The Rubber Bag

What a piece of work is man! how noble in reason! how infinite in faculty! in form and moving how express and admirable! in action how like an angel! in apprehension how like a god! the beauty of the world! the paragon of animals!

—Shakespeare, Hamlet, Act II, Scene II

Man is but a bubble, or bladder of the water.

—Desiderius Erasmus, Adagia (1508)

The truth, I suspect, lies somewhere between these extremes. Nonetheless, when it comes to gaining and losing weight, the human body is remarkably akin to a rubber bag. Fad diets and gimmick nutritional plans obscure this simple yet essential fact of weight control: if you eat more calories than you burn, you gain weight; if you eat fewer calories than you burn, you lose weight.

Here's your body, reduced to a rubber bag.

What goes in

“What goes in” is everything you eat and drink. Humans, like bears and raccoons, are omnivores—we can eat just about anything, and as long as we get a reasonable variety, we'll be O.K. You don't see a 'coon stalking away from an overturned garbage can because the contents are low in calcium, nor a bear turning up his nose on finding the sandwiches in your picnic basket aren't made with the latest trendy low-sodium lecithin-enriched oat bran bread. There's no reason you should be obsessive about food either. Since we're efficient food processing machines, it's possible to reduce all the complexity of food to a single number that gives the total energy the body can extract from it—the calorie. The essential thing you need to know about what goes in is the total number of calories you eat in a day. All the rest are minor details.

What you burn

“What you burn” is the number of calories your body uses to provide the energy for everything you do, from heartbeats and breathing to running a marathon. The daily calorie requirement varies quite a bit from person to person depending on size, shape, basic metabolic rate, and degree of physical activity. A rough estimate of calories per day can be obtained by multiplying the ideal weight for your height and body type by a number based on your level of physical activity, ranging from 11 for a pure couch potato to 17 for a person engaged in heavy physical labour or strenuous exercise on a daily basis.

The following tables give estimates of the calories burned per day for men and women at their ideal weight, based on height and body type. The lower number is based on a level of activity characteristic of an office worker who does not exercise, and the high number assumes a moderate degree of physical activity, either as part of your work or through an exercise program. No table like this can be precise—use these numbers only as general guidelines. As you gain control over your weight, you'll determine precisely how many calories you burn every day.

Height in these tables is your barefoot height. “Frame” is a measure of the robustness of your skeleton; people vary in this regard from the extremes of “fragile wisp” to “hulkin' bruiser.” If you aren't sure where you fall on that scale, don't sweat it. As you can see from the table, the variation based on your level of activity and other factors accounts for almost as much as your frame size.

The odds are the number of calories you burn every day will fall within the range given in these tables based on your sex, height, and build. This number is of surpassing importance to anybody interested in controlling his or her weight, yet few people are aware of how many calories they burn every day.

What comes out

This isn't a glamorous topic, but it's worth considering briefly to complete our understanding of the rubber bag. Every day, you put in some quantity of food and drink. For the most part, your body efficiently disassembles these complex substances into their molecular constituents and makes them available to power the cells of your body. As in any chemical process, there's a residue of waste, and your body excretes this in the well-known ways.

As an omnivore, your body is very efficient. You can use all kinds of odd stuff as food. Conversely, the substances your body can't use—the discard pile of the chemical card game of metabolism—are genuinely nasty stuff; the sooner you're rid of them the better.

Unfortunately, as you bring your weight down to your personal optimum level, the reduced quantity of food you're eating and the odious chemicals released as you burn up excess fat create a tendency for these poisons to stay inside the rubber bag. Means to ameliorate this situation will be discussed, tastefully I hope, later on.

Inside the rubber bag

Intake, burning, and excretion determine, in large part, how you look, how you feel, and how many years you'll live. They do this because, through simple arithmetic, they control the contents of the rubber bag. Living, as we do, inside the bag, it's worth understanding how we're affected by these processes, then using that understanding to gain control of them.

Assume you eat just enough every day to meet the needs of your body. What goes in is broken down into the molecules to power your body and the result precisely equals what you burn. The residue, what comes out, is discarded to make room for the next day's food.

This is the condition of stable weight. The entire purpose of this book is to allow you to attain this state. Regrettably, many of us have spent most of our lives oscillating between the following two situations.

Too much goes in

You eat too much. “How could I have finished that entire pizza?” “Those doughnuts cried out, ‘Eat me!’”. When what goes in exceeds what you burn, your body has left-over nutrients floating around in the bloodstream.

We evolved in a world where the normal conditions of life were hunger and cold. On those rare occasions the body enjoyed a feast it, like the prudent squirrel, made provisions for the hard times that would surely follow.

Fat cells are the body's equivalent of a piggy bank. Fat cells sit on the banks of the bloodstream and, whenever they see excess food, snatch it out and build molecules of fat to stuff in their little cellular storehouse. Each fat cell is, in essence, a little rubber bag: when it sees too much food it snarfs it up and expands.

When this goes on, the larger rubber bag expands: you gain weight.

Too little goes in

You skip a meal, or decide that a scoop of cottage cheese is a wiser choice for lunch than a double beef bozoburger with bacon, guacamole, and cheese.

Before long, the energy-distributing molecules in your bloodstream start to become scarce. Your body starts slowing down to adjust to the situation. You may feel cold, since less energy is available to be burned. Your stomach starts sending telegrams to central control, “Hey, what happened to lunch?”

As the bloodstream becomes depleted in energy, the fat cells notice this and respond; now's the time to draw down the reserves. Perhaps the boss is stalking a mammoth and doesn't have time to scarf up some fruit and berries along the way (or maybe Monday Night Football's gone into overtime and the fridge is forgotten in the heat of the moment—the world of the fat cell is a simple one, hardly cognizant of such modern problems). Individual fat cells begin to tap their storehouses and release energy into the bloodstream to ameliorate the shortfall.

When this goes on, the rubber bag contracts: you lose weight.

Seizing control

Understanding how a system works is the first step in controlling it. Thinking of yourself as a rubber bag may not be glamorous, but it casts the realities of weight control in stark contrast, dispelling the myths and misconceptions that collect around the subject. Compared to most systems engineers design, this one is pretty simple. Let's look at how to control it.

The first step is identifying what we want to control. Well, that's obvious: the goal is control our weight. Our weight is just the contents of the rubber bag.

So, what are the inputs to the system? Again, simple. There's only one input: how much we eat, measured in calories per day.

What are the outputs from the system? Almost as simple: how much we burn, again measured in calories per day, and what comes out. But since what comes out is for all intents and purposes simply the discarded waste products from processing what's been eaten and, in any case isn't subject to control, we can ignore it.

Thus we've simplified the rubber bag even further, to the following system:

Now we're getting somewhere! Calories in—calories out: both readily calculated. You get calories in by adding up the calories of everything you eat in a day: good old “calorie counting.” Calories out, the calories you burn in a day, can be initially estimated based on your sex, height, and frame size using the above tables for men and women. Later, you'll be able to refine this estimate as you monitor your weight.

To determine whether you'll gain or lose weight—whether the rubber bag will grow or shrink—just take the number of calories in, what you eat, and subtract the number of calories you burn. If the number's positive, you're eating too much and the excess calories will stay in the bag; you'll gain weight. If the result is negative, you're burning more calories than you're putting in; the bag will shrink as the reserves stored in fat cells are drawn down to meet the body's energy needs; you'll lose weight.

To complete our understanding of the rubber bag, we need but one more fact: a number that relates an excess or shortfall in calories to pounds on the scale. That's given by the number of calories of energy stored in a pound of fat: about 3500 calories per pound. (Fat is really remarkable stuff when you think about it from the standpoint of biochemistry rather than belt size. Life has discovered, in fat, an extremely compact and efficient way to store energy. We often think of sugar as “pure calories,” but a cup of sugar contains only 750 calories. A cup of lard, essentially pure fat, contains more than 1800 calories, almost two and a half times the content of sugar. Is it any wonder flaky pie crust is purgatory in a pan for anybody with a weight problem?)

If, over a period of time, the calories in the food you eat exceed the calories you burn by 3500, you'll put on about a pound. Conversely, if you reduce your food intake so that you burn 3500 calories more than you eat, you'll lose about a pound.

Please reread that last paragraph. It contains essentially everything there is to know about weight control. All the rest are tools, techniques, and details, important ones to be sure, but useless unless you first understand the system. Any tools that achieve the same end, balancing the calories you eat against the calories you burn, will have the same results. (You can dig a ditch with a pointed stick, a shovel, or a backhoe. The result is the same, but you can get the job done faster and with less effort by using the best tool. Still, don't confuse the shovel [the means] with the ditch [the objective], as most diet books tend to.)

Note the phrase “over a period of time,” in connection with a calorie excess or deficit. One single event: eating a half gallon of ice cream by yourself, right from the box, at one sitting, or going 36 hours without eating as you drive the Cannonball, doesn't have the impact of a consistent calorie excess or deficiency over an extended period of time.

Once you understand these simple facts, the realities of weight control can be reduced to calculations you work out in your head or on the back of a napkin (a particularly appropriate place for them!). Assume you're male, 5'11" barefoot, with an average build. You burn in the vicinity of 2200 calories a day. As long as you eat about that much every day, your weight will stay the same.

Suppose you start putting in an extra 250 calories a day. That sounds like a lot, but consider the following:

These little compensations for life's vicissitudes can add up. Indeed they do…to the tune of an extra 1750 calories per week based on a daily excess of 250 calories (250×7=1750). The weekly surplus of 1750 calories equals half the calories in a pound of fat (3500/2=1750). As week gives way to week, you'll find you're gaining about half a pound a week. Two pounds per month. About 25 pounds a year, by which time none of your clothes will fit, you'll look awful, be depressed about the situation, and feel unable to get a handle on it unless you've grasped the simple arithmetic at the heart of the problem.

But consider the flip side of this calculation. Passing by any of the treats listed above, or its equivalent in other foods, hardly constitutes starvation or survival rations. And yet, simply by eating that little bit less every day for a year, you can subtract 25 pounds from your weight in the space of a single year (assuming you weren't gaining weight before).

We'll look at these kinds of calculations in more detail when it comes planning your weight loss, but first let's consider the two sides of the rubber bag, what you eat and what you burn, from the standpoint of the control you can exert over them.

Controlling what you burn

We all enjoy eating. The prospect of eating less seems inseparably coupled to going hungry. Many people in industrialised countries have no real experience with hunger other than when trying to lose weight. That connection only reinforces our disinclination to diet.

Ever resourceful, we seize on the other side of the ledger sheet. How can you increase what you burn? There are two basic ways. You can increase basal metabolism, the rate your body burns calories all the time, or you can add physical activity to your life to consume some additional calories.

It'd be great if we all came with a knob in some convenient place that adjusted our metabolism to meet the challenges of fast food. Regrettably, evolution, not having the time as yet to come to terms with deep dish garbage pies with swimmers (thick crust “everything” pizza with shrimp and anchovies, for those unfamiliar with the delectation), has neglected to equip us with such a welcome refinement. Regular exercise increases the metabolism a little, but for the most part you have to play the metabolic hand you're dealt. Since a large portion of the calories burned go toward keeping your body at 98.6° F you could apply for a job at the South Pole or, failing that, move your desk into the meatlocker at a nearby supermarket. You'd burn calories at a prodigious pace, but somehow I doubt you're thrilled at the prospect.

How about exercise? “If only I were more active, I could eat as much as I want (in other words, the same way I do now), and lose weight.” After all, everybody can point to friends that bound out of bed at the crack of dawn for a few furious rounds of tennis before breakfast, then dash off to play handball after work. These lean and lanky types all seem to say they just eat whatever they want and never worry about their weight.

It's a glorious idea to control your weight without changing the way you eat, but like so many attractive ideas, it doesn't work. But what about the sports fanatic? Ask him if he's ever had a weight problem. Odds are he'll say, “Of course not. I've always been in shape.” People who have trouble with their weight are different from those who don't. That doesn't mean they're defective or inferior, no more than people who need eyeglasses to see clearly are lesser men than those born with 20/20 vision. In the next chapter we'll examine why some people never have a weight problem while others remain locked in a lifelong struggle with the scale. We'll see how weight problems can be solved just as effectively as eyeglasses or contact lenses fix imperfect vision. Here, the focus is purely on why weight control by exercise alone is an illusion.

The problem is a simple matter of numbers. Consider the 5'11" medium build male we discussed earlier. This individual burns around 2200 calories a day, roughly 100 calories an hour. If, overweight and fed up with being fat, he vows to exercise a full hour every day for the rest of his life, here's roughly how many extra calories he'll burn each day by taking up each of the following.

At first glance, this looks pretty good. After all, an hour of tennis, at 500 calories, represents almost a 25% increase in calories burned. Indeed, if you expend 500 extra calories a day while holding what you eat the same, you'll burn off 3500 calories and a pound of fat every week. Fifty-two pounds a year without ever dieting sounds like a perfect racquet, even if you don't enjoy the game.

Regrettably, there are several thorns in this rosy picture. First, consider the fundamental assumption that you're going to spend a full hour each and every day engaged continuously in a given activity. Where, precisely, is that hour going to fit into your day? Before breakfast? After work? When? And how will it fit into your weekend schedule? If, like most of us, you can barely find time for all the things you have to do, not to speak of the ones you'd like to get around to, seven hours a week is a big chunk of time to devote to anything.

Second, those calorie counts are for a full hour spent nonstop in each sport or exercise. While anybody can, after a while, get used to walking or bicycling nonstop for an hour (which, however, only uses up 300 calories), when's the last time you or anybody you know spent a full hour jogging, swimming, or playing basketball without a break? Even if you found the time and spent the months it would take to get into condition so you could, is this the way you'd want to spend one hour of every day for the rest of your life?

Once you start to make the inevitable compromises with reality: planning, instead, to work out three times a week, to spend 45 minutes each time rather than an hour, and so on, things begin to come apart on the calorie burning front. For if you do faithfully play 45 minutes of active tennis (in an hour session) every Monday, Wednesday, and Friday, that totals only 135 minutes a week: two and a quarter hours. At 500 calories an hour, that only adds 1125 calories per week to what you burn. Spread out over 7 days, that's equivalent to just 160 calories of food a day. In other words, you can achieve equivalent weight loss by reducing your daily food intake by items such as:

Don't misunderstand me. I'm not suggesting exercise is unimportant. Exercise plays an essential role in maintaining your health, and in the What, Me Exercise? chapter I'm going to climb on the soap box and try to convince you to start exercising this very day, following a program I've crafted to fit realistically into the lives of busy, harried people like ourselves—a program you're likely to stay with through the years as opposed to more ambitious schemes that end up abandoned after a few months.

Nor do I mean to imply that exercising won't help you lose weight. Far from it: exercise doesn't just burn calories, it also raises your general level of metabolism so you burn more calories even when you're resting and, in some people, it seems to suppress appetite. Adopting a comprehensive exercise plan, whether the one in this book or another of your choice, and making it part of your regular routine will certainly help you lose weight in addition to the numerous other benefits you'll accrue.

But don't delude yourself into thinking that exercise can do the whole job. For many of us, exercising just causes us to eat that little bit more that cancels out its benefits. The calories burned by exercising, even counting the secondary effects on metabolism, can be erased by even the slightest increases in food intake. No, we'll have to look at what goes in to achieve real and permanent control over weight.

So, exercise if you can and expect ample rewards, but don't exercise thinking that it, alone, will achieve your weight goal. Not only are you likely to be disappointed when the weight doesn't come off, you'll then be tempted to abandon the exercise program in disgust, compounding the problem. On the other hand, if you've sworn not to spend a single minute from now until the day you die engaged in any form of exercise (even knowing that your dying day may, through that very pledge, come sooner), you still needn't be overweight. You can manage your weight quite effectively using the program in this book without ever exercising. Is that a good idea? No it's not, but if you're determined to be out of shape you're better off at the right weight than 50 pounds too heavy and out of shape.

Controlling what goes in

What it all comes down to, of course, is this: if you want to lose weight, you have to eat less. Eat less. It sounds like a sentence handed down by a stern faced judge to a forlorn prisoner in the dock. “Look, eating is one of the few things in life that's pure, simple, pleasure. Now you're going to take that away and tell me I have to be hungry all the time?”

The stark reality is that permanent weight control requires permanent attention to what you eat. Life long, permanent attention. The monumental pile of nonsense, mysticism, and bad advice associated with dieting stems from the all-too-human tendency to deny this simple fact. But fact it is, and like most unpleasant facts, it's best faced squarely and treated as a challenge to be overcome.

Many people have little or no difficulty controlling their weight. Slim people aren't that way because they're willing to go hungry all the time. They're slim because they're eating the right amounts of food at the right times, putting in just the amount of food their bodies are burning. Because they're meeting their bodies' needs, they aren't hungry: the hunger signal goes off only when too little goes in. Even most overweight people maintain a constant weight without hunger. It's just that the weight they're at is way too high.

This book shows you how to join the ranks of the slim people. Thereafter, you need never be hungry again. As you'll see in the next chapter, people who never get overweight have a mechanism in their bodies that tells them when to eat and when to stop. We who have trouble with weight either seem to have that mechanism broken, or else we're eating too frequently or too much for other reasons; we're eating not because our bodies need the food but to satisfy psychological needs the exposition of which in various bubbleheaded psychobabble diet books has leveled vast forests.

I prefer to focus not on why people may tend to eat too much, but rather on how to stop doing it. Once they've stopped overeating, and in doing so cured their weight problem, they may find, as I did, that a lot of the other more subtle problems simply melt away, just as the fat did.

Another unpleasant fact of dieting it's worth facing up front is that while you don't need to go hungry to maintain your weight, you will need to go hungry in order to lose it. It's the rubber bag again. The only way those fat cells are going to be persuaded to dig into their reserves and start dumping them back into the bloodstream is by eating less food than's needed to fill the bloodstream with nutrients. When you do that the hunger alarm is going to go off: “Hey! Up there! Not enough food down here! How about sending down some pizza?”

This is not at all pleasant, but it needn't be incapacitating. Further, you only have to put up with it for a limited amount of time and, with this plan, you'll be able to watch your progress, know how long you'll have to spend to achieve your ideal weight, and build ever-growing confidence in your ability to control your weight as you wish.

Many things in life are unpleasant. Most are far more irritating than the day to day process of losing weight, and few yield comparable benefits. Controlling your weight holds the key to a reward no amount of money, no degree of knowledge, no position of power or influence can bring: a longer life and better health to enjoy it more.

And as with many challenges, you can turn the discomfort of dieting into an advantage once you've succeeded. For what better motivation is there to maintain your weight than recalling how awful you felt when overweight and what you went through to shed that excess poundage?

This isn't to imply that losing weight, even many pounds in a relatively short time, is akin to a stint in the Siberian Gulag. Cutting your food intake by 250 calories a day, the equivalent of foregoing french fries with your lunchtime burger or passing up your mid-afternoon “pick me up” candy bar, is enough to tilt the balance so you'll lose two pounds a month. Weighing the prospect of being 25 pounds lighter in a year against that little morsel of food each day shows how effectively you can manage major changes in your weight once you master the tools that allow you to make such decisions intelligently.

Input/Output

Keeping in mind that what you burn can be expressed simply as a number of calories, it's enlightening to look at what goes in and what comes out in somewhat more detail than you might have ever contemplated.

Consider this view of human as rubber bag presented at a NASA conference on the exploration of Mars.

From this all-inclusive perspective, which accounts for the oxygen in the air we breathe, moisture lost through the skin, and water generated by the reactions that break down the food we eat and reassemble it into the cells of our body, a human being, the “beauty of the world! the paragon of animals!” resembles a water pump more than the most intelligent known life form in the universe.

This is important information, not just to Mars mission planners or inveterate collectors of fascinating details, but to anybody interested in controlling their weight. Explained here are the reasons so many people misunderstand how their bodies react when they're trying to lose weight, why so many people become frustrated and abandon sincerely undertaken efforts to control their weight.

It's the water. On a day to day basis, the water you consume, whether directly in beverages or as part of the foods you eat, and the water you excrete in your various excursions to the hydraulic accommodations, dwarfs the weight of the food you eat and the solid waste you dispose of. To this extent: 68% of the mass you consume every day is water, and 81% of what goes out is likewise water. Startling, until you recall the human body is, by weight, about three quarters water. Average the percentages of water in and water out, and you get…75%: three quarters.

Every day your body ingests plenty of water and disposes of even more. Most of the changes in weight you see from day to day on a scale reflect nothing more than how much water is in the rubber bag at the moment. Consider: if you pig out to the extent of three slices of pizza before bedtime every night for a whole month, you'll gain about four pounds as the lingering souvenir of your month of wild abandon. Yet even that extreme weight gain is less than half your daily intake and disposal of water.

Most of the changes in weight you see have nothing to do with how many calories you're eating or burning. Instead, all you're seeing is how many pounds of water happen to be inside the rubber bag at the moment. How many bleak mornings of dark despair endured by forlorn dieters who indulged in a bowl of salted popcorn at midnight then slaked their thirst with a large glass of water in the middle of the night, would have been taken in stride had only the implications of human being as water pump been fully comprehended?

Food fads

Attempting, for four decades or more, to remain rooted in the tenuous and shifting soil of reality tends to make one skeptical of suggestions of grand conspiracies by insiders pulling the strings that run the world. And yet, and yet….

It seems like every few months a new “scientific discovery” about food and health bursts upon the scene. How far do you go back? Remember…

• 100% polyunsaturated fat!
• With the iron that women need!
• High-fibre!
• Enriched with zinc!
• More calcium than the leading brand!
• Now with oat bran for your heart!

Fuzzy thinking

First, a legitimate researcher publishes a study in the New England Journal of Medicine that claims, heavily hedged and based on largely statistical evidence, to demonstrate a connection between a certain dietary component and some aspect of health, for example, a particular kind of fibre and serum cholesterol levels. That night, the evening news trumpets, “Researchers at the University of Sausalito have discovered a connection between peach fuzz and heart disease. In a study of 100 peach pickers and packers…”. Before you know it, the Sunday supplement's bulging with recipes for peach pie with fuzzy crust.

Meanwhile, the advertising engine is coming up to speed. Full page ads sponsored by the Georgia Peach Association proclaim, “Look for ‘Fresh Georgia Peaches’ on the bag. And remember, only Georgia peaches have 25% more fuzz”. Oat-this and oat-that breakfast cereals begin to vanish from the supermarket, displaced by the arrival of Peachies, Fuzz-chex, and Teenage Mutant Fuzzy Ninja Turtles. Soon, the whole supermarket looks like it's been sprayed with minoxodil. Whole grain cookies enriched with peach fuzz. Fuzz-tab supplements. Fuzzy toothpaste. “Fizzy fuzz” peach champagne.

Now everybody else tries to jump on the bandwagon. The Soybean Institute launches a new promotion to remind people that soybeans are the “hairy legume.” Cheesemakers remind consumers “Cheese—so good for you it grows its own fuzz in the fridge.” “The Fuzzy Way To Health,” “Dr. Harry's Fuzz Diet,” and “The Plantation Peach-Fuzz Cookbook” contend for space in the bookstore window, and their authors make the rounds of the talk shows.

The silliness builds to a crescendo of absurdity, around which time the medical journals start to publish papers such as “Peach Fuzz: No More Effective Than Sawdust” and “No Fuzz-Cholesterol Link In Rats.” As the wave begins to recede, another article is published, “Possible Correlation Between Sesame Seed In Diet and Immune System Performance.” And away we go again.

Food and fact

The rubber bag view of the body and considering only the calorie content of food is obviously oversimplified. There is a difference between eating a varied diet and chowing down on a cup of lard and sugar once a day. Programmers know this instinctively: they balance their daily menu among the four major food groups: caffeine, sugar, grease, and salt.

In reality, food satisfies two distinct needs of the body. The first is for energy. A substantial amount of energy is needed just to maintain a constant body temperature and keep the heart, lungs, and the rest of the body's mechanisms running. The energy consumed by a human body is comparable to a 100 watt light bulb. Food also supplies the raw materials the body uses to manufacture all the chemicals it needs, including those needed to build new cells.

From the standpoint of energy, almost any food will do; you can assume that all foods with the same calorie content are interchangeable. Eating the right mix of food only becomes important when you consider food as raw material. For the most part the body breaks food down into small molecules composed of carbon, hydrogen, oxygen, and nitrogen and then manufactures what it needs from these building blocks. However, certain structures in the body require other constituents. For example, iron is needed to form the hæmoglobin that carries oxygen in red blood cells, and calcium forms the matrix that strengthens bones. In addition, there are a number of complicated organic molecules our bodies require but cannot, for one reason or another, manufacture. These raw materials, minerals and vitamins, must be furnished or else the body begins to develop deficiency diseases such as scurvy and rickets.

If you eat a reasonable selection of food, varied within each meal as well as from meal to meal, it's extremely unlikely you'll come up short one of these crucial substances. (Vegetarians have to be careful, as some nutrients abundant in meat are present only in a limited number of plant foods: these considerations are discussed in detail in numerous books describing vegetarian diets, and I won't go into them here.)

The reason we focus entirely on calories when talking about weight control is that the energy-producing aspect of food is what determines whether you gain or lose weight. Unless your diet is wildly out of whack, which particular foods you eat has very little effect on your weight, compared to the calorie total. To lose weight, you have to eat less. When you eat less, you'll not only be putting less energy in the rubber bag, but also supplying less of the raw materials the body needs. It is, therefore, important to maintain a balanced diet as you lose weight.

Be reasonable. I think the main reason so many diet books are packed with information about food, special recipes, and the like is that it's a useful way to pad out the essential message of a diet book, “eat less food,” into something thick enough to be visible on the shelf. As long as you vary what you eat and choose your foods from all around the supermarket, the probability you'll develop a deficiency disease whilst dieting is extremely remote. If you supplement your food with a multivitamin every day (any one that provides 100% or more of the RDA of the big name nutrients is fine), you have even less cause for concern.

If you adopt the “Clam juice and brown rice quick-loss diet” from the supermarket tabloid, good luck. At least eat some peach fuzz along with it.

Summary

Human beings are the most intelligent form of life on Earth and, as far as we know, the only sentient beings in the Universe. From the neck down, however, we aren't much different from bears or raccoons—we're omnivores—we can eat just about anything and turn it into energy or, alas, if we eat too much, fat.

Notwithstanding our complexity, and regardless of our aspirations, at the most fundamental biological level we're not all that different from a rubber bag. Every day we take in some food and water, burn some amount of energy to sustain us, and dispose of the waste that's produced in the process. If we take in more than we burn and dispose of, the rubber bag expands: we get fat. If we burn and dispose of more than we take in, the rubber bag contracts: we lose weight.

From an engineering standpoint this is a simple system. We have virtually no control of what comes out; that's just the waste products of the factory. We have little effective control over what we burn: in theory our bodies are at our command but the constraints of modern life sorely limit the extent we can exercise.

Consequently, the only real control we have is over what goes in: what, when, and how much we eat. Weight control can be reduced to a very simple matter of arithmetic. Total the number of calories in the food you eat per day, averaged over a period of time. Take the number of calories you burn per day, roughly the same for everybody of your sex, height, build, and level of activity. Subtracting the calories burned from the calories eaten gives excess calories per day. This number times thirty is excess calories per month. A pound of fat is equivalent to about 3500 calories. If you eat 3500 calories more in a month than you burn, you'll gain a pound that month. If you burn 3500 calories more than you eat, you'll lose a pound. All the weight you gain or lose is the consequence of these simple numbers.

The most advanced racing engine is, basically, an air pump. Humans, notwithstanding our pretensions of transcendence are, at a comparable level, water pumps. Every day, the quantity of water we take in and dispose of dwarfs the other physical interactions with our environment. This means that day to day weight figures primarily measure only how much water happens to be inside the rubber bag at the moment. They're of no use in managing one's health. Instead, it's necessary to extract the signal from the noise, the reality from the raw data. Learning how to do this and applying that information to controlling your weight will be discussed in the Signal and Noise chapter.