Heart disease, type-2 diabetes and cancer are all diseases linked to obesity. Heart disease may be linked to obesity because an obese person has more body mass; therefore they have more blood, and a larger area that the blood needs to circulate through. This puts pressure on the heart to pump harder, and it strains the heart, leading to heart disease. Type-2 diabetes may be linked to obesity because often obese people consume large amounts of sugar. The body then tries to balance the blood sugar levels by overproducing insulin. Since the body is trying to produce so much insulin, it develops a resistance to insulin, or it cannot produce the right amount of insulin to correct the blood sugar levels. Cancer may be linked to obesity because an obese person would have more body mass, so they would have more cells in their body, and a higher chance of mutation among those cells. Cancer also may be linked to obesity because the systems of defence that a human body has to prevent abnormal cell growth may be compromised with the excess weight.
The varying obesity rates among countries may be linked to immigration. In North America, the rates of obesity are very high, and this may be because many of the first European inhabitants of the continent would have had to survive long winters without the help of doctors or farmers. Many of the early European inhabitants of North America were also descended from countries in Europe that also had high obesity rates, such as England and Spain, so the thrifty gene may have been passed down from their ancestors.
The thrifty gene is a theory that many humans may have inherited a gene that causes them to be more susceptible to storing fat. Their ancestors may have only survived famines because they were able to store more fat, and the gene that enabled them to do so may have been passed down to the next generation to store much more fat.
The thrifty gene theory could explain the varying prevalence of obesity in different...