Obesity: Why Is It So Dangerous?

What Is Obesity?

Obesity is defined as the excessive accumulation of body fat to the point where health is impaired, and is one of the main health issues facing societies today. Rates of obesity have more than doubled since 1980 and continue to increase worldwide, with more than one in ten of the world’s adult population now obese. In the USA more than two thirds of the population are overweight or obese – and the UK is not far behind.

The most commonly used method for assessing whether someone is overweight or obese is the Body Mass Index (BMI), which is defined as a person’s weight in kilograms divided by the square of their height in metres (kg/m²). The World Health Organisation defines ‘overweight’ as a BMI above 25 and ‘obese’ as BMI above 30. This is a useful measure as it is height-independent and easy to calculate, however it does not distinguish between fat and lean tissue or water, nor does it identify whether fat is accumulated in particular sites such as the abdomen, where it has more serious metabolic consequences. For this reason, a more useful measure of risk for obesity-related diseases may be waist circumference. To measure waist circumference, a tape measure should be placed around the abdomen - roughly level with the bellybutton - so that it is flat to the skin but does not compress it, and a measurement taken. For men, a waist circumference of 94cm or above is considered to be indicative of an increased risk and 102cm or above is a substantially increased risk. For women the figures are 80cm and 88cm respectively.

Why Is Obesity So Dangerous?

Obesity is responsible for at least 2.8 million deaths each year. Obesity is a significant contributing factor to five of the ten leading causes of death in the USA: heart disease, stroke, cancer, kidney disease and diabetes. It is the leading preventable cause of death worldwide, with more people now dying from overweight and obesity than from underweight. I will now give an overview of some of the most serious medical consequences of obesity. Much of my data is for the USA as this is where the pandemic is most advanced, however the rest of the world should be aware that they are heading in the same direction. The UK in particular is estimated to reach the levels of obesity currently in the USA in just 10 years.

Type 2 Diabetes

Type 2 diabetes mellitus is a metabolic disorder characterised by high blood glucose due to insulin resistance and relative insulin deficiency. Insulin is the essential hormone produced by the pancreas in response to a rise in blood glucose levels which acts upon body tissues, particularly skeletal muscle, adipose (fat) tissue and the liver, to encourage (among other things) uptake of glucose from the bloodstream. In type 2 diabetes this action is impaired, leading to potentially dangerously high levels of glucose in the blood. In healthy, non-diabetic individuals, fasting blood glucose is usually somewhere between 4 and 5mmol/l. A person is diagnosed as diabetic when their fasting blood glucose level is at 7mmol/l or above. Someone with a fasting blood glucose level between 6 and 7mmol/l is classified as “pre-diabetic” meaning they have impaired glucose tolerance and are likely to develop type 2 diabetes within the next few years unless significant diet and lifestyle changes are made. While the precise mechanisms causing insulin resistance are not yet fully understood, it is clear that there is a strong link with obesity, and particularly with the presence of excess fat in the abdominal region.

Type 2 diabetes is the most significant medical consequence of obesity for a number of reasons. As well as being both difficult and expensive to manage, it is exceedingly and increasingly common, with more than 25 million Americans already diabetic and a further 79 million pre-diabetic. Worse, a child born in the United States in 2000 has a 1 in 3 lifetime chance of developing the disease – and if they are African-American or Latino the risk is 1 in 2. Type 2 diabetes mellitus was once referred to as “adult-onset diabetes” because it occurred exclusively in adults, predominantly the elderly. Now, however, due to the rapid rise in obesity, this disease is being seen in younger and younger patients, and even children.

Most people do not realise how serious diabetes can be. When left untreated, or indeed just poorly managed (as is too often the case) diabetes can lead to heart disease, stroke, blindness, kidney disease, nerve damage and amputations... leading to disability (and therefore reduced quality of life) and premature mortality. On average, having diabetes reduces an individual’s life by 8-10 years, and it is estimated that diabetes may contribute to as many as 40% of deaths in the USA each year.

Cardiovascular Disease

The term cardiovascular disease (CVD) includes heart disease, stroke, and all other diseases of the heart and circulation. The most common of these is coronary heart disease (CHD) which is the number one cause of death worldwide. More than 36% of American adults have cardiovascular disease.

CHD is predominantly caused by atherosclerosis – a narrowing of the arteries caused by a build-up of plaque (fatty deposits, including cholesterol.) Atherosclerosis is progressive and can begin in childhood (the Bogalusa Heart Study in America found that 20% of autopsied children had plaques in their coronary arteries, some as young as five!) Being obese, having high blood pressure, high cholesterol or diabetes and being physically inactive all increase the risk of atherosclerosis, and it typically gets worse as an individual gets older. In time, the arteries can become so narrow that they can no longer deliver enough oxygenated blood to the heart. This can cause angina – pain or discomfort in the chest, usually brought on by exertion or stress. Sometimes a piece of plaque from the artery wall will break off and cause a blood clot which then becomes lodged in the already narrowed artery, completely restricting the flow of blood. If this occurs in the arteries supplying blood to the heart muscle it is known as a myocardial infarction or heart attack and is often fatal. A blockage may also occur in the arteries supplying blood to the brain which is what causes a stroke.

Cancer

Cancer is the second biggest cause of death in the developed world, and it is estimated that 20% of cancer deaths in women and 14% in men can be attributed to overweight and obesity. Obesity is not only a factor in causing numerous types of cancer including breast, colorectal, oesophageal, pancreatic, kidney and thyroid cancer, but is also associated with poorer treatment outcomes and hence increased mortality.

Cancer is primarily a result of damage to the DNA which causes a cell to begin multiplying uncontrollably, forming a tumour. Several possible mechanisms have been suggested to explain the link between obesity and a higher risk of cancer, including excess oestrogen (produced by adipose tissue) which is associated with a higher risk of breast, endometrial and some other types of cancer. Insulin is also an important factor as it is known to promote the growth of tumours. Patients who are obese, and particularly those with insulin resistance, are therefore at greater risk of most types of cancer due to a higher level of circulating insulin.

Other Risks

Being obese is associated with numerous other health problems on top of the ones I have outlined above. For example, an obese individual is 83% more likely to develop kidney disease and 80% more likely to develop dementia. Being overweight or obese increases a child’s risk of developing asthma by 52% and makes the condition more serious once developed. In addition, more than 66% of arthritis sufferers are overweight or obese, and they generally experience greater pain than leaner arthritis sufferers due to their excess weight.

Being obese is clearly a problem for an individual, but it also affects society as a whole, not least because of the increased healthcare costs – at current rates of increase obesity related health-care costs are projected to exceed $300 billion by 2018. But how did so many people get so fat so quickly? And what can be done about it? I will be addressing these questions in my next entry.