It is well documented that obesity is associated with an increased risk of cardiovascular disease and a higher overall mortality.
Obesity also correlates with an increased risk of Alzheimer’s disease and many types of cancer. It is estimated that severe obesity can reduce the lifespan up to ten years. This is comparable to the effect of smoking.
Obesity is defined as a high body mass index (BMI). It is characterized by the accumulation of fat in the body.
But what’s wrong with walking with a little extra weight? Why is excess body weight associated with the risk of heart disease, cancer and premature death?
When we talk about obesity, we usually look mainly at body weight. This may be wrong. In fact, body fat does much more for our health than occupying space and increasing weight.
Fat cells are biologically active, and their function or dysfunction can affect our health in many ways. For example, fat cells produce and secrete important biological substances.
One of these substances is called adiponectin. In fact, adiponectin could represent one of the missing links between obesity and the increased risk of diabetes, heart disease and cancer.
The body has the ability to store extra energy in the form of fat in adipose tissue. Adipose tissue is a loose connective tissue that is composed mainly of cells called adipocytes. It is usually located under the skin and around the internal organs (visceral fat).
It is possible to assess what amount of body weight is composed of fat. Although it can vary a lot, men and women of normal weight have about 15 percent and 30 percent body fat, respectively.
Adipose tissue seems to be an important endocrine organ. It produces hormones such as leptin and estrogen , as well as cytokines, which play an important role in cell signaling. The cytokines secreted by adipose tissue are called adipokines.
Visceral and subcutaneous fats
The shape of the body and the regional distribution of fat seem to be more important for health than the total amount of adipose tissue. For example, the accumulation of fat around the internal organs can be more harmful than the accumulation of fat elsewhere.
The excess accumulation of this type of fat is called visceral obesity.
In the 1940s, a professor named Jean Vague pointed out that women normally had twice as much fat mass as men. However, he also discovered that the metabolic complications associated with obesity were much less common among women than among men.
Vague defined two different body shapes. Android obesity or the shape of the apple refers to the accumulation of fat in the upper part of the body.
Gynecological obesity or pear shape refers to the accumulation of fat in the hips and thighs. The latter is more common among women. This is very well demonstrated in Pierre-Auguste Renoir’s painting above.
The accumulation of visceral fat is associated with insulin resistance , small and dense LDL particles, high blood pressure , high triglyceride levels, low HDL cholesterol levels, and an increased risk of diabetes and even cardiovascular diseases.
However, subcutaneous fat seems much more innocent than visceral fat. In fact, recent studies suggest that subcutaneous abdominal fat is not associated with risk factors for cardiovascular disease. This suggests a possible protective effect of subcutaneous fat.
In the 1990s, scientists found a protein secreted by adipocytes and called it adiponectin.
Although adiponectin is secreted only from adipose tissue, the plasma concentration of adiponectin is much lower in obese subjects than in non-obese healthy volunteers.
In individuals with visceral obesity the plasma levels of adiponectin are especially low. It is believed that adiponectin deficiency can play an important role for many of the negative metabolic consequences of visceral fat accumulation.
The clinical term for low levels of adiponectin in plasma is hypoadiponectinemia.
So, although adiponectin is produced by adipose tissue, its production is abnormally low in obese individuals, particularly those with visceral obesity.
Some adipokines can adversely affect health. For example, many adipokines are proinflammatory and can support low-grade chronic inflammation in the body. On the other hand, adiponectin is protective and appears to reduce inflammation.
Studies show that low levels of adiponectin are associated with elevated levels of several different markers of inflammation.
Adiponectin and Obesity
Obese people have lower levels of adiponectin in their blood than people of normal weight. In addition, reducing obesity increases adiponectin levels. In general, it seems that losing weight through diet, exercise, medications and surgery will increase adiponectin levels in the blood.
Low levels of adiponectin are more strongly associated with the amount of visceral fat than subcutaneous fat.
The development of subcutaneous fat is an active process in childhood, adolescence and pregnancy. In middle-aged and elderly people, over-nutrition does not lead to an effective storage of energy as subcutaneous fat. In contrast, the accumulation of visceral fat becomes more common.
Lifestyle factors such as overeating and physical inactivity in young and middle-aged people seem to increase the risk of visceral obesity.
Fat cell dysfunction is more common in visceral fatty tissue than subcutaneous adipose tissue. This dysfunction can cause an imbalance in the production of adipokines that leads to an excessive production of offensive adipokines and in the production of defensive adipokines such as adiponectin.