Obesity may be defined as an abnormal excess deposition of fat in the body. Obesity is caused due to increased size (hypertrophy) or increased number (hyperplasia) of adipocytes or both.
Obesity is the major cause of overweight. Obesity & overweight according to reference height-weight table have to be carefully reviewed in terms of the lean body mass and body muscle to fat.
An athlete will have highly developed muscle mass and therefore may be overweight according to reference height – weight table.
But athletes body has more muscle mass than fat in proportion. Therefore, obesity is not only a matter of weight. One must be able to distinguish between weight due to well developed muscle mass (athletes) and due to excessive fat deposition.
In simple words, overweight is usually due to obesity but also can arise due to excess muscle development. It can also be caused due to abnormal fluid retention.
Obesity refers to an excess of body fat. In healthy individuals, body fat accounts for approximately 25% of body weight in women and 18% in men.
Overweight refers to weight above some reference norm, typically standards derived from actuarial or epidemiological data. In most cases, increasing weight reflects increasing obesity.
Body mass index (BMI) is calculated by dividing weight in kilograms by height in meters squared.
Although there is debate about the ideal BMI, it is generally thought that a BMI of 20 to 25 kg² represents healthy weight,
A BMI of 25 to 27 kg2 is associated with somewhat elevated risk,
A BMI above 27 kg/m² represents clearly increased risk, and a BMI above 30 kg/m² carries greatly increased risk.
In the United States, over 50% of the population is overweight (defined as a BMI of 25.0 to 29.9 kg/m²), whereas 30% are obese (defined as a BMI >30 kg/m²).
Extreme obesity (BMI ≥40 kg/m²) is found in about 3% of men and 7% of women.
The prevalence of obesity is highest in minority populations, particularly among non-Hispanic black women.
More than one half of these individuals 40 years of age or older are obese and more than 80% are overweight.
The prevalence of overweight and obesity in children and adolescents in the United States has also increased substantially.
About 18% of adolescents and about 10% of 2 to 5-year-olds are overweight.
Causes of Obesity
Obesity results from a chronic imbalance between energy intake and energy expenditure. Major contributing factors are excessive calorie consumption more than the body need and / or lack of physical activity.
Genetic (hereditary) factors also contribute to the condition.
Obesity can also result from hormonal disorders like hypothyroidism, hypogonadism, Cushing’s syndrome and hypopituitarism.
Persons accumulate fat by eating more calories than are expended as energy, thus intake of energy exceeds its dissipation.
If fat is to be removed from the body, fewer calories must be put in or more calories must be taken out than are put in.
An error of no more than 10% in either intake or output would lead to a 30-pound change in body weight in 1 year’s time.
Satiety. The feeling that results when hunger is satisfied is satiety. A metabolic signal derived from food receptor cells, probably in thehypothalamus, produce satiety.
Studies have shown evidence for dysfuntion in serotonin, dopamine, and norepinephrine involvement in reguleing eating behavior through the hypothalamus.
Other hormonal fact that may be involved include corticotrophin releasing factor, neuropetide Y, gonadotropin-releasing hormone, and thyroid-stimulating hormone.
A new substance, obestatin, made in the stomach, is a hormone that, in animal experiments, produces satiety and may have potential as a weight-loss agent in humans.
Eating is also affected by cannabinoid receptors, which, when stim lated, increases appetite.
Olfactory system. The olfactory system may play a role in satiety. Expreiments have shown that strong stimulation of the olfactory bulbs in the nose with food odors by use of an inhaler saturated with a particular sm produces satiety for that food. This may have implications for t obesity. therapy
Factors that Contribute to Obesity
About 80% of patients who are obese have a fam history of obesity, although no specific genetic marker of obesity been found.
Studies show that identical twins raised apart can both be obese, an observation that suggests a hereditary role.
Obesity that begins early in life is characterized by adipose tissue with an increased number of adipocytes (fat cells) of increased size.
Obesity that begins in adult life, on the other hand, results solely increase in the size of the adipocytes. In both instances, weight reduction produces a decrease in cell size.
Physical activity factors.
The marked decrease in physical activity affluent societies seems to be the major factor in the rise of obesity a public health problem.
Physical inactivity restricts energy expe ture and may contribute to increased food intake. Although food inta increases with increasing energy expenditure over a wide range of energy demands, intake does not decrease proportionately when physical activ falls below a certain minimum level.
Psychological factors. Although psychological factors are evidently crucial to the development of obesity, how such psychological factors result in obesity is not known.
In only a small number of cases of obesity, the consequence is identifiable illness.
Such cases include a variety of rare genetic disorders, such as Prader-Willi syndrome, as well as neuroendocrine abnormal ities.
Hypothalamic obesity results from damage to the ventromedial region of the hypothalamus (VMH), which has been studied exten sively in laboratory animals and is a known center of appetite and weight regulation.
In humans, damage to the VMH may result from trauma, surgery, malignancy, or inflammatory disease.
Some forms of depression, particularly seasonal affective disorder, are associated with weight gain.
Most persons who live in seasonal climates report increases in appetite and weight during the fall and winter months, with decreases in the spring and summer. Depressed patients usually lose weight, but some gain weight.
A variety of clinical disorders are associated with obesity. Cushing’s disease is associated with a characteristic fat distri bution and moonlike face.
Myxedema is associated with weight gain, although not invariably.
Psychotropic drugs. Long-term use of steroid medications is associated with significant weight gain, as is the use of several psychotropic agents.
Patients treated for major depression, psychotic disturbances, and bipolar disorder typically gain 3 to 10 kg, with even larger gains with chronic use. This can produce the so-called metabolic syndrome.
Obesity has adverse effects on health and is associated with a broad range of illnesses. There is a strong correlation between obesity a cardiovascular disorders.
Hypertension (blood pressure > 160/95 Hg) is three times higher for persons who are overweight, and hypholesterolemia (blood cholesterol >250 mg/dL) is twice as common.
The recovery for weight reduction is poor, and the course of obesity tends toward inexorable progression. Of patients who lose significant amounts of weight, 90% regain it eventually.
The recovery is particularly poor for those who become obese in childhood.
Juvenile-onset obesity tends to be more severe, more resistant to treament, and more likely to be associated with emotional disturbance then is adult obesity.
Complications of obesity
Obese persons are more prone to diabetes mellitus (Type II), coronary heart disease (like artherosclerosis, hypertension) and conditions like fungal infection etc.
The basis of weight reduction is simple-establish a caloric deficit by bringing intake below output. The simplest way to reduce caloric intake is by means of a low-calorie diet.
The best long-term effects are achieved with a balanced diet that contains readily available foods, For most persons, the most satisfactory reducing diet consists of their usual foods in amounts determined with the aid of tables of food values that are available in standard books on dieting.
Such a diet gives the best chance of long-term maintenance of weight loss.
Total unmodified fasts are used for short-term weight loss, but they have associated morbidity including orthostatic hypotension, sodium diuresis, and impaired nitrogen balance
Ketogenic diets are high-protein, high-fat diets used to promote weight loss. They have a high cholesterol content and produce ketosis, which is associated with nausea, hypotension, and lethargy.
In general, the best method of weight loss is a balanced diet of 1,100 to 1.200 calories. Such a diet can be followed for long periods but should be supplemented with vitamins, particularly iron, folic acid, zinc, and vitamin B.
1- Increased physical activity is an important part of a weight-reduction regimen. Because caloric expenditure in most forms of physical activ ity is directly proportional to body weight, obese persons expend more calories than persons of normal weight with the same amount of activity.
2. Increased physical activity may actually decrease food intake by formerly sedentary persons. This combination of increased caloric expenditure and decreased food intake makes an increase in physical activity a highly desirable feature of any weight-reduction program.
3. Exercise also helps maintain weight loss.