Please enable JavaScript.
Coggle requires JavaScript to display documents.
Obesity - Coggle Diagram
Obesity
Why study obesity
Suffering from obesity is associated with development of health risks: cardiovascular disease, type 2 diabetes, common cancers
-
-
-
Defining Obesity
-
Fat accumulation is measured by BMI >30 (KG/Height). This is easy to calculate and so is a common method, however, it doesnt measure body fat- so those with a high muscle mass would be overweight
Asian heritage are at higher risk of disease at lower BMI, so the relationship varies between ethnicities
Another method is to look at body fat distribution: Apple VS Pears. Fat around the abdomen (apple shaped) associated with health risks- this fat can be measured by calculating the waist to hip ratio
Causes of Obesity
Energy balance Equation: the energy intake is higher than energy output. Obesity is a state of positive energy balance
Our environment now involves a lot of sedentary work, activities (computer games), more roads over pedestrian paths.
Westerterp and Speakman (2008) measure of energy expenditure using double labelled water: Amount of energy expended from physical activity is unchanged despite society developing
What are the components of energy expenditure? Physical activity expenditure, resting energy expenditure and thermic effect of food
-
Food intake
-
-
The current food environment in which we live (wide variety and food with high energy density value) these types of environments may be a driver promoting higher energy intakes which may be moderated by the social environment that we live in. This may lead to more food consumption and less physical activity.
Obesity is inheritable (65% of variation is due to genetics). This genetic predisposition is only expressed under certain conditions (geneXenvironment interaction)
Thrifty Gene hypothesis: our ability to store fat is an adaptive trait. So these genes are being selected for and will become common in the population
This is no longer advantageous and so no longer adaptive. BUT if the theory is correct we should all have these genes and should have all obesity.
Drifty gene hypothesis (2008): Early humans being under a selection pressure to avoid starvation and predation, so evolution of behaviours that ensure body weight does not go too high or low which randomly drifted through the population through random mutation.
Predation risk minimised by social/cognitive advances of living, meaning there is no selection pressure on genes working against accumulation of body fat. So now genes that predispose to obesity have drifted through the population
Some forms of obesity result from a single gene mutation (Monogenic forms): these are relatively rare.
Two types: Syndromic obesity associated with neurodevelopmental genetic conditions. Non-Syndromic incl. the obesity gene which codes for leptin which tells the brain how much stored fat we have, this mutation leads to no leptin being produced so there is no signal to the brain. also Incl. mutation of melanocortin receptor involved in food intake.
Polygenic model: we cannot explain obesity alone from the monogenic forms. Instead people are mostly suffering from numerous gene variants with individually small effects creating a culminative effect. Loci carry genes involved in appetite (MC4R and FTO)
Some possible phenotypes: Low satiety, reward driven eating, low cognitive control, emotional eating