can be discouraging and misleading, because it does not give you the complete picture, even when good things are going on inside. And never forget that additional muscle mass means that more energy is being burned, even while you are at rest. Think about an 8-cylinder engine versus a 4-cylinder engine, with the larger engine burning more gas even while idling.
Becoming fit is the way to go. It improves your general health and enhances your body’s ability to handle many types of stress.
Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 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.