How Dieting Works
by Marshall Brain
 

 

 

Dieting is one of those things that is completely integrated into American culture. On any given day, a huge portion of the U.S. population is "on a diet" and "counting calories" in one way or another. And look at how many of the diet names in the following list that you recognize:

  • The Atkins Diet
  • The Cabbage Soup Diet
  • The Grapefruit Diet
  • The Hollywood Miracle Diet
  • The Rice Diet
  • The Scarsdale Diet
  • Weight Watchers
  • The Zone Diet

You probably recognize many of these names because you hear them all the time!

In this edition of How Stuff Works we will look first at weight gain and why gaining weight is so easy. Then we will look at what you can do about weight gain -- in the form of diet and exercise -- to maintain a consistent weight. What you learn in this article will amaze you because it is so simple!

Your Body's Efficiency
Have you ever wondered why, for so many people (and especially for anyone older than 30 years old), weight gain seems to be a fact of life? It's because the human body is way too efficient! It just does not take that much energy to maintain the human body at rest, and when exercising, the human body is amazingly frugal when it comes to turning food into motion.

At rest (for example, while sitting and watching television), the human body burns only about 12 calories per pound of body weight per day (26 calories per kilogram). That means that if you weigh 150 pounds (68 kg), your body uses only about:

 

150 X 12 = 1,800 calories per day

Twelve calories per pound per day is a rough estimate -- see How Calories Work for details.

Those 1,800 calories are used to do everything you need to stay alive:

  • They keep your heart beating and lungs breathing
  • They keep your internal organs operating properly
  • They keep your brain running
  • They keep your body warm

In motion, the human body also uses energy very efficiently. For example, a person running a marathon (26 miles or 42 km) burns only about 2,600 calories. In other words, you burn only about 100 calories per mile (about 62 calories per km) when you are running.

You can see just how efficient the human body is if you compare your body to a car. A typical car in the United States gets between 15 and 30 miles per gallon of gasoline (6 to 12 km/L). A gallon of gas contains about 31,000 calories. That means that if a human being could drink gasoline instead of eating hamburgers to take in calories, a human being could run 26 miles on about one-twelfth of a gallon of gas (0.3 L). In other words, a human being gets more than 300 miles per gallon (120 km/L)! If you put a human being on a bicycle to increase the efficiency, a human being can get well over 1,000 miles per gallon (more than 500 km/L)!

That level of efficiency is the main reason why it is so easy to gain weight, as we will see in the next section...

Taking Calories In
The 1,800 calories that a typical person at rest needs per day is just not that many. For example, if you go to your neighborhood McDonald's restaurant and order the Big Xtra meal, you will get a sandwich, a large order of french fries and a large Coke. This meal contains:

 

  • 710 calories in the sandwich*
  • 540 calories in the french fries*
  • 310 calories in the drink*

(*See the McDonald's Nutrition page for details.)

 


A meal at McDonald's can add up to almost a whole day's worth of calories.

In other words, just this one meal provides 1,560 calories you need during a day. If you get an M&M McFlurry with it for dessert, you'll get 630 more calories so you are already consuming almost 2,200 calories just at this one meal!

Similarly, if you go to Pizza Hut and get a Meat Lover's Pan Pizza, each slice contains 360 calories*. If you eat three slices and get a large drink to go with it, that's 1,390 calories -- just 410 calories shy of a full day's worth of calories. (*See the Pizza Hut Nutrition Page for details.)

Similarly, if you eat 12 SnackWell's Crème Sandwich Cookies -- which, if you think about it, really is not that hard to do -- you've taken in 660 calories. That's more than one-third of the daily caloric intake.

 


These 3 cookies contain 165 calories.

The point here is not to slam these products or make them look bad. For example, I've got two kids and I go to McDonald's at least once a week. The point is that, in America and most other developed countries, it is incredibly easy to find and consume calories today.

And, add the fact that a typical day might look like this:

  • You might have two Pop-Tarts for breakfast
  • Then hit Pizza Hut for lunch
  • Grab some SnackWell's and a cola for a snack
  • Head for McDonald's for dinner
  • and top it off with some potato chips while watching TV

You can see how the number of calories coming in can easily reach 3,000, 4,000 or 5,000 per day without any effort at all. That's the problem.

Your body, it turns out, is extremely efficient at capturing and storing excess calories. Whenever your body finds that it has excess calories on hand, it converts them to fat and saves them for a rainy day. (See How Calories Work and How Fat Cells Work for details). It only takes 3,500 excess calories to create 1 pound of new fat on your body. If you are taking in just 500 extra calories per day, then you are gaining a pound of fat per week (500 calories x 7 days in a week = 3,500 calories/week). Since it is easy to get 500 calories from just one ice cream cone or a few cookies, you can see that weight gain is completely effortless in today's society. Food is just too easy to find!

The Idea Behind Dieting
Let's imagine that you are overweight and you would like to lose several excess pounds. To lose one pound of fat, what you have to do is burn off 3,500 calories. That is, over a period of time, you have to consume 3,500 calories less than your body needs. There are several ways you can create that deficit. If you assume that you weigh 150 pounds and that your body at rest needs 1,800 calories per day (150 * 12 = 1,800) to live, here are several examples (some realistic, some not):

  • You could lie in bed and starve yourself. Since you are lying in bed you are consuming 1,800 calories per day. Since you are starving yourself you are taking in no calories. That means that, every day, you create a 1,800 calorie deficit and, approximately every two days, you will lose 1 pound of body weight.

     

  • You could consume fewer calories than your body needs. For example, you might choose to consume 1,500 calories per day rather than the required 1,800 by controlling what you eat. That creates a 300-calorie deficit every day. That means that approximately every 12 days, you will lose 1 pound of weight (12 days x 300 calories = 3,600 calories).

     

  • You could consume 1,800 calories per day and then choose to jog 2 miles (3.2 km) every day. The jogging would burn about 200 calories per day, and over the course of 18 days you would burn about a pound of body weight (18 days x 200 calories = 3,600 calories).

     

  • You could consume 2,500 calories per day and run 10 miles per day. You will burn 1,800 calories per day at rest and then 1,000 calories per day running, for a total of 2,800 calories. You are consuming 300 calories fewer than you need, so you would lose a pound every 12 days or so (300 calories x 12 days = 3,600 calories).

As you can see from these examples, the only way to lose a pound of fat is to consume fewer calories per day than your body needs. For every 3,500 calories that you body takes from its fat reserves, you lose 1 pound (0.45 kg) of body fat. You can create the deficit either by monitoring and restricting your intake of calories, or by exercising, or both.

The idea behind most diets -- everything from Weight Watchers to the grapefruit diet -- is simply to help you somehow lower the number of calories that you consume each day. That's all they do.

Why Diets Tend Not to Work
The reason why most diets tend not to work for very long is because they are not sustainable. A person gains weight because he or she consumes more calories per day than needed. The diet creates a temporary deficit. When the diet ends, the person goes back to normal eating and the weight comes back.

Let's look at an example. Say that you weigh 150 pounds. That means that you burn 1,800 calories per day in a resting state. Let's also imagine that in the course of a day you burn 200 more calories living your life -- walking up and down steps, carrying in the groceries and so on. Your calorie needs then are, on average, 2,000 calories per day. Now let's further imagine that, on average, you consume 2,050 calories per day. On a daily basis your body is taking in, and therefore storing, 50 calories more than it needs. So every 70 days (3,500 calories in a pound / 50 calories each day = 70 days) you gain 1 pound (0.45 kg). If that "50-extra-calories-per-day" trend continues, then over the course of a year you would gain 5 pounds. This, by the way, is the pattern for a big portion of the U.S. population. If you over-consume by just a few calories per day then, over time, you will gain weight. Keep in mind that just one Oreo-type cookie contains 50 calories, so over-consuming is incredibly easy.

 


One cookie contains 50 calories.

Now, you go on a diet -- the amazing "Palm Beach Miracle Diet." On this diet, you consume nothing but 2 cups of brown rice and a can of Vienna sausages, along with all the onions you care to eat, every day. You start this diet and you are consuming only 1,000 calories per day. You also start jogging 2 miles a day. That means that, on a typical day, you are consuming 1,200 calories less than you need. Over the course of three days (3,500 calories in a pound / 1,200 calories each day = approximately 3 days), you will lose 1 pound of weight. You keep on this diet for two months and lose 20 pounds.

The day you go off this diet, what is going to happen? First, you are probably going to eat a lot more than normal because you have been eating nothing but rice and Vienna sausages for two months! Then you will settle into your "normal eating pattern" that you had before the diet. And eventually all of the weight comes back.

This is why diets don't work for most people. You do lose weight, but then go off the diet and gain it back. What is needed instead is a sustainable diet -- a food consumption and exercise plan -- that lets you live a normal life and eat normal foods in a normal way.

Building a Sustainable Diet
Building a sustainable diet and exercise plan is the key to maintaining a consistent weight. This is not easy for many people. As described above, the landscape is literally covered with calories and exercise takes time and energy.

The first step is to start counting the calories that you consume in a day so that you become conscious of two things:

  • You need to understand exactly how many calories you are eating on a "normal" day.

     

  • You need to realize where each calorie comes from -- you need to build a calorie database in your brain so that you know, whenever you eat something, just how many calories it is supplying.

In the United States, any food that you buy in the grocery store is required by the U.S. Food & Drug Administration to have a nutritional label with that food's calorie content (or see a chart like this one). Any chain restaurant will supply you with nutrition information both at the store and on the Web (or see a Web site like this).

The second step is to figure out how many calories in a day that you need. You can use the "12 grams per pound" rule, or you can get more precise by looking at the formulas on on the calorie page.

Pick your "ideal weight" -- the weight that you would like to maintain. Then calculate how many calories a day you can consume to maintain that weight.

The third step is to compare the two numbers -- You may be startled by the difference between the "number of calories you need" and "the number of calories that you take in" in a day! That is where the extra pounds are coming from.

The fourth step is to figure out how to bring the two numbers in line. What you will soon realize is that 1,600 or 1,800 or 2,000 calories per day just isn't that many. You have to watch and count everything you eat and drink every day and stick to your daily limit.

The fifth step might be to add exercise to the mix so that you can raise the number of calories you can consume per day. Online resources like this exercise calculator or this exercise chart will show you how many calories different forms of exercise can burn. Burning 250 or 500 calories per day on exercise can make a big difference.

In an effort to reduce the number calories you take in per day, here are several strategies that you might find effective:

  • Be conscious of every calorie you consume, and keep a daily journal. Stick a 3- x 5-inch index card in your pocket each day and write down everything you eat and drink.

     

  • Eliminate the food myths from your mind, as described later.

     

  • Eliminate all calories that come in through drinking. In other words, drink water. The problem with drinks -- everything from cola to orange juice to beer -- is that they can bring in lots of calories and they have absolutely no effect on your appetite. For example, if you drink 10 ounces of orange juice (300 ml), you take in 140 calories but it does nothing to curb your appetite. If, on the other hand, you eat an orange, three things happen:
    • you take in fewer calories
    • you get to chew the orange, which has a psychological effect.
    • it fills your stomach, which curbs your appetite. An orange actually gives you a feeling of fullness, while orange juice does not.

    The same holds true of any beverage that contains calories -- the calories come in but your appetite remains the same.

     

  • Eliminate white sugar. If you say to yourself, "I will eat no white sugar," it has an interesting effect. It eliminates all sorts of high-calorie foods:

     

    • cookies
    • cake
    • ice cream
    • cola
    • candy
    • candy bars

    By simply refusing all foods that contain lots of sugar, you make it easy to eliminate a big class of snack foods.

     

  • Similarly, try eliminating all fried foods, including:

     

    • potato chips
    • cheese crisps
    • french fries
    • onion rings
    • donuts
    • fritters
    • fried chicken

    Fat from deep frying gives these foods lots of calories for their size. Eliminating fried foods and sugar together pretty much eliminates all high-calorie snacks. Entire aisles in the grocery store become irrelevant to you.

     

  • Try to replace high-density foods with low-density foods. A cookie is a high-density food. It contains lots of sugar and fat, so it is lots of calories in a small package. One or two bites and you've taken in 50 or 100 calories. A banana, on the other hand, is low-density. It takes many bites to eat a banana, but you take in only 100 calories.

     


    Apples contain few calories for their size.

    Here's a good mental exercise that helps you understand the point: Most people would not find it hard to eat a dozen Oreo-type cookies. Or a dozen SnackWell's cookies. That's 600 calories. Now imagine trying to eat six bananas at one sitting -- you would explode! But it's the same number of calories. Look for low-density foods like bananas that fill you up without giving you that many calories. Foods that are low-density include:

     

    • Just about any fruit or vegetable in its natural state
    • Many non-sugared breakfast cereals, like shredded wheat
    • Rice cakes
    • Unbuttered popcorn
    • Whole-grain bread, preferably with lots of fiber
    • Brown rice

    Things that are high-density include any food or beverage high in sugar and/or fat. Nuts, most meats, candy, cookies, crackers, potato chips, fried anything, cola, beer, and so on are all high-density and should be avoided.

     

  • Try wearing form-fitting clothes instead of sweats. The tight clothing acts as a subliminal reminder of what you are trying to accomplish.

If you follow these guidelines and, through diet and exercise, keep the number of calories you consume below your calories needed, you will lose weight and maintain a consistent weight.

Fitting in Exercise
Exercise is one tool you have to control your weight because exercise is a way to increase the number of calories that you burn off in a day. Online resources like this exercise calculator or this exercise chart will show you how many calories different forms of exercise can burn. One way to make the most of exercise is to integrate some form of exercise into your daily routine. Here are several examples:

  • Try to find some type of exercise that you enjoy (or at least can tolerate) and do it every day for 30 minutes, 60 minutes or more. It might be walking, riding an exercise bike while watching TV, or working out in a gym at lunch.

     

  • Try to fit micro-exercises into your daily life. For example, instead of taking the elevator, take the stairs. Park farther away from stores in parking lots. Things like that.

     

  • Put a set of weights at your desk and use them 3 or 4 times during the day as you think or talk on the phone.

     

  • Find an exercise partner. Exercise, for some people, is a lot easier if there is someone to talk to. A partner will also help make exercise a routine.

     

  • Try to exercise every day. It is easier to remember to do something if you do it every day.

Weight Loss Myths
There are dozens of weight-loss myths that help to derail people. Here are some of the most common, so you can avoid them:

  • The myth that some kinds of calories are different from others -- A calorie is a calorie. If you consume 4,000 calories by eating 1,000 grams of white sugar or 4,000 calories by eating 444 grams of fat, your body doesn't care. It is still 4,000 calories.

     

  • The myth that low-fat foods are OK -or- the myth that you can eat as much as you want if it is low fat. A product can have 0 grams of fat but can still have lots of calories. Many fat-free foods replace the fat with sugar and contain just as many or more calories as a fat-containing product.

     

  • The myth that any passive device -- weird acupressure rings and bracelets or soaps or whatever -- can help. There is no way to burn calories but to burn them.

     

  • The myth that you can lose 54 pounds in 6 weeks -- Despite what the ads say (e.g., I LOST 54 POUNDS IN 6 WEEKS WITHOUT DIETS OR EXERCISE!!! or LOSE 10 POUNDS THIS WEEKEND!), you cannot lose a pound of fat unless you burn off 3,500 calories. To lose 54 pounds in 6 weeks, you would need to lose 9 pounds in 7 days, or 1.3 pounds per day. 1.3 pounds of fat is equal to 4,500 calories, so you would have to burn off 4,500 calories per day. The only way to do that would be to eat nothing AND run a marathon every day for 42 days. That's impossible. The only way to lose that much weight that quickly is either through dehydration or amputation. The ads are lying.

     

  • The myth that anything can create an "enzyme-driven fat-burning cycle" -- All sorts of things, from nettle seeds to apple pectin, are supposed to contain enzymes that create an ENZYME-DRIVEN FAT BURNING CYCLE THAT BURNS CALORIES 24-HOURS-A-DAY!!! No.

What is true is that you have to eat fewer calories than you burn in a day if you want to lose weight. You can do that by eating fewer calories than you need, or by exercising more, or both. It is true that some people burn more calories per day than others (just as some people are taller than others, some people have to use the restroom more frequently than others, some people lose their hair faster than others and so on -- people are different). You simply have to find the number of calories your body burns in a day and consume fewer calories than your body needs. That's not to say it's easy -- the psychology of food is very powerful. But that is what you have to do. It is a mental game, and there is no way around it. Now you know the rules of that mental game!

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