Obesity I Lecture 15 & 16 PSYU3352 PDF

Obesity I Appetite: The psychology of eating and drinking 1 1 Introduction The aim of this lecture is to: – Outline what obesity is – Outline how obesity is measured –...

Obesity I Appetite: The psychology of eating and drinking 1 1 Introduction The aim of this lecture is to: – Outline what obesity is – Outline how obesity is measured – Describe its prevalence (i.e., % in population) In the US, Worldwide, Australia and NSW With respect to ethnicity, age and SES – Examine its medical and financial costs to individuals and society 2 2  What is obesity? The body utilises fat cells for The reason they're brown is long-term energy storage because they're very rich in We have 2 types of fat cell mitochondria and they're used to Brown fat cells (BAT) are used to generate heat. generate heat and are located either side of the spinal column (shoulders) BAT are rich in mitochondria (hence high energy use) and are not directly implicated in obesity BAT cells contain 30-50% fat BAT constitute 5% of the body mass of babies to generate heat The distinction between the 2 types may not be absolute 3 3 White fat cells White fat cells have several functions: – They insulate the body A person with 2mm of subcutaneous fat will feel as comfortable at 15C as a person with 1mm will feel at 16C – They cushion the internal organs – They form the bodies long-term energy store Each white fat cell is 85% fat This is stored in a single large vacuole It is not currently known whether obesity is the result of the progressive enlargement of a set number of white fat cells or enlargement plus the addition of new white fat cells – White fat cells serve an important endocrine function Leptin Resistin (producing insulin resistance in a variety of cell types) Fasting-inducing Adipose Factor (akin to Leptin in action) The full variety of this endocrine role is not as yet fully elucidated Resistin is a hormone 4 4  White fat cells Around 20% of an average weight woman and around 15% of an average weight man is composed of white fat cells This represents roughly 1 months store of energy White fat cells are distributed in different ways in men and women Women more on hips/thighs and men more on the waist Subcutaneously and around organs in both When we ingest more energy than we use we are in positive energy balance It is under these conditions that we start to turn this excess energy into fat which is stored in the white fat cells It is this process which can ultimately result in obesity 5 5 Measurement of obesity The aim of all forms of obesity measurement is to estimate the proportion of a person’s body which is made of fat (i.e., white fat cells) The most frequently used measure is the Body Mass Index (BMI) or Quetelet’s index. To calculate your BMI you divide your weight in Kilograms by the square of your height in Metres – For an average Australian man weighing 85 Kg and 1.79 M tall – Their BMI = 85/(1.79 x 1.79) = 85/3.2 = 26.6 What does this mean? 6 6  BMI* for adults BMI’s below 18.5 are in the underweight range BMI’s of 18.5-24.9 are in the normal range BMI’s of 25.0-29.9 are in the overweight range BMI’s above 30 are in the obese range – Moderate obesity 30.0-34.9 – Severe obesity 35.0-39.9 – Very severe obesity 40.0+ (or Morbid obesity) There is some argument about where cut-offs fall (*WHO classification scheme, 1998) 7 7 The additional weight they're carrying is muscle mass weight rather than fat Pro’s and Con’s of BMI For – Easy to use – Can be measured remotely – Accurate – Correlates with adiposity (r = 0.4 to 0.9) Against – Takes no account of fat distribution (abdominal vs. other) – Takes no account of variation in muscle mass (e.g., many professional athletes have BMIs in 25-32 range) – Influenced by age – Influenced by trunk to leg length 8 8  Other measures Skin fold thickness (Calipers) – Stomach and top of arm/leg – Does not provide measure of general adiposity (adiposity= overall fat) – Difficulty of definition Waste circumference – Around stomach (or waist to hip ratio) – Good for estimating a separate risk factor for heart disease and stroke Excess risk occurs in men with waists 94cm+ and in women with waists 80cm+ – Does not provide measure of general adiposity – Difficulty of definition, especially in the obese Bioelectrical impedance – Indirectly estimates % body fat by measuring the resistance to flow of electricity through the body – Very sensitive to hydration status of body – Only provides a rough overall measure of body fat Other measures – Ultrasound, Chemical [metabolic rate], Computerised Tomography/MRI 9 9 Prevalence There is a consensus that we are in the midst of an obesity epidemic – This is affecting men and women, (and boys and girls), to a similar extent, which is why most of the statistics to come are not divided by gender For reasons that should now be clear, most large scale studies rely upon using BMI We will look at data from large scale surveys in the US, Worldwide, Australia and NSW We will start with the US 10 10  Prevalence data in the USA The CDC (Centre for Disease Control) provides the worlds most comprehensive set of data on body weight These data come from the Behavioral Risk Factor Surveillance System (BRFS) which is a telephone interview conducted with a representative sample of Americans in all states every year Note that the CDC slides to follow just show obesity (BMI 30+) – The first set of slides cover 1990-2006, where you can see the epidemic unfolding before your very eyes (and the epidemic really starts in the early 1980s) – and so I’m going to scroll through these fairly quickly – This is followed by data from 2007 and from 2019, which we will look at in a little more detail (and noting the legend changes too) Studies consistently show that telephone surveys systematically underestimate levels of obesity and overweight (by around 5%) so these are conservative estimates This view is supported by the National Health and Nutrition Examination Survey (NHANES) which actually measures people and indicates broadly similar results 11 11 Obesity Trends* Among U.S. Adults BRFSS, 1990 (*BMI ≥30, or ~ 30 lbs. overweight for 5’ 4” person) No Data