Metabolism is a misunderstood biochemical process that gets a lot of bad press. The idea of a ‘slow metabolism’ is often blamed as the reason why some people find it difficult to lose weight, and many believe their metabolic rate can be tricked into performing faster with a few ‘super foods’ and dieting techniques. We take a look at some of the biggest misunderstandings surrounding metabolism, and explain exactly what’s going on.
What is metabolism?
Metabolism is a blanket term for lots of chemical processes which are constantly taking place in your body. They are processes necessary for maintaining basic bodily functions, such as growing new tissue, repairing damage, reproducing cells, and helping your body respond to different environments.
There are two main types of metabolic processes which take place in every cell in your body: catabolism and anabolism. The first breaks down large molecules into smaller pieces, whilst the second creates larger structures out of small units. As an example, catabolism is needed to break down stored energy to fuel our body, whereas anabolism is needed to grow new muscle.
Both processes use energy in order to occur, and catabolism itself can release the energy required for anabolism to take place. Put simply, catabolism is how we release energy into our bodies, and anabolism is how we use energy up.
What is metabolic rate?
Your metabolic rate refers to the number of calories you burn during a day to keep you basic bodily functions working.
Your metabolic rate can be broken into three main categories:
- Basal metabolic rate (BMR): energy burned at rest just to keep all your systems working, such as breathing and pumping blood. These processes use the main amount of energy.
- Physical activity: energy required to move, which is insignificant compared to that required for BMR.
- Digestion (thermogenesis): a tiny fraction of energy is used for breaking down, absorbing and storing food.
Your metabolic rate has very little to do with speed. It refers, rather, to the total amount of energy you use. Whilst some people use more energy to fuel these processes, it doesn’t necessarily mean they have a ‘quicker’ metabolic rate, and you can’t technically make your metabolic rate go ‘faster’.
What affects your basal metabolic rate (BMR)?
As the largest drain on your energy supplies, your basal metabolic rate – the energy required for keeping basic bodily functions working – is the most significant in terms of how you process energy.BMR varies from person to person based on the following:
- Body mass
- Hormonal balances
- Environment temperature
- Illness and health problems
One of the most important variables in terms of metabolic rate relates to how much body fat a person has in relation to their muscle mass. Fat cells burn much less energy than most body cells, whereas muscle cells require a lot of energy to build and maintain. As such, someone with more muscle mass than fat will burn more calories at rest than someone with a higher fat percentage, even if both people are the same age and weight. Since men tend to have a higher muscle-to-fat ratio than women, they tend to have higher BMRs.
Metabolism and food
As detailed above, your BMR rises every time you eat, as a little amount of energy is required to process and absorb food. Some foods require more energy to break down, and as such place different demands on your BMR. Protein, for example, takes much more energy to digest than fat and carbohydrates.
However, it’s important to get something straight: there are no miracle foods which significantly boost your metabolism into performing at an unusually high rate. The effect of foods like coffee, green tea, spicy food and citrus fruit are commonly misrepresented by the media; responses to each depends from person to person, and there is no substantial evidence supporting any significant impact on metabolic rates. Whilst it is true that the body needs a little more energy to process iced water over room temperature water, the energy expenditure is again rather insignificant.
If you are trying to lose weight, crash dieting or fasting can actually work against your metabolic rate. Your body may be forced to break down muscle mass, which we already know demands the largest amount of calories to maintain, and your metabolism will slow as a result. Your body prepares itself for ‘survival mode’, slowing to conserve energy, and you may find you put on fat quickly when you end the diet.
Metabolism and age
Metabolism seems to ‘slow’, as our bodies start to require fewer calories to perform everyday bodily processes.
This can be partly due to hormonal changes. As men age, they produce less testosterone, and in women the production of oestrogen slows after the menopause. Both of these hormones are energy-intensive, so their depletion will mean your body will use fewer calories as part of your BMR.
Hormones play an important part in regulating metabolism. If you are putting on or losing weight even though you maintain a healthy lifestyle, you may want to look into potential hormonal problems, particularly those involving the hormone thyroxine, such as hyperthyroidism and hypothyroidism.
People also tend to be less physically active as they age. Exercise is the only form of energy expenditure impacting your BMR that you actually have any influence over. Since your muscles need more energy during exercise, your body will need to use more calories than normal and your metabolic rate will seem to increase. The amount of energy you use will depend on your individual biology and the intensity of exercise you are performing.
Being less and less physically active, people tend to lose muscle mass as they age and become susceptible to having a higher fat-to-muscle ratio. As discussed above, since fat cells require less energy to build and maintain than protein cells, your metabolic rate will seem to slow as a result. Try performing strength and resistance exercises regularly to preserve your muscle mass; the more muscle you have, the more energy you will burn at rest.
‘overweight people have a low metabolic rate and leaner people have a high one’
There is absolutely no truth in this. In fact, since overweight people have more cells in which metabolism can occur, they most likely have higher BMRs than leaner people of the same age and height. This misconception also implies that metabolism defines whether someone is over or underweight, whereas this is actually determined by energy imbalances.
‘If only I could speed up metabolism, I could lose weight’
Firstly, there’s very little besides exercising you can do to influence your metabolism and make your body burn more calories than normal. Secondly, your metabolic rate does not relate to any sense of speed (you cannot burn calories any faster), but rather the amount of calories used across a set period of time.
‘Exercise can increase my metabolism’
Again, see the note on speed above. Exercise actually has a rather nominal impact on your daily calorie usage, and its influence on metabolism actually relates to your muscle mass. Exercising helps maintain and produce more muscle. Since building muscle requires a lot of energy, people with a high muscle-to-fat ratio tend to have a higher metabolic rate.
‘Certain foods boost metabolism’
Technically, your metabolic rate will always rise to a certain extent when you eat anything, as you need energy to break down your food. However, there is little evidence suggesting coffee, green tea or spicy food has any real influence over your BMR. Disregard dietary supplements promising to boost your metabolic rate – apart from disappointing, they may also bring unexpected side effects.
Final piece of advice? Give your metabolism a break. Weight gain and energy usage are complex processes involving a lot of different factors, such as diet, exercise, biological make-up, and health status – metabolism alone cannot be held accountable.
If you’re looking to lose weight, use a metabolic calculator to see how much energy your body actually needs each day. The results can be surprising – you may be taking on far more energy than your body would ever require! The result will be able to show you how many excess calories you need to cut out of your daily intake.