What is metabolism?
What is metabolism exactly? According to the NHS, metabolism describes the collection of chemical processes that happen continuously inside your body to keep you alive and your organs and body systems functioning normally (i). These include breathing, keeping your heart beating, adjusting hormone levels, repairing cells and digesting food.
All of these chemical processes need energy from food (calories), and the minimum amount of energy your body needs to keep your metabolism working is called your basal metabolic rate (BMR).
Resting metabolic rate: the difference between men and women
If you’re trying to lose weight, how quickly, easily and successfully you achieve your goal may not just depend on your willpower. Of all the factors that come into play where losing weight is concerned, perhaps the most unfair – at least for half the population – is gender. In other words, if you’re an average adult woman you may lose weight less effectively than an average adult man.
There are a number of theories and explanations for why this may be the case, but arguably the most persuasive is the difference in metabolism between men and women.
BMR vs RMR
If BMR is your basal – or base level – metabolic rate, then what exactly is RMR?
RMR stands for resting metabolic rate, and the two terms are often used interchangeably – though strictly speaking they’re not exactly the same. Both measure the amount of energy you need to keep your body working while at rest, with the average adult using around 1.1 calories per minute to maintain essential bodily functions (ii).
However BMR is measured under strict laboratory or clinical conditions after fasting for 12 hours and usually on waking in the morning (the test requires complete inactivity). RMR, meanwhile, is measured by using a simple equation. And while RMR may not be quite as accurate as BMR it’s much more widely used thanks to its accessibility. So when people talk about their BMR, unless they’ve spent a night in a hospital or clinic to have theirs checked, what they probably mean is their RMR.
BMR, then, for most of us will be theoretical. However anyone can easily work out their RMR – find out more including how to calculate your RMR here.
Metabolism: gender differences
Your BMR accounts for quite a large part of your daily calorie requirement – between 40 - 70 per cent, says the NHS (i). If yours is at the lower end of this range you’re classed as having a low BMR (or a slow metabolism). Whether your metabolism is slow, medium or fast depends on a number of factors.
For instance, babies and young children often have a proportionately high BMR for their size because they are growing and developing so quickly. Other things that can affect your BMR include your age (older people tend to have lower BMRs than younger people), your lifestyle (the more active you are the higher your BMR will usually be) and – last but by no means least – your gender.
Many researchers have shown an interest in this subject, asking questions such as whether a lower RMR in women may explain why obesity affects more women than men (the most recent UK figures show 30 per cent of women in the UK are obese compared with 27 per cent of men (iii)). And yes, some studies do suggest women have a lower RMR than men (iv), with others showing that older adults have lower RMRs than those who are younger too (v).
Some of the differences in RMR between men and women – as well as between people of different ages – are thought to be related to muscle mass. In general, men typically have more muscle than women, while younger people tend to naturally have more lean muscle than older people. But lean body tissue or muscle is more metabolically active than fat, so the more muscle (or metabolically active tissue) you have, the higher your RMR.
That’s not the whole picture, however. According to the NHS your metabolism may be partly determined by your genes – though we don’t yet fully understand how (i). But it may have something to do with the fact that genes affect your muscle size as well as your ability to gain muscle, both of which affect your metabolism.
Is a slow metabolism making you fat?
Some believe the difference in RMR between men and women might explain why some men seem to be able to eat more food than women without gaining weight so easily. But if you’re a man or a woman, can you blame the fact that you struggle to lose weight on a slow metabolism?
The NHS suggests there’s little evidence to support the idea that a slow metabolism causes weight gain (i). Indeed, it says research shows overweight people have faster metabolisms than thinner people – that’s because the bigger you are, the more energy your body needs to carry out basic functions.
NHS experts do say, however, that going on a crash diet could slow your metabolism. That’s because with some very restrictive diets your body has to break down muscle to use for energy, and the less muscle you have, the slower your metabolism.
Having an underactive thyroid, on the other hand, could be causing a problem with your weight. Your thyroid gland is important since the hormones it produces regulate your metabolism, keeping it under control. If your thyroid doesn’t produce enough hormones it can slow down your metabolic rate.
But while weight gain is one of the symptoms of a clinically underactive thyroid, you’d most likely be having other symptoms too, including tiredness, sensitivity to the cold, dry skin and hair, muscle aches and low mood. Getting treatment for an underactive thyroid should, however, mean your hormone levels – and your metabolic rate – will return to normal.
Can you raise your RMR?
If women have naturally slower RMRs than men, is there anything they can do to make their metabolic rate higher? While there’s no quick or easy way to really shake up your metabolism, there are a few things you could try that may give it a little bit of a nudge in the right direction.
Be more active
Regular physical activity is an effective way to burn calories, so try to make sure you’re doing at least 150 minutes of moderate activity every week (if you want to lose weight you may need to do more than this). It’s also a good idea to try to be more active in general – try walking more, for instance, instead of using public transport or driving your car, and be more active around the house (if you have a cordless phone you could try walking around when you’re using it instead of sitting and talking).
You could also try standing more often rather than spending all day sitting. One study has found standing up at work during an afternoon can burn an extra 174 calories than if you spent the same time sitting (vi). If you can’t do your job standing up, just try to break up the period of time you spend sitting by getting up and stretching your legs every now and then.
If you already have a good standard of fitness you could also try doing high-intensity interval training (HIIT) workouts as there’s some evidence it could help increase your metabolic rate even after you’ve finished working out (vii).
Work your muscles
Since muscle is more metabolically active than fat, doing strength training exercises that work all your major muscle groups can help you burn more calories and lose weight.
Strength training doesn’t have to mean you’ll start bulking up like a body builder – but if you are interested in gaining muscle size take a look at our article on muscle building.
UK exercise guidelines suggest all adults do strengthening activities that work their legs, hips, back, stomach, chest, shoulders and arms on at least two days of the week. Examples of muscle-strengthening activities include lifting weights, working with resistance bands, doing body-weight exercises (such as push-ups and crunches, for instance), yoga, Pilates, lifting heavy shopping and doing heavy gardening (viii).
Always eat protein with your meals
After you eat, your digestive system burns calories as it breaks down, processes and digests your food – this is called the thermic effect of food (TEF for short, though it’s also called thermogenesis). So whenever you eat, your metabolism increases a little bit for a few hours. However certain foods need more calories for their digestion, with one study suggesting protein boosts your metabolic rate by 15 - 30 per cent, compared to 5 - 10 per cent for carbohydrates and 0 - 3 per cent for fats (ix).
Try to make sure you have protein with every meal – choose from foods such as fish, eggs, beans, tofu, Quorn, pulses, lentils, nuts and meat.
Drink water
Researchers involved in a small-scale study have found water may have a thermogenic effect when you drink it (x). The study even goes as far as claiming that drinking an extra 1.5 litres of water a day could increase your energy expenditure by around 200kJ (48 calories), and that drinking 500ml of water may increase your metabolic rate by 30 per cent for more than an hour. The same study suggests drinking cold water has an even greater calorie-burning effect, since your body has to use energy to heat the water to body temperature.
Have a cuppa
If you’re a tea drinker, having green or oolong tea could help give your metabolism a small but nevertheless welcome boost. Studies suggest these two types of tea may increase the amount of energy you burn by up to five per cent (xi). If you’re not a tea fan you may like to try taking a supplement that contains green tea extract. Or instead of tea you could drink coffee, since there’s evidence that caffeine (also found in tea) may trigger a temporary increase in metabolic rate (xii).
Take a look at our other sports articles for information on a range of subjects designed to help you work out smarter.
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Christine
Christine Morgan has been a freelance health and wellbeing journalist for almost 20 years, having written for numerous publications including the Daily Mirror, S Magazine, Top Sante, Healthy, Woman & Home, Zest, Allergy, Healthy Times and Pregnancy & Birth; she has also edited several titles such as Women’ Health, Shine’s Real Health & Beauty and All About Health.
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