Hi Monique:
I have a question about measuring my Resting Metabolic Rate. I wouldlike to make some adjustments to my nutrition plan this winter. When itcomes to measuring my RMR, can I simply wear a heart rate monitor for a24 hour period to determine more accurately how many calories I burn ina given day? Isn't this method more accurate than using a formula?
CD
 Dear CD,
The upcoming winter season is definitely a great time to not only restand have some changes in your training program, but also to lose some bodyweight and body fat, and to incorporate some new foods and recipes intoyour diet. Understanding your body's nutritional requirements is one importantelement of updating and improving your diet. If you plan to work with asports dietitian in the coming months, your RMR is an important part ofthe energy balance equation.RMR is the amount of calories that your body burns at rest (such assitting on the couch all day and do nothing else) to perform basic functionssuch as breathing, circulation of blood, maintaining body temperature,and represents how may calories your body requires to survive and keepyou alive at your current weight. Your RMR can represent anywhere fromtwo-thirds to three-fourths of your total caloric expenditure for the day.The more your actual body weight, the higher your RMR. Muscle mass alsoburns more calories at rest than fat, so building muscle can increase yourRMR. Men have a higher RMR than a women of the same body weight becausethey have more muscle mass. Genetics can also affect your RMR. Decreasesin RMR with aging are mainly due to a decrease in muscle mass.In addition to your RMR, your daily calorie burning (not including training)is also affected by your lifestyle expenditure. If you have more or lessa desk job, the amount of calories that you burn in your daily life wouldbe lower than someone with a job that requires more daily activity. Theamount of lifestyle calories that you burn can make up about 10-percentof your total calorie burning for the day.Finally, a small number of calories are burned when your body digestsand absorbs the food you consume. This number can vary with the type ofmeal or snack that you consume and is referred to as the thermic effectof food (TEF). While you can increase your daily activity in a varietyof ways, TEF is what it is.Of course your daily training or exercise expenditure is the most variablecomponent of the amount of calories that you burn in a day, ranging fromseveral hundred to even several thousand calories depending on the durationand intensity of your training.You are correct in that using an equation to estimate your RMR may notbe highly accurate, as there can be wide variability in RMR even amongpersons of the same body size. The only true way to really obtain an RMRmeasurement is with a machine referred to as a metabolic cart, often usedin the hospital setting. Several companies now make portable metaboliccarts, and this service is now more accessible and affordable. You cancheck into the BodyGem by HealtheTech or MetaCheck by Korr, and see ifthey are available at a fitness or testing center in your area.These machines have a high level of accuracy because they measure thevolume of oxygen that you breathe in and out at rest when you breathe intoa mouthpiece for several minutes. This provides an accurate measurementof your metabolism, as oxygen is needed to break down the food you consume.You will need to avoid food, caffeine, and exercise for a few hours beforebeing tested.So you daily calorie expenditure is a sum of your:Resting metabolic rateDaily lifestyle activityThermic effect of foodTrainingWhen heart rate monitor is used to measure energy expenditure, it is based on a linear relationship between heart rate and oxygen consumption that exists for each person. However, the same heart rate may not correspond to the same level of oxygen consumption in each person, and there is individual variability, so it is only estimation. When you input your weight into the heart rate monitor and estimate your max heart rate, this results in only an estimate of the calories burned based on a one size fits all equation.If your plan is lose weight and body fat during the winter season, Iwould suggest that you have a direct measurement of oxygen consumptionto measure your resting metabolic rate. Your RMR also decreases if youlose about 5 to 10-percent or more of your body weight, so it could bebeneficial to have it retested when you reach a weight goal. However, youcan keep your RMR humming with resistance training and building lean bodymass.
Monique Ryan