Healthy Weight Maintenance Flashcards
Evaluating Body Weight
Use body mass index = weight (kg) over height (m) squared.
Body composition
Fat distribution
BMI
Weight to height ratio (kg/m2)
Minimally invasive.
Limitations with athletes as if you are too muscular for your height, you will be labelled as overweight even if you aren’t.
BMI is directly associated morbidity and mortality
-as BMI increases, morbidity and mortality go up.
-directly go up with males, but females is not directly related.
Body Composition
Percentage of mass accounted for by fat and lean tissue (2 compartment model).
Common 2 compartment techniques include underwater weighing (must ensure no air bubbles/pockets), skinfolds, bioelectrical impedance analysis (must control for hydration).
Dual Energy X absorptometry (DEXA) is a 3 compartment model where it takes into account bone density and can look at muscle and fat too.
Fat Distribution
Waist to hip ratio (WHR) = ratio fo waist compared to hips.
-waist circumference measured at narrowest part of the waist, between the lowest rib and iliac crest.
-hip circumference measured at the widest area of the hips at the greatest protuberance of the buttocks.
High risk for men = WHR >1
High risk for women = WHR >0.85
Increased abdominal fat is directly associated with morbidity and mortality among men and appears even more so among women.
Physiology of Fat Cells
Overweight children develop more fat cells.
Extra fat cells develop in the abdomen.
Abdominal fat is more sensitive to hormones.
Metabolically active fat cells rapidly store and release fat.
Fatty acids get dumped almost directly into liver.
Fatty acids dumped on the liver increase LDL and decrease HDL.
Elevated free fatty acids in the blood induce insulin resistance.
What are some big ideas with weight maintenance?
Variety of ways to evaluate body weight.
Fat distribution varies among men and women.
Abdominal obesity is associated with disease.
Energy Balance
Energy intake = energy expenditure
Environmental factors disrupt this balance.
Weight is maintained when isocaloric balance where calories in = calories out.
Weight loss when negative caloric balance where calories in < calories out.
Weight gain when positive caloric balance where calories in > calories out.
Components of Total Energy Expenditure
Includes…
-basal metabolic rate (BMR) = ~30%
-thermic effect of food = ~10%
-activity energy expenditure = ~60%
BMR
Energy to maintain body function
Influenced by thyroid hormones and muscle mass.
After 30, BMR declines ~3.5% per decade due to loss of muscle mass.
Factors Increasing BMR
High lean body mass
Greater height
Younger age
Elevated thyroid hormones
Acute stress (exercise, frightened, chronic stress, fever/illness
Pregnancy and lactation
Stimulants (coffee, tobacco)
Factors Decreasing BMR
Lower lean body mass
Lower height
Older age
Depressed thyroid hormones
Starvation, fasting, caloric restriction
Television (when watching TV, we can decrease BMR)
BMR and Caloric Restriction
Caloric restriction decreases BMR.
Results in a 6-20% decrease in BMR among obese adults and adolescents.
BMR returns to normal levels once energy balance is achieved.
Thermic Effect of Food
Energy expended digesting, transporting, storing, and metabolizing nutrients.
5-10% of a mixed meal (25-50 kcal of 500 kcal meal)
Fat requires little energy to digest, transport, and store.
Activity Energy Expenditure
Body movement/muscular work = highly variable
Metabolic Equivalent (MET)
Standardized approach for quantifying activity energy expenditure.
1 MET = 1kcal/kg/hr = energy cost of sitting quietly
1 MET = 3.5 ml/kg/O2
3 MET = moderate physical activity = 3 times the energy cost of sitting.
Activities involving more/larger muscle groups expend more energy
Factors Affecting Body Weight
Little control = genetics (25%)
-overfeeding responses of identical twins illustrates genetic predispositions to gain weight
Lots of control = lifestyle choices (75%)
-non-genetic (lifestyle) factors play a larger role than genetics in the accumulation of body fat
Overfeeding Twin Studies
Found variability/heritability of weight gain
Can show how genetics control within a gene pool but there is much variability outside of it.
Early Theories of Genetic Factors of Weight Maintenance
Thrift gene theory = bodies efficient at storing fat for lean tissue.
Set-Point theory = body defends weight within narrow limits; calorie reduction results in BMR reductions and vice versa
Thrifty phenotype = womb environment impacts development of metabolic syndrome
Epigenetic’s
Our behaviours up and down regulate gene expression
Non-Genetic Factors for Weight Maintenance
Physical environment, personal, socio-cultural
Complex and interrelated.
Physical Environment and Weight Maintenance
Home, schools, workplaces, communities
The Built Environment and Weight Maintenance
Influences diet and activity
Relationship between physical activity and the built environment.
Socio-Cultural Factors and Weight Maintenance
Parents, friends, cultural beliefs and practices
The attack on appetite = media, the science of junk food, portion distortion
Childhood Obesity
Obesity tracks from childhood to adulthood.
-50% of obese kids become obese adults
-70% of obese adolescents become obese adults.
Children have little control over their environment
Having obese parents increases the risk of obesity.
Physical inactivity tracks
-inactive children become inactive adults
Sedentary and poor eating behaviours track.
Personal Factors and Weight Maintenance
Personal behaviours, lifestyle choices, higher education and income are linked to better health.
Obesity
Is a polygenetic and environmental problem.
-Interactions between genes and between genes and the environment.
