Obesity

• Obesity is most often measured by body mass index (BMI), which looks at body weight compared with height.
  Someone is of healthy weight if his or her BMI is 18.5–24.9. 
  • It is healthy to have some body fat. In fact, a healthy level of body fat is needed to survive. 
  • Fat cells give energy and help get rid of waste in the body. They also release substances of their own.
  Someone is overweight (meaning some extra body fat over healthy levels) if his or her BMI is 25.0–29.9.
  Someone is obese if his or her BMI is 30 or higher.
• Being obese can have many harmful health effects.
  Being obese harms the body because of the way fat cells act.
  Substances made by too many fat cells cause low-level inflammation, or swelling, that doesn’t go away. This can harm blood vessels, muscles (including the heart) and organs, such as the liver and pancreas. It also raises the risk for many types of cancer.
  By having extra fat mass, someone who is obese has more strain on his or her joints and tissues, causing more pain.

Causes

Obesity most often starts in childhood, and children who are above a healthy weight are much more likely to be obese as adults. While there is some data that show genetic links (meaning if someone in your family is obese, you are more likely to be obese as well), there are many things that could lead to obesity.

Diet

• The modern Western diet includes:
  Many high-calorie, low-nutrition foods (refined carbohydrates, hydrogenated fats and animal fats).
  Not enough nutritious fruits, vegetables and whole-grain foods.
  Excessively large portions. 
  Way too little dietary fiber.
• Today, food that is healthy and has fewer calories is often less accessible and costs more money. 
• Fast food, which is more convenient and costs less, often has fewer nutrients, bigger portions and more calories from sugars and fat.
  Many people don’t realize how many calories are in the food they are eating, or they underestimate how much they are eating.
  Larger portions are more common, and getting more food for less money is thought to be a good value, even if it is not healthy.
  Many extra calories are in things people drink, like sodas, juices and sweetened coffee and tea.

Social Causes

• The demands of a busy life handling work and family (and often much more) leaves little time for many to cook at home.
• Many modern advances (cars, working from home, TV and social media, etc.) have made people less active and lacking in regular exercise. 
• Many people also feel comforted by food, or they use eating as a way of dealing with stress. 

Secondary Causes

• Some causes of being overweight or obese come from other health issues or treatment of those health issues.
• Some medications cause weight gain, even when a healthy diet and exercise program are followed.

Physiological Causes

• There was a time when humans had to hunt or gather their own food. With this, human bodies stored calories to keep from starving when there was little food.
• Conserving energy to prevent weight loss is no longer needed, since our access to food has changed greatly, but our bodies have not adapted to help us regulate against weight gain.
• Low thyroid hormones in some people can slow metabolism and cause weight gain. 
• New data show how special hormones and other substances in the body can impact feelings of hunger and fullness. In people with obesity, these substances are changed. More research is needed to better understand this complex process.

Gut Microbiome

• Between the Western diet and the common use of antibiotics, it has been found that many of us do not have the proper balance of bacteria in our guts.
• New data shows that this lack of diversity can impact how a body handles calories and weight gain.
• More studies are needed to explore this potential cause.

Conditions Linked to Obesity

Experts have been able to show a link between high body mass index (BMI; being overweight or obese) and a higher risk of many health issues, such as :

• Heart disease.
• Stroke.
• High blood pressure.
• Type 2 diabetes.
• Many types of cancer (such as endometrial, breast and colon cancer).
• Liver disease.
• Gallbladder disease (such as gallstones).
• Infertility (not being able to make a baby).
• Osteoarthritis.
• Depression.
• Sleep apnea.
• Heartburn (reflux).
• High cholesterol and triglycerides (linked to heart disease and stroke).

Some of these may not seem as serious, but some can be very dangerous. More than one of these health issues can team up to harm your heart and blood vessels.