According to 2007 statistics from the World Health Organization (WHO), Australia has the third-highest prevalence of overweight adults in the English-speaking world.Obesity in Australia is an "epidemic" with "increasing frequency." "The Medical Journal of Australia" found that obesity in Australia more than doubled in the two decades preceding 2003, and the unprecedented rise in obesity has been compared to the same health crisis in America. The rise in obesity has been attributed to poor eating habits in the country closely related to the availability of fast food since the 1970s, sedentary lifestyles and a decrease in the labour workforce.

Obesity in Mexico is a relatively recent phenomenon, having been widespread since the 1980s with the introduction of processed food into much of the Mexican food market. Prior to that, dietary issues were limited to under and malnutrition, which is still a problem in various parts of the country. Following trends already ongoing in other parts of the world, Mexicans have been foregoing traditional whole grains and vegetables in favor of a diet with more animal products, more fat, and more sugar much of which is a consequence of processed food. It has seen dietary energy intake and rates of overweight and obese people rise with seven out of ten at least overweight and a third clinically obese.

The degree to which a person is overweight is generally described by the body mass index (BMI). "Overweight" is defined as a BMI of 25 or more, thus it includes pre-obesity defined as a BMI between 25 and 30 and obesity as defined by a BMI of 30 or more. Pre-obese and overweight however are often used interchangeably, thus giving overweight a common definition of a BMI of between 25–30. There are, however, several other common ways to measure the amount of adiposity or fat present in an individual's body.

- Body mass index

- Body volume index

- Simple weighing

- Skinfold calipers or "pinch test"

- Bioelectrical impedance analysis

- Hydrostatic weighing

- Dual-energy X-ray absorptiometry (DEXA)

The most common method for discussing this subject and the one used primarily by researchers and advisory institutions is BMI. Definitions of what is considered overweight vary by ethnicity. The current definition proposed by the US National Institutes of Health (NIH) and the World Health Organization (WHO) designates whites, Hispanics and blacks with a BMI of 25 or more as overweight. For Asians, overweight is a BMI between 23 and 29.9 and obesity for all groups is a BMI of 30 or more.

BMI, however, does not account extremes of muscle mass, some rare genetic factors, the very young, and a few other individual variations. Thus it is possible for an individuals with a BMI of less than 25 to have excess body fat, while others may have a BMI that is significantly higher without falling into this category. Some of the above methods for determining body fat are more accurate than BMI but come with added complexity.

If an individual is overweight and has excess body fat it can create or lead to health risks. Reports are surfacing, however, that being mildly overweight to slightly obese – BMI being between 24 and 31.9 – may be actually beneficial and that people with a BMI between 24 and 31.9 could actually live longer than normal weight or underweight persons.

Obesity in Greece is a growing health concern with health officials stating that it is one of the leading causes of preventable deaths in Greece.

Obesity in North Africa and the Middle East is a notable health issue. In 2005, the World Health Organization measured that 1.6 billion people were overweight and 400 million were obese. It estimates that by the year 2015, 2.3 billion people will be overweight and 700 million will be obese. The Middle East, including the Arabian Peninsula, Eastern Mediterranean, Turkey and Iran, and North Africa, are no exception to the worldwide increase in obesity. Subsequently, some call this trend the New World Syndrome. The lifestyle changes associated with the discovery of oil and the subsequent increase in wealth is one contributing factor.

Urbanization has occurred rapidly and has been accompanied by new technologies that promote sedentary lifestyles. Due to accessibility of private cars, television, and household appliances, the population as a whole is engaging in less physical activity. The rise in caloric and fat intake in a region where exercise is not a defining part of the culture has added to the overall increased percentages of overweight and obese populations. In addition, women are more likely to be overweight or obese due to cultural norms and perceptions of appropriate female behavior and occupations inside and outside of the home.

The first problems to occur in obese children are usually emotional or psychological. Obese children often experience bullying by their peers. Some are harassed or discriminated against by their own family. Stereotypes abound and may lead to low self-esteem and depression.

Until the late 20th century, dietary issues in Mexico were solely a question of undernutrition or malnutrition, generally because of poverty and distribution issues. For this reason, obesity was associated with wealth and health, the latter especially in children. Despite changes in the Mexican diet and food distribution, malnutrition still remains problematic in various parts of the country.

Body mass index (BMI) is acceptable for determining obesity for children two years of age and older. It is determined by the ratio of weight to height.

The normal range for BMI in children vary with age and sex. While a BMI above the 85th percentile is defined as overweight, a BMI greater than or equal to the 95th percentile is defined as obesity by Centers for Disease Control and Prevention. It has published tables for determining this in children.

The US Preventive Service Task Force reported that not all children with a high BMI need to lose weight though. High BMI can identify a possible weight problem, but does not differentiate between fat or lean tissue. Additionally, BMI may mistakenly rule out some children who do have excess adipose tissue. It is therefore beneficial to supplement the reliability of a BMI diagnosis with additional screening tools such as adipose tissue or skin fold measurements.

Obesity 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 (BMI) and further evaluated in terms of fat distribution via 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 thus have not been affected by the recent increases in weight. BMI is defined as the subject's weight divided by the square of their height and is calculated as follows.

BMI is usually expressed in kilograms per square metre, resulting when weight is measured in kilograms and height in metres. To convert from pounds per square inch multiply by .

The most commonly used definitions, established by the World Health Organization (WHO) 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. The surgical literature breaks down class II and III obesity into further categories whose exact values are still disputed.

- Any BMI ≥ 35 or 40 kg/m is "severe obesity".

- A BMI of ≥ 35 kg/m and experiencing obesity-related health conditions or ≥40–44.9 kg/m is "morbid obesity".

- A BMI of ≥ 45 or 50 kg/m is "super obesity".

As Asian populations develop negative health consequences at a lower BMI than Caucasians, some nations have redefined obesity; Japan have defined obesity as any BMI greater than 25 kg/m while China uses a BMI of greater than 28 kg/m.

Obesity in Germany has been increasingly cited as a major health issue in recent years. The federal government has declared this to be a major issue.

Data released by the World Health Organisation in 2014 showed that while an issue of growing concern, within the European Union, Germany had a lower incidence of overweight and obese adults as a percentage of the total population at 54.8% in comparison with France at 60.7%, Spain at 60.9% or the United Kingdom at 63.4%.

Being overweight is having more body fat than is optimally healthy. Being overweight is especially common where food supplies are plentiful and lifestyles are sedentary.

Excess weight has reached epidemic proportions globally, with more than 1 billion adults being either overweight or obese in 2003. In 2013 this increased to more than 2 billion. Increases have been observed across all age groups.

A healthy body requires a minimum amount of fat for proper functioning of the hormonal, reproductive, and immune systems, as thermal insulation, as shock absorption for sensitive areas, and as energy for future use. But the accumulation of too much storage fat can impair movement, flexibility, and alter the appearance of the body.

Obesity is defined as the excessive accumulation of fat and is predominately caused when there is an energy imbalance between calorie consumption and calorie expenditure. Childhood obesity is becoming an increasing concern worldwide and Australia alone, recognizes that 1 in 4 children are either overweight or obese.

For Australians aged between 4 and 17 years, obesity is a very concerning condition as once gained it is favourably harder to be liberated from. Short-term effects on children can mean a decrease in their psychological well-being (stigmatisation and poor self-esteem) as well as physical deteriorations such as sleep apnea, breathlessness and cardiovascular disease. With an increase risk of adult obesity being associated with childhood obesity there are numerous long-term effects that can ultimately hinder the life expectancy of individuals including the development of serious diseases.

In order to combat the worldwide epidemic of childhood obesity it is imperative that the issue is addressed in its early stages. The main preventative measures to be implemented include increasing physical exercise, dietary knowledge and decreasing sedentary behaviours.

Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have a negative effect on health. People are generally considered obese when their body mass index (BMI), a measurement obtained by dividing a person's weight by the square of the person's height, is over , with the range defined as overweight. Some East Asian countries use lower values. 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 generally 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. Changes to diet and exercising are the main treatments. Diet quality can be improved by reducing the consumption of energy-dense foods, such as those high in fat and sugars, and by increasing the intake of dietary fiber. Medications may be used, along with a suitable diet, to reduce appetite or decrease fat absorption. If diet, exercise, and medication are not effective, a gastric balloon 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 (12%) and 100 million children were obese. Obesity is more common in women than men. 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 (particularly in the Western 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 world. In 2013, the American Medical Association classified obesity as a disease.

Obesity has been observed throughout human history. Many early depictions of the human form in art and sculpture appear obese. However, it was not until the 20th century that obesity became common — so much so that, in 1997, the World Health Organization (WHO) formally recognized obesity as a global epidemic. Obesity is defined as having a body mass index (BMI) greater than or equal to 30 kg/m, and in June 2013 the American Medical Association classified it as a disease, with much controversy.

In countries of the Organisation for Economic Co-operation and Development (OECD), one child out of five is overweight or obese. Once considered a problem only of high-income countries, obesity rates are rising worldwide. Globally, there are now more people who are obese than who are underweight, a trend observed in every region over the world except parts of sub-Saharan Africa and Asia. In 2013, an estimated 2.1 billion adults were overweight, as compared with 857 million in 1980. Of adults who are overweight, 31% are obese. Increases in obesity have been seen most in urban settings.

Since body fat can be measured in several ways, statistics on the epidemiology of obesity vary between sources. While BMI is the most basic and commonly used indicator of obesity, other measures include waist circumference, waist-to-hip ratio, skinfold thicknesses, and bioelectrical impedance. The rate of obesity increases with age at least up to 50 or 60 years old.

The OECD notes that — given the health, economic, and social consequences of obesity — many countries have built multi-stakeholder networks involving civil society and the business sector in order to devise appropriate public health policies and solutions for obesity prevention.

The medical condition of being overweight or obesity is defined as "abnormal or excessive fat accumulation that may impair health". It is measured through the Body Mass Index (BMI), defined as a person's weight, in kilograms, divided by the square of the person's height, in meters. If an individual has a BMI of 25–29, he or she is overweight. Having a BMI of 30 or more means an individual is obese. The greater the BMI, the greater the risk of chronic diseases as a result of obesity. These diseases include cardiovascular diseases, diabetes, musculoskeletal disorders, cancer, and premature death.

Obesity in the United Kingdom is a significant contemporary health concern, with officials stating that it is one of the leading preventable causes of death. In February 2016, Health Secretary Jeremy Hunt described rising rates of childhood obesity as a "national emergency".

Data published as a part of the World Health Organisation (WHO) study in 2014 indicated that 28.1% of adults in the United Kingdom were recognised as clinically obese with a Body Mass Index (BMI) greater than 30. In 2014 62% of adults in England were classified as overweight (a body mass index of 25 or above) or obese, compared to 53% 20 years earlier. More than two-thirds of men and almost six in 10 women are overweight or obese.

Experts have predicted that by the year 2020 one third of the United Kingdom population could be obese. Rising levels of obesity are a major challenge to public health. There are expected to be 11 million more obese adults in the UK by 2030, accruing up to 668,000 additional cases of diabetes mellitus, 461,000 cases of heart disease and stroke, 130,000 cases of cancer, with associated medical costs set to increase by £1.9–2.0B per year by 2030. Adult obesity rates have almost quadrupled in the last 25 years.

For children, data from the Health Survey for England (HSE) conducted in 2014 and examining patterns of overweight and obesity among children aged 2–15, showed that 17% of children were obese and an additional 14% of children were overweight.

Combing three years of data (2012, 2013 and 2014) Public Health England identified Barnsley, South Yorkshire as the local authority with the highest incidence of adult obesity (BMI greater than 30) with 35.1%. Data from the same study revealed that Doncaster, South Yorkshire was the local authority with the highest overall excess weight with 74.8% of adults (16 years and over) with a BMI greater than 25. In previous Public Health England studies based on 2012 data, Tamworth in Staffordshire had been identified as the fattest town in England with a 30.7% obesity rate.

Abdominal obesity, also known as central obesity, is when excessive abdominal fat around the stomach and abdomen has built up to the extent that it is likely to have a negative impact on health. There is a strong correlation between central obesity and cardiovascular disease. Abdominal obesity is not confined only to the elderly and obese subjects. Abdominal obesity has been linked to Alzheimer's disease as well as other metabolic and vascular diseases.

Visceral and central abdominal fat and waist circumference show a strong association with type 2 diabetes.

Visceral fat, also known as organ fat or "intra-abdominal fat", is located inside the peritoneal cavity, packed in between internal organs and torso, as opposed to subcutaneous fat, which is found underneath the skin, and intramuscular fat, which is found interspersed in skeletal muscle. Visceral fat is composed of several adipose depots including mesenteric, epididymal white adipose tissue (EWAT) and perirenal fat. An excess of visceral fat is known as central obesity, the "pot belly" or "beer belly" effect, in which the abdomen protrudes excessively. This body type is also known as "apple shaped", as opposed to "pear shaped", in which fat is deposited on the hips and buttocks.

Researchers first started to focus on abdominal obesity in the 1980s when they realized it had an important connection to cardiovascular disease, diabetes, and dyslipidemia. Abdominal obesity was more closely related with metabolic dysfunctions connected with cardiovascular disease than was general obesity. In the late 1980s and early 1990s insightful and powerful imaging techniques were discovered that would further help advance the understanding of the health risks associated with body fat accumulation. Techniques such as computed tomography and magnetic resonance imaging made it possible to categorize mass of adipose tissue located at the abdominal level into intra-abdominal fat and subcutaneous fat.

Obesity in France is a growing health issue. Obesity in children is growing at a faster rate than obesity in adults.

Based on World Health Organisation (WHO) data published in 2014, 23.9% of French adults (age 18+) were clinically obese with a body mass index (BMI) of 30 or greater. The data showed the incidence of obesity in French women in 2014 was 24.0% and among French men 23.8%. Overall adult obesity rates in France were significantly ahead of the Netherlands at 19.8%, Germany at 20.1% and Italy at 21.0%, but behind the United Kingdom and the United States at 28.1% and 33.7% respectively.

Based on 2014 WHO data, France was ranked as the 122nd fattest country in terms of mean BMI for adults of both sexes, with a mean BMI score of 25.3.

Obesity in the United States has been increasingly cited as a major health issue in recent decades, resulting in diseases such as coronary heart disease that lead to mortality. While many industrialized countries have experienced similar increases, obesity rates in the United States are the highest in the world.

Obesity has continued to grow within the United States. Two of every three American men are considered to be overweight or obese, but the rates for women are far higher. The United States contains one of the highest percentage of obese people in the world. An obese person in America incurs an average of $1,429 more in medical expenses annually. Approximately $147 billion is spent in added medical expenses per year within the United States. This number is suspected to increase approximately $1.24 billion per year until the year 2030.

The United States had the highest rate of obesity within the OECD grouping of large trading economies. From 23% obesity in 1962, estimates have steadily increased. The following statistics comprise adults age 20 and over. The overweight percentages for the overall US population are higher reaching 39.4% in 1997, 44.5% in 2004, 56.6% in 2007, and 63.8% (adults) and 17% (children) in 2008. In 2010, the Centers for Disease Control and Prevention (CDC) reported higher numbers once more, counting 65.7% of American adults as overweight, and 17% of American children, and according to the CDC, 63% of teenage girls become overweight by age 11. In 2013 the Organisation for Economic Co-operation and Development (OECD) found that 57.6% of American citizens were obese. The organization estimates that 3/4 of the American population will likely be overweight or obese by 2020. The latest figures from the CDC as of 2014 show that more than one-third (36.5%) of U.S. adults age 20 and older and 17% of children and adolescents aged 2–19 years were obese. A second study from the National Center for Health Statistics at the CDC showed that 39.6% of US adults age 20 and older were obese as of 2015-2016 (37.9% for men and 41.1% for women).

Obesity has been cited as a contributing factor to approximately 100–400 000 deaths in the United States per year and has increased health care use and expenditures, costing society an estimated $117 billion in direct (preventive, diagnostic, and treatment services related to weight) and indirect (absenteeism, loss of future earnings due to premature death) costs. This exceeds health care costs associated with smoking and accounts for 6% to 12% of national health care expenditures in the United States.

There are various ways of measuring abdominal obesity including:

- Absolute waist circumference (> in men and > in women)

- Waist–hip ratio (the circumference of the waist divided by that of the hips of >0.9 for men and >0.85 for women)

- Waist-to-height ratio

- Sagittal Abdominal Diameter

In those with a BMI under 35, intra-abdominal body fat is related to negative health outcomes independent of total body fat. Intra-abdominal or visceral fat has a particularly strong correlation with cardiovascular disease.

BMI and waist measurements are well recognized ways to characterize obesity. However, waist measurements are not as accurate as BMI measurements. For this reason, it is recommended to use both methods of measurements.

While central obesity can be obvious just by looking at the naked body (see the picture), the severity of central obesity is determined by taking waist and hip measurements. The absolute waist circumference in men and in women) and the waist-hip ratio (>0.9 for men and >0.85 for women) are both used as measures of central obesity. A differential diagnosis includes distinguishing central obesity from ascites and intestinal bloating. In the cohort of 15,000 people participating in the National Health and Nutrition Examination Survey (NHANES III), waist circumference explained obesity-related health risk better than the body mass index (or BMI) when metabolic syndrome was taken as an outcome measure and this difference was statistically significant. In other words, excessive waist circumference appears to be more of a risk factor for metabolic syndrome than BMI. Another measure of central obesity which has shown superiority to BMI in predicting cardiovascular disease risk is the Index of Central Obesity (waist-to-height ratio - WHtR), where a ratio of >=0.5 (i.e. a waist circumference at least half of the individual's height) is predictive of increased risk.

Another diagnosis of obesity is the analysis of intra-abdominal fat having the most risk to one's personal health. The increased amount of fat in this region relates to the higher levels of plasma lipid and lipoproteins as per studies mentioned by Eric Poehlman (1998) review.

An increasing acceptance of the importance of central obesity within the medical profession as an indicator of health risk has led to new developments in obesity diagnosis such as the Body Volume Index, which measures central obesity by measuring a person's body shape and their weight distribution. The effect of abdominal adiposity occurs not just in those who are obese, but also affects people who are non-obese and it also contributes to insulin sensitivity

Obesity in New Zealand has become an important national health concern in recent years, with high numbers of people afflicted in every age and ethnic group. As of June 2008, 26.5% of New Zealanders are obese, a number only surpassed in the English-speaking world by the United States.

Obesity in pets occurs when excessive adipose tissue accumulates in the body, and is generally defined as occurring when an animal's body weight is at least 20% greater than its optimal body weight. Obesity is associated with metabolic and hormonal changes.

Weight gain will occur when an animal is in a positive energy balance, meaning energy provided as calories in the diet exceed calories expended. Evidence suggests that middle-aged cats and dogs, especially those between the ages of 5 and 10, may be at an increased risk of obesity. This is supported by studies showing that as cats age from 2 years to approximately 11.5 years of age their energy requirements decreased. Weight gain will occur if calories from the diet do not decrease with the animal’s energy requirements.

Obesity in pets is usually due to excessive food intake or lack of physical exercise. Owners may view food as a way to reward and treat their pets, which contributes to overfeeding. Pets confined to a house or small yard which are not regularly exercised are more prone to obesity.

The risk of obesity in dogs (but not in cats) is related to whether or not their owners are obese.

In cats, neutering increases the risk of obesity, partly because the alteration in sex hormones after neutering lowers the basal metabolic rate, and partly because neutered cats have a reduced inclination to roam compared to non-neutered cats.

Cardiovascular disease is the principal cause of death in the UAE, constituting 28 percent of total deaths; other major causes are accidents and injuries, malignancies, and congenital anomalies.

Weight is measured by using the Body Mass Index scale (BMI). This is determined by dividing weight in kilograms by height in metres, squared. If someone is overweight their BMI will be at 25 or more. If someone is obese their BMI will be at 30 or more.