So, it could be a virus after
all! Many of us wonder why we put on so much weight despite regular workouts
and controlled diet. Scientists are of the opinion that obesity maybe the
result of 'combination of issues including virus infection' and they call it
infectobesity. They concluded that apart from obvious explanations such as
over-eating, lack of exercise, accumulation of endocrine-disrupting chemicals,
and other reasons, (don't forget the genetics factor!) obesity is of infectious origin. Researchers have even published
their findings in Proceedings of the Royal Society B.
A number of research studies were
undertaken to prove and resolve this theory:
• 'Animals experimentally
infected with SMAM-1, an avian adeno-virus, or two human adenoviruses,
adenovirus type 36 (Ad-36) and Ad-37, developed adiposity. Notably, SMAM-1 and Ad-36 were associated with
obesity in humans
. Although more research is needed to further define the
mechanisms and the role of pathogens in the etiology of obesity, they should be
included in the long list of potential etiological factors for obesity.'
• 'The concept of virus-induced
obesity is not new. Eight viruses have been shown to cause obesity in animals
and there is evidence for virus-induced obesity in humans. Recent evidence on
animal and human adenoviruses suggests that these adenoviruses may infect
adipocytes to alter enzymes and transcription factors resulting in accumulation
of triglycerides and differentiation of preadipocytes into mature adipocytes.
The E4orf1 gene of Ad-36 has been shown to be responsible for the adipogenic
effect. It appears that a portion of the worldwide epidemic of obesity since
1980 could be due to infections with human adenoviruses.'
'In recent years viral infections
have been recognized as possible cause of obesity, alongside the traditionally
recognized causes (genetic inheritance, and behaviour/environmental causes such
as diet exercise, cultural practices and stress). Although four viruses have
been reported to induce obesity (infectoobesity) in animal models (chickens,
mice, sheep, goat, dogs, rats and hamsters), until recently the viral etiology
of human obesity has not received sufficient attention, possibly because the
four viruses are not able to infect humans. In a series of papers over the last
ten years, however, the group of Prof. Dhurandhar (Pennington Biomedical
Research Center, LA, USA) demonstrated that a human adenovirus, adenovirus-36
(Ad-36), is capable of inducing adiposity in experimentally infected chickens,
mice and non-human primates (marmosets). Ad-36 is known to increase the
replication, differentiation, lipid accumulation and insulin sensitivity in fat
cells and reduces those cells' leptin secretion and expression. It also affects
human primary preadipocytes. In rats increased adiposity was observed due to
Ad-36 infection. Recent studies have shown that, in the USA, antibodies to
Ad-36 were more prevalent in obese subjects (30%) than in non-obese subjects
(11%). We postulate that Ad-36 may be a contributing factor to the worldwide
rising problem of obesity. If you are not much into medical jargon, here's what
they are trying to say. Once you have an infection, you develop antibodies
to that infection
. Antibodies are proteins produced by the immune system to
detect and destroy the virus and bacteria that invade the body. Now, these
scientists have found that the adenovirus SMAM-1 that infects birds enters the
'pre-fat' cells and through certain biochemical changes accumulates large
amount of triglycerides thus increasing the number of fat cells especially in
the abdomen of the chicken. Adenovirus is a virus that infects the upper
respiratory system causing symptoms similar to a cold or flu. Remember bird
has been found to infect human beings as well. The
acts in the same
way causing adiposity (accumulation of fat) in a number of animals including
human being. The virus stimulates the pre-fat cells to differentiate into
mature fat cells thereby increasing the number of fat cells and their lipid
content. Researches to find the relationship between Ad-36 and obesity in
people showed that 30 percent of the obese people screened had antibodies to
Ad-36 whereas only 11 percent of lean people had these antibodies.
Although researchers don't have
the complete picture about the possible causes of obesity and its connection
with these adenoviruses, they suggest that the viral gene E4orf1
is responsible for the conversion of pre-fat cells into fat
Interestingly, they also found
that these obesity viruses improved cholesterol levels even when they increased
fat cells in the body. Insulin sensitivity also increased in these obese
In conclusion it can be said that
research on these adenoviruses and their effect on obesity can lead to better
understanding of obesity and its causes, and of course, it could aid in
developing treatments for obesity and, yes, high cholesterol.
1. Dhurandhar NV. Contribution of pathogens in human obesity.
Drug News Perspect. 2004 Jun;17(5):307-13.
2. Atkinson RL. Could viruses contribute to the worldwide
epidemic of obesity? Int J Pediatr Obes. 2008;3 Suppl 1:37-43.
3. van Ginneken V, Sitnyakowsky L, Jeffery JE.
Infectobesity: viral infections (especially with human adenovirus-36: Ad-36)
may be a cause of obesity. Med Hypotheses. 2009 Apr;72(4):383-8. Epub 2009 Jan