enough iron).
And on, and on, and on. Understanding how good nutrition protects you requires a familiarity with the language and concepts of nutrition.
Knowing some basic chemistry is helpful. (Don’t panic: Chemistry can be a cinch when you read about it in plain English.) A smattering of sociology and psychology is also useful, because although nutrition is mostly about how food revs up and sustains your body, it’s also — as I explain in Chapter 15 — about the cultural traditions and individual differences that explain why you like the food you like.
You’ve heard “You are what you eat” before. As a matter of fact, it’s the first sentence at the top of this chapter. But it bears repeating, because the human body is built with the nutrients it gets from food: water, protein, fat, carbohydrates, vitamins, and minerals.
Nutrition’s primary task is to figure out which foods and beverages (in what quantities) are required to construct and maintain every one of your organs and systems. To do this, nutrition concentrates on food’s two basic attributes: energy and nutrients.
Energy is the ability to do work. The amount of energy in food is measured in calories, the amount of heat produced when food is burned (metabolized) in your body cells. You can read all about calories in Chapter 5, but for starters, all you need to know is that food is the fuel on which your body runs. Without enough food, you don’t have enough energy. No surprise there.
Nutrients are the natural chemical substances your body uses to build, maintain, and repair tissues. They also make it possible for cells to send messages back and forth to conduct essential chemical reactions such as the ones that make it possible for you toBreatheMoveEliminate wasteThinkSeeHearSmellTasteand do everything else common to a healthy living body.
Breaking nutrients into two groups
Each of the nutrients in food fall into one of two distinct groups, macronutrients and micronutrients:
Macronutrients (macro = big): Protein, fat, carbohydrates, and water
Micronutrients (micro = small): Vitamins and minerals and a multitude of other substances
What’s the difference between these two groups? The amount you need each day.
Your daily requirements for macronutrients generally exceed 1 gram. An ounce of solid material, such as chicken, has 28 grams, and an ounce of liquid, such as water, has 30 grams. To give you an idea of how that translates into nutrient requirements, the average man needs about 63 grams of protein a day (slightly more than 2 ounces), and the average woman needs about 50 grams (slightly less than 2 ounces).
And remember: That’s grams of protein, not grams of a high-protein food such as meat, fish, or poultry.
For example, the USDA National Nutrient Database for Standard Reference (http://ndb.nal.usda.gov), one of the ten thoroughly reliable sources listed in Chapter 27, provides the following information for grams of meat versus grams of protein:
Chicken: 3 ounces/86 grams breast meat (no bones, no skin), roasted, provides 26.7 grams/0.96 ounces protein
Lean ground beef (7% fat): 4 ounces/113 grams provides 23.6 grams/0.86 ounces protein
Canned salmon: 3.5 ounces/100 grams provides 19.68 grams/0.70 ounces protein
Your daily requirements for micronutrients are much smaller. Consider vitamins. The Recommended Dietary Allowance (RDA) for vitamin C is measured in milligrams (1/1,000 of a gram), while the RDAs for vitamin D, vitamin B12, and folate are even smaller, measured in micrograms (1/1,000,000 of a gram). For more about the RDAs, including how they vary for people of different ages, check out Chapter 3.
Looking at essential nutrients
A reasonable person may assume that an essential nutrient is one you need to sustain a healthy body. But who says a reasonable person thinks like a nutritionist? In nutrition speak, an essential nutrient is a very special thing:
An essential nutrient can’t be manufactured in the body. You have to get essential nutrients from food or from a nutritional supplement.
An essential nutrient is linked to a specific deficiency disease, such as scurvy, the deficiency disease that may afflict people who go without sufficient vitamin C for extended periods of time, or kwashiorkor, the protein deficiency disease. A diet rich in the essential nutrient prevents or cures the deficiency disease, but you need the proper nutrient. In other words, you can’t cure a vitamin C deficiency with extra amounts of protein.
WHAT’S A BODY MADE OF?
Sugar and spice and everything nice well, more precisely water and fat and protein and carbohydrates (the simple and complex sugars described in Chapter 8) and vitamins and minerals.
On average, when you step on the scale, approximately 60 percent of your weight is water, 20 percent is body fat (slightly less for a man), and 20 percent is a combination of mostly protein, plus carbohydrates, minerals, vitamins, and other naturally occurring biochemicals.
Based on these percentages, you can reasonably expect that an average 140-pound person’s body weight consists of about
84 pounds of water
28 pounds of body fat
28 pounds of a combination of protein (up to 25 pounds), minerals (up to 7 pounds), carbohydrates (up to 1.4 pounds), and vitamins (a trace)
You’re right: Those last figures do total more than 28 pounds. That’s because “up to” (as in “up to 25 pounds of protein”) means that the amounts may vary from person to person. Ditto for minerals and carbohydrates.
Why? And how? Because a young person’s body has proportionately more muscle and less fat than an older person’s, and a woman’s body has proportionately less muscle and more fat than a man’s. As a result, more of a man’s weight comes from protein and muscle and bone mass, while more of a woman’s weight comes from fat. Protein-packed muscles and mineral-packed bones are denser tissue than fat.
Weigh a man and a woman of roughly the same height and size, and his greater bone and muscle mass means he’s likely to tip the scale higher every time.
Here are three other examples of nutrients that are essential for some pets and plants but not necessarily for humans:
Myo-inositol: Myo-inositol, an organic compound similar to glucose — the fuel we get from carbohydrates — is an essential nutrient for gerbils and rats who can’t make it in their own bodies and thus must get what they need from food. It’s nonessential for human beings who can synthesize myo-inositol and then use it in dozens of important body processes, such as transmitting signals between cells.
Taurine: The amino acid taurine is essential for cats, but conditionally essential for humans,