science of body weight week 1 Flashcards
what is the equation for BMI
weight (kh)/ height2 (m), in children z scores take into account age and growth in height. overweight= 25-30
what is the history of BMI
- health insurance companies
- 1900s: normal weight tables…
- relative scarcity of women and racial and ethnic minorities in underlying datasets
- 1937 : body frame added to table
- 1972 : quetelet indexed from 1832 and renamed it to BMI
what are the strengths of using BMI
- simple and low cost
- strong correlation between self-report and measured BMI
- correlated with direct measures body fat such as underwater weighing and dual energy x-ray absorptiometry.
what are the cons of using BMI
- no account for age in adults, race and gender - higher bone density and muscles mass in black people compared to white.
- indirect measures of body fat (does not reflect changes in body fat and muscle mass)
what are the trends in body weight
- 2016: 1.9 billions adults overweight
- 41 million under 5 and 340 million aged 5-19
- decreasing trend in moderate to sever underweight.
-strong regional division : overweight in developed countries
why is it important to look at weight
child obesity and overweight are associated (risk factors) with type 2 diabetes, metabolic syndrome in youth and obesity in adult
For adults: cardio vascular disease, type 2, some cancers
how can we study genes vs environment in regards to body weight
Adoption studies
adopted children bmi compared to parents, and biological parents.
Twin studies : MZ (concordance rate higher, suggest genetic basis) and DZ, concordance rate.
how can we find which genes have an influence on bodyweight
Genome wide association studies : section of genome can be different people, different snips for different people. meta-analysis (combine results=more reliable), range of different snips related to BMI, correlation doesn’t mean causation.
genetically, why are some individuals more predisposed to bodyweight then others.
evolutionary : natural selection (how organism evolve), means genetic variation (random mutation = might be more advantageous).
thrifty gene hypothesis
Neel,1962 : original explanation for type 2, suggesting genes for this were previously advantageous. More fat = more survival at times of famine
when food abundant: prepares humans for famine that never comes.
what are the criticism of the thrift gene hypothesis
- all humans should have an obesity problem
- famine not a frequent feature of our evolutionary past, much shorter time, thrifty genes haven’t spread so far
- selection pressure would have to be huge to have spread that far.
drifty gene hypothesis
Speakman (2008) : other processes other then thrifty gene. e.g. genetic drift (non-adaptive evolutionary change)
- body weight in animal well regulated between a lower level (starvation risk) and upper (risk of predation) - not applied to humans as predation risk disappeared (social behaviours, weapons/fire) . without selection pressure genes were subject to random mutation and genetic drift
criticism of drift gene hypothesis
- why hasn’t the obesity epidemic been around for the last 20,000 years if we have the same genetic architecture as Cro-Magnon humans?
why hasn’t the obesity epidemic been around for the last 20,000 years if we have the same genetic architecture as Cro-Magnon humans?
- not the abundance of food available at that point, insufficient food for bodyweight to increase up towards the drifted upper level
- but with an abundant food supply that was not the case.
what is the overall criticism for evolutionary theory
- tend to treat humans as homogenous block : fail to account for interethnic differences in obesity
- selleyah: unify theory ( differences, culture and social)
- maladaptive scenario: genes provide cold adaption rather than heat adaption also influence increase in metabolic rate (way of burning off excess food)
