Considering the number of books written on the subject, the stacks of pamphlets available at any doctor’s office, and the fact that a column concerning it already appears in weekly newspapers across the province (I used to edit a weekly newspaper, so I know), you could consider it an act of hubris that this week I have chosen to write about–nutrition. (Thought I’d never get to the point, didn’t you?)

However, I had to do all this research on nutrition for a new exhibit at the Saskatchewan Science Centre, and in the interest of conservation of brain power…

It’s not really surprising nutrition is a topic about which information bombards us. After all, name the three most important elements of life: food, water and air, right? Food and water are both part of nutrition, so you could say nutrition is two thirds of what keeps us alive.

Nutrition is defined as “the means by which we obtain the substances required for growth and the maintenance of life.” What we call “essential nutrients” are all those substances which our bodies require which cannot be synthesized within our own cells.

Human nutrients fall into five main groups: proteins, lipids (fats), carbohydrates, vitamins and minerals.

For energy we depend primarily on fats and carbohydrates. As a result, we require these substances in relatively large amounts (though not always in as large amounts as we choose to ingest them!) The amount of energy we extract from them is measured in calories–though what we call a calorie when we’re talking about food is really a kilocalorie, or 1,000 gram calories. A gram calorie is the energy it takes to raise the temperature of one gram of water one degree Celsius, so a food calorie is the energy it takes to raise the temperature of 1,000 grams of water–one litre–one degree Celsius.

The average-sized male burns about 3,000 calories a day–enough energy to turn 30 litres of water from ice to steam. (Talk about being hot stuff . . . )

You don’t have to exercise to burn calories, either. Even at rest your body needs energy to maintain your tissues, repair damage, keep your heart pumping and your lungs breathing, and, if you’re a kid, grow. A 65-kilogram man expends about 1.25 calories per minute just doing that, while a 55-kilogram woman expends about 0.9 calories per minute. A brisk walk expands the energy requirement to four times as much, and more vigorous exercise, such as tennis, boosts the requirement six times.

You get the most calories by weight from fats, which have about twice as many calories for a given weight as carbohydrates. As just about everyone knows by now, there are two main kinds of fats, saturated and polyunsaturated; the former, which are solid or semi-solid at room temperature and are found especially in animal products, boost blood cholesterol levels, while the latter, found mainly in vegetables and fish, can help reduce cholesterol.

High cholesterol levels in the bloodstream have been linked to arteriosclerosis, the build-up of fatty substances lining the blood vessels, sometimes causing blockages. However, many people don’t realize that most cholesterol is produced by our own bodies, and that it is, in fact, essential to life. It’s just the excess that’s the problem.

Excess is a problem in many areas of nutrition. Take vitamins, for example. Or not. There seems to be a feeling that you can never take too many vitamins–but in fact, these complex organic molecules are needed in very small quantities and can easily be obtained simply by eating a properly balanced diet. Some people take massive doses in pill form; a pretty futile exercise, since in most cases the excess is simply excreted.

Worse, it’s even possible to poison yourself with vitamins. Excess vitamin C, for example, is converted to a product, oxalic acid, that is toxic. Excess vitamin A over long periods can cause loss of hair, bone and joint pains and loss of appetite. Too much vitamin D can cause an overload of calcium in the blood. Megavitamin therapy should therefore always be supervised by a physician.

We also need certain non-organic substances, or minerals, in small amounts–very small amounts in most cases, since almost all of these minerals would be lethal if ingested on a large scale.  (Arsenic, for example, plays a small but important role in the body.)

Some of the more vital minerals are calcium, needed particularly for bones and teeth; potassium and sodium, which maintain the normal flow of nerve signals and muscle movements, and iron, which helps your body carry the oxygen used to release energy from the foods you eat.

The other major kind of nutrient humans require is protein. Contrary to what a lot of people believe, protein isn’t as important as a source of energy–carbohydrates and fats, remember, provide most of that–as it is as a source of certain vital amino acids required for growth and renewal. On average we need 0.5 to 0.7 grams of protein per kilogram of body weight per day. Growing children require four or five times as much.

If all this talk of nutrients has left you dry, then consider the importance of water. About half the weight of ordinary food is water (certain baked goods I’ve made in my own kitchen notwithstanding). In a temperate climate, someone doing light work requires about two litres of water each day to replace what is lost, leaving about one litre to be drunk as liquid. In the tropics workers sometimes have to consume as much as nine litres daily.  Water does help cool us down, but it’s most important as a “universal solvent” for digestion and the many other chemical reactions that take place in our bodies.

Of course, all this is just the briefest overview of the topic of nutrition. One could talk about oat bran, one could talk about leafy green vegetables, one could talk about the benefits and problems associated with vegetarianism, one could discuss our societal love affair with dieting–one could go on and on on the subject, until one’s readers were sick of it.

But not this one. This one is done.

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