Obesity

Overweight and obesity are states of increased body weight due to excess adipose tissue. These are risk factors for severe disease, including cardiovascular disease, cerebrovascular disease, and cancer. Obesity (and to a lesser extent overweight) is a chronic disease which leads to significant excess morbidity and mortality. It’s also an epidemic that is rising for every year, and is associated with many diseases, including diabetes, hypertension and physical inactivity.

The Body Mass Index (BMI) is used to defined overweight and obesity, although it has its imperfections. It is closely correlated with body fat. However, the BMI will not be the right method to choose if you have a lot of muscle, as the density of muscle tissue is higher than that of fat.

Overweight is defined as a BMI of 25 – 30, while obesity is defined as a BMI > 30. BMI of more than 35 or 40 (depending on the source) is sometimes referred to as morbid obesity.

Overweight and obesity are preventable causes of morbidity, mortality, and healthcare costs. Overweight and obesity cause more deaths worldwide than underweight. 4 million people die every year due to disease caused by overweight or obesity. Around 4-8% of cancers are attributed to obesity.

Etiology

Overweight and obesity is the result of a long-term positive energy balance (more calories in than calories burnt), but the cause of this is multifactorial. Many lifestyle factors, like physical inactivity, poor sleep, and poor diet, are associated with it. However, studies suggest than genetic predisposition accounts for 40 – 70% of the etiology contribution of overweight. Having one overweight parent increases the risk threefold, and having two overweight parents increases the risk tenfold. However, these genetics factors are not due to any single genes but rather many; the inheritence for obesity is polygenic. Research shows that twins who grow up separately with separate foster parents have a body composition more similar to their biological parents than their foster parents.

One theory is the following: The human body evolved to be in activity every day due to unpredictable lives where food was scarce and not readily available. The body is therefore not well adapted to environments where we have too much food and where physical activity is not necessary for survival. In the modern world, there is suddenly a lot of tasty food, but not enough activity.

Important to note that in many countries (like Norway), the prevalence of overweight and obesity has increased over a period during which the average person ate less and healthier, and worked out more.

Types

Obesity can be divided into central and peripheral obesity.

Central obesity

Central obesity, also known as visceral or abdominal obesity, is characterized by fat accumulating in the trunk and in the abdominal cavity around the organs and in the mesentery. Central obesity is more harmful than peripheral obesity, because visceral adipose tissue is more hormonally active than nonvisceral adipose tissue. People with central obesity have an increased waist circumference, which is a risk factor for other diseases independent of the BMI itself.

Peripheral obesity

Peripheral obesity is accumulation in subcutaneous tissue, as in the thighs, breasts and arms.

Pathology

Adipose tissue, especially visceral adipose tissue, is hormonally active, producing different hormones and molecules, including adiponectin, leptin, tumour necrosis factor, and interleukin 6, which cause chronic inflammation and disease. Increased mass of visceral adipose tissue causes excess release of free fatty acids, which leads to insulin resistance.

Overnutrition makes the blood glucose level rise, so the insulin production increases to be able to lower the blood glucose. The insulin receptors will open up for glucose intake, making the cells store glucose as fat. This overnutrition makes the adipocytes full of fat and the muscles and liver full of sugar and glycogen, so they can’t handle any more glucose and shut down their insulin receptors. Pancreas try to produce more and more insulin to lower the sugar levels, but it will all result in hyperglycemia and hyperinsulinemia. High insulin levels prevent lipolysis and fat oxidation, but the patient is still hungry and tired. It becomes a viscous circle.

High levels of insulin may increase levels of Insulin-like-growth-factor-1, (IGF-1), which stimulates growth and survival of cancerous cells. This may explain the increased risk for cancer in obesity.

Complications

Obesity itself is a chronic disease which may lead to a number of other diseases:

• Type 2 diabetes mellitus
• Ischaemic heart disease
• Stroke
• Peripheral vascular disease
• Hypertension
• Atrial fibrillation
• Cancer (breast, colorectal, oesophageal, gastric, gallbladder, endometrial, pancreatic, ovarian)
• Nonalcoholic steatohepatitis
• Cholelithiasis
• GERD
• Osteoarthritis
• Gout
• Infections
• Gynaecomastia
• Decreased fertility
• Pregnancy complications
• Psychosocial problems
• Chronic kidney disease
• Obesity hypoventilation syndrome (Pickwick syndrome)
• Obstructive sleep apnoea
• Asthma
• Depression
• Dementia

References

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