Susan Bowerman, MS, RD, CSSD
Many of my overweight patients blame their struggles on their “slow metabolism”. Whenever I hear that, I realize that a lot of people aren’t exactly sure what metabolism really is and whether or not there’s anything they can do to speed it up. But it’s not that complicated, and if you understand what determines your metabolic rate, it’s a lot easier to understand what you can and can’t do about it.
Simply put, your metabolic rate is the number of calories your body uses every day just to keep your vital processes going. Sometimes it’s called your ‘resting metabolic rate’, because it’s referring only to those calories you burn at rest to keeping organs like your brain, heart and lungs functioning. And about 75% of all the calories you burn every day are used just for these basic processes. The rest of the calories you use during the day go to fuel your activity, and to digest and process your food.
Each of us has our own unique resting metabolic rate that’s determined primarily by how much lean body mass we have. You can think of your body as divided into two parts; the fat mass, and the lean mass that’s made up of everything that isn’t fat like muscles, bones and organs. Every pound of body fat you have burns only about 2 calories a day. But every pound of lean mass burns 7 times that amount.
So the more lean mass you have, the higher your metabolic rate. Since a big portion of your lean body mass is made up of muscle, one of the best things you can do to boost your metabolic rate is to do some strength training exercises that will build muscle.
This is one of the reasons that weight tends to creep up with age. As people get older, they tend to exercise less, and less intensely. So they lose lean mass over time, which drops the metabolic rate. And if they don’t cut calories to offset this decline, the pounds start to pile up.
It is true that your metabolic rate can slow a bit when you start dieting and cut calories. It’s your body’s natural response to try to conserve if it senses that fewer calories are coming in. But, the decrease in metabolic rate is relatively small, and if you become more active as you lose weight, you can offset these small changes. It’s also a good idea to eat small, frequent meals to keep the body from shifting into conservation mode.
And if you know someone who seems to eat all the time and yet never puts on an ounce, you might want to chalk up their good luck to a ‘fast metabolism’. That could be - they may have more muscle than the average person, which would make for a higher metabolic rate. However, naturally slender people also tend to move around more; they fidget, they talk with their hands, they walk down the hall to talk to a colleague instead of e-mailing. And more activity means more calories burned. So, once you’ve made the commitment to boost your metabolism by building more muscle, go ahead and put those muscles to use and move around frequently throughout the day.