Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have a negative effect on health. Obesity increases the likelihood of various diseases and conditions. particularly cardiovascular diseases, type 2 diabetes, obstructive sleep apnea, certain types of cancer, osteoarthritis, and depression. Obesity is most commonly caused by a combination of excessive food intake, lack of physical activity, and genetic susceptibility. A few cases are caused primarily by genes, endocrine disorders, medications, or mental disorder.
The view that obese people eat little yet gain weight due to a slow metabolism is not medically supported.
On average, obese people have a greater energy expenditure than their normal counterparts due to the energy required to maintain an increased body mass. Obesity is mostly preventable through a combination of social changes and personal choices. If diet, exercise, and medication are not effective, a gastric bypass or surgery may be performed to reduce stomach volume or length of the intestines, leading to feeling full earlier or a reduced ability to absorb nutrients from food.
Obesity is a leading preventable cause of death worldwide, with increasing rates in adults and children. In 2015, 600 million adults and 100 millionchildren were obese in 195 countries. Authorities view it as one of the most serious public health problems of the 21st century.
Obesity is stigmatized in much of the modern world, though it was seen as a symbol of wealth and fertility at other times in history and still is in some parts of the 2013, the American Medical Association classified obesity as a diseased world.
Classification and BMIObesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health It is defined by body mass index and further evaluated in terms of fat distribution is the waist-hip ratio and total cardiovascular risk factors. BMI is closely related to both percentage body fat and total body fat. In children, a healthy weight varies with age and sex Obesity in children and adolescents is defined not as an absolute number but in relation to a historical normal group, such that obesity is a BMI greater than the 95th percentile. The reference data on which these percentiles were based date from 1963 to 1994. and have not been affected by the recent increases in weight. BMI is defined as the subjects’ weight divided by the square of their height and is calculated as follows. BMI is usually expressed in kilograms of weight per meter squared of height. To convert from pounds per inch squared multiply byThe most commonly used definitions, established by the World Health Organization in 1997 and published in 2000, provide the values listed in the table.
Some modifications to the WHO definitions have been made by particular organizations.Any BMI 35 or 40 kg/m2 is severe obesity.A BMI of 35 kg/m2 and experiencing obesity-related health conditions or 240-44.9 kg/m2 is morbid obesity.A BMI of 45 or 50 kg/m2 is super obesity As Asian populations develop negative health consequences at a lower BMI than Caucasians, some nations have redefined obesity, Japan has defined obesity as any BMI greater than 25 kg/m2.Effects on healthExcessive body weight is associated with various diseases and conditions, particularly cardiovascular diseases, diabetes mellitus type 2, obstructive sleep apnea, certain types of cancer, osteoarthritis. A number of reviews have found that mortality risk is lowest at a BMI of 20-25 kg. This appears to apply in at least four continents.
In contrast, a 2013 review found that grade 1 obesity was not associated with higher mortality than normal weight, and that overweight was associated with lower” mortality than was normal weight. Other evidence suggests that the association of BMI and waist circumference with mortality is U. or J-shaped, while the association between waist-to-hip ratio and waist-to-height ratio with mortality is morepositive. In Asians, the risk of negative health effects begins to increase between 22-25 kg m2 A BMI above 32 kg m2 has been associated with a doubled mortality rate among women over a 16-year period. In the United States, obesity is estimated to cause 111.909 to 365,000 deaths per year.
On average, obesity reduces life expectancy by six to seven years, a BMT of 30-35 kg m2 reduces life expectancy by two to four years.Complications are either directly caused by obesity or indirectly related through mechanisms sharing a common cause such as a poor diet or a sedentary lifestyle. The strength of the link between obesity and specific conditions varies. One of the strongest is the link with type 2 diabetes. Excess body fat underlies 64% of cases of diabetes in men and 77% of cases in womenHealth consequences fall into two broad categories: those attributable to the effects of increased fat mass and those due to the increased number of fat cells. Increases in body fat alter the body’s response to insulin, potentially leading to insulin resistance. Increased fat also creates a pro-inflammatory.Survival paradoxAlthough the negative health consequences of obesity in the general population are well supported by the available evidence, health outcomes in certain subgroups seem to be improved at an increased BMI, a phenomenon known as the obesity survival paradox.
The paradox was first described in 1999 in overweight and obese people undergoing hemodialysisIn people with heart failure, those with a BMI between 30.0 and 34 9 had lower mortality than those with a normal weight. This has been attributed to the fact that people often lose weight as they become progressively more ill Similar findings have been made in other types of heart disease. People with class I obesity and heart disease do not have greater rates of further heart problems than people of normal weight who also have heart disease. In people with greater degrees of obesity, however, the risk of further cardiovascular events is increased Even after cardiac bypass surgery, no increase in mortality is seen in the overweight and obese. One study found that the improved survival could be explained by the more aggressive treatment obesepeople receive after a cardiac event Another found that if one takes into account chronic obstructive pulmonary disease in those with PAD.
A 2006 review identified ten other possible contributors to the recent increase of obesity insufficient sleep, endocrine disruptors, decreased variability in ambient temperature, decreased rates of smoking, because smoking suppresses appetite, increased use of medications that can cause weight gain, proportional increases in ethnic and age groups that tend to be heavier, pregnancy at a later age, epigenetic risk factors passed on generationally, natural selection for higher BMI, and assortative mating leading to increased concentration of obesity risk factors. While there is evidence supporting the influence of these mechanisms on the increased prevalence of obesity, the evidence is still inconclusive, and the authors statethat these are probably less influential than the ones discussed in the previous paragraph.
Map of dietary energy availability per person per day in 1961 and 2001-2003 Dietary energy supply per capita varies markedly between different regions and countries. It has also changed significantly over time. Total food energy consumption has been found to be related to obesity.The widespread availability of nutritional guidelines has done little to address the problems of overeating and poor dietary choice. From 1971 to 2000, obesity rates in the United States increased from 14.5% to 30.9% During the same period, an increase occurred in the average amount of food energy consumed. For women, the average increase was per day, while for men the average increase was per day. Most of this extra food energy came from an increase in carbohydrate consumption rather than fat consumption. The primary sources of these extra carbohydrates are sweetened beverages, which now account for almost 25 percent of daily food energy in young adults in America. Consumption of sweetened drinks such as soft drinks, fruit drinks, iced tea, and energy and vitamin water drinks is believed to be contributing to the rising rates of obesity and to an increased risk of metabolic syndrome and type 2 diabetes Vitamin D deficiency is related to diseases associated with obesity.
As societies become increasingly reliant on energy dense, big portions, and fast-food meals, the association between fast-food consumption and obesity becomes more concerning. In the United States consumption of fast-food meals tripled and food energy intake from these meals quadrupled between 1977 and 1995.Agricultural policy and techniques in the United States and Europe have led to lower food prices. In the United States, subsidization of corn, soy,wheat, and rice through the U.S. farm bill has made the main sources of processed food cheap compared to fruits and vegetables. Calorie count laws and nutrition facts labels attempt to steer people toward making healthier food choices, including awareness of how much food energy is being consumed. Obese people consistently under-report their food consumption as compared to people of normal weight. This is supported both by tests of people carried out in a calorimeter room and by direct observation.
A sedentary lifestyle plays a significant role in obesity. Worldwide there has been a large shift towards less physically demanding work, and currently, at least 30% of the world’s population gets insufficient exercise. World trends in active leisure time physical activity are less clear The World Health organization indicates people worldwide are taking up less active recreational pursuits, while a study from Finland found an increase and a study from the United States found leisure-time physical activity has not changed significantly. A 2011 review of physical activity In children found that it may not be a significant contributor.In both children and adults, there is an association between television viewing time and the risk of obesity. A review found 63 of 73 studies showed an increased rate of childhood obesity with increased media exposure, with rates increasing proportionally to time spent watching television.
Like many other medical conditions, obesity is the result of an interplay between genetic and environmental factors. Polymorphisms in various genes controlling appetite and metabolism predispose to obesity when sufficient food energy is present. As of 2006, more than 41 of these sites on the human genome have been linked to the development of obesity when a favorable environment is present. People with two copies of the FTO gene have been found on average to weigh 3-4 kg more and have a 1.67-fold greater risk of obesity compared with those without the risk allele. The differences in BMI between people that are due to genetics varies depending on the population examined from 6% to 85%. Obesity is a major feature in several syndromes, such as Prader-Willi syndrome, Bardet-Biedl syndrome, Cohen syndrome, and MOMO syndrome. In people with early-onset severe obesity, 7% harbor a single point DNA mutation. Studies that have focused on inheritance patterns rather than on specific genes have found that 80% of the offspring of two obese parents were also obese, in contrast to less than 10% of the offspring of two parents who were of normal weight. Different people exposed to the same environment havedifferent risks of obesity due to their underlying genetics.The thrifty gene hypothesis postulates that due to dietary scarcity during human evolution, people are prone to obesity. Their ability to take advantage of rare periods of abundance by storing energy as fat would be advantageous during times of varying food availability, and individuals with greater adipose reserves would be more likely to survive famine. This tendency to store fat, however, would be maladaptive in societies with stable food supplies. This theory has received various criticisms, and other evolutionarily based theories such as the drifty gene hypothesis and the thrifty phenotype hypothesis have also been proposed.
Certain physical and mental illnesses and the pharmaceutical substances used to treat them can increase the risk of obesity. Medical illnesses that increase obesity risk include several rare genetic syndromes as well as some congenital or acquired conditions hypothyroidism Cushing’s syndrome, growth hormone deficiency, and the eating disorders: binge eating disorder and night eating syndrome. The risk of overweight and obesity is higher in patients with psychiatric disorders than in persons without psychiatric disorders.
Certain medications may cause weight gain or changes in body composition, these include insulin sulfonylureas, thiazolidinediones, atypical antipsychotics, antidepressants, steroids, certain consultants, protein, and some forms of hormonal contraception. Though it is accepted that energy consumption in excess of energy expenditure leads to obesity on an individual basis, the cause of the shifts in these two factors on the societal is much debated. There are a number of theories as to the cause but most believe it is a combination of various factors.The correlation between social class and BMI varies globally. A review in 1989 found that in developed countries women of a high social class were less likely to be obese. No significant differences were seen among men of different social classes. In the developing world, women, men, and children from high social classes had greater rates of obesity. An update of this review carried out in 2007 found the same relationships, but they were weaker. The decrease in strength of correlation was felt to be due to the effects of globalization. Among developed countries, levels of adult obesity, and percentage of teenage children who are overweight are correlated with income inequality. A similar relationship is seen among US states: more adults, even in higher social classes, are obese in more unequal states.
Many explanations have been put forth for associations between BMI and social class. It is thought that in developed countries, the wealthy are able to afford more nutritious food, they are under greater social pressure to remain slim, and have more opportunities along with greater expectations for physical fitness. In undeveloped countries, the ability to afford food, high energy expenditure with physical labor, and cultural values favoring a larger body size are believed to contribute to the observed patterns. Stress and perceived low social status appear to increase the risk of obesity. Smoking has a significant effect on an individual’s weight. Those who quit smoking gain an average of 44 kilograms for men and 50 kilograms forwomen over ten years. However, changing rates of smoking have had little effect on the overall rates of obesity. In the United States, the number of children a person has is related to their risk of obesity.
A woman’s risk increases by 7% per child, while a man’s risk increases by 4 per child. This could be partly explained by the fact that having dependent children decreases physical activity in Western parents. In the developing world, urbanization is playing a role in increasing the rate of obesity In China overall rates of obesity are below 5%, however, in some cities rates of obesity are greater than 20%. Malnutrition in early life is believed to play a role in the rising rates of obesity in the developing world Endocrine changes that occur during periods malnutrition may promote the storage of fat once more food energy becomes available. Whether obesity causes cognitive deficits or vice versa is unclear at present. Gut bacteriaThe study of the effect of infectious agents on metabolism is still in its early stages. Gut flora has been shown to differ between lean and obese humans. There is an indication that gut flora in obese and lean individuals can affect the metabolic potential. This apparent alteration of the metabolic potential is believed to confer a greater capacity to harvest energy contributing to obesity. Whether these differences are the direct cause or the result of obesity has yet to be determined unequivocally.
The use of antibiotics among children has also been associated with obesity later in life. An association between viruses and obesity has been found in humans and several different animal species. The amount that these associations mayhave contributed to the rising rate of obesity is yet to be determined.A number of reviews have found an association between short duration of sleep and obesity. Whether one causes the other is unclear Certain aspects of personality are associated with being obese, Neuroticism, impulsivity, and sensitivity to reward are more common in people who areobese while conscientiousness and self-control are less common in people who are obesePathophysiologyThere are many possible pathophysiological mechanisms involved in the development and maintenance of obesity. This field of research had been almost unapproached until Friedman’s laboratory. While leptin and ghrelin are produced peripherally, almost unapproached until the leptin gene was discovered in 1994. In particular other appetite-related hormones act on the hypothalamus, a region of the brain central to the regulation of food intake and energy expenditure There are several circuits within the hypothalamus that contribute to its role in integrating appetite, the melanocortin pathway being the most well understood. The arcuate nucleus contains two distinct groups of neurons. Obesity is a public health and policy problem because of its prevalence, costs, and health effects.
The United States Preventive Services Task. Recommends screening for all adults followed by behavioral interventions in those who are obese. Public health efforts seek to understand and correct the environmental factors responsible for the increasing prevalence of obesity in the population Solutions look at changing the factors that cause excess food energy consumption and inhibit physical activity. Efforts include federally reimbursed meal programs in schools, limiting direct junk food marketing to children, and decreasing access to sugar-sweetened beverages in schools. The World Health Organization recommends the taxing of sugary drinks. When constructing urban environments, efforts have been made to increase access to parks and to develop pedestrian routes.