It’s the fat and fuel-burning furnace in your cells and it determines whether you’ll be nicely muscled or marshmallowy. Good news: you’ll burn kilojoules just learning about metabolism!

Burning Truths?

Skinny people have fast metabolisms
Verdict: Sometimes
“There are slim people with slightly low metabolisms who just don’t eat very much,” says Dr Michael Jensen, an endocrinologist with the Mayo Clinic. “And there are heavy people with really high metabolisms who eat a huge amount.”

Lean tissue burns more kilojoules than fat does, even while you’re asleep
Verdict: True
“Your brain, heart, liver and kidneys use a lot of energy, even when you’re lying still,” says Jensen. Muscle and the GI tract don’t use much at rest; fat burns practically nothing. His estimate: you burn about four kilojoules per minute at rest. A quarter of that is torched by muscle and one-fiftieth of it is burned by fat.

Some guys can only slim down by slashing kilojoules
Verdict: False
“In 30 years I’ve never seen anyone with a truly low metabolic rate,” says Jensen. “People who think they need a 4 000kJ diet often have resting metabolic rates of 6 270kJ.” So why can’t they slim down? They’re often eating many more kilojoules than they realise. His fix: accurately record everything you eat for two weeks. Unhealthy trends may emerge.

Cutting 2 000kj a day 
 means you’ll lose half a kilo a week
Verdict: Not Quite
Half a kilo of fat does equal 14 630kJ and you may lose half a kilo in the first week. “But when you eat less, you lose lean tissue, so your basal metabolic rate goes down,” says Jensen. Surprise: 
you may gain more than half a kilo after a 14 630kJ pig-out, since kilojoules stored as sugar cause you to retain water.

How Many Kilojoules Do You Need?
You can’t know exactly how much energy you’re torching, but you can estimate your resting metabolic rate. A study in Clinical Nutrition compared seven ways; only this one works:

How to calculate resting metabolic rate (RMR) for men –
(weight in kilograms) × 10
+
(height in centimetres) × 6.25

(age × 5) + 5

Total RMR Multiplied by: Your daily activity –
1.20 – Sedentary (little or no exercise)
1.37 – Lightly Active (Light exercise 1-3 days/week)
1.55 – Moderately Active (Moderate exercise 3-5 days/week)
1.72 – Very Active (Hard exercise 6-7 days/week)
1.90 – Extremely Active (Twice-daily exercise & physical job)

Equals:
Number of calories you should consume per day.

The Best Workout To Boost Your Metabolism:
Fire up your body’s furnace with a lifting circuit that has eight to 12 exercises requiring flexion and extension, says Dr James Churilla, a physical activity epidemiologist. Do two or three sets of 10 to 15 reps each, lifting 60 to 80% of your one-rep max. Keep switching muscle groups and don’t rest between exercises.