Energy Metabolism Flashcards
Energy Balance
Energy input = Energy output
Energy intake = energy expenditure
Negative Energy Balance
the body does not meet its energy requirements through diet
energy intake < energy expenditure for basal function
- loss of adipose tissue
- loss of muscle
- weight loss
Causes:
- insufficient food availability
- anorexia nervosa
- bulima nervosa
- cancer
Anorexia
- highest -> psychiatric disorder
- onset -> pre- or postpuberty; possible at any age
- more females
- preoccupation with food, refusal to healthy body weight
- weight loss -> excessive dieting and exercising
- damage occurred in various tissues and organs, loss of hairs, change in skin colour, teeth/bine degradation, organ failure
Bulimia Nervosa
- life-threatening eating disorder
- binging and purging; forced vomiting or excessive exercise
- preoccupation with body shape and weight; fear of gaining weight; feeling of uncontrolled eating behaviour; eating until the point of discomfort or pain
- risk: female, young age, family history, psychological and emotional issues, performance pressure in sports
- health problems: dehydration, heart failure, amenorrhoea, anxiety
Female Athlete Triad
A syndrome of 3 interrelated conditions:
- disordered eating
- irregular menstruation
- low bone density
How does it develop:
- excessive exercise combined with eating disorder -> irregular menstruation -> associated w/ low estrogen levels and results in low bonded density
Manage the disorder:
- reduce preoccupation w/ foods, weight, body fat
- inc. meals and snacks to the appropriate amount
- achieve weight for height
- dec. training time and/or intensity by 10-20%
What is Relative Energy Deficit in Sport?
a syndrome of poor health and declining athletic performance that happens when athletes do not get enough fuel through food to support the energy demands of their daily lives and training
Positive energy balance
Energy input > energy output
- gain of adipose tissue
- gain of muscle and bone tissue
- weight gain
- overweight, obesity
Causes:
- excessive caloric intake
- too little energy output for the amount of caloric consumed
- genetic/biochemical mechanisms
What are the potential mechanisms for regulating body weight and composition?
- Dietary composition
- Portion size and frequency of meal consumption
- food intake regulation/satiety
- Genetic influences
- Exercise
Dietary composition
- high-fat food products
- sweetened beverages
Portion size and frequency of meal consumption
Obesity-related to larger portion sizes of main meals
- omitting meals -> gain weight
food intake regulation/satiety
Hormones => hypothalamus -> connecting nervous system and endocrine system
Two groups of neurotransmitters:
1. melanocyte-stimulating hormone (MSH) => dec. hunger -> cholecystokinin, insulin, leptin -> stimulate the release
2. neuropeptides Y (NPY) and agouti-related protein (ARP): inhibits MSH -> inc. hunger -> Ghrelin -> stimulate the release of them
Leptin
- secreted by adipose tissue
- stimulates MSH; dec. hunger
- leptin receptors “defective” in obese people
-> No suppression of hunger by elevated leptin levels - weight loss -> dec. leptin -> response to starvation
- weight gain -> inc. leptin -> response to obesity
Genetic influences
Melanocortin receptor (MSH = a melanocortin) => defect leads to loss of regulation for hunger -> obesity
Fat mass and obesity-associated gene (FTO) => polygenic effect on obesity: variation in FTP strongly contributes to early onset
Heritability: body weight and composition
Leptin receptor
Exercise
- can lead to a negative energy balance
- beneficial for obese/overweight individuals; detrimental for individuals with eating disorders
Methods for measuring body composition focus on two compartments
- Fat mass => triacylglycerols, other lipids, little water, electrolyte
- Fat-free body mass => water, muscle, bone, connective tissue, organs
- lean-body mass => fat-free plus essential fats
what are the compartments:
- Density
- Ability to conduct an electrical current
- Electrolytes content
- X-ray density
Methods to measure fat-free mass
- Total body water
- bioelectrical impedance analysis
- dual-energy x-ray absorptiometry
Methods to measure fat mass
- Anthropometry
- densitometry
- dual-energy x-ray absorptiometry
Anthropometry
- **caliper to measure skin fold thickness **
- direct relationship between total body fat and fat deposited beneath the skin
- higher potential error
waist circumference and waist/hip ratio - both correlate with visceral fat
- both associated w/ CVD risk
- waist/hip less accurate
- waist circumference => predictor for risk of heart disease, stroke, high blood pressure, high blood cholesterol, type 2 diabetes
Densitometry
underwater weighing = measurement of body fat
Advantage:
- non-invasive
- precise
Challenging:
- high equipment cost
- extreme cooperation and time required of subjects
- not suitable for young children, older adults, unhealthy people
calculation based on the assumption
- fat mass has no constant density; consists of different components that have different densities (bone, muscle, organs, etc)
- leads to errors in calculating body fats
Absorptiometry
Dual photon absorptiometry and Dual-energy x-ray absorptiometry (DEXA, DXA)
- measures the attenuation of X-rays while passing over the body
- flux of x-ray -> across the fat and fat-free masses
- correlated w/ other body composition methods => estimation of %, fat mass, fat-free mass, bone mineral density
Challenge:
- high equipment cost, trained personnel, inaccurate for patients w/ metal implants
Bioelectric Impedance Analysis
Measurement of electrical conductivity in the body:
- instrument induces -> electrical current
- measures proportional to electrolytes and water content
- electrolytes are mostly associated w/ lean body mass
Challenges:
- expensive, readings affected by hydration and electrolyte imbalance
Total Body Water
use of stable isotope labelled water (D2O)
Principle:
- injection/ingestion of labelled water
- distribution of isotope in body water (w/in 2-6hours)
- measurement of labelled water in body fluids
calculation = based on the assumption that water content of lean body mass = 73%
challenge:
- requires trained personnel
- hydration status impacts results
- degree of hydration in lean tissue carried considerably
- adipose tissue contains 15% water by weight
BMI
- inexpensive and simple
- used for the classification of a person’s risk of developing health problems
- does not directly measure body fat -> indirect parameter for body fat
methods -> underwater weighing and dual-energy x-ray absorptiometry (DXA)
