Food labels seem to provide all the
information a thoughtful consumer needs, so counting calories should be simple.
But things get tricky because food labels tell only half the story.
A calorie is a measure of usable
energy. Food labels say how many calories a food contains. But what they don’t
say is that how many calories you actually get out of your food depends on how
highly processed it is.
Processed
Food Makes You Fatter
Food-processing includes cooking,
blending and mashing, or using refined instead of unrefined flour. It can be
done by the food industry before you buy, or in your home when you prepare a
meal. Its effects can be big. If you eat your food raw, you will tend to lose
weight. If you eat the same food cooked, you will tend to gain weight. Same
calories, different outcome.
For our ancestors, it could have
meant the difference between life and death. Hundreds of thousands of years
ago, when early humans learned to cook they were able to access more energy in
whatever they ate. The extra energy allowed them to develop big brains, have
babies faster and travel more efficiently. Without cooking, we would not be
human.
More
Processed = Digested More Completely
Animal experiments show that
processing affects calorie gain whether the energy source is carbohydrate, protein
or lipid (fats and oils). In every case, more processed foods
give an eater more energy.
Take carbohydrates, which provide
more than half of the world’s calories. Their energy is often packaged in
starch grains, dense packets of glucose that are digested mainly in your small
intestine. If you eat a starchy food raw, up to half the starch grains pass
through the small intestine entirely undigested. Your body gets two-thirds or less
of the total calories available in the food. The rest might be used by bacteria
in your colon, or might even be passed out whole.
Even among cooked foods,
digestibility varies. Starch becomes more resistant to digestion when it is
allowed to cool and sit after being cooked, because it crystallizes into
structures that digestive enzymes cannot easily break down. So stale foods like
day-old cooked spaghetti, or cold toast, will give you fewer calories than the
same foods eaten piping hot, even though technically they contain the same
amount of stored energy.
Softer
Foods Are Calorie-Saving
Highly processed foods are not only
more digestible; they tend to be softer, requiring the body to expend less
energy during digestion. Researchers fed rats
two kinds of laboratory chow. One kind was solid pellets, the type normally
given to lab animals. The other differed only by containing more air: they were
like puffed breakfast cereal. Rats eating the solid and puffed pellets ate the
same weight of food and the same number of counted calories and they exercised
the same amount as each other. But the rats eating the puffed pellets grew
heavier and had 30% more body fat than their counterparts eating regular chow.
The reason why the
puffed-pellet-eaters gained more energy is that their guts didn’t have to work
so hard: puffed pellets take less physical effort to break down. When rats eat,
their body temperature rises due to the work of digestion. A meal of puffed
pellets leads to less rise in body temperature than the same meal of solid
pellets. Because the puffed pellets require less energy to digest, they lead to
greater weight gain and more fat.
Our bodies work the same way. They
do less work when eating foods that have been softened by cooking, mashed or
aerated. Think about that when you sit down to a holiday meal or dine in a fine
restaurant. Our favorite foods have been so lovingly prepared that they melt in
the mouth and slide down our throats with barely any need for chewing. No
wonder we adore them. Our preference is nature’s way of keeping as much as
possible of these precious calories.
Why
Food Labels Don’t Tell the Full Story
Unfortunately, of course, in today’s
overfed and underexercised populations, nature’s way is not the best way. If we
want to lose weight we should challenge our instinctive desires. We should
reject soft white bread in favor of rough whole wheat breads, processed cheese
in favor of natural cheese, cooked vegetables in favor of raw vegetables. And
to do so would be much easier if our food labels gave us some advice about how
many calories we would save by eating less-processed food. So why are our
nutritionist advisers mute on the topic?
For decades there have been calls by distinguished committees and
institutions to reform our calorie-counting system. But the calls for change
have failed. The problem is a shortage of information. Researchers find it hard
to predict precisely how many extra calories will be gained when our food is
more highly processed. By contrast, they find it easy to show that if a food is
digested completely, it will yield a specific number of calories.
Our food labeling therefore faces a
choice between two systems, neither of which is satisfactory. The first gives a
precise number of calories but takes no account of the known effects of
food-processing, and therefore mis-measures what our bodies are actually
harvesting from the food. The second would take account of food-processing, but
without any precise numbers.
Faced by this difficult choice,
every country has opted to ignore the effect of processing and the result is
that consumers are confused. Labels provide a number that likely overestimates
the calories available in unprocessed foods. Food labels ignore the costs of
the digestive process – losses to bacteria and energy spent digesting. The
costs are lower for processed items, so the amount of overestimation on their
labels is less.
Time
For a Change?
Given the importance of counting
calories correctly, it’s time to re-open the discussion. One idea would develop
a “traffic-light” system on food labels, alerting consumers to foods that are
highly processed (red dots), lightly processed (green dots) or in-between
(yellow dots).
Public health demands more education
on the effects of how we prepare our food on our individual weight gain.
Calorie-counting is too important to allow a system that is clearly limited to
be the best on offer. We need a major scientific effort to produce adequate
numbers on the effects of food-processing.
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