Obesity is Infectious!

Researchers have long known that obesity runs in families, that there is a genetic component to the condition. A recent study noted that the risk of obesity increased by 30% in persons that have a single copy of the high-risk allele for the FTO gene, linked with fat mass and obesity, by 67% in those who carry two, who averagely gained 3.0 kg (6.6 lb) or more1 roughly one sixth of the population of European descent homozygous for this allele, this link between the FTO gene and obesity seems strong.

Obesity however, is not all about genes. A study published in the July 26, 2007 issue of the New England Journal of Medicine, indicates that friends play an even more significant role in someone’s risk of obesity than do genes2. The researchers recreated a social network among participants of the Framingham Heart Study that showed the ties between friends, neighbors, spouses, and family members. They noted the risk of someone becoming obese increased by 171%, if another, a friend, became obese during a given time period.

The researchers also noted that the risk of one sibling in a pair of adult siblings becoming obese increased by 40%, the other obese, and the clustering of obesity in communities, the risk of an obese person’s friend’s friend being obese, roughly 20%. This was higher in the observed than in a random network, the effect erased only by the 4th degree of separation.

This study not only has important health policy and public health implications, but also underscores the increasing interest in interconnectedness and the role of networks in health and disease. Indeed, networks, including social networks would become increasingly prominent in health issues, for example, social networks and their effect on the spread of obesity or pathogens, including influenza, severe acute respiratory syndrome (SARS) or the human immunodeficiency virus (HIV) 3.

Neural networks also play a key role in various psychiatric and neurodegenerative diseases and cellular networks are potential conduits for the propagation of genetic defects to other non-defective genes4. Indeed, network medicine research focuses on understanding the links between the cellular, disease, and social networks in the mechanisms of disease causation, among others, including mechanism of drug actions and their side effects.

Thus, obesity, for example, has associations with seven diseases, including asthma, lipodystrophy, and glioblastoma, and genetic probably explains obesity being a risk factor for diabetes, both diseases linked with a number of genes, including ectoenzyme nucleotide pyrophosphate phosphodiesterase (ENPP1), peroxisome-proliferator–activated receptor γ (PPARγ), and, now, FTO. Now also, research evidence for the social networks involved with obesity has emerged as noted earlier, hence the multilevel-cellular, disease, and social networks that underpin obesity.

Furthermore, the large number of genes shared by often quite dissimilar disorders not only suggests that the disease may have common genetic origins, but also that we would soon need to rethink our conceptualization of and classification of diseases. Indeed, network medicine constitutes a major paradigmatic shift in medical thinking that would also have profound influence on medical research and practice.



1. Frayling TM, Timpson NJ, Weedon MN, et al. A common variant in the FTO gene is associated with body mass index and predisposes to childhood and adult obesity. Science 2007; 316:889-94.

2. Christakis NA, Fowler JH. The spread of obesity in a large social network over 32 years. N Engl J Med 2007; 357:370-9.

3. Barabasi A. Network Medicine-From Obesity to the “Diseaseome”. N Engl J Med 2007; 357:404

4. Barabási A-L, Oltvai ZN. Network biology: understanding the cell's functional organization. Nat Rev Genet 2004; 5:101-15