What is a calorie?
● How are calories in food determined?
● How many calories do we REALLY need?
● Limitations of the calorie?
● So should food labels be trusted?
What Is a Calorie?
A calorie is a unit of measure for energy, that our body uses for all of
our vital process. You are constantly burning calories, even during
sleep, although the rate at which calories are burned falls dramatically
while at rest.
One Calorie = 4.18400 joules
kcal is the symbol of
●One kilocalorie is equal to
One kilocalorie is equal to
1000 small calories:
1 kcal = 1000 cal
One kilocalorie is equal to 1
1 kcal = 1 Cal
Small calorie (cal) is the
energy needed to increase 1
gram of water by 1ºC at a
pressure of 1 atmosphere.
Large calorie (Cal) is the
energy needed to increase 1
kg of water by 1ºC at a
pressure of 1 atmosphere.
Large calorie is also called
food calorie and is used as a
unit of food energy.
So how are calories in food
The original method used to determine the
number of kcals in a given food directly
measured the energy it produced.The food
was placed in a sealed container surrounded
by water--an apparatus known as a bomb
calorimeter. The food was completely burned
and the resulting rise in water temperature
So how are calories in food
The NLEA requires that the Calorie level placed on a
packaged food be calculated from food components.
According to the National Data Lab (NDL), most of the
calorie values in the USDA and industry food tables are
based on an indirect calorie estimation made using the
so-called Atwater system. In this system, calories are
not determined directly by burning the foods. Instead,
the total caloric value is calculated by adding up the
calories provided by the energy-containing nutrients:
protein, carbohydrate, fat and alcohol. Because
carbohydrates contain some fiber that is not digested
and utilized by the body, the fiber component is usually
subtracted from the total carbohydrate before
calculating the calories.
The Atwater System Values
The Atwater system uses the average values
of 4 Kcal/g for protein, 4 Kcal/g for
carbohydrate, and 9 Kcal/g for fat. Alcohol is
calculated at 7 Kcal/g. (These numbers were
originally determined by burning and then
averaging.) Thus the label on an energy bar
that contains 10 g of protein, 20 g of
carbohydrate and 9 g of fat would read 201
kcals or Calories.
So how many calories do we need?
Well now this is the contradicting part.
For a man it's 2,500 a woman it's 2,000 a
BUT THE TRUTH OF THE MATTER IS
2000 calories a day is not what any average adult
needs to maintain her health, weight and wellbeing.
That’s an inadequate daily energy intake. That’s
right. It’s too low. And if you are younger than 25,
then it’s far too low.
So how many calories?
On average most adult Women actually eat
2500 kcal/day to maintain their health and
Females under the age of 25 actually require
somewhere between 2800 to 3100 calories per
day to maintain health and weight.
Limitations of the calorie: How
We’re consistently told the simplest and most effective way to maintain a healthy weight is to take in no
more than 2,000 calories a day.
But sticking to that figure may not be as straightforward as it seems because calories work differently in
the body depending on which food they come from.
Protein foods such as chicken are estimated to use ten to 20 times as much energy to digest as fats.
And many highly processed or sugary foods like honey seem to barely tax the digestive system at all,
meaning no extra calories are needed to eat them.
But this isn’t accounted for on food packaging. So while a lemon muffin and a flapjack may contain the
same calories, the body uses more calories to break down the flapjack, so you’ve notched up fewer after
Similarly, a sandwich of wholemeal bread and peanut butter might have the same calories as one with
white bread and smooth peanut butter, but it takes more energy to eat so the calorie count from your
meal will be lower.
Rick Miller, a clinical dietitian and spokesman for the British Dietetic Association, says: ‘The texture and
consistency of a food influences the amount of energy you need to digest it.
'Soft and highly processed foods require less effort to chew, so you use fewer calories.
High-fibre foods require more chewing and are more difficult to digest, so you use up more calories
Limitations of the calorie: Raw food
There is plenty of evidence that cooking makes food easier and less time-consuming to digest by altering its structure,
meaning you take on board more calories.
Some experts have even suggested that our ancestors, who had to hunt for food, invented cooking partly as a way to
access as many calories as quickly as possible.
Rachel Carmody, a researcher at Harvard University’s department of human evolutionary biology, has shown that sweet
potatoes provide more calories when cooked because the starch they contain is better digested by the body.
In her latest study, she gave raw and cooked beef to mice and found that, unsurprisingly, the cooked meat was easier to
The mice lost 2g of body weight on a raw meat diet but just 1g on cooked meat.
During cooking, proteins were broken down, and so were easier to digest.
It may also be possible that because the heat killed bacteria, the immune system had less work to do — another energy
So lightly steamed vegetables or medium-to-rare cooked meat could cut calories, while well-cooked food could add them.
Bridget Benelam, a scientist at the British Nutrition Foundation, says: ‘There are a lot of variables when it comes to
measuring accurate calorie content.
'Foods vary in the way they are produced and cooked, which can affect their calories.
'It can become very difficult to measure calories in a mixed food such as a ready meal.’
Limitations of the Calorie: Quality or
One of the problems with calorie counting is that it focuses too much on the quantity of food rather than
the quality, say experts.
In her controversial book The Obesity Epidemic, obesity researcher Zoe Harcombe reported that despite
the UK National Food Survey confirming that we ended the last century eating 25 per cent fewer
calories than in the Seventies, the obesity rate has increased six-fold since then.
‘It is insane that we ignore these facts and stick resolutely to calorie counting,’ Harcombe says.
‘There is a lot seriously wrong with calorie advice.’
So how can we be eating fewer calories yet be getting fatter?
It’s probably down to our love of fast food and microwave meals — which take no calories at all to digest
but are proportionately high in the most ‘fattening’ types of calories, sugar and fat.
Britain’s best-known weight-loss organisation, Weight Watchers, recently overhauled its points system
to take into account the type of food — not just the calorie content.
A chocolate bar and steak might have had the same value in the old system because they contained the
same calories, but in the new scheme the steak has fewer points because the body uses up much more
energy processing it.
Dr Matthew Capehorn, clinical director of the National Obesity Forum, says: ‘We should view calories as
a useful tool, and the 2,000-a-day figure as a general guideline, but nothing more.
‘Overall, calories should not be the only focus in weight loss.’
Limitations of the calorie: Low fat
A recent, pioneering study showed that our religious counting of calories may explain why our weightloss attempts are so often in vain.
In the research, published in the Journal of the American Medical Association, scientists at the New
Balance Foundation Obesity Prevention Centre at the Boston Children’s Hospital compared the effects
of three popular diet approaches over four weeks.
These were a low-fat diet that limited fats to 20 per cent of total calories, a low carbohydrate diet based
on the Atkins approach (cutting carbs to 10 per cent of total calories) and a low glycaemic index (GI) diet
containing 40 per cent fat, 40 per cent carbohydrate and 20 per cent protein.
All the dieters ate the same number of calories.
The results were telling. Those on the low-fat diet burned the fewest calories of all three groups. Their
triglycerides (blood fats) rose while their ‘good cholesterol’ levels dropped, raising the risk of heart
Those following the low-carbohydrate diet burned around 300 extra calories a day than those on the
low-fat diet — but they also had raised levels of the stress hormone cortisol and other markers for heart
disease and diabetes.
By far the most effective plan was the low glycaemic one, which led to an extra 150 calories being
burned than on the low-fat diet but had no negative impact on hormone or blood-fat levels.
David Ludwig, the professor of nutrition who led the study, concluded that the beneficial effects boiled
down to the type of carbohydrates consumed in the low GI diet — i.e., minimally processed foods that
are slow to be digested such as beans, pulses, and non-starchy vegetables like cauliflower and broccoli.
So your saying we shouldn't trust
Not only is it wrong to think calories from different foods are the same, but you shouldn’t always trust the number
of calories printed on labels, say experts.
The calorie tables used by manufacturers were put together more than 100 years ago by an agricultural chemist
called Wilbur Olin Atwater.
He literally burned samples of food, then measured the amount of energy released from the heat they produced.
He worked out that every gram of carbohydrate and protein produced four calories, and every gram of fat
What concerns experts today is that Atwater’s figures are estimates based on averages that don’t take into
account variations in food make-up, preparation and processing techniques. Many of his measurements were
based on food in its raw state.
Dietitian Rick Miller says: ‘We’ve known for some time that the calculations for certain foods such as vegetables
and high-fibre foods are inaccurate.
‘The calorie figure you see on a food label isn’t always the amount you will ingest.’
As research into calories begins to escalate, so more irregularities are unearthed.
Take nuts, for example. Peanuts, pistachios and almonds seem to be less completely digested than previously
thought — possibly because of their tough cell walls — a study by the U.S. Department of Agriculture has found.
So while most packaging will say a 30g handful of pistachios provides 170 calories, the reality is a more waistfriendly 160.
‘If you adhere to calorie counting and reading
labels, then there is a chance you could be
getting more than you imagined,’ says
‘What’s important is to balance out the foods
you eat, so there is less refined produce,
more fresh food and plenty of fibre.
‘Calories are often not what we think.’