The first recorded effort of someone changing his diet to lose weight may have been William the Conqueror. In 1087, he discovered he was too fat to ride his horse. He confined himself to bed and stopped eating food - taking in only alcohol. No word on how much weight he lost - but he was reported to have ridden his horse later that year.

There's nothing magical to losing weight. The average 150-pound person burns about 1,800 calories a day just in the act of living. Add any kind of activity to that, and your body will need more fuel to maintain that weight. If you increase your activity but keep your calorie intake the same, you will eventually lose weight.

The bottom line: if you consume more calories than you burn, you will gain weight. And it doesn't take long. For every 3,500 excess calories consumed, you will gain a pound. You can do that every two months or so by eating one cookie a day. Or you could burn off that cookie by running a little under a kilometre.

Low-carb, low-fat, high-carb, high-fat - to your body, a calorie is a calorie - and if you take in more of them than you need, you will gain weight.

Still, diets are a multibillion-dollar industry as people look for ways to help themselves lose weight. Much research has been conducted to try to determine if some regimens do help people achieve their goals.

Here's a brief look at some of them.

Banting

In the first documented low-carb diet, London undertaker William Banting devises a food plan that includes four meals a day, chosen from protein (meat, poultry or fish), green vegetables, a little unsweetened fruit, several glasses of dry wine and a little dry toast. Banting shuns root vegetables, potatoes, bread, sugar, sweetened drinks and pastries or desserts. He loses 50 pounds at the rate of about one pound per week - by eating in moderation and cutting out starchy extras. Overjoyed at his success, he writes what turns out to be the world's first diet book. It becomes a bestseller.

Atkins

The diet that sparked the current low-carb craze. Dr. Robert Atkins argued that traditional low-fat, calorie counting diets all include some degree of deprivation. You rarely feel satisfied. Low-fat, high-carb foods are digested quickly. They lead to blood-sugar spikes, which lead to blood-sugar nosedives, which lead to more hunger.

On a controlled-carbohydrate eating plan, which allows you to fill up on satiating proteins and fats and select the carbohydrates that don't send your blood sugar soaring, the theory goes, you shouldn't feel hungry.

The two main stages of the diet are weight loss and weight maintenance. After you reach your goal weight, you switch to a maintenance program during which some carbohydrates are reintroduced to the diet. The diet does stress that some foods should always be avoided - like sweets. The diet also says that once on maintenance, you can enjoy the occasional potato.

South Beach

Devised by a Miami cardiologist for his patients in the 1990s, this diet shares several features with the Atkins diet. But the diet's creator, Dr. Arthur Agatston, stresses that South Beach is not a low-carb diet. He focuses on a healthy balance between "good" carbs and fats. Highly processed foods, like baked goods and soft drinks are banished on the South Beach Diet. Agatston argues that by decreasing these kinds of carbs, your body will metabolize what you eat better and will also improve insulin resistance, leading to weight loss.

In the first phase of the diet - which lasts two weeks - you cut all fruit, bread, rice, potatoes, pasta, sugar, alcohol and baked goods. In the second phase, you begin to reintroduce some of the banished foods, and in the third, you bring back some more. But you have to be choosy - and are advised not to fall back to your old eating patterns.

Scarsdale

Devised by Dr. Herman Tarnower, the Scarsdale Diet preached a high-protein, restricted calorie regimen. The breakdown is 43 per cent protein, 22.5 per cent fat and 34.5 per cent carbohydrates - and only about 1,000 calories.

Meats had to be lean - skin and visible fat removed before cooking. The diet also promised rapid weight loss - up to 20 pounds in two weeks. But the low calorie intake left many feeling weak.

Tarnower was shot and killed by his lover in 1980, and in the following years the popularity of his diet slipped.

Deal a Meal

Devised by exercise and weight-loss guru Richard Simmons in the 1980s, Deal a Meal is more a product than a diet. The program relied on three basic premises: teaching good eating habits, emphasizing the importance of exercise and promoting a positive mental attitude.

Through a series of colour-coded index cards, people who bought the diet were taught proper food combinations. Dieting became more of a card game: once you consumed the proper combinations as dictated by your cards, you were finished eating for the day.

Weight Watchers

One of the most successful diet support groups. Founded in the early 1960s by Jean Nidetch. She began inviting friends into her Queens, N.Y., home once a week, to discuss how best to lose weight. Weight Watchers says it's more about giving people information on making the lifestyle choices that are right for them. Diet consists of a points program. Foods are assigned points and you are allowed a certain number in your individual program.

Pritikin Program for Diet & Exercise

Developed by Dr. Robert Pritikin to deal with his own heart disease. It's a low-fat, high-fibre diet that includes a moderate exercise program. His objective was to help other people with similar medical problems restore their health. The diet is almost completely vegetarian, and encourages the consumption of large amounts of whole grains and vegetables. It is high in fibre, low in cholesterol, and extremely low in saturated fat and total fat, containing less than 10 per cent of total daily calories from fat.

Processed foods such as pasta and white bread are banned, as are most animal proteins. Diet was revised to include limited amounts of "healthy" fats high in omega-3 fatty acids.

The Beverly Hills Diet

Promises weight loss of up to 15 pounds over five weeks. Relies heavily on fruit. It recommends eating fruit by itself and never eating protein with carbohydrates, in order for food to be properly digested and not stored as fat. The diet begins with a 35-day plan that specifies items to be eaten at each meal, without counting calories or fat grams.

In the first 10 days, you can only eat fruit. On day 11, carbohydrates and butter are added and on day 19, protein is added. Fatty treats are permitted.

Gained popularity when word spread that several Hollywood stars were on it.

Judy Mazel, actress and founder of the diet plan, promised not only that you'll lose weight, but that you'll be "skinny."

G.I. diet

The G.I. — or Glycemic Index — diet, was developed by Dr. David Jenkins, a professor of nutrition at the University of Toronto. It's based on the speed at which the body breaks down foods to form glucose, the body’s source of energy.

High G.I. foods tend to be heavily processed, such as those made from white flour. They break down quickly, leaving your body looking for more fuel sooner. More fuel means more calories consumed.

According to the diet, low G.I. foods break down more slowly, leaving you feeling fuller for a longer time. Low G.I. foods include fruits, vegetables, nuts, legumes, whole grains, lean meat, fish and low-fat dairy. They are rich in nutrients essential for your good health.

The diet categorizes foods as:

• Red light: avoid them if you want to lose weight.
• Yellow light: eat occasionally.
• Green light: eat as much as you like.

The G.I. diet is similar to the South Beach diet — but it does not start with a crash diet.

Sonoma diet

Yet another California-concocted diet, the creators of the Sonoma diet describe it as an approach in which "meals are about celebration, not deprivation." It is based on a Mediterranean diet and lists 10 key foods: · Almonds · Bell peppers · Blueberries · Broccoli · Grapes · Olive oil · Spinach · Strawberries · Tomatoes · Whole grains The diet is structured in three waves. The first contains more restrictions on what you can eat. The second phase is the main weight loss period. The final phase is the life-long maintenance plan. The diet also recommends using different size plates for different meals — and it instructs how to fill the plates in each phase of the diet.

Grapefruit diet

Another very low calorie diet. The premise is to consume only 800 calories a day through eating lots of "fat-burning" grapefruits to kick-start your metabolism. The 21-day program calls for mostly grapefruits, some protein (mainly boiled eggs), and some vegetables. As much coffee as you like.

The Cambridge Diet

A series of weight-loss programs developed in Britain. Originated as a very low calorie diet. If used as your sole source of nutrition, you buy prepackaged food from the company. Company says that approach is the surest way to lose weight quickly.

May combine Cambridge products with conventional food for slower weight loss.

The Zone

Another diet that preaches the evils of refined carbohydrates like pasta, white bread and bagels. You are in The Zone if you eat five times a day, if the protein you consume is the size of the palm of your hand and your carbs are the size of your fist.

Relies heavily on the glycemic index, a ranking of carbohydrates based on their immediate effect on blood glucose (blood sugar) levels. The theory (as in other low carb diets) is that diets relying on foods with a low glycemic index make it easier to lose weight.

Off the beaten path...

The Last Chance Diet

Not so much a diet as a fast. Under this program, developed by Dr. Robert Linn in the 1970s, people ate nothing at all. But several times a day the fast was broken by a small drink of the concoction that Linn had invented called Prolinn. It was a liquid protein that provided fewer than 400 calories a day, consisted of ground-up and crushed animal horns, hooves, hides, tendons, bones and other slaughterhouse byproducts that were treated with artificial flavors, colours and enzymes to break them down.

Fletcherism

In 1898, Horace Fletcher advocated the slow chewing of food. He came up with the approach after he was denied life insurance because of his weight. Fletcher lost 40 pounds by chewing his food very slowly.

Vinegar

In 1811, poet Lord Byron decided vinegar is the key to weight loss. He drenches his food in vinegar and goes from 194 pounds to less than 130.

Dr. Sawdust

The Rev. Sylvester Graham, nicknamed "Dr. Sawdust," rails against the sin of gluttony, which he says leads to lust, indigestion and the rearing of unhealthy children. Graham devises a Spartan diet of coarse, yeast-free brown bread (including the famous Graham cracker), vegetables and water.