BMR Defined:
BMR stands for… Basal Metabolic Rate. Yeah, that means nothing to me either. Let’s break it down…
Basal = Refers to the body’s minimum energy requirement when at complete rest.
Metabolic = Relating to metabolism. Refers to the body’s ongoing processes that use energy, even when you’re not physically active
Rate = The amount of energy used over a period of time, normally expressed as calories per day
So BMR really means… Your body’s minimum daily energy requirements (in calories) to maintain good health.
Your body is still using energy while you sleep or sit quietly. Your heart beats, lungs work, your brain operates, your kidneys filter blood, cells maintain themselves, and your body maintains its temperature.
So, for example, if your BMR were 2,000 kcal/day, that doesn’t mean you should eat 2,000 calories per day. It means you body would require roughly that much energy simply to maintain its basic functions under resting conditions.
Your actual daily energy expenditure is higher because you also expend energy through:
- walking and other movement
- exercise
- digestion
- maintaining posture
- everyday activities
This is where BMR gets interesting…
Your body needs energy continuously. Its first and most convenient option is Plan A: get the energy from food. You eat a meal. Your digestive system breaks it down. The resulting nutrients become available to your cells, and some of the energy is stored for later.
If you’ve supplied more energy than you need, your body has no particular reason to throw the surplus away. It stores it. Some can be stored as glycogen, but the body’s great long-term energy warehouse is body fat.
This makes perfect evolutionary sense. Food isn’t guaranteed to arrive at 8:00 am, 12:30 pm and 7:00 pm every day. Your body therefore developed a rather clever backup system.
Which brings us to Plan B.
This is where BMR becomes your Ally…
Let’s say your BMR is 2,000 per day and you maintain this by lying down and immobile all day. Let’s also assume you eat 2,000 calories per day. In this case, energy in = energy out and your weight will be stable.
Now let’s say you go for a walk. In this case you’re using more energy than you take in. Alternatively, let’s say you vegetate for the day but eat fewer calories, so again you’re supplying fewer calories than your body requires.
But your body’s requirements in this instance are a fixed number, so if you can’t satisfy need this through food intake, what then? This is where your body will see that it’s primary source of energy (i.e. food) is lacking, so it will move to ‘Plan B’ and take the energy it needs from it’s fat reserves.