Several studies have shown that obese men tend to have a lower sperm count, fewer rapidly mobile sperm and fewer progressively motile sperm compared to normal-weight men.

Obesity in Germany has created a cholesterol problem. High cholesterol is known to cause premature death, angina, heart disease and strokes.

There has been an increase of children with Type 1 diabetes between 1996 and 2011. Diabetics are at higher risk for complications such as heart attack and stroke. In Germany, 600,000 people suffered from diabetes near the end of World War II compared to eight million now.

Obesity can increased risk for secondary diseases such as diabetes, cardiovascular disease, certain cancers and Alzheimer's. Children who get diabetes can expect to lose 10 to 15 years off of their lives. Diabetes also affect the eyes, kidneys and nerves in the legs.

Obesity is a "very strong promoter of cancer." Obesity causes an increased risk for colon cancer and breast cancer.

Genes partly play a role in obesity. Scientists at the German Institute of Human Nutrition and the University Hospital of Leipzig stated that identified two genes that promote fat accumulation in the abdominal cavity. The increased activity of the genes also promotes the release of an enzyme that is responsible for the formation of cortisol. A permanent increase in cortisol levels contribute to obesity.

In 1985 the UAE established a national program to prevent transmission of acquired immune deficiency syndrome (AIDS) and to control its entry into the country. According to World Health Organization estimates, in 2002−3 fewer than 1,000 people in the UAE were living with human immunodeficiency virus (HIV)/AIDS.

Obesity is a growing health concern with health officials stating that obesity is one of the leading causes of preventable deaths in the United Arab Emirates. According to Forbes, United Arab Emirates ranks 1 on a 2007 list of fattest countries with a percentage of 68.3% of its citizens with an unhealthy weight.

Obesity is a chronic health problem. It is one of the biggest factors for a type II diabetes, and cardiovascular disease. It is also associated with cancer (e.g. colorectal cancer), osteoarthritis, liver disease, sleep apnea, depression and other medical conditions that affect mortality and morbidity.

According to the NHANES data, African American and Mexican American adolescents between 12 and 19 years old are more likely to be overweight than non-Hispanic White adolescents. The prevalence is 21%, 23% and 14% respectively. Also, in a national survey of American Indian children 5–18 years old, 39 percent were found to be overweight or at risk for being overweight. As per national survey data, these trends indicate that by 2030, 86.3% of adults will be overweight or obese and 51.1% obese.

A 2007 study found that receiving Food Stamps long term (24 months) was associated with a 50% increased obesity rate among female adults.

Looking at the long-term consequences, overweight adolescents have a 70 percent chance of becoming overweight or obese adults, which increases to 80 percent if one or more parent is overweight or obese. In 2000, the total cost of obesity for children and adults in the United States was estimated to be US$117 billion (US$61 billion in direct medical costs). Given existing trends, this amount is projected to range from US$860.7-956.9 billion in healthcare costs by 2030.

Food consumption has increased with time. For example, annual per capita consumption of cheese was in 1909; in 2000; the average person consumed of carbohydrates daily in 1970; in 2000; of fats and oils in 1909; in 2000. In 1977, 18% of an average person's food was consumed outside the home; in 1996, this had risen to 32%.

According to Cleveland Clinic, cultural, social, and environmental factors, among others, all affect eating behaviors.

Various developmental factors may affect rates of obesity. Breast-feeding for example may protect against obesity in later life with the duration of breast-feeding inversely associated with the risk of being overweight later on. A child's body growth pattern may influence the tendency to gain weight. Researchers measured the standard deviation (SD [weight and length]) scores in a cohort study of 848 babies. They found that infants who had an SD score above 0.67 had catch up growth (they were less likely to be overweight) compared to infants who had less than a 0.67 SD score (they were more likely to gain weight).

A child's weight may be influenced when he/she is only an infant. Researchers also did a cohort study on 19,397 babies, from their birth until age seven and discovered that fat babies at four months were 1.38 times more likely to be overweight at seven years old compared to normal weight babies. Fat babies at the age of one were 1.17 times more likely to be overweight at age seven compared to normal weight babies.

The causes of childhood obesity can be based on both a combination of individual choices and socio-environmental adaptions with genetic factors playing an important role also.

Children's food choices are also influenced by family meals. Researchers provided a household eating questionnaire to 18,177 children, ranging in ages 11–21, and discovered that four out of five parents let their children make their own food decisions. They also discovered that compared to adolescents who ate three or fewer meals per week, those who ate four to five family meals per week were 19% less likely to report poor consumption of vegetables, 22% less likely to report poor consumption of fruits, and 19% less likely to report poor consumption of dairy foods. Adolescents who ate six to seven family meals per week, compared to those who ate three or fewer family meals per week, were 38% less likely to report poor consumption of vegetables, 31% less likely to report poor consumption of fruits, and 27% less likely to report poor consumption of dairy foods. The results of a survey in the UK published in 2010 imply that children raised by their grandparents are more likely to be obese as adults than those raised by their parents. An American study released in 2011 found the more mothers work the more children are more likely to be overweight or obese.

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.

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.

Genetics, according to the Australian Health Survey plays a primary role in determining obesity. In 2011/2012 it was recorded that 90% of the Australian population had inherited their obese tendencies due to the epigenetic modifications of their mothers during pregnancy. Interchanging closely with the genetic factor, the environment and individual temptations are also highlighted as contributing causes to the worldwide epidemic. The genetic configuration influences the tendencies to become overweight, and diet and physical activity determines to what extent those tendencies are elaborated.

Causes cited for the growing rates of obesity in the United Kingdom are multiple and the degree of influence of any one factor is often a source of debate. At an individual level, a combination of excessive food energy intake and a lack of physical activity is thought to explain most cases of obesity. Reduced levels of physical activity due to increased use of private cars, desk bound employment, a decline in home cooking skills and the ready availability of processed foods high in sugar, salt and saturated fats, are variously cited as contributing factors.

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. This is primarily due to increasing use of mechanized transportation and a greater prevalence of labor-saving technology in the home. In children, there appear to be declines in levels of physical activity due to less walking and physical education. 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 (86%) showed an increased rate of childhood obesity with increased media exposure, with rates increasing proportionally to time spent watching television.

Obesity is one of the leading preventable causes of death worldwide. A number of reviews have found that mortality risk is lowest at a BMI of 20–25 kg/m in non-smokers and at 24–27 kg/m in current smokers, with risk increasing along with changes in either direction. This appears to apply in at least four continents. In contrast, a 2013 review found that grade 1 obesity (BMI 30-35) was not associated with higher mortality than normal weight, and that overweight (BMI 25-30) was associated with "lower" mortality than was normal weight (BMI 18.5-25). 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 more positive. In Asians the risk of negative health effects begins to increase between 22–25 kg/m. A BMI above 32 kg/m 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, while 1 million (7.7%) of deaths in Europe are attributed to excess weight. On average, obesity reduces life expectancy by six to seven years, a BMI of 30–35 kg/m reduces life expectancy by two to four years, while severe obesity (BMI > 40 kg/m) reduces life expectancy by ten years.

The MONICA Project, sponsored by the World Health Organization, discovered that 30% of the population in the Arab World is overweight or obese, including adolescents and adults. This percentage is smaller for North African countries than oil-producing countries, but is still a prevalent trend. The spread of the Western lifestyle, defined as "the intake of attractive energy dense food with undesirable composition, increased consumption of animal fats and sugars and reduced consumption of dietary fiber, along with a lack of sufficient physical activity", is one of the leading causes. Specifically in the Arabian Peninsula, "physical activity of the population has significantly diminished with the availability of housemaids, private cars, television, and sophisticated household appliances. In addition, the types of food and fat intake have changed...".

Other common factors, besides a sedentary lifestyle and unhealthy food choices, across the Arab world include urbanization, technology, and a cultural appreciation of female plumpness and the practice of "leblouh" ("fattening").

Researchers from the NIH's National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) conducted a study and found that early-onset paternal obesity is connected with an increased risk of liver disease in their kin. Researchers found that obese fathers had an elevated level of serum alanine aminotransferase (ALT), a liver enzyme, compared to fathers who were not obese. They did a secondary analysis that excluded obese offspring. Children who were a normal weight but had obese fathers still had elevated ALT levels, which indicated that a child's ALT levels are not dependent upon the child's own BMI.

This is a list of the states of India ranked in order of percentage of people who are overweight or obese, based on data from the 2007 National Family Health Survey.

Obese women have an increased risk of pregnancy-related complications, including hypertension, gestational diabetes, and blood clots. Also, the mother is at risk of going into preterm labor. Maternal obesity is also known to be associated with increased rates of complications in late pregnancy such as cesarean delivery, and shoulder dystocia. A meta-analysis estimated that Cesarean delivery rates increased with odds ratios of 1.5 among overweight, 2 among obese, and 3 among severely obese women, compared with normal weight pregnant women. In addition, morbidly obese women who have not had children before are at increased risk of all–cause preterm deliveries. It is well recognized that obese women are at increased risk of preeclampsia and that women who have never been pregnant are at higher risk of preeclampsia than women who have had children in the past.

Several studies have shown that obese men tend to have a lower sperm count, fewer rapidly mobile sperm and fewer progressively motile sperm compared to normal-weight men. Researchers in France have said that poor children were up to three times more likely to be obese compared with wealthier children.

In French society, the main economic subgroup that is affected by obesity is the lower class so they perceive obesity as a problem related to social inequality.

As much as 64% of the United States' adult population is considered either overweight or obese, and this percentage has increased over the last four decades.

Diet and lifestyle are major factors thought to influence susceptibility to many diseases. Drug abuse, tobacco smoking, and alcohol drinking, as well as a lack of or too much exercise may also increase the risk of developing certain diseases, especially later in life. Between 1995 and 2005 813,000 Australians were hospitalised due to alcohol

In many Western countries, people began to consume more meat, dairy products, vegetable oils, tobacco, sugary foods, Coca-Cola, and alcoholic beverages during the latter half of the 20th century. People also developed sedentary lifestyles and greater rates of obesity. In 2014 11.2 million Australians were overweight or obese Rates of colorectal cancer, breast cancer, prostate cancer, endometrial cancer and lung cancer started increasing after this dietary change. People in developing countries, whose diets still depend largely on low-sugar starchy foods with little meat or fat have lower rates of these cancers. Causes are not just from smoking and alcohol abuse. Adults can develop lifestyle diseases through behavioural factors that impact on them. These can be unemployment, unsafe life, poor social environment, working conditions, stress and home life can change a person’s lifestyle to increase their risk of developing one of these diseases.

While the negative health outcomes associated with obesity are accepted within the medical community, the health implications of the overweight category are more controversial. The generally accepted view is that being overweight causes similar health problems to obesity, but to a lesser degree. A 2016 review estimated that the risk of death increases by seven percent among overweight people with a BMI of 25 to 27.5 and 20 percent among overweight people with a BMI of 27.5 to 30. The Framingham heart study found that being overweight at age 40 reduced life expectancy by three years. Being overweight also increases the risk of oligospermia and azoospermia in men.

Katherine Flegal et al., however, found that the mortality rate for individuals who are classified as overweight (BMI 25 to 30) may actually be lower than for those with an "ideal" weight (BMI 18.5 to 25).

Being overweight has been identified as a cause of cancer, and is projected to overtake smoking as the primary cause of cancer in developed countries as cases of cancer linked to smoking dwindle.

Psychological well-being is also at risk in the overweight individual due to social discrimination. However, children under the age of eight are normally not affected.

Being overweight has been shown not to increase mortality in older people: in a study of 70 to 75-year old Australians, mortality was lowest for "overweight" individuals (BMI 25 to 30), while a study of Koreans found that, among those initially aged 65 or more, an increase in BMI to above 25 was not associated with increased risk of death.

Obesity in China is a major health concern according to the WHO, with overall rates of obesity below 5% in the country, but greater than 20% in some cities. This is a dramatic change from times when China experienced famine as a result from ineffective agriculturalization plans such as the Great Leap Forward.

Currently, obesity in China is mostly confined to the cities where fast food culture and globalization have taken over, in comparison to poorer rural areas. Despite this concentration of obesity, the sheer size of China's population means that over one fifth of all one billion obese people in the world come from China.

In 2013 there were 147,678 deaths within Australia mostly from lifestyle diseases including smoking of tobacco, alcohol use and other drugs, violence and unhealthy weight have impacted on Australians' death rate. The leading cause of death of Australian males was heart disease with 11,016 deaths, followed by lung cancer with 4,995 deaths, and chronic pulmonary disease killing 3,572. All these conditions were mainly attributed to smoking, alcohol abuse or unhealthy lifestyle. In 2013 coronary heart disease was the leading cause of death in 8,750 women, mainly as a result of their lifestyle. Dementia and Alzheimer disease came second, affecting 7,277 females and thirdly, cerebrovascular disease, killing 6,368. These top three causes of deaths could be minimized through lifestyle changes within the Australian population.

Table Shows that ages of people dying and the top five diseases of which they are dying.