In his book “The Lost Continent” (1989), an autobiographical-travel log of 1980s America, Bill Bryson tells the story of his grandmom coming to stay with his family because she was dying of colon cancer. Their cleaning lady, a good Catholic, wanted to quit because she didn’t want to catch cancer from Bill Bryson’s grandmother. His mother explained that you can’t “catch cancer.” So with ill-disguised reluctance [the cleaning lady] stayed on. And about three months later, she caught cancer and, with alarming swiftness, died.” (chapter 26, p 310)
It’s also not readily believable that obesity could be contagious, although there have been studies of viral infections in chickens that caused those birds to get fat. But there is a new report using math that I don’t understand, that puports to show that besides the important genetic component, there is a component of the epidemic of obesity that is, or seems to be, contagious and that contagion must be social.(1)
Remember our famous conundrum number one — How can obesity be genetic and yet the epidemic has happened much faster than genes in our population could have changed.
Strictly speaking, an epidemic refers to an infectious disease. So when we say an epidemic of obesity or a natural disaster etc., we are making a poetic analogy. An infectious epidemic occurs when there is a new germ or new variant of an old germ or when a new population of victums without immunity is exposed. Epidemics can be defined and modeled by complicated math that describes how many people need to have the infection and be exposed to the infection for it to “take off.”(2,3,4)
I am not clear how the authors of this report make the leap from saying that non-genetic factors are socially contagious. They conclude that “the socially contagious risk factor had a greater overall impact on the distribution of the population with obesity than did spontaneous weight gain risk or mother‐to‐child obesity transmission risk.” Part of the evidence for this assertion comes from the observation that obesity happened in the U.S. first, and is now spreading around the world.
I need to study this more, but I think conundrum number one still remains conundrumatical.
1. Ejima K, Thomas DM, Allison DB. A Mathematical Model for Predicting Obesity Transmission with Both Genetic and Nongenetic Heredity. Obesity May,2018; 26(5);927-33.
2. Kermack W, McKendrick A (1991). “Contributions to the mathematical theory of epidemics—I”. Bulletin of Mathematical Biology. 53 (1–2): 33–55. doi:10.1007/BF02464423. PMID 2059741.
3. Kermack W; McKendrick, A (1991). “Contributions to the mathematical theory of epidemics—II. The problem of endemicity”. Bulletin of Mathematical Biology. 53 (1–2): 57–87. doi:10.1007/BF02464424. PMID 2059742.
4. Kermack W, McKendrick A (1991). “Contributions to the mathematical theory of epidemics—III. Further studies of the problem of endemicity”. Bulletin of Mathematical Biology. 53 (1–2): 89–118. doi:10.1007/BF02464425. PMID 2059743.
6. Clark CCT. Is obesity actually non-communicable? Obesity Medicine 2017;8:27-8
John DiTraglia, M.D., is a pediatrician in Portsmouth. He can be reached by email at firstname.lastname@example.org or call 740-354-6605.