You can't go anywhere without being confronted by calories. You go to the supermarket and there they are, stamped on every box and bottle. You hop on the treadmill and watch your 'calories burned' click upward. If you type 'calorie' into Google, it returns 117,00,000 results.
But just what are calories? The more we take in, the more weight we put on, and if we cut back on them, the flab starts to recede, right? So, calories seem to be the factor by which all foods should be judged. But if that were true, 500 calories of parsnips would equal 500 calories of Mars bars. Not quite.
No, there's nothing simple about calories, so we're here to clear up the confusion. (Incidentally, there are about 280 calories in a Mars bar and about 66 in 11g of parsnips.)
Myth: Calories fuel our bodies
Truth: Actually, they don't
A calorie is simply a unit of measurement for heat; in the early 19th century, it was used to explain the theory of heat conservation and steam engines. The term entered the food world around 1890, when the US Department of Agriculture appropriated it for a report on nutrition. Specifically, a calorie was defined as the unit of heat required to raise 1g of water 1 degree Celsius.
To apply this concept to foods such as sandwiches, scientists would set food on fire (really) and then gauge how well the flaming sample warmed a water bath. The warmer the water, the more calories the food contained. (Today, a food's calorie count is estimated from its carbohydrate, protein and fat content.) In the calorie's leap to nutrition, its definition evolved. The calorie we now see cited on labels (as kcal) is the amount of heat required to raise 1kg of water by 1 degree Celsius.
Here's the problem: your body isn't a steam engine. Instead of heat, it runs on chemical energy, fuelled by the oxidation of carbohydrates, fat and protein that occurs in your cells' mitochondria. "You could say mitochondria are like small power plants," says Maciej Buchowski, a research professor of medicine at Vanderbilt University medical centre in Nashville, Tennessee. "Instead of one central plant, you have several billion."
Do this: Track carbs, fats, and protein - not just calories - when evaluating foods.
Myth: All calories are created equal
Truth: Not exactly
Our fuel comes from protein, carbohydrates and fat. "They're handled by the body differently," says nutritionist Alan Aragon. So that old 'calories in, calories out' formula can be misleading. "Carbs, protein and fat have different effects on the equation," he says.
For every 100 carbohydrate calories you consume, your body expends around 10 per cent in digestion. With fats, you expend slightly less. The calorie-burn champion is protein: for every 100 protein calories you consume, your body needs 20-30 for digestion, says Buchowski. Carbohydrates and fat supply quick energy and, in effect, yield more usable energy than protein does.
Do this: If you want to stay lean, make protein a priority at every meal.
Myth: A calorie ingested is a calorie digested
Truth: It's not that simple
Just because the food is swallowed doesn't mean it will be digested. It passes through your stomach and then reaches your small intestine, which slurps up all the nutrients it can through its spongy walls. But five to 10 per cent of calories slide through unabsorbed. Fat digestion is relatively efficient - fat easily enters your intestinal walls. As for protein, animal sources are more digestible than plant sources, so the protein from a piece of sirloin will be better absorbed than protein from tofu.
Different carbohydrates are processed at different rates, too: glucose and starch are rapidly absorbed, while fibre dawdles
in the digestive tract.In fact, the insoluble fibre in some complex carbs, such as that in vegetables and whole grains, tends to block the absorption of other calories. "With a very high-fibre diet, say 60g a day, you might lose as much as 20 per cent of the calories you consume," says Wanda Howell, a professor of nutritional sciences at the University of Arizona.
So, a useful measure of calories is difficult. A lab technician might find that a piece of chocolate and a piece of broccoli have the same number of calories. But in action, the broccoli's fibre ensures that the vegetable contributes less energy. A study
in the Journal of Nutrition found that a high-fibre diet leaves roughly twice as many calories undigested as a low-fibre diet does. And fewer digested calories means less flab.
Do this: Aim to consume at least 35-40g of fibre every day.
Myth: Exercise burns most of our calories
Truth: Not even close
Most of your calories burn at a constant simmer, fuelling the automated processes that keep you alive (your basal metabolism), says Warren Willey, author of Better Than Steroids. If you want to burn more fuel, hit the gas in your everyday activities.
"Some 60 to 70 per cent of our total caloric expenditure goes toward normal bodily functions," says Howell. This includes replacing old tissue, transporting oxygen, mending minor shaving wounds and so on. For men, these processes require about 11 calories per 0.45kg of body weight a day, so a 90kg-man will incinerate 2,200 calories a day - even if he sits in front of the TV all day.
Then there are the calories you lose to non-exercise activity thermo-genesis or NEAT. This consists of the countless daily motions you make outside the gym or in training sessions - the calories you burn while making breakfast or chasing the bus. According to Brandon Alderman, director of the exercise psychophysiology lab at Rutgers University, New Jersey, emerging evidence suggests that "a conscious effort to spend more time on your feet might net a greater calorie burn than 30 minutes of daily exercise".
Of course, a triathlete will burn heaps of calories in a race, which means you need to have enough on board. Three-time Ironman world champion Chrissie Wellington takes in about 4,000 calories a day.
Do this: Take breaks from your desk to burn bonus calories.
Myth: Low-calorie foods help you lose weight
Truth: Not always
Processed low-calorie foods can be weak allies in the weight-loss war. Omitting sugar is an easy way to cut calories, but food manufacturers generally replace the sugars with calorie-free sweeteners, such as aspartame. And artificial sweeteners can backfire. One University of Texas study found that consuming as few as three diet drinks a week increases a person's risk of obesity by more than 40 per cent. And in a 2008 study from Purdue University, Indiana, rats that ate artificially sweetened yoghurt took in more calories at subsequent meals. The theory is that the promise of sugar without the caloric payoff may lead to overeating.
Do this: Avoid artificial sweeteners and load up your plate with low-calorie saviours: fruits and vegetables.
Triathletes tend to eat sensibly but the more you know about what you're putting into your body, and what happens that food when it gets there, the more likely you are to stick to the good stuff.