When a food label lies...

The nutrition information is shown on the back of a Campbell's Chicken Noodle soup can in Washington, Wednesday, Jan. 8, 2014. Some of the nation's largest food companies have cut their calories by the trillions according to a new study. (AP Photo/J. David Ake)

The nutrition information is shown on the back of a Campbell's Chicken Noodle soup can in Washington, Wednesday, Jan. 8, 2014. Some of the nation's largest food companies have cut their calories by the trillions according to a new study. (AP Photo/J. David Ake)

Published Jan 16, 2015

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Washington – 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 they do not say how many calories you actually get out of your food, which 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 learnt to cook, they were able coax more energy from their food. This allowed them to develop big brains, have babies faster and travel more efficiently. Without cooking, we would not be human.

More processed foods are digested 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 highly processed foods give 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 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 crystallises 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 hot, even though 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, things 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 exercised the same amount. But the rats eating the puffed pellets grew heavier and had 30 percent more body fat than their counterparts eating regular chow.

The puffed pellet eaters gained more energy because 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.

Our bodies work the same way. They do less work when eating foods that have been softened by cooking, mashing or aeration. Think about that when you sit down to a special meal or dine in a fine restaurant. Our favourite 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 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 favour of rough wholewheat breads, processed cheese in favour of natural cheese, cooked vegetables in favour 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 the 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.

Food labelling 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 mismeasures 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 invariably 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 reopen 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 (amber 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.

The Conversation/Washington Post

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