Lecture 7-Obesity Flashcards
What is Obesity?
Obesity is defined as a BMI >=30 kg/m².
What are the measures?
Computerised tomography/MRI/Ultrasound
Skinfold thickness
Waist/hip ratio
Underwater weighing
What are some Health consequences associated with Obesity?
Type 2 diabetes
Not all countries obesity rates are the same
THUS, environment may influence extent of obesity
Interactions with an ‘obesogenic environment’
Sources of negative feedback
Leptin- fat signal
Researchers discovered genetic mutation in 60s’ that caused obesity in mice
Perhaps gene responsible for obesity?
Zang et al (1994)
The ob gene encodes for a hormone that Inhibits food intake. ‘Leptin’ provides Negative feedback from adipose tissue.
Leptin responsibility for regulating food intake
Ghrelin (gastric hormone) down regulated in obese individuals; form of negative feedback
Or become resistant to inhibitory effect of leptin, causes obesity was another proposed idea
Homeostatic (set point) model of eating and energy balance
▪ Intake and expenditure are not coupled in the short-term, but over time they roughly balance
▪ A ‘settling point’ model of energy balance
▪ Relatively weak weight-related negative feedback control of appetite
Larger you are the more fat tissue you will have and more energy you expend
Weight of barrel; as water increase, pressure on hose increase, this will limit the amount of water that can enter in the first place
Energy balance though of the occurrence of a number of different factors acting in constant to develop a settling point
Prentice & Jebb (1995)
Obesity is due to…
Decrease in physical activity
Westerterp & Speakman (2008)
Obesity must be due to increased food intake
Looked a really accurate measure of energy balance
Daily energy Expenditure is not significantly difference from individuals in the first world
THUS, increase focus on nutrition
Thrifty-gene hypothesis – OBESE BY DESIGN-
Argued; inherited thrifty genes; enable us to collect and process food in order to despot fat in period of food abundance (helpful for hunter-gatherers)
We are thrifty by design; when we encounter food, we eat it whenever it is available
It is a historically adaptive strategy; if food abundance is followed by famine
Designed to protect our self from famine
Thrift genotype prepares individuals for a famine that never comes; causes wide spread obesity as a result
Evidence against thrift gene hypothesis
SPEAKMAN (2007)
- Famines were irregular and quite rare
- Strongest evidence against thrifty gene: Modern hunter/gathers are not obese
- Why are we all not obese? 30% are obese in the US – if there was a strong selection
Drift-gene hypothesis – OBESE BY ACCIDENT
Humans would have heavily predated in the past
BUT now there is a change in predation (no predators)
Don’t need to uphold a high body weight
Strong disease related pressure against lowering the lower intervention point
No selective pressure constraining the upper intervention point
Mutations increases upper limit remain
Mutations lowering in the lower intervention point would be selected against
Over time interventions points drift apart
Since then, genes that coded for an ‘upper defense’ of body weight has been left to ‘drift.’
Protein-leverage hypothesis – OBESE BY NECESSITY
Perhaps we are adapted to take an interest in our protein intake
Minimum protein required that MUST be defended above all other requirements
Diets with less protein; deficit of minimum protein requirement; in response we increase our total requirement of food in order to reach target
Risk factors
Early development
-> Catch-up growth
Chaotic eating
Food insecurity
Food insecurity: Insurance hypothesis
Obesity is not currently adaptive but rather reflects a strategy that promoted fitness over evolutionary time (a form of evolutionary mismatch)
So do food insecure populations in low-income countries want to be fatter? Yes
It is costly to become obese; argues that a higher BMI protective against food shortages
Socioeconomic status could be seen as a proxy for concern about future food
Reflects a strategy of promoted fitness (evolutionary mis-match)
