Recent studies have shown that the United States, Canada and now the United Kingdom are experiencing an obesity epidemic. Despite the fact that supermarket shelves are full of low-fat and nonfat foods and that as a society we are spending millions on weight-loss products, health magazines, diet books, weight-management clinics and health spas, it appears that, as a population, we are getting steadily fatter. This would suggest that the problem is not a lack of awareness or interest in addressing the problem, but is due to certain other factors that at first may appear only indirectly relevant. Statistical evidence has shown us that we have become more and more inactive owing to the introduction of labour-saving devices, computers and television. It is also apparent that we have a greater tendency to drive rather than walk, even if the distance we need to travel is minimal. All these factors combined have resulted in today's population leading a largely sedentary lifestyle, which implies that we are not expending enough energy to work off the calories that we consume. This leaves us more susceptible to weight gain, but also, and more dangerously perhaps, cements us into an unhealthy lifestyle, which could potentially be extremely damaging to our health.

An Evaluation of Popular Diets and Weight Loss Techniques

Designing a means of achieving weight-loss to help shed surplus pounds and devising the 'perfect diet' have become hot topics of discussion in the media today. There is evidence to show that more and more people are developing an interest in finding a short cut to achieve effective weight-loss, and are often willing to spend significant sums of money in an attempt to try the various methods that are advertised or promoted by the media. With the obesity epidemic to their left and the prevailing fetish for ultra-thinness to their right, it is only natural that people are concerned about their weight. In the fast-moving world that we live in today many people cannot find the time, or do not wish to make the time to increase their energy expenditure through regular exercise as a method of losing weight. For this reason, many people choose to modify the other variable in the energy balance equation (see panel) by reducing the energy they consume in an attempt to lose weight. It appears that over the past few decades an increasing amount of emphasis has been placed on body image and physical appearance in the fashion, music and film industries.

In newspapers and magazines, many celebrities have publicly revealed the secrets of their success in achieving effective weight-loss and in doing so have encouraged the general public to subscribe to similar dietary regimes. It is important, however, to understand that not all of these diets are necessarily beneficial to our health and some are even potentially damaging. Below we examine the theory behind some of the dietary methods that are currently popular and assess their relative advantages and drawbacks in terms of palatability, ease of application and potential effectiveness.

High Protien Diet

The theory behind this method is that protein intake should be increased almost twofold (to up to 30% of total calories) and the amount of carbohydrates and fats consumed should be reduced. There are many variations on this diet, including the very popular "low-carb" diet. According to this theory, consuming a large amount of carbohydrate blocks calorie and fat utilisation as it stimulates insulin release into the bloodstream (insulin is known as the fat-promoting hormone owing to its role in metabolism).

Evaluation - This diet appears to go against all current theories about the importance of eating carbohydrates in order to achieve the right fibre intake. Restricting the amount of fibre consumed is known to cause constipation, bowel problems and even bowel cancer. Another problem is that a diet high in protein can cause damage to the liver and can also lead to excessive excretion of certain vitamins and minerals. Protein molecules contain nitrogen, so when they are burned for energy they leave ammonic, a toxic substance, which has the following effects on the body:

• Increased workload for the liver and kidneys
• Possible exposure of organs to toxic metabolic wastes

Conclusion - Not very easy to incorporate in a busy lifestyle, not particularly palatable and, according to scientific knowledge, not even that healthy!

The Hay Diet (Food Combining)

The theory behind this method is that mixing protein and carbohydrate in the same meal results in an inefficient breakdown of the two fuels. Fruit and vegetables must not be eaten in main meals but must nevertheless form a large part of the diet. Only unrefined, wholegrain starches should be eaten, and four hours should elapse between meals. Certain other foods such as milk are also restricted.

Evaluation - The truth of the matter is that protein and carbohydrates are digested differently: the former is broken down in the acid environment of the stomach, while with the latter digestion begins in the mouth and is completed in the more alkaline environment of the small intestine. However there is no grounded scientific evidence to prove that the simultaneous intake of protein and carbohydrate impedes the efficiency with which our body breaks down and digests food. In any case, many of the starchy foods that the diet recommends actually contain a certain amount of protein (grains and potatoes), which goes against the theory.

Conclusion -Very difficult to adhere to this diet fully owing to the complex rules and difficult to incorporate in a modern lifestyle. Not overly palatable, but relatively effective in the short term.

The Low-Fat Diet

Fat is the most calorie-dense nutrient, and this dietary method can therefore be very effective in reducing calorie intake. According to scientific evidence, limiting the amount of fat consumed can also reduce the likelihood of certain related ailments and diseases. From this perspective the 'low-fat diet' is beneficial to overall health. It is important however to ensure that you are taking in the essential fatty acids found in fish oils, olive oil, nuts and seeds and avocados. So, although it is good to cut down on fat intake, it is doubly important to ensure that you distinguish between the good fats and the bad, and do not overly reduce your consumption of the former.

Evaluation - This dietary method is potentially a very healthy one as long as it is mainly saturated fat that is cut out of the diet. Reducing consumption of polyunsaturated and monounsaturated fats may lead to a deficiency in the fat-soluble vitamins A, D, E and K. There is also some evidence to suggest that perhaps the consumption of essential fatty acids may even help to promote weight-loss rather than hinder it.

Conclusion - Relatively easy to incorporate into the routine, and generally a good start to building an overall healthy lifestyle. Scientifically proved to be effective and relatively palatable as long as you allow your palate to adapt over time without giving in to the temptation of sugary, high-fat snacks or fast-foods in the first few weeks of the diet.

The Calorie-Counting Diet

The theory behind this weight-loss technique appears relatively basic: if you monitor your daily calorie intake and keep it below your average daily calorie expenditure (about 2000 calories a day for women and 2500 for men) it seems fair to assume that you will achieve weight-loss.

Evaluation - Unfortunately the flaw in this theory is that it fails to take account of our body's survival mechanism, which copes with frequent variations in food intake. Our metabolic system has two sophisticated mechanisms that govern our weight:

• The speed at which energy is derived from food varies according to the amount of calories consumed. If our body is subjected to a low calorie intake over a certain period of time, it will naturally become more efficient with the calories that it does receive and therefore will not need to burn off fat stores to meet the calorie deficit.
• The body has a set point at which it decides to keep body weight constant. While there are effective methods to shift that set point, calorie counting is not one of them.

Conclusion - This weight-loss technique is not particularly easy to put into practice, as it requires a large amount of time and effort. Although reducing calorie intake can be effective to a certain extent if combined with regular exercise, it must be understood that not all calories are equal. For example, a regular diet of 1200 calories a day will not promote weight-loss if it consists entirely of foods containing saturated fat and refined 'fast sugar' carbohydrates.

The Key to Success

Unfortunately, contrary to popular opinion and media hype, there is no quick and easy short cut to effective weight loss. When embarking on a mission to lose weight, we must ensure that we can do so within our daily routine. The key to success is adopting a plan that is sustainable and easily adaptable to our lifestyle. To lose weight effectively and keep it off, it is essential to treat a new weight-loss regime as a 'way of life' rather than use a crash diet to shed a few pounds. Losing weight is a step-by-step process, and if treated as such should be easy to incorporate in the daily routine. The diet and exercise guidelines, linked below, should be relatively easy to follow, and if the required lifestyle changes are made, will result in effective long-term weight loss while also giving an energy boost that will leave you feeling revitalised.