Obesity: Causes, consequences and interventions
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What is BMI?
Body mass index : weight (kg) / height m2
What BMI constitutes as being obese?
Above 30 kg/m2 • Obese I = 30-34.9 • Obese II = 35-39.9 • Obese III = 40+ (morbidly obese)
What BMI is healthy?
18.5 - 24.9 kg/m2
What are the problems with BMI?
• Doesn’t allow for difference in weight between muscle and fat • Doesn’t consider location of fat
Why is waist circumference important?
It considers the location of fat, abdominal fat predicts some conditions (eg. type-2 diabetes) and associated with CV risk
How can you measure percentage body fat?
• Skinfold calipers • Bioelectrical impedance • Hydrostatic weighing • DEXA - dual energy x-ray absorptiometry
What are percentage body fat thresholds for men and women?
Men = 25% Women = 32%
How does hydrostatic weighing work?
Bone and muscle are denser than water so someone with a larger percentage of fat free mass will weigh more in the water and have a lower % body fat
How does dual energy X-ray absorptiometry (DEXA) work?
Divides body into total body mineral, fat-free soft mass and fat tissue mass
How much is life expectancy reduced by grade I obesity (bmi 30-34.9)?
Reduced by 3 years
How much is life expectancy reduced by grade III/Morbid obesity (bmi 40+)?
By 8-10 years, equivalent to effects of lifelong smoking
What are main health risks associated with obesity?
• Some cancers: eg. breast, colon • Musculoskeletal: osteoarthritis, lower back pain • Circulatory: high BP, CHD, DVT • Metabolic/Endocrine: T2 Diabetes, cholesterol, metabolic syndrome • Repro/Uro: Stress incontinence, menstrual abnormalities, infertility, erectile dysfunction • Respiratory: sleep apnoea, asthma • Non-alcoholic fatty liver disease • GI disease: gall stones • Psychological and social problems: stress, depression, low selfesteem
Are men or women more likely to gain abdominal fat?
Men
What 4 theories underly the causes of obesity?
• Genetic • Economic • Behavioural • Psychological
What two studies support than genes are related to obesity?
• Twin studies: Obesity far more similar in identical twins reared apart than in non-idential twins reared together • Adoptee studies: Adoptee’s weight far more strongly related to biological parents
How likely will a child be obese if they have (i) one obese parent (ii) two obese parents (iii) healthy BMI parents
(i) 40% (ii) 80% (iii) 7%
What does the metabolic theory suggest in regards to genetic vulnerability?
Resting metabolic rate is heritable and is associated with weight gain, however RMR is now lower in obesity.
What does the fat cell theory suggest in regards to genetic vulnerability?
Cell number mainly genetically determined, severely obese have larger and more cells, can increase number of cells especially in childhood
What does the appetite theory suggest in regards to genetic vulnerability?
Leptin regulates appetite, lack of evidence to show that obese produce less leptin
What does the economic theory suggest about obesity?
Cost of food as a proportion of our expenditure has decreased, high energy food are cheaper and time to prepare a meal has been reduced.
What are the behavioural explanations for obesity?
How the intake of food is greater than energy expanded, so eating more than burning. Some evidence for obese eating more fats relative to carbs, and eating more foods with high glycemic index.
Do the obese eat for different reasons than non-obese?
Unsubstantiated theory that obese respond more to external cues (sight of food) than to internal cues (hunger)
What are the reasons for a societal reduction in physical activity?
• Work patterns • Technology • Transport
What are the psychological explanations for obesity?
• Thinness associated with attractiveness • Aversion to fat • Stigma/blame • Low self-esteem, poor self-image • Is depression higher in obese? • Attitudes and beliefs associated with eating and PA levels