What is anabolism (biosynthesis)?

Processes involved in synthesizing the molecules needed for cellular growth and maintenance. Thus the formation of PROTEIN, DNA, RNA, LIPID, CARBOHYDRATE, FAT, and GLYCOGEN are anabolic processes. Anabolism consumes chemical energy in the form of ATP and NADPH (a reducing agent), which are supplied by CATABOLISM, the energy-yielding oxidative processes involved in degradation. Optimal function and health rely upon a balance of anabolic and catabolic processes (homeostasis). These two branches of metabolism are controlled by the ENDOCRINE SYSTEM, which in turn responds to external influences such as diet. Anabolic processes require small building blocks supplied by breaking down STARCH, PROTEIN, and FAT in foods to build larger molecules. GLYCEROL and FATTY ACIDS are the subunits of fat; AMINO ACIDS yield proteins; and glucose yields glycogen. Fat and carbohydrate degradation provides an energized form of ACETIC ACID (acetyl CoA) to synthesize fatty acids and cholesterol. Other specialized products are also assembled from several different types of smaller precursors. For example, heme, the iron-containing pigment of the oxygen transport protein HEMOGLOBIN, is synthesized from an amino acid (GLYCINE) and SUCCINIC ACID, a common intermediate in energy-producing pathways.
Growth and an anabolic state, seen as an increase in body mass and muscle mass, occur during childhood, adolescence, pregnancy, and strenuous physical activity, such as body building. The weight gained in these situations represents increased protein, bone, or fat, not fluids. Increased fat stores and accumulated body fat represent stored surplus energy in adults and can result from too little exercise, the over-consumption of FOOD, heredity, or a combination of the above factors.

How many calories do you really need?

Figuring out ex-act-ly how many calories to consume each day can be a, well, consuming task. Luckily, the Dietary Guidelines for Americans 2005 lays out a list of the average daily calorie allowance for healthy adults with a healthful BMI — 21.5 for women and 22.5 for men — based on the amount of activity a person performs each day. Note that in this context, sedentary means a lifestyle with only the light physical activity associated with daily living; moderately active means a lifestyle that adds physical activity equal to a daily 1.5–3 mile walks at a speed of 3–4 miles per hour; active means adding physical activity equal to walking 3 miles a day at the 3–4 mph clip.

Facing the numbers when they don’t fit your body

Right about here, you probably feel the strong need for a really big chocolate bar (not such a bad idea now that nutritionists have discovered that dark chocolate is rich in disease-fighting antioxidants). But it also makes sense to consider the alternative: realistic rules that enable you to control your weight safely and effectively. Check out the following:

• Rule No. 1: Not everybody starts out with the same set of genes — or fits into the same pair of jeans. Some people are naturally larger and heavier than others. If that’s you, and all your vital stats satisfy your doctor, don’t waste time trying to fit someone else’s idea of perfection. Relax and enjoy your own body.
• Rule No. 2: If you’re overweight and your doctor agrees with your decision to diet, you don’t have to set world records to improve your health. Even a moderate drop in poundage can be highly beneficial. According to The New England Journal of Medicine (www.nejm.org on the Net), losing just 10 to 15 percent of your body weight can lower high blood sugar, high cholesterol, and high blood pressure, reducing your risks of diabetes, heart disease, and stroke.
• Rule No. 3: The only number you really need to remember is 3,500, the number of calories it takes to gain or lose one pound of body fat. In other words, one pound of body fat equals 3,500 calories. So if you simply
• • Cut your calorie consumption from 2,000 calories a day to 1,700 and continue to do the same amount of physical work, you’ll lose one pound of fat in just 12 days.
• • Go the other way, increasing from 1,700 to 2,000 calories a day without increasing the amount of work you do, 12 days later you’ll be one pound heavier.
• Rule No. 4: Moderation is the best path to weight control. Moderate calorie deprivation on a sensible diet produces healthful, moderate weight loss; this diet includes a wide variety of different foods containing sufficient amounts of essential nutrients. Abusing this rule and cutting calories to the bone can turn you literally into skin and bones, depriving you of the nutrients you need to live a normal healthy life.
  
• Rule No. 5: Be more active. Doing exercise allows you to take in more calories and still lose weight. In addition, exercise reduces the risk of many health problems, such as heart disease. Sounds like a recipe for success.

How reliable are the numbers? Considering confounding variables

Weight charts and tables and numbers and stats are so plentiful that you may think they’re totally reliable in predicting who’s healthy and who’s not. So here’s a surprise: They aren’t.

The problem is that real people and their differences keep sneaking into the equation. For example, the value of the Body Mass Index in predicting your risk of illness or death appears to be tied to your age. If you’re in your 30s, a lower BMI is clearly linked to better health.

If you’re in your 70s or older, no convincing evidence points to how much you weigh playing a significant role in determining how healthy you are or how much longer you’ll live. In between, from age 30 to age 74, the relationship between your BMI and your health is, well, in-between — more important early on, less important later in life.

In other words, the simple evidence of your own eyes is true. Although Americans sometimes seem totally obsessed with the need to lose weight, the fact is that many larger people, even people who are clearly obese, do live long, happy, and healthy lives. To figure out why, many nutrition scientists now are focusing not only on weight or weight/height (the BMI) but on the importance of confounding variables, which is sciencespeak for “something else is going on here.”

Here are three potential confounding variables in the obesity/health equation:

• Maybe people who are overweight are more prone to illness because they exercise less, in which case stepping up the workouts may reduce the perceived risk of being overweight.
• People who are overweight may be more likely to be sick because they eat lots of foods containing high-calorie ingredients, such as saturated fat, that can trigger adverse health effects; in this case, the remedy may simply be a change in diet.
• Maybe people who are overweight have a genetic predisposition to a serious disease. If that’s true, you’d have to ask whether losing 20 pounds really reduces their risk of disease to the level of a person who is naturally 20 pounds lighter. Perhaps not: In a few studies, people who successfully lost weight actually had a higher rate of death.

Adding to the confusion is the fact that an obsessive attempt to lose weight may itself be hazardous to your health. Every year, Americans spend $30 billion to $50 billion (yes, you read that right) on diet clubs, special foods, and over-the-counter remedies aimed at weight loss. Often the diets, the pills, and the foods don’t work, which can leave dieters feeling worse than they did before they started.

The chance that the diet fails is only half the bad news. Here’s the rest: Some foods that effectively lower calorie intake and some drugs that effectively reduce appetite have potentially serious side effects. For example, some fat substitutes prevent your body from absorbing important nutrients, and some prescription diet drugs, such as the combination once known as Phen-Fen, are linked to serious, even fatal, diseases.

What do they mean when they say that you’re fat?

Obesity is a specific medical condition in which the body accumulates an overabundance of fatty tissue. One way American nutritionists determine who’s obese is by comparing a person’s weight with the figures on the weight/height charts:

• If your weight is 20 to 40 percent higher than the chart recommends, you’re mildly obese.
• If your weight is 40 to 99 percent higher, you’re moderately obese.
• If your weight is more than double the weight on the chart, you’re severely obese.

Fittest and fattest U.S. cities

June is bustin’ out all over. How about you? For several years, the guys at Men’s Fitness magazine have rated the top 25 fattest and fittest cities in the United States. Of course, Men’s Fitness is published in Southern California, where long legs, slim hips, tight abs, and a taste for sprouts are handed out at birth. As a result, the magazine’s pundits may not know that in other places like, oh, New York, Chicago, Milwaukee, youpick-it, Americans come in all shapes and sizes. And they may have missed the fact that running for a bus or climbing subway stairs constitutes a daily workout in metro areas. Or that compared to high-fat, goat-cheese pizza, a West Coast fave, city bagels are health food.

Nonetheless, the magazine’s lists are a warning for the weighty. I’ll tell you right off the bat that in 2005, the 25 fittest cities (starting with the best) were Seattle, Honolulu, Colorado Springs, San Francisco, Denver, Portland (Oregon), Tucson, San Diego, Albuquerque, Boston, Virginia Beach (Virginia), Minneapolis, Fresno, Milwaukee, Omaha, San Jose (California), Jacksonville, Austin, Oakland, Los Angeles, Arlington (Texas), Washington, D.C., Cleveland, and Nashville-Davidson. Yay!

The 25 fattest (starting with the worst) were Houston, Philadelphia, Detroit, Memphis, Chicago, Dallas, New Orleans, New York, Las Vegas, San Antonio, El Paso, Phoenix, Indianapolis, Fort Worth, Mesa (Arizona), Columbus (Ohio), Wichita (Kansas), Miami (Florida), Long Beach (California), Oklahoma City, Tulsa, Atlanta, Charlotte (North Carolina), and Baltimore. Shape up, guys. Men’s Fitness is watching you!

Energy for work

Your second largest chunk of energy is the energy you withdraw to spend on physical work. That’s everything from brushing your teeth in the morning to hoeing a row of petunias in the garden or working out in the gym. Your total energy requirement (the number of calories you need each day) is your REE plus enough calories to cover the amount of work you do.

Does thinking about this use up energy? Yes, but not as much as you’d like to imagine. To solve a crossword puzzle — or write a post of this blog — the average brain uses about 1 calorie every four minutes. That’s only one-third the amount needed to keep a 60-watt bulb burning for the same length of time.

Are you a sensible foodie? If you’re supposed to have no more than 2,000 calories a day, can you pack all the vitamins, minerals, protein, heart-healthy fats, and carbs you need into 1,800 calories? Do that, and the folks who wrote the Dietary Guidelines for Americans 2005 say, reward yourself.

Use the “leftover” 200 calories — called discretionary calories — for anything that makes your mouth water. Naturally, some expert spoilsports disagree. They say that giving you an inch (those leftover calories) means you’ll take a mile (three pieces of chocolate cake). Prove them wrong and celebrate your smarts. Yum!

How your hormones affect your energy needs?

If you’re a woman, you know that your appetite rises and falls in tune with your menstrual cycle. In fact, this fluctuation parallels what’s happening to your REE, which goes up just before or at the time of ovulation. Your appetite is highest when menstrual bleeding starts and then falls sharply. Yes, you really are hungrier (and need more energy) just before you get your period.

Being a man (and making lots of testosterone) makes satisfying your nutritional needs on a normal American diet easier. Your male bones are naturally denser, so you’re less dependent on dietary or supplemental calcium to prevent osteoporosis (severe loss of bone tissue) late in life. You don’t lose blood through menstruation, so you need only two-thirds as much iron. Best of all, you can consume about 10 percent more calories than a woman of the same weight without adding pounds.

Teenage boys’ developing wide shoulders and biceps while teenage girls get hips is no accident. Testosterone, the male hormone, promotes the growth of muscle and bone. Estrogen gives you fatty tissue. As a result, the average male body has proportionally more muscle; the average female body, proportionally more fat.

Muscle is active tissue. It expands and contracts. It works. And when a muscle works, it uses more energy than fat (which insulates the body and provides a source of stored energy but does not move an inch on its own). What this muscle versus fat battle means is that the average man’s REE is about 10 percent higher than the average woman’s. In practical terms, that means a 140-pound man can hold his weight steady while eating about 10 percent more than a 140-pound woman who is the same age and performs the same amount of physical work.

No amount of dieting changes this unfair situation. A woman who exercises strenuously may reduce her body fat so dramatically that she no longer menstruates — an occupational hazard for some professional athletes. But she’ll still have proportionately more body fat than an adult man of the same weight. If she eats what he does, and they perform the same amount of physical work, she still requires fewer calories than he to hold her weight steady. And here’s a really rotten possibility. Muscle weighs more than fat.

This interesting fact is one that many people who take up exercise to lose weight discover by accident. One month into the barbells and step-up-step-down routine, their clothes fit better, but the scale points slightly higher because they’ve traded fat for muscle — and you know what that means: Sometimes you can’t win for losing. (Sorry, but I just couldn’t resist.)

Sex, glands, and chocolate cake

A gland is an organ that secretes hormones, which are chemical substances that can change the function — and sometimes the structure — of other body parts. For example, your pancreas secretes insulin, a hormone that enables you to digest and metabolize carbohydrates. At puberty, your sex glands secrete either the female hormones estrogen and progesterone or the male hormone testosterone; these hormones trigger the development of secondary sex characteristics, such as the body and facial hair that make us look like either men or women.

Hormones can also affect your REE, how much energy you use when your body’s at rest. Your pituitary gland, a small structure in the center of your brain, stimulates your thyroid gland (which sits at the front of your throat) to secrete hormones that influence the rate at which your tissues burn nutrients to produce energy.

When your thyroid gland doesn’t secrete enough hormones (a condition known as hypothyroidism), you burn food more slowly and your REE drops. When your thyroid secretes excess amounts of hormones (a condition known as hyperthyroidism), you burn food faster and your REE is higher. When you’re frightened or excited, your adrenal glands (two small glands, one on top of each kidney) release adrenaline, the hormone that serves as your body’s call to battle stations.

Your heartbeat increases. You breathe faster. Your muscles clench. And you burn food faster, converting it as fast as possible to the energy you need for the reaction commonly known as fight or flight. But these effects are temporary. The effects of the sex glands, on the other hand, last as long as you live. Read on.

Resting energy expenditure (REE)

Even when you’re at rest, your body is busy. Your heart beats. Your lungs expand and contract. Your intestines digest food. Your liver processes nutrients. Your glands secrete hormones. Your muscles flex, usually gently. Cells send electrical impulses back and forth among themselves, and your brain continually signals to every part of your body.

The energy that your resting body uses to do all this stuff is called (surprise! surprise!) resting energy expenditure, abbreviated REE. The REE, also known as the basal metabolism, accounts for a whopping 60 to 70 percent of all the energy you need each day.

To find your resting energy expenditure (REE), you must first figure out your weight in kilograms (kg). One kilogram equals 2.2 pounds. So to get your weight in kilograms, divide the number in pounds by 2.2. For example, if you weigh 150 pounds, that’s equal to 68.2 kg (150 ÷ 2.2). Plug that into the appropriate equation in Table below — and bingo! You have your REE.

How Many Calories Do You Need?

Think of your energy requirements as a bank account. You make deposits when you consume calories. You make withdrawals when your body spends energy on work. Nutritionists divide the amount of energy you withdraw each day into two parts:

• _ The energy you need when your body is at rest
• _ The energy you need to do your daily “work” To keep your energy account in balance, you need to take in enough each day to cover your withdrawals.

As a general rule, infants and adolescents burn more energy per pound than adults do, because they’re continually making large amounts of new tissue.

Similarly, an average man burns more energy than an average woman because his body is larger and has more muscle, thus leading to the totally unfair but totally true proposition that a man who weighs, say, 150 pounds can consume about 10 percent more calories than a woman who weighs 150 pounds and still not gain weight.

Every calorie counts

People who say that “calories don’t count” or that “some calories count less than others” are usually trying to convince you to follow a diet that concentrates on one kind of food to the exclusion of most others. One common example that seems to arise like a phoenix in every generation of dieters is the high-protein diet.

The high-protein diet says to cut back or even entirely eliminate carbohydrate foods on the assumption that because your muscle tissue is mostly protein, the protein foods you eat will go straight from your stomach to your muscles, while everything else turns to fat. In other words, this diet says that you can stuff yourself with protein foods until your eyes bug out, because no matter how many calories you get, they’ll all be protein calories and they’ll all end up in your muscles, not on your hips.

Boy, wouldn’t it be nice if that were true? The problem is, it isn’t. Here’s the absolute truth: All calories, regardless of where they come from, give you energy. If you take in more energy (calories) than you spend each day, you’ll gain weight. If you take in less than you use up, you’ll lose weight. This nutrition rule is an equal opportunity, one-size-fits-all proposition that applies to everyone.

Measuring the number of calories

Nutrition scientists measure the number of calories in food by actually burning the food in a bomb calorimeter, which is a box with two chambers, one inside the other. The researchers weigh a sample of the food, put the sample on a dish, and put the dish into the inner chamber of the calorimeter. They fill the inner chamber with oxygen and then seal it so the oxygen can’t escape.
The outer chamber is filled with a measured amount of cold water, and the oxygen in the first chamber (inside the chamber with the water) is ignited with an electric spark. When the food burns, an observer records the rise in the temperature of the water in the outer chamber. If the temperature of the water goes up 1 degree per kilogram, the food has 1 calorie; 2 degrees, 2 calories; and 235 degrees, 235 calories — or one 8-ounce chocolate malt!

Empty calories

All food provides calories. All calories provide energy. But not all calories come with a full complement of extra benefits such as amino acids, fatty acids, fiber, vitamins, and minerals. Some foods are said to give you empty calories. This term has nothing to do with the calorie’s energy potential or with calories having a hole in the middle. It describes a calorie with no extra benefits.

The best-known empty-calorie foods are table sugar and ethanol (the kind of alcohol found in beer, wine, and spirits). On their own, sugar and ethanol give you energy — but no nutrients People who abuse alcohol aren’t always thin, but the fact that they often substitute alcohol for food can lead to nutritional deficiencies, most commonly a deficiency of thiamin (vitamin B1), resulting in loss of appetite, an upset stomach, depression, and an inability to Of course, it’s only fair to point out that sugar and alcohol are ingredients often found in foods that do provide other nutrients. For example, sugar is found in bread, and alcohol is found in beer — two very different foods that both have calcium, phosphorus, iron, potassium, sodium, and B vitamins.

In the United States, some people are malnourished because they can’t afford enough food to get the nutrients they need. The school lunch program started by President Franklin Delano Roosevelt in 1935 and expanded by almost every president, Republican and Democrat, since then has been a largely successful attempt to prevent malnutrition among poor schoolchildren.

But many Americans who can afford enough food nevertheless are malnourished because they simply don’t know how to choose a diet that gives them nutrients as well as calories. For these people, eating too many foods with empty calories can cause significant health problems, such as having weak bones; being underweight (yes, being too thin can be a problem); getting bleeding gums, skin rashes, and other nasties; and developing mental disorders, including depression and preventable retardation.

Counting the Calories in Food

When you read that a serving of food — say, one banana — has 105 calories, that means metabolizing the banana produces 105 calories of heat that your body can use for work.
You may wonder which kinds of food have the most calories. Here’s how the calories measure up in 1 gram of the following foods:

• Protein: 4 calories
• Carbohydrates: 4 calories
• Alcohol: 7 calories
• Fat: 9 calories

In other words, ounce for ounce, proteins and carbohydrates give you fewer than half as many calories as fat. That’s why — again, ounce for ounce —high-fat foods, such as cream cheese, are high in calories, while low-fat foods, such as bagels (minus the cream cheese, of course), are not. Sometimes foods that seem to be equally low-calorie really aren’t. You have to watch all the angles, paying attention to fat in addition to protein and carbohydrates.

Here’s a good example: A chicken breast and a hamburger are both high-protein foods. Both should have the same number of calories per ounce. But if you serve the chicken without its skin, it contains very little fat, while the hamburger is (sorry about this) full of it. A 3-ounce serving of skinless chicken provides 140 calories, while a 3-ounce burger yields 230 to 245 calories, depending on the cut of the meat.

About Calories

Automobiles burn gasoline to get the energy they need to move. Your body burns (metabolizes) food to produce energy in the form of heat. This heat warms your body and (as energy) powers every move you make. Nutritionists measure the amount of heat produced by metabolizing food in units called kilocalories. A kilocalorie is the amount of energy it takes to raise the temperature of 1 kilogram of water 1 degree on a Centigrade (Celsius) thermometer at sea level.

In common use, nutritionists substitute the word calorie for kilocalorie. This information isn’t scientifically accurate: Strictly speaking, a calorie is really 1⁄1000 of a kilocalorie. But the word calorie is easier to say and easier to remember, so that’s the term you see whenever you read about the energy in food. And few nutrition-related words have caused as much confusion and concern as the lowly calorie. Read on to find out what calories mean to you and your nutrition.