the science of bodyweight

Question 1

what is weight stigma

Answer 1

blaming people for uncontrollable factors relating to weight

Question 2

what does bmi stand for

Answer 2

body mass index

Question 3

how to calculate bmi

Answer 3

weight (kg) / height2 (m)

Question 4

interpreting bmi

Answer 4

bmi charts used to indicate weight classification
different when interpreting for children

Question 5

who stated bmi is a contested method

Answer 5

foresight 2007

Question 6

what is the history of bmi

Answer 6

-health insurance companies in USA started it as weight is a risk factor for insurance companies so they composed weight height charts
-1900s companies further improved these tables using datasets of people they have insured
-1937 added body frame to tables (small, med, large)
-keys found quetelet index from 1832 and renamed it bmi

Question 7

what is a weakness in the history of bmi

Answer 7

tested mainly white men

Question 8

advantages of bmi

Answer 8

+ simple, low cost (kennedy 2012)
+ strong correlation between self report and measured bmi (despite height often overestimated and weight underestimated)
+ correlated with direct measures of body fat such as underwater weighing

Question 9

weaknesses of bmi

Answer 9

• no adequate account for race, age, gender, especially in terms of standard cut offs e.g black people tend to have higher bmis (kennedy et al)
• indirect measure of body fat, does not reflect changes in body fat and muscle mass (rothman 2008)

Question 10

3 bodyweight trends

Answer 10

stats from 2016 (published 2018 by WHO)
- 1.9 billion adults overweight, 650 million obese
- 41 million children under 5 + 340 million aged 5-19 overweight or obese
-8.4% moderately/severely underweight in girls

Question 11

what risk factors are child obesity/overweight associated with

Answer 11

type II diabetes (biro 2010)
metabolic syndrome in youth (biro 2010)
obesity as an adult (biro 2010)

Question 12

what risk factors are adult obesity/overweight associated with

Answer 12

cardiovascular disease (ortega 2016)
type II diabetes (monkdad 2003)
some cancers (fon + burgada 2016)

Question 13

what do adoption studies show

Answer 13

suggests genetic influence but doesnt indicate type of influence
environment also affects obesity

Question 14

what do twin studies show

Answer 14

look at concordance rates for mz and dz twins for bmi
concordance higher for mz than dz suggesting genetic link

stunkard et al 1986: MZ twins reared apart showed high within pair correlation in BMI (no correlation with adoptve parents and adoptee)

Question 15

genes and bmi

Answer 15

two genes have been identified that relate to bmi
- correlation used so no cause and effect, is bodyweight influencing genes or vice versa

Question 16

why are there genes predisposing people to obesity

Answer 16

-evolutionary explanation
-darwin origin of species
-organisms evolve through natural selection
-genetic variations occur spontaneously (if advantageous they are passed on)
-there must have been fitness benefit in past to have genes for obesity

Question 17

why is there survival advantage to genetic predisposition to obesity

Answer 17

-having adaptation is not disadvantageous so gene drifted (drifty gene hypoth)
-thrifty gene hypoth

Question 18

what is the thrifty gene hypoth

Answer 18

Neel 1962
-explanation for type 2 diabetes
-genes for diabetes previously advantageous as having more fat = better able to survive famine
-when food is abundant, adaptation prepares for famine which doesnt come

Question 19

weaknesses of thrifty gene hypoth

Answer 19

• strong selective force so everyone would have obesity but this is not case (speakman 2007)
  -famine not frequent in past, only issue was 12,000 yrs ago, selective pressure would have to be huge for gene to spread over 12000 yrs

Question 20

what is the drifty gene hypoth

Answer 20

speakman 2008
-questions the assumption that evolution is through natural selection
-believes many processes lead to genetic change e.g genetic drift
-body weight in animals is well regulated between lower and upper level (selected for by different evolutionary pressures: lower level = starvation risk and upper level = predation risk)
-2 - 2.5 million yrs ago predation risk disappeared due to: social behaviours, predator risk, weapons, fire
-without selective pressure, those genes were subject to random mutation and genetic drift

Question 21

what is genetic drift

Answer 21

change in frequency of a particular variant of a gene (allele) due to chance rather than reproductive success

Question 22

weakness of drifty gene hypoth

Answer 22

-why hasnt obesity been around for 20000 yrs
speakman argues: abundance of food was not available at that time, insufficient food for bodyweight to increase to drifted upper level

Question 23

what is the overarching criticism

Answer 23

selleyah 2019
-evolutionary theories treat humans as homogenous block failing to account for interethnic differences

Question 24

what is selleyahs theory

Answer 24

-unifying theory to account for social and cultural factors
-maladaptive scenario: genes that provide cold adaptation rather than heat also influence increase in metabolic rates (providing way to burn off excess energy when food is abundant