Over the past few years a trend has emerged of “finding your Basal Metabolic Rate.” In order to determine how many calories you should be eating and then extrapolating from that how many calories you need to burn and eat to lose weight. While this is a great theory, it oversimplifies the human body processes to the point that it is completely inaccurate and ineffective….So why?
The problem with this entire ethos is that our BMR is not a constant number, it’s not even close to constant. In fact, the very process of eating drastically effects our BMR…..For instance, let’s say you calculate your BMR to be 2000 calories per day. Then, you plan to sit on the couch all day and do nothing two days in a row….On day 1, you eat 1000 total calories for the day. SO, according to the BMR theory, you should burn 1000 calories additional to what you eat, and you will lose 1000 calories worth of weight correct? NO..The very fact that you reduced your caloric intake to 1000 calories significantly slows your metabolism. SO, for that day, you maybe burned 1700 calories, another day at 1000 calorie intake, you may use only 1550, and each consecutive day it will decrease as your body essentially LEARNS to survive on 1000 calories per day. Conversely, let’s say on day two you binge and eat 5000 calories, in response to this, your metabolism will ignite and you may end up burning 4000 calories that day, simply as a response to drastically increased food intake. This is how cheat meals work…they spike your metabolism, IE increase your BMR.
To better understand…consider miles per gallon of a car. If a car averages 30 miles per gallon, using the constant BMR assumption, we can assume that for every gallon we burn, we will travel exactly 30 miles, regardless of any other variables. So we could just tune the motor to dump more fuel into the motor then correct? Of course not….The truth is though, many other factors, like vehicle speed, braking, and rate of acceleration all greatly impact fuel consumption.
Similarly, there are hundreds of factors that determine how many calories we burn on a particular day, even if our activity level remains constant…Further, 20 minutes on the treadmill may burn 200 calories, however 60 minutes will not burn 600 calories, as the body gets more efficient and learns to use LESS energy to complete the task. Each subsequent day we walk an hour on the treadmill, our calorie consumption from doing so decreases each time.
Your BMR is not a constant from day to day or even hour to hour. It should be defined as a Current Metabolic Rate (CMR) that can be influenced by many factors and manipulated to burn fat and lose weight.