You’re eating a balanced, nutrient-rich diet, you’re regularly working up a sweat in your local spin studio, and you’ve put a virtuous ban on all after-work wines. So, when you step on the scales after weeks of blood, sweat and tears, why has your weight-loss progress stubbornly plateaued?
Perhaps it’s your genes, rather than your lack of gusto on the treadmill, that holds the answer.
Chances are you’ll have heard someone blame their slow metabolism for their weight-loss struggles at some point. The general idea is that if you’ve been blessed with an overactive or fast one, you can eat more, work out less, and still maintain a svelte figure.
But what exactly is the mythical ‘M’ word, how does it work, and can it really be the reason why some people find it harder to lose weight than others? We asked some experts to weigh in.
The metabolism in a nutshell
Your metabolism isn’t a single organ. It’s actually an umbrella term that’s used to describe lots of different metabolic reactions that occur in the body, whose job it is to keep you alive (it’s about way more than just controlling weight and body fat).
“These reactions do a variety of things, like generate energy, regulate growth, repair and general body maintenance,” explains Dr Sarah Brewer, medical director at Healthspan.
Think of it like the engine that keeps your body running. If you lay in bed all day and didn’t move a muscle, the calories you’d burn just from staying alive would be what’s known as your ‘basal metabolic rate’. This explains why, if you wear an activity tracker, you might see a fairly hefty calorie burn for the hours you’ve been asleep in bed.
Generally speaking, the speed of your metabolism is judged on the number of calories you burn in a given amount of time. On top of your basal rate, how ‘fast’ your internal engine runs is based on how many calories it takes to digest and process food, undertake exercise and perform activities like fidgeting, changing posture, standing and walking around.
It’s as simple as this: the faster your metabolism, the more calories your body needs. This is the reason some people can eat a lot without gaining weight, while others seem to need less to accumulate fat.
So why do some people have a faster metabolism than others?
“The rate at which you burn calories depends on many factors, including your age, gender, hormone balance, level of physical activity and your diet and lifestyle,” says Dr Brewer. “It also depends on your weight and, in general, the more you weigh, the higher your resting metabolic rate.”
Dr Brewer explains that your metabolism is also partly regulated by the thyroid gland, which produces two iodine-containing hormones, thyroxine and triiodothyronine. These hormones enter cells and ‘switch on’ genes that boost the burning of glucose, fat and protein to generate energy.
If you have an underactive thyroid gland, low levels of these hormones can cause your resting metabolic rate to slow by as much as 40 per cent, so you’ll gain weight more easily. If it’s overactive? Excess production of these hormones can cause it to increase by as much as double, making it conversely difficult to gain weight.
Your metabolic rate also depends on your lean body mass percentage, as muscle burns more energy than fat, and it’s also affected by your level of physical activity.
“Even your diet and lifestyle play a part too,” says Dr Brewer. She explains that eating protein-based foods, for example, uses up more energy and generates more heat during processing than eating fat and carbohydrates.
“This effect, known as ‘dietary-induced thermogenesis’, can account for 10 per cent or more of the energy provided by foods – especially protein-rich foods.”
Sadly, there’s no food that burns more energy during processing than it provides. Even celery and grapefruit, which are often touted as ‘negative-calorie’ foods.
How does having a slow or fast metabolism affect weight gain?
If you have a slower metabolism, you’ll burn less glucose and fat, and may gain weight if your energy intake is more than your energy expenditure. The evidence seems to suggest that, generally speaking, the metabolism slows down as we get older, which may be why some people suddenly find it harder to keep extra weight off (but, of course, this isn’t the case for everyone).
“Weight is put on more easily in later years because of changes in your body and lifestyle,” explains Dr Brewer. “The most significant change is loss of lean muscle tissue, which is mostly replaced with fat. This process, known as ‘sarcopenia’, will occur naturally – unless you continue to follow a muscle-building regime and obtain sufficient protein in your diet to build new muscle.
“Resting metabolism also slows by around 5 per cent every 10 years after age 25 and, as a result, your daily need for calories goes down. By the time a woman is 75, she actually needs around 300 calories less per day than when she was 18, and 130 calories less per day than when she was 50. The difference is even greater in men, who need around 655 fewer calories per day at age 75 than when they were 18 years old.”
Bottom line: Is your metabolism to blame?
When it comes to weight, metabolism is important, and while some believe that genetics play a part in its speed, it’s still an area that needs further research.
“In a sense, your metabolism may play a small part in whether you lose or put on weight,” says Dr Will Hawkins, a nutritionist from Push Doctor. “However, the main contributor to weight-loss or gain is always how many calories you’re eating vs how many calories you’re expending.”
If you’re looking to lose weight for summer, Dr Hawkins believes the best way to see results is to make sure you balance the calories you take in against the calories you burn up through good old-fashioned exercise.
Can you speed up your metabolism?
Experts seem to think it’s possible. “One of the easiest ways to boost your metabolism is to increase your exercise,” says Dr Hawkins, “whether that be a brisk walk, run or gym activities.”
High intensity interval training (HIIT) is one of the most effective types of exercise you can do. “It increases your heart rate, burns more calories and helps you lose more fat than more traditional forms of exercise, and clinical trials also show that the fat-burning effects of HIIT last for a significant length of time after the exercise is over,” says Dr Brewer.
Dr Hawkins adds: “If you’re not an active person, then a good way of speeding up your metabolism would be to concentrate on non-exercise activity thermogenesis activities instead.”
If you spend a lot of time sitting, such as an office environment, he suggests moving around as much as possible regularly throughout the day – standing up, stretching your legs and walking around, using a standing desk, and opting for the stairs rather than the lift, etc.
Finally, good nutrition is vital for a healthy metabolism, and some foods also have a significant effect on metabolic rate. When you eat a hot curry and start to sweat, for example, this is partly because substances present in the chillies (capsaicinoids) and turmeric (curcumin) increase the thermogenesis process.
If you’re concerned about rapid weight loss or weight gain, you should always speak to your GP.
Have you ever gained or lost a significant amount of weight? Do you think you have a fast or slow metabolism?
– With PA
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Disclaimer: This article contains general information about health issues and is not advice. For health advice, consult your medical practitioner.