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| Obesity The number of people who are obese is rising rapidly throughout the world, making obesity one of the fastest developing public health problems in the Western world. The World Health Organisation (WHO) has described the problem of obesity as a "worldwide epidemic". It is estimated that around 250 million people worldwide are obese, about 7% of the adult population. An Obese Person Is:
The Body Mass Index The Body Mass Index calculation provides doctors with the ability to classify obesity. Anybody with a BMI of over 35 greatly increases his or her risks of developing co-morbidities (diseases directly linked or caused by being obese). This includes diabetes, arthritis, heart disease and some forms of cancer. Reducing weight by even 5 BMI points significantly reduces these risks. The ideal BMI for any person is 25, which may be a target out of reach for many obese people but the challenge is to find a treatment that brings a permanent significant reduction in BMI. Obesity often develops in a "yo-yo" pattern as patients go through non-surgical weight loss programmes losing weight and then regain it after the programme has finished. Studies have shown that for treating morbid obesity (BMI greater than 35) conventional non-surgical weight loss regimes have little chance of success. Surgery has been successful over the years and involves altering the anatomy of the stomach and intestine to reduce intake and absorption of food. Results are good in terms of sustained weight loss but some side effects can occur such as persistent diarrhoea, vitamin deficiencies and the surgical alterations breaking down. These procedures have been performed for over 15 years and are mainly performed via a laparotomy (opening the abdomen surgically). Historically, obesity was associated with affluence and this is still the case across societies. Within developing countries such as India, Africa and South America, obesity is a particular problem amongst the recently affluent classes, where being overweight is seen as a sign of prosperity. However, in developed countries there is an inverse relationship between obesity and social class, with a much greater proportion of obese people in the lower social classes than in professional groups. How obesity develops Obesity develops gradually over a period of time as weight is gained. Weight gain occurs when the amount of energy (calories) consumed as food and drink exceeds the energy, which is used for exercise and other metabolic processes of the body. This is known as positive energy balance. The excess energy is stored principally as fat. Each kilogram of fat stores approximately 9000kcal. This fat can only be lost when the body requires more energy than is available from food and thus draws upon its energy stores. This is known as negative energy balance. Energy balance Energy balance is tightly regulated in most people and does not usually require conscious control. A change in life circumstances that altars either the diet (and thus energy intake) or activity (and thus energy expenditure) can lead to weight gain or loss. It is often difficult to identify these changes as only a small imbalance can lead gradually, but perceptibly, to changes in body weight and fatness. Obesity is a condition of excess fat. In the short term, small fluctuations in body weight can result from fluid retention or loss. Changes in body weight of 1 - 2 kg can be explained by short-term changes in the body's water and glycogen (carbohydrate) stores. During the early days of weight loss the body burns its glycogen stores. Since each gram of glycogen binds with 3 g of water, there is a proportionally large decrease in weight relative to the energy imbalance. Conversely, following a period of energy restriction, a large meal will refill these glycogen stores plus the water associated with them. This apparent rebound in weight after a period of weight loss can be very disheartening but is a necessary part of establishing the normal physiological equilibrium. Energy Intake Many people are familiar with counting calories (or joules, which is the metric term for calories). The calorie is the unit used to describe the energy content of food and drinks. Recommended energy intakes change with age and lifestyle but are approximately 2000 - 2500 kcal per day for women and 2500 - 3000 kcal for men. When counting calories it is easy to forget just how much we eat - studies have shown that some people, when asked to keep a record of what they eat and drink, under-report their intake by nearly 1000 kcal per day. It is clear that more and more food is now being consumed outside the home and this makes it more difficult to collect accurate records of the exact types and amounts of food eaten. The proportion of fat in the diet has increased dramatically since the Second World War and most obesity experts agree that this is partly to blame for the increasing prevalence of obesity. Resting Metabolic Rate (RMR) The amount of energy we use up can also be measured in calories. Even if we stayed in bed all day we would still need to use large amounts of energy just to maintain the body’s normal functions. This energy is called resting metabolic rate and is analogous to the fuel used by a car when the engine is idling but the car isn't moving. Based on gender, age and weight, it is possible to predict an individual’s RMR to within about 10%. Men have a higher RMR (due to their greater muscle mass) than women, and it decreases slightly with age in both sexes. Body weight is the main determinant of RMR. The heavier a person is, the higher there RMR. It is a fallacy that overweight and obese people have a low metabolic rate. In fact their RMR is higher than that of lighter people as the heart, liver and other vital organs are bigger and need more energy to function. For example, a 40 year old woman weighing 60 kg will have a RMR of about 1340 kcal per day whereas a 100 kg woman will burn off 1660 kcal, an extra 24%. In general, an increase in weight will produce an increase in daily energy expenditure of about 12 kcal/kg in women and 16 kcal/kg in men. Back to top Thermo genesis Small additional amounts of energy (around 10% of the total energy expenditure) are used to keep us warm, to digest food and in response to stress. This is called thermo genesis. Some evidence suggests that obese people may have lower levels of thermo genesis than thin people but any difference is very small. Over the years, there has been much discussion about brown fat or "Brown Aadipose Tissue" (BAT). In small mammals (including human infants) this has been found to dissipate the energy derived from food as heat and is an important part of the thermoregulation system. It has been suggested that lean people may have more BAT than those who are obese, and are able to burn off any extra energy, which is consumed, a process known as luxus consumption. However, studies have shown that when overfed under controlled conditions, lean and obese subjects gained weight at the same rate. Today, the consensus of evidence is that, in adult humans, BAT activity is quantitatively unimportant in terms of total energy expenditure. Physical Activity In most people, RMR accounts for between a half and three quarters of the energy required each day. Much of the remainder is used in physical activity. This includes all physical activity over and above lying in bed, such as housework, walking, gardening and so on. Work, sport and other energetic exercise will also contribute to overall energy expenditure. However, for a similar task, an obese person will spend more energy than a lean person since it costs more in energy terms to move a heavy body compared to a light one. Over the last twenty years or so the energy that we use in physical activity has decreased markedly. Cars and buses have replaced walking and cycling, manual occupations have been phased out in favour of office based jobs and almost every household task is now aided by a labour saving device of some sort. Perhaps most importantly, TV viewing now plays an increasing part in our lives. The average adult watches over 26 hours of TV each week - an almost totally sedentary activity. Low levels of physical activity are part of the explanation for the rise in obesity and other forms of ill health. Since it is difficult to change resting metabolic rate it follows that increasing physical activity is the best way of increasing total energy expenditure. Energy Balance and Obesity Weight gain results from positive energy balance where more energy is consumed than expended and the excess is then stored, mainly as fat. This is sometimes called the dynamic phase of obesity. However, as weight increases, the energy requirements of the body also increase. If energy intake remains the same, the body will gradually return to energy balance, albeit at a higher level of intake and expenditure. Most obese people are in energy balance for most of the time. Although they are heavier and have more fat than is desirable for good health, their weight is stable and no longer increasing. This is sometimes referred to as the static phase of obesity. For an obese person to lose weight, they must achieve a state of negative energy balance, either by eating less or using up more energy. To maintain weight loss, a permanently lower energy intake and/or higher level of energy expenditure must be maintained life-long since the reduced-weight body requires and uses less energy. Unfortunately, it seems that many or all of the body's physiological controls serve to defend weight and diminish weight loss. In evolutionary terms, the imperative is to store fat for times of food shortage. It appears that the drive to eat has a much stronger physiological basis than the signals, which indicate fullness. This is sometimes described as the 'asymmetry of appetite'. It helps to explain why weight loss and weight loss maintenance are so hard to achieve. Diet Modification Whether you are trying to lose weight or maintain your weight, you must improve your eating habits. Eat a variety of foods, especially pasta, rice, wholemeal bread, and other whole-grain foods. Reduce your fat- intake. You should also eat lots of fresh fruits and vegetables. Exercise Plan Making physical activity a part of your daily life is an important way to help control your weight. Try to do at least 30 minutes of physical activity a day on most days of the week. The activity does not have to be done all at once. It can be done in stages: 10 minutes here, 20 minutes there, providing it adds up to 30 minutes a day. Little and often, seems to be the key. Back to top |
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