What is your metabolism and can you really rev it up? Brooke Longfield asks nutrition experts for the facts on how we benefit from a healthy metabolism.
“I can’t lose weight; I must have a slow metabolism”. We use this reason a lot, but is a slow metabolism really to blame for weight woes?
Your metabolism explained
Metabolism or ‘metabolic rate’ is a bit like a car using petrol to drive. It is the energy spent by your body to stably function under different conditions, University of Auckland School of Biological Sciences and Department of Medicine Professor Sally Poppitt explains.
The amount of energy burned when your body rests is your ‘basal metabolic rate’ (BMR). “It is the energy required for your cells, tissues and organs to function”, Professor Poppitt says, “If you eat, need to stay warm, or do any activity, then your metabolic rate increases.” The energy for these functions comes from the food you eat.
BMR accounts for about 50—80 per cent of your daily energy expenditure. Digesting food spends around 10 per cent, and the remaining 10—40 per cent burns in movement, according to Royal Prince Alfred Hospital Metabolism and Obesity Services dietitian Janet Franklin. Our genes dictate the fuel mix we burn. Some of us burn more carbohydrate and less fat, even though the total energy used is the same. Not being able to burn fat well is behind most states of overweight and obesity, Glycemic Index Foundation expert Jennie Brand-Miller explains.
Is weight gain due to a slow metabolism?
Rather than thinking ‘slow’ or ‘fast’ it’s more helpful to think of low or high metabolic rate.
A high BMR burns more energy. But a low BMR doesn’t necessarily predispose you to gaining weight.
Do thin people have a higher metabolic rate?
No. In fact, larger bodies have a higher BMR than leaner bodies, as they have more muscle and bigger organs, requiring more energy to keep working. People carrying extra weight use more energy just to move.
Not only does this highlight that drastic dieting doesn’t work, it suggests it may be doing your metabolism long-term harm.
How can I burn more energy?
To not gain weight we must use up the same amount of energy as we take in. The part of energy usage we can directly control is what we burn through physical activity. A combination of changes to your routine, applied each day until they become second nature — in other words, new healthy habits — will burn more kilojoules on a daily basis.
Using your muscles in any way means you’re burning more kilojoules. Even fidgeting plays a part. And moving more doesn’t just mean getting to the gym more often. The more incidental or unplanned activity you do each day, the more kilojoules you burn without even realising.
Housework and gardening or washing the car are all big kilojoule-burners. And at work, make an effort to get out of your chair every half hour. Even standing up uses more energy than sitting in a chair.
Try adding half an hour of heart-pumping exercise to your daily routine. Find something you love doing so you’re more likely to stick to it. If you like to socialise, join an outdoor walking group or sign up to a group exercise programme. If a quieter pace is more your thing, try yoga or Pilates.
A significant contributor to metabolic rate is the amount of muscle tissue you have. Muscle burns about four times more kilojoules than fat tissue. “The more muscle you have, the more energy you burn,” says Dr Franklin. “That’s why men tend to burn up more energy than women.”
Resistance training is a great way to build and maintain muscle. It doesn’t have to involve lifting heavy weights; using your own body weight counts as resistance training. For example, try doing squats, lunges, push-ups and tricep dips. Resistance bands, Pilates and yoga are also effective.
Lose weight but don’t crash diet
Losing weight comes down to eating fewer kilojoules than you burn off, but be aware that severely restricting kilojoules can actually backfire. There’s mounting evidence that drastic dieting can actually decrease your metabolic rate.
“Quite simply, your body’s survival instinct kicks in and it goes into starvation mode,” says Dr Franklin. When faced with starvation, “your body wants to protect and hold on to fat stores because it doesn’t know when the next food will be available.” And severe restriction results in the body sacrificing muscle as fuel.
This explains why you feel so hungry when you start a diet. “When the body detects it’s losing weight, a whole range of hormones are released that trigger your appetite so you go and seek food. And we’re not talking lettuce here; it’s high-energy, quick-consumption foods that the body wants,” explains Dr Franklin. “The body thinks it’s in an environment where there is very little food available and so, to survive, it needs to stock its pantry.”
For now, experts agree a gradual and steady loss of between 500g and 1kg per week is a healthy, safe amount of weight to lose, if you need to. For the average person, this means reducing the kilojoules you eat each day by around 2000kJ (500cal). See our Kick-start Plan (ADD LINK TO Oct16 back issue) for a seven-day meal plan based on consuming 6000kJ a day, which will result in gradual weight loss while still eating three meals a day and healthy snacks. This is the minimum energy advised for weight loss, suitable for a woman of around 1.6m tall.
Why does metabolism slow with age?
“The main reason is because people lose muscle mass as they age,” says Dr Franklin. This is usually through becoming less active. And in women after menopause, changing hormones promote fat storage. So by carrying more fat and having less muscle mass, an older woman will have a lower BMR. The best thing we can do for our metabolism as we age is to build and maintain muscle.
Rev up your metabolism
Burn energy faster by walking!
One of the healthiest ways to increase your metabolic rate is to move, and walking is a great form of exercise for all ages. For best effect, you need to walk each day.
Think of a time of day that fits into your schedule — early morning before work, sunset after a busy day, a revitalising lunchtime stroll, or whenever suits you best.
Pressed for time? Short bursts of higher intensity exercise can reap the same, if not better, rewards than long walks, as you’ll burn more kilojoules in the same amount of time. Walking up stairs burns 400 per cent more energy than a leisurely stroll on the flat, according to University of Pennsylvania School of Medicine researchers.
Walking uphill also uses more muscles than walking on the flat, and builds muscle too.
Step it up
- Find a route with steep uphill sections to help rev up your heart rate.
- Live in a flat area? Look for a long set of stairs. Climb up at a moderately fast pace, then slowly walk back down. Repeat 3—5 times.
- Get into the habit of taking the stairs instead of lifts or escalators. Every bit of movement counts!
Another way to challenge your muscles and burn more energy is to increase your pace. This doesn’t have to be sprinting; even power walking increases your huff and puff. Pump your arms back and forth as you walk — this propels you and burns more kilojoules.
Interval training is one of the best ways to maximise the kilojoule-burn of your workout, and improve fitness. This involves short bursts of movement at a high intensity, followed by a period of active recovery (walking rather than sitting down). This type of training, called EPOC (elevated post-exercise consumption), burns kilojoules even after the workout has finished — twice as much as low-intensity walking.
Step it up
- Combine walking with running/power walking. Use street signs or power poles to mark intervals. For example, jog the distance of two power poles or street signs, then walk to recover for the next two. Repeat for 10—15 minutes.
- Sign up for a 5km fun run to give you something to train for. Better still, sign up with your partner, family or friend/s so you can push each other.
- Aim for at least two interval-style sessions each week.
Many of us are creatures of habit and when you do the same exercise over and over, your body gets used to it and no longer has to work as hard. This means you start to burn fewer kilojoules and don’t get the same aerobic benefit.
The solution? Challenge your body by frequently changing your exercise routine. Each time you do this, your body has to use new muscles to adjust to the change in activity.
Before you get started…
Get the all-clear from your doctor. Start each workout with a stretch and a five-minute gentle walk to warm up, and finish with a stretch to prevent injury. Finally, listen to your body. If it hurts, or doesn’t feel right, take a rest and just do what you can.
What else influences metabolism?
- Life stage: Metabolic demand is dramatically increased in babies and toddlers, during puberty and during pregnancy. In contrast, ageing decreases muscle mass, lowering metabolic rate.
- Environment: Being in an extremely cold climate dramatically increases energy demands just to maintain the core temperature of the body, in some cases double the energy demands of a person in a temperate climate.
- Genes: It was previously thought genes mainly play a part in appetite regulation when it comes to overweight and obesity, but new research shows genetic differences in the way fat is metabolised also potentially play a part.
- Disease: Diseases that can affect metabolic rate include hyper or hypoactive thyroidism, cancers, and excessive cortisol (the stress hormone) or adrenaline levels.
- Energy your body needs to function comes from carbohydrates, fats and protein and each are digested and used in different ways.
- Losing a lot of weight in a short space of time potentially lowers basal metabolic rate, which then stays low even after weight is regained.
- Maintaining muscle mass protects against weight gain.
- People who fidget burn more energy.
The Biggest Loser effect
It makes dramatic TV to see contestants shed 50—60kg. But what happens to the weight when filming stops? An explosive study published this year tracked the fates of 14 contestants on the US version of The Biggest Loser for six years after the show. All but one contestant has regained most of the weight lost, and four now weigh more than they did before going on the show. What’s more, tests showed the metabolic rates of these contestants to have dramatically changed, so they now burn 500 calories per day less than others of the same weight.
What is resistance training?
Body-weight exercise, such as squats, lunges, push-ups and tricep dips, counts as resistance or strength training. For each exercise, start with one set of about 8—10 repetitions. As you get stronger you can increase the number of sets, and also the amount of weight you lift.
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