BMRs: Calories, body fat and burning energy
A personal trainer can achieve better results for their clients if they have an understanding of Basal Metabolic Rates, or BMRs.
Our bodies burn energy 24/7, even when we are sedentary or asleep, and BMRs can help us work out how much. Age, gender and activity levels are all relevant when calculating BMRs, as are the person’s somatotype: whether they are tall, thin ectomorphs; short, bulkier endomorphs; athletic mesomorphs; or a combination of these body types. Anyone wanting to become a personal trainer should be aware of somatotypes and how BMRs work.
To achieve their BMR, a sedentary individual should consume 25 calories per kilo of bodyweight per day. To maintain bodyweight, an inactive man of 75 kilos would need to eat:
75 kilos x 25 calories = 1,875 calories a day
At the same time, a personal trainer should be aware of how body fat percentage can affect these figures. Ideally, for an average individual, women should be around 30-35% body fat and men should be around 15% – although a fit, athletic man could be 10% body fat or even lower.
If we assume our 75kg man has 20% body fat, this means around 15kg of his body weight is fat. Fat burns no calories, so we have to take this into account when working out his BMR. In other words, we need to work to a figure of:
75kg – 15kg body fat = 60kg
If his aim is to retain his lean percentage but while reaching a goal of 10% body fat, he needs to lose 9 kilos of fat.
So instead of weighing: 60kg + 15kg (15% fat) = 75 kg
He is aiming for: 60kg / 0.90 = 66.6kg (10% fat) = 66.6kg
Using the formula of 25 calories per kilo of bodyweight, he should be aiming for a daily intake of:
25 x 66.6 = 1,666 calories
Anyone with, say, a desk job should add another 20% to this figure and active gym goers might need to add another between 50-100%.
The best personal trainers will be aware of good practice in eating habits: for example, it’s best to eat four or five smaller meals a day or at least have a healthy snack between your three meals a day, and foods that release energy slowly will leave you feeling full for longer, encouraging you to eat less.
Losing 1lb a week is a good result. If an individual eats significantly below their BMR, then they are encouraging their body to go into ‘starvation mode’. This is not helpful for health or weight loss, as your body’s instinct will be to slow down your metabolic rate and store what you consume as fat, even though you are not overeating. This is why eating lettuce all week then having a blowout at the weekend is counterproductive to weight loss.
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