Introduction

In the context of physical health , weight loss is the process of losing body weight, usually by losing fat. To achieve healthy weight loss, most experts recommend a combination of healthy eating patterns and regular physical exercise .

Obesity is generally a result of a combination of factors:

• Genetic predisposition
• Energy-rich diet
• Limited exercise and sedentary lifestyle
• Underlying illness (e.g. hypothyroidism )
• An eating disorder (such as binge eating disorder )
• Stressful mentality (debated)
• Insufficient sleeping (debated)

Although there is no definitive explanation for the recent epidemic of obesity, the evolutionary hypothesis comes closest to providing some understanding of this phenomenon. In times when food was scarce, the ability to take advantage of rare periods of abundance and use such abundance by storing energy efficiently was undoubtedly an evolutionary advantage. This is precisely the opposite of what is required in a sedentary society, where high-energy food is available in abundant quantities in the context of decreased exercise. Although many people may have a genetic propensity towards obesity, it is only with the reduction in physical activity and a move towards high-calorie diets of modern society that it has become widespread. Significant proportions (up to 30%) of the population in wealthy countries are now obese, and seen to be at risk of ill health .

The number of calories you eat and the number of calories you use each day control your body weight. So to lose weight, you need to take in fewer calories than you use. You can do this by becoming more physically active, by eating less or both. Your weight loss program should also help you make changes that you can maintain for the rest of your life.

Are you overweight?

The most common way to decide if you are overweight is to determine your Body Mass Index (BMI). The BMI looks at how much you should weigh based on your height. It is a relative comparison of the proportion of fat versus lean in your body.

You can determine your BMI by using the following formula: 1.Divide your weight (in pounds) by your height (in inches) squared 2.Multiply the results of Step 1 by 705. For example, if you are 5'3'' (63 inches) and weigh 138 pounds, the equation looks like this: BMI=(138/(63x63)) x705=24.5

A person with a BMI over 25.0 kg / m 2 is considered overweight ; a BMI over 30.0 kg/m 2 is considered obese. A further threshold at 40.0 kg/m 2 is identified as urgent morbidity risk. The American Institute for Cancer Research considers a BMI between 18.5 and 25 to be an ideal target for a healthy individual (although several sources consider a person with a BMI of less than 20 to be underweight ). The BMI was created in the 19th century by the Belgian statistician Adolphe Quetelet . The cut-off points between categories are occasionally redefined, and may differ from country to country. In June 1998 the NIH brought official US category definitions into line with those used by the WHO , moving the American 'overweight' threshold from BMI 27 to BMI 25. About 30,000,000 Americans moved from "ideal" weight to being 1–10 pounds (0.5–5 kg) "overweight" as a result.