By Matt O'Neill, MSc(Nut&Diet), APD
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When you boost your metabolic rate, you burn more calories, which is an advantage for fat loss. Knowing the fitness, food or supplement factors that can elevate your metabolic rate helps you advise clients correctly and helps them get better results. Here are six factors that can have an impact.
At rest, the average 70kg person burns around 1 Calorie per minute. Walking burns 3-4 Calories per minute and you'll burn around 8-10 Calories per minute running fast.
These figures reinforce the simple idea that the more effort you put into moving your body, the more calories you burn. Just getting out of bed doubles your metabolic rate. Walking triples it and an intense boot camp-style session can generate a 10-fold increase in metabolic rate.
This doesn't mean flogging clients at every session. But it does mean that higher effort level training sessions, like HIIT (High Intensity Interval Training) delivered safely can provide a greater calorie burn and fitness gains in shorter sessions.
Every kilogram of muscle on your body burns around 10 Calories per day at rest. It may seem small, but over a year the energy burning bonus from just 1kg of additional muscle equals 3,650 Calories. This is the equivalent of about 0.5 kg of body fat.
Build and maintain 5kg of lean muscle and your metabolic rate jumps up by 18,250 (5 x 3,650) Calories. That's 2.5kg body fat a year burnt up before you even move your muscles.
By contrast, body fat is less metabolically active and only burns around 4.5 Calories per kg per day.
Eat more protein
Protein in food costs more energy to digest and absorb than carbohydrate or fat. Eating protein-rich foods like eggs, fish, chicken and lean meat makes your body work harder to digest and absorb calories.
This doesn't mean you should load up on protein supplements. You still need to keep your diet balanced and ensure you work within the Acceptable Macronutrient Distribution Range (AMDR) of 15 to 25% of daily energy intake as protein.
Hard data is scarce on the actual calorie burning benefit that can result from switching from a 15% protein diet to a 25% protein diet. But it can be expected to translate into a few kilograms of body fat per year.
Eat enough calories
Avoiding crash diets will help you minimise the normal slow-down in metabolic rate associated with caloric restriction. Reducing calorie intake from 2500 to 1100 Calories a day has resulted in a 5-10% decline in daily metabolic rate after just one day.
Continuing on a severely calorie restricted diet for days and weeks will likely result in significant lean muscle loss as well as fat loss. This is because muscle is broken down and converted into glucose that your brain needs for fuel during a process called ketosis. Up to around one third of weight loss can be from muscle loss in extreme cases.
No amount of resistance training can prevent severe dieting-induced muscle loss. Appropriate daily calorie targets for fat loss and responses to dieting are highly individual, but the key message is don't starve yourself.
Consume chilled water
When you consume cold water, your body expends energy to increase the water temperature. Drinking around 500mL of cold water could boost your metabolic rate by around 30% above rest for an hour after drinking. This is only 25 Calories, but it becomes significant when you drink more chilled water over a day. Two litres could burn you 100 Calories a day or 36,500 Calories a year, which is almost 5kg of body fat.
Drink green tea
Unlike many so-called `thermogenic' supplements, which are either dangerous, useless or both, drinking enough green tea might give your metabolic rate a nudge up of around 70 Calories a day.
You'll need to consume at least 4-5 cups of strong green tea to achieve a dose of around 300mg of catechins - the active ingredient. Always check with your Doctor before drinking high doses of tea or taking supplements.
Note that not all research shows benefits of chilled water or green tea. Some people won't respond and your body could adapt of time, so the return on effort may transfer into lesser results.
What about eating every 3 hours?
You may have heard that eating every three hours speeds your metabolism. However, your 24-hour metabolic rate will actually be no different, whether you eat the same foods in six smaller meals versus three larger meals. It costs your body the same energy to digest and process. So, don't freak out about your metabolic rate if you've missed a snack and can catch up later.
Take home messages
To boost metabolic rate safely and effectively, increasing regular physical activity is the factor that will fire up your metabolism the most.
Building and keeping muscle needs to be a priority for successful long term weight management.
Avoiding crash diets that waste muscle will be a particular focus for some clients.
Larger intakes of chilled water and green tea (after checking with your Doctor) offer additional techniques that could be of benefit to some people.
Supplements that claim to enhance or elevate metabolic rate may either contain potentially dangerous stimulants or are likely to be making false claims.
What is metabolic rate?
Your metabolic rate is the rate at which your body burns energy. Total daily (or 24-hour) metabolic rate (TMR) is comprised of; (1) Resting metabolic rate (RMR) which accounts for 50-80% of your TMR and is the energy cost when your body is idling at rest, (2) Thermic effect of food (TEF) uses up around 5-10% of TMR and is the energy costs of digesting and absorbing food, and (3) Physical activity (PA) which accounts for an average 20% of TMR, but can be significantly greater in active people.
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