Obesity is infectious intestinal disease, scientists say

"I put on weight even if I look at a piece of cake," some people may often say. They are right. Many obese people find it extremely hard to lose weight. At the same time, a human being with a normal weight may not eat just for one day to lose up to a kilo of his or her weight. Why does it happen like that? Scientists say that the reason for obesity lies in intestines. Does it mean that obesity can be contagious?

Recipes of new magical diets and weight loss pills appear on a regular basis. However, the number of obese people in the world continues to grow. The share of overweight people among the adult population of the planet increased during the recent 12 years from 8.5 in 1997 to 14.5 percent in 2009 - by 6.5 million people. It goes without saying that some reasons that make people gain excessive weight are obvious (redundant nutrition or sedentary lifestyle, etc). However, there are many other important, albeit unknown, theories.

The phenomenon of infectious obesity became known as "infectobesity." The term was coined in 2001 by Indian professor Nikhil V. Dhurandhar.

There are as many as 100 quintillion bacteria living on a human being. Five hundred pairs of various bacteria species live inside the human body. The quantity of bacteria is the largest in the human intestines. One of the main functions of intestinal bacteria is to help the body digest food. The bacteria also protect the body from the intervention of pathogenic microorganisms. The bacteria also help us receive the maximum from the food that we eat. For example, they turn lipids into the nutrients that humans are capable of digesting.

Most of the bacteria can be divided into two groups: Bacteroidetes and Firmikutes. The Firmikutes participate in the decomposition of carb-rich food, whereas the Bacteroidetes decompose the food rich with proteins, as well as vegetable food. The intestinal flora of obese individuals is richer with the Firmikutes, whereas the people with normal weight have more Bacteroidetes in their intestines.

US scientists confirmed the theory of the Indian professor. Dr. Jeffrey Gordon, the chief of the Center for Genome Sciences in Washington  published the results of the research in the November issue of Science Translational Medicine (2009). The scientists conducted the experiments on mice.

All mice are born with sterile intestines. The intestines get filled with bacteria during the first food intake. Obesity-prone mice - the ones born from obese mothers - have a larger percentage of the Firmikutes in their intestines as opposed to the mice with a normal build. The more carbs a mouse consumes, the faster the Firmikutes grow.

The entire system of obesity is like a snowball. The more you eat, the more Firmikutes appear in the intestines. The better the carbs digest, the more you want to eat, and so on and so forth.

The most interesting aspect that was revealed during the experiments was the following. Intestinal bacteria would change their structure against the background of a changing diet. When researchers transplanted the intestinal flora from fat to slender mice, the latter started putting on weight as well, even if they had a non-fat diet. However, the mice would put on weight only during a certain period of time. The researchers discovered that their intestinal flora would gradually change too. To put it in a nutshell, when the mice began to eat less, the Firmikutes would die and then be replaced with the Bacteroidetes. As a result, the mouse would lose weight.

The human intestinal bacteria work the same way. When a group of obese individuals was transferred to the diet with no sweet and no fat products, they lost 25 percent of their weight during a year. The people also lost a great deal of their Firmikutes. The latter were replaced with Bacteroidetes.  

US scientists currently conduct a new experiment. They take the intestinal flora of the children who live in impoverished regions of the world and transplant the flora to the intestines of mice. There are many factors - genetic, cultural and ecological - that stand behind the human obesity. The scientists need to learn to control them, Gordon said.

Another theory proposed by Dr. Nikhil V. Dhurandhar says that obesity can be caused by one of over 50 adenoviruses known as Ad-36. The viruses accumulate fat in the body and trigger the development of flu-like symptoms such as the running nose.

Dr. Dhurandhar conducted tests among 500 people. Three hundred and sixty of them were obese. The experiment revealed that 30% of obese patients had Ad-36 adenovirus. As for the normally built people, the virus was found with only eleven percent of them. The scientists also discovered that the level of cholesterol with the obese people was below the norm.

How does the virus develop obesity? One of the theories says that the Ad-36 shows direct influence on fat cells. The virus makes them grow and save fat. Another theory says that the adenovirus disrupts the ability of the body to regulate the consumption of fat. As a result, the body accumulates fat uncontrollably.

Alexander Orlov

Medpulse