There is no real mystery to losing weight. The body needs energy, which it obtains from the calories in food. The caloric parts of food consist of three types: fats, carbohydrates, and proteins. Fat is a more efficient energy store than the other two: it has 9 calories per gram, while carbohydrates and proteins have 4 calories per gram. Most energy that the body uses comes from adipose tissue. A pound (454 grams) of adipose tissue, which is approximately 85% fat, has 3500 calories. Thus, if you eat 3500 calories less than your body needs, it will get the energy by burning off a pound of adipose tissue, and you will weigh one pound less.
That's the theory, and it's more or less correct, although 3500 calories is not a precise amount for everyone at all times. The key point is that to lose weight, you need to use more calories than you eat. It doesn't really matter where the calories come from: the body converts unused protein and carbohydrate calories to fat for storage, so eating no fat won't stop your body from producing extra fat. It also doesn't matter how you go about using more calories: you can consume fewer calories, or expend more calories, or a combination of both.
An average woman burns 11 calories per pound of body weight per day; the average man burns 12 calories per day. Thus a 167-pound man will burn approximately 2000 calories per day. Those are averages that can vary widely for different people, based on their metabolic rate. This is where exercise can help. Besides burning extra calories while actually exercising, it can increase your metabolic rate while at rest, and also may build muscle, which consumes more calories at rest than adipose tissue does.
The Weight Watchers plan is simple: all foods are assigned a "point" value. To compute points, start with the calorie count; add a bit for every gram of fat, and subtract a bit for every gram of fiber, to get what I will call "adjusted calories". Fifty adjusted calories equals one point. (The point calculation is not presented as such, but rather as a mystical black box which takes three inputs--calories, fat grams, and fiber grams--and then runs them through a slide-rule-like gizmo, or a Weight Watchers calculator, to produce the point value.) Weight Watchers publishes books listing the point values for many common foods, as well as for common dishes at well-known restaurants. (Weight Watchers used to use a more complicated formula in which foods were classified in a manner similar to the American Diabetes Association's Dietary Exchange Lists. This system was more precise, but also harder to follow; the result was more like being on the Zone Diet, which advocates a 40-30-30 percent balance between carbohydrates, protein, and fat.)
Following the Weight Watchers plan involves determining the proper number of points that you should consume each day (actually a range of values, based on your current weight), and then tracking all the food you consume to ensure that you keep to that number. The exact number of calories you are allowed to consume will depend on how much fat and fiber you include in your diet, but it will very likely be less than you burn simply keeping your body running (the 167-pound man who burns 2000 calories at rest will likely eat fewer than 1500 calories on Weight Watchers).
To encourage exercise, Weight Watchers plan gives you credit, in the form of extra points that are earned based on the duration and intensity of the exercise. This lets you eat a bit more, while avoiding the problem of overcompensating ("I ran for 15 minutes, so here goes a banana cream pie").
By contrast, the Atkins Diet does not worry about all calories, but instead only about carbohydrates. It's simpler to calculate, since carbohydrate information is generally known, and there is no need to do any conversion to points.
Initially, participants are restricted to 20 grams of carbohydrates a day. That is a very low amount: 1/4 cup of flour, or a single slice of typical bread. Eventually, this amount can be raised to 40 to 60 grams a day, depending on how much an individual can eat and still lose weight. Since many carbohydrate-rich foods (especially starchy vegetables) have important vitamins, participants in the Atkins Diet also take a multivitamin every day.
The theory behind the low carbohydrate diets is that excessive carbohydrate intake causes a rapid rise in the glucose levels in the blood (also known as blood sugar level), which causes large amounts of insulin to be released by the pancreas. This is followed by a sudden drop in blood glucose levels, which quickly makes you hungry again. Limiting carbohydrate intake prevents this effect.
The low carbohydrate diet literature diverges a bit on why this helps you lose weight. Some claim that too much insulin speeds the conversion of carbohydrates to stored fat; some state that the absence of carbohydrates cause the body to enter a (possibly dangerous, although this is disputed) state called ketosis, in which the body excretes fat; others explain that fats just fill you up more, or that the spike-and-crash cycle makes you eat more because you feel hungry again sooner. Whether the claims are made with scientific or empirical evidence, the conclusion is the same: eat fewer carbohydrates, lose weight.
Weight Watchers and the Atkins Diet have one important thing in common, the most important thing there is for losing weight and keeping it off: they make you pay attention to what you eat. You have to read the Nutrition Facts label on foods you buy, and if there isn't one, such as with produce or restaurant food, you need to be aware of what you are eating. Shoppers on either diet will spend a lot of time scanning the labels, although what they are looking for is different.
In fact neither wants to be thought of strictly as a diet. They are ways of watching how much you eat; how much you want to eat depends on your goals. With Weight Watchers, you first set your daily points total low enough to lose weight, then you move it higher until you find a level that lets you maintain your weight. The same is true with Atkins and carbohydrates: first find out a daily amount that lets you lose weight, then raise it to a maintenance level.
The United States Department of Agriculture's Food and Nutrition Information Center publishes the Food Guide Pyramid, which advocates a carbohydrate-rich diet with few fats. (For those who are interested, the USDA web site has a document showing how US dietary recommendations have changed over the years, and another comparing government food guidelines around the world. The USDA's Center for Nutrition Policy and Promotion also has some good documents and links.) The Food Guide Pyramid matches up with the Recommended Dietary Allowances that are shown on the Nutrition Facts label. The RDA for a 2000-calorie diet is 300 grams of carbohydrates and 65 grams of fat. That is 1200 calories from carbohydrates and almost 600 calories from fat, leaving room for only 200 calories from protein.
That seems like a lot of carbohydrates to many people, although carbohydrates should not all be lumped together. Carbohydrates can be grouped into sugars, starches, and fiber. Sugars are what are known as "simple carbohydrates", and starches and fiber are "complex carbohydrates". Fiber, which is mostly indigestible to humans, is more-or-less acknowledged by everyone to be a good thing. For a while it was thought that simple carbohydrates caused blood glucose levels to rise and complex carbohydrates did not, but now that has been shown to be too simplistic. Instead, a new term has arisen, glycemic index, which directly measures the effect of food on blood glucose levels. Glycemic index is not obvious: different beans, grains, and rices can have wildly varying glycemic indices. It can even depend on how the food is prepared. The few carbohydrates consumed on the Atkins diet should be ones with a low glycemic index, although this is often generalized to simply avoid white flour, white rice, potatoes, and sugar.
Avoiding sugar isn't new. In fact there are diets, such as Sugar Busters, built around avoiding sugar. I once offered one of the thinnest women I knew a single Jelly Belly jelly bean, which has one gram of sugar (that's basically all it is: one gram of sugar, four calories). "No Sugar!" she exclaimed in horror, her eyes wide, backing away from me as if I were proffering a vial of bubonic plague. My parents claimed that as a child I got too agitated if I had too much sugar. Next to fat, sugar is probably the most vilified food out there, and the realization that many fat free and low fat foods have simply replaced fat with sugar is causing some people to return to the full fat products.
The Weight Watchers point system provides an easy way to figure out tradeoffs between different foods. Should you eat a large apple or 3 ounces of tuna fish? An egg or an Oreo cookie? A can of corn or 8 ounces of milk? (Answer: they are all the same in the eyes of Weight Watchers). To help you stick with the program, Weight Watchers also encourages you to attend weekly meetings (although you can do it online without those), at which you weigh in and get encouragement and advice from other participants. If you meet your weight-loss goal, you can come to the meetings for free as long as you maintain your weight--which ideally is for the rest of your life.
When you start Weight Watchers, you spend time counting up all your points, and searching for the elusive "zero-point snack," a little pick-me-up that doesn't count any points at all. After a period of eating such delicacies as spinach 'n' salsa and hearts of palm in mustard, you will probably get a feel for what constitutes a proper-sized serving of various kinds of foods, and what appropriate snacks are, without actually counting all your points. You contemplate a piece of Chocolate Motherlode Cake at Claim Jumper and you cannot bring yourself to eat it. Is it that you physically feel full? Or that you mentally don't want to have to eat less for so long to make up for it? Or do you fear the opprobrium of your fellow meeting attendees if you 'fess up? Who knows, but likely you go home and have a Skinny Cow ice-cream sandwich instead.
Weight Watchers, unlike the low carbohydrate diets, does not limit what type of food you can eat; anything is fine as long as it is within the points allowed (and you can balance out points over a week, if you splurge on one meal). Sugar and protein are viewed as equal: you may be told, anecdotally, that protein makes you less likely to feel hungry sooner, but this is presented as accumulated wisdom, not something based in science.
The big draw of the Atkins diet is what you can eat: protein/fat combinations like steak, butter, eggs, cheese, and nuts. Those are the poster children for low carbohydrate diets and they may conjure up the impression of gorging yourself on whatever you want, but this is misleading. The true treats in our modern diet are the carbohydrate/fat combinations like muffins, cookies, candy bars, ice cream, and French fries. With the Atkins diet, you have to permanently excise these items. I personally love bread; contemplating a life without butter on toast, it's not clear that I miss the butter more than the toast.
On the positive side, being able to eat as much steak and eggs as you want can make it easier to stick with a diet, which is one of the main claims that the Atkins diet makes. And eating out is easier with Atkins. With Weight Watchers, ordering in a restaurant is difficult because the fats that foods are often cooked in--butter, oil, cream--are extremely high in points. Was the food cooked in one tablespoon of olive oil, or three? The difference between those is equivalent to half a cup of Haagen-Dazs ice cream, or a McDonald's hamburger. Meanwhile, it is much harder for you to eat carbohydrates without being aware of it: the odd gram of sugar might sneak through, but fundamentally a food either has flour, rice, or potatoes in it, or it doesn't. Since the daily carbohydrate limits are so low, you might as well just skip any food that has carbohydrates in it. You have to be careful with vegetables, which can vary in how starchy they are, but at least you will usually know what vegetables appear in a dish in quantities significant enough to be an issue. The Atkins restaurant game plan is easy: avoid all non-fiber carbohydrates. With Weight Watchers you can't avoid all foods that have non-zero point values, so you are left trying figure out the number of points in a meal whose ingredients, let alone amounts, you are unaware of.
It's also possible to combine the diets in some ways. Simply knocking most of the carbohydrates off the USDA Recommended Dietary Allowance would give you a diet that would make both Weight Watchers and Atkins happy, as long as the carbohydrates you did eat had a low glycemic index (those tend to have a bit more fiber, although often not enough to actually lower the all-important Weight Watchers point count for a single serving). On the other hand, you could eat nothing but Atkins contraband like bread and Kool-Aid and still keep within your Weight Watchers limit, while dousing all your food in butter and oil would annihilate your points limit, but elicit nary a peep from Atkins.
Can Atkins really work with all that fat? Consider those pre-cooked beef sausages you can get from places like Swiss Colony. Some of these have a gram or so of sugar per serving, but some don't - they are pure protein and fat, especially fat. A 10 ounce one would blow past your entire daily allowance for Weight Watchers, and would make a low-fat diet advocate faint. Yet with the Atkins diet, you could eat those all day. But would you? Sure they taste good, but they are kind of filling. Would I want to eat for a while after putting one of those babies away? Atkins is saying that the old saw, about how after eating a rice-heavy Asian meal you feel hungry an hour later, may have some truth to it.
When I first heard about low carbohydrate diets, I figured that nutritionists, in response to pressure from fat-starved dieters, had finally come up with a way to separate two previously linked concepts: eating healthy and losing weight. But now it appears that having that fat in your diet does not automatically make it an unhealthy diet. And furthermore, the benefits of losing weight, however it is done, may be more than the negative effects of eating fat (although there are limits to this: tobacco is an appetite suppressant, but no serious nutritionist would recommend taking up smoking to lose weight).
There are indications that the food industry is waking up to people's desire for low carbohydrate foods. You can now find low carbohydrate content emphasized on the labels of tortillas and bread (one bread, from Food for Life, has only 4 grams of carbohydrates per slice). At In-N-Out Burger you can order your burgers "protein style", wrapped in lettuce instead of a bun.
A redesign of the Nutrition Facts label redesign is further away. The label is slow to change, so it sometimes reflects the food concerns of a previous decade. The current one shows cholesterol, from back when it was thought that cholesterol intake was the main factor in blood cholesterol levels (it isn't for most people), and also sodium, from when salt was a big bugaboo (it is now considered benign for most people without high blood pressure, as long as you drink enough water - and both Weight Watchers and Atkins want you to drink a lot of water, even though there may not be any benefit to doing so). In the future the label may include such details as splitting fat into saturated, monounsaturated, and polyunsaturated; counting trans-fats (which are bad for your cholesterol level); splitting fiber into soluble and insoluble (both are considered beneficial, although they have different effects); and possibly even listing the glycemic index. Then there is caffeine. Although it is generally acknowledged that caffeine is not a great thing to eat, and consumers are worried enough about it that drinks like ginger ale are now prominently labeled "caffeine free," diets usually allow it within reason (Atkins says that it stimulates insulin production, but allows it as long as you are not "addicted," dependent on it for energy). This is either because it does have zero calories, or out of fear that any diet that outlawed caffeine would not gain many adherents in a coffee-addicted society. Still, we may see caffeine on nutritional labels someday.
Public opinion might come around also, but it will be slower. The US government still officially supports the low-fat, high-carbohydrate diet that is laid out in the Food Guide Pyramid, although that is due for a redesign next year. It is almost obligatory, when writing about a greasy Atkins-compliant meal, to include a phrase like "I could feel my arteries clogging." In the future, will writers addressing themselves to a loaf of sourdough bread state, "I could feel my blood sugar rising"? It remains to be seen.
So what is the best way to lose weight? The short answer is, whatever works for you. For someone who has had trouble staying on a diet, I would recommend starting with the Atkins Diet. It should give you some quick results, allow you to eat some comfort foods without feeling guilty, while still getting you in the habit of keeping track of what you eat. However, I would suggest switching over to Weight Watchers within a few months, while sticking to foods that have a lower glycemic index where possible (such as whole wheat flour instead of white flour). There are concerns about possibly long-term health issues with low carbohydrate diets, and I think that if you are contemplating keeping track of your food for the rest of your life (which you should be), it is easier to imagine simply eating less of all foods than it is permanently giving up some foods. In addition, with Weight Watchers, the occasional high-calorie slip-up is just a physical thing: you've consumed extra points, you'll eventually work them off, and all will be well. With a low carbohydrate diet, going overboard with carbohydrates is more like emotional cheating: you may have messed up your body's chemistry for a while, and who knows how long those sugar-induced hunger pangs will continue.
In a way, diets are like disciplining a small child. Different parents have different areas they focus on: some want respect, others want clean rooms, others want good behavior at meals. But the main thing is to be consistent, in order to get the children used to listening to you and suppressing their desire to misbehave, in at least some aspect of their life. A diet is like disciplining your unruly appetite. You may want to limit calories, or you may care about carbohydrates, but the main thing is to be consistent, and get your body used to listening to your brain and suppressing its desire to overeat.