We’ve all got one but few of us know just what metabolism does and why it’s so important
What is metabolism?
Metabolism comes from the Greek word to change’, and that’s basically what it involves converting the fuel we put into our bodies into life-giving energy. Basically if we didn’t have metabolism, our body would grind to a halt.
Keith Frayn, Professor of Human Metabolism at Oxford University, says, ‘Metabolism is controlled by hormones, especially the thyroid, and is the sum total of all the chemical reactions in the body that turn food into energy and waste.’
What is your resting metabolic rate? Your resting metabolic rate (RMR) is the amount of energy in calories that you burn doing absolutely nothing. Between 60 and 70 per cent of your daily energy expenditure is consumed by the simple process of keeping you alive.
While there has been much talk about individuals being predisposed to obesity because of naturally sluggish metabolic rates, RMRs don’t differ that much between individuals. Frayn says, ‘There is some genetic component to metabolism, but it doesn’t significantly vary much from one person to another. People’s metabolic rate is by and large determined by their physique, meaning their fat-to-muscle ratio.’
Overweight people who say, ‘It’s the fault of my metabolism,’ are fooling themselves, as everybody automatically uses the correct amount of calories in order to function. Fatness cannot be blamed on metabolism.
What determines your RMR?
As Frayn says, it’s the amount of fat-free mass (muscle, bone and major organs – your brain and liver are highly metabolic for example) that largely dictates the rate at which your body uses energy. A study by Wayne Westcott, fitness research director at South Shore YMCA, USA, showed that muscle burns about 30-50 calories a day, which means just 0.5kg of extra muscle uses up 350 more calories a week just to keep ticking over.
Frayn says, The only way to increase metabolism is by exercising, because your body automatically needs extra energy to replace the energy that it has lost through exercise, and so speeds up to provide it. Similarly, when you sleep your metabolism slows down as you don’t need the same level of energy.’ The post-exercise elevation of RMR is known as excess post-exercise oxygen consumption (EPOC), or the more snappy ‘after-burn’.
Are there foods that rev-up the metabolism? Yes and no. ‘There is some truth in this, because fat is less readily burned by the body and therefore easily stored, but there is little difference in the rate at which the main food groups are used by the body,’ says Fran. Coconut oil for example contains saturated acids, but they are other type of acids which also speed up metabolism. Learn more about coconut oil and weight loss effect. ‘Protein has been held up as a food that stimulates the metabolism, but what has become apparent from the Atkins diet is that people lose weight because they’re eating fewer calories rather than protein being a stimulus for weight loss.’
As for crash dieting, it brings your metabolism to a near standstill as your body battles to cling on to all available energy. It will rebalance itself if you start eating properly again and exercise, but Frayn warns that yo-yo dieting can increase the risk of heart disease, due to a fluctuating metabolism