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The Basal Metabolic Rate

The Basal Metabolic Rate

What is the Basal Metabolic Rate?

Firstly your metabolism is the chemical process that helps you maintain life. It helps your body maintain the correct body temperature, helps pump the blood around the body by maintaining a heartbeat, helps with brain, lung, skin, liver, kidney function, cell regeneration and growth and muscle contraction.

It takes energy to work this process and the energy used comes from the food you eat in the form of calories. The rate at which it does this over a 24 hour period can be measured as follows:

Basal Metabolic Rate (BMR) measures how much energy it takes to keep you at the correct temperature, your heart beating, your respiration system working and cell regeneration, it does not however include energy needed for physical activity or the digesting of food, you are at complete rest and this measurement is normally taken in the morning before you eat (empty stomach) or do any activity.

Resting Metabolic Rate (RMR) is also measured at complete rest (actually when you are asleep) and includes the BMR processes, plus the processing of food and normal day to day activity. The digesting of food requires energy to absorb, process and store its nutrients.

Most people looking to lose weight will be concerned with their BMR due to the more precise calculations that can be done, as activity and food consumption levels can vary from day to day, depending on what you eat and how active you have been, making the RMR less precise.

Many people can have a BMR as low as 40% while others as much as 70%. i.e. between 40%-70% of the energy used from the food you eat will be used for daily processes and functions to keep you alive. As you can see there is a huge difference and one of the reasons why there are people who can eat lots of food and not get fat, while there are people who eat much less but struggle to keep their weight in check. Therefore the faster your metabolism the more calories you burn just carrying out your daily activities and processes to live.

So up to 70% of the calories digested goes towards your BMR, 20% to everyday activities and 10% for digesting and processing food. What’s left over is then stored for long term energy in the form of body fat, so reducing calories means less stored body fat, and being more active means less also being stored.

What effects your BMR and how do you increase it?

Your BMR can be affected by your genetics, age, gender, height, weight, body composition and even by diseases and other medical conditions you may have.

Children tend to have a faster metabolic rate and as we age it tends to slow down at a rate of about 0.5% every year after you reach your late teens / early 20’s and in my opinion even more so in your late 30’s / early 40’s (known as middle age spread).

Much of the slowing down due to age is because we start to lose muscle mass and muscle needs more energy to exist, so we end up in a catch 22 situation, we lose muscle and gain fat and it is one of the reasons why women get fatter than men on average (more fat cells and less muscle). Of course we also tend to become less active as we get older as well.

Muscle burns many more calories than fat, around three times as much. However, you are not likely to be carrying 20-30 lbs of extra muscle, when you are more likely to be carrying that in fat. So let’s not get beyond ourselves. However every little bit helps and the fact that actually doing resistance training will burn energy and need energy to recover and repair itself helps also.

Now having just said all that, larger people need more energy to maintain their larger size, while skinny people need less. This often leads to the body actually speeding up the metabolism in the overweight person, yes that’s right you can have a faster metabolism if you are overweight. The issue is that larger people then consume way too many calories and are often less active and unfortunately can’t use enough energy to compensate for the calories they consume.

Unfortunately just going on a crash diet will slow your metabolism down also, plus you will lose muscle. Crash diets also send your brain signals to produce more hunger hormones to protect itself. Even going too long before eating again can trigger the starvation survival mode and make you over hungry and slow your metabolism down. So don’t skip breakfast and make sure you spread your food out over the course of a day. This is why I suggest a much slower reduction in calories and following a healthy fulfilling nutrition plan (see the Nutrition Plan). As a side note, you need to remember it takes energy to consume food and to digest it. There is also a thermic effect when digesting food, this is the energy needed to process the food and can vary widely depending on the food you eat. But obviously I’m not suggesting you eat more food to burn more energy as you will of course be consuming more energy in the food than burning through digestion. As a another side note, protein has the highest thermic affect and takes around 30% of its calories to be processed in the body.

So while dieting can slow your metabolism down, physical activity will help up your metabolic rate. Apart from the health benefits from exercise, using it to maintain or even build muscle will help keep your body working harder to burn energy consumed. Resistance training can also help increase your testosterone levels, which also helps build more muscle. Muscle needs more energy to maintain itself and therefore will slightly increase your resting metabolic rate.

It’s important to say that exercise will only increase your BMR by a small amount, even adding a good amount of muscle isn’t going to make you a fat burning machine. Your calorie intake is the key to reducing stored body fat, but as stated before reducing calorie intake can slow down your BMR. This is then were exercise is key to counter this. It will allow you to keep your BMR at a higher level and this is will help in maximising fat loss and changing your body’s composition.


Altering your metabolic rate will help with fat loss. Sort your diet out first, add exercise and keep moving. The sum of all this is the key to a healthy weight loss and healthy life.

Those who are obese and looking to lose body fat will find it useful to know how many calories you need and your BMR. There are scales on the market that can give you a rough idea of your BMR, but these are very rough calculations. There’s also calculators on-line that will give you a basic BMR based on your age, height, weight and gender. I’ll leave that up to you to decide if you want to try one of these scales and/or online calculators.