Whenever we talk about a diet we hear the word metabolism almost all the time:
– My metabolism is slow
– If you can speed up your metabolism you can burn more fat
– Metabolism gets slower when you get older
So what is metabolism? In simple English, it is the engine within your cells that turns your food into energy needed by your cells to function, and in a larger scale: for your heart to keep pumping, your brain to keep working, your muscles to support your body, and your blood to continue circulating,.. you get the idea. Since all these are happening in your cells regardless of whether you are active or not, your cells/organs will require the fuel/energy even when you are resting. Therefore, when somebody says that her metabolism is slow, she means her cells/body do not require that much food/fuel/energy to function which can be measured in calories. The right term for the amount of calories needed in a given time period when a person is at rest is Basal Metabolic Rate (BMR).
Your BMR is dependent on your gender, age, body weight, and height. If you are into formulas, you can find one in Lazzer et al.’s article. In the same article, the authors also suggested a formula for calculation of daily energy consumption estimate of a person by taking her daily activities into account. We are not going to get into details here but we will take a look at their Physical Activity Ratios (PAR) for some activities. PAR is a measure of the activity relative to BMR of that person. For example, table tennis PAR is 3.5. This means, based on my BMR, if I use 100 calories by resting 1 hour, I will use 350 calories if I play table tennis for one hour. This ratio is good for understanding the relative calorie consumption during each activity. Here are some examples:
Basal Metabolic Rate 1
Sitting Watching Television 1.57
Table Tennis 3.5
Changing Linens 4.01
Walking 4.3 km/h with 3% slope 5.46
Walking 4.8 km/h with 9% slope 8.77
The obvious conclusion here is that your body needs energy when you are resting but it needs much more energy when you are active. If you are just cleaning the house and changing the linens you are using 4 times more energy than when you are resting. In a not-so-accurate way you can say that your metabolism is 4 times faster.
So this comes to fundamentals of pretty much every diet: Exercise more, eat less. Even though this in general is a true statement, there is more to it because cell metabolism is more complex than what we summarized here.