11.1 Energy Balance and Body Composition Flashcards
What does energy balance refer to?
- Ideally, energy intakes cover energy expenditure
- Body weight is stable when energy consumed is equal to energy expended
What does positive energy balance refer to?
When energy consumed is greater than energy expended, weight increases
What does negative energy balance refer to?
• When energy consumed is less than energy expended, weight decreases
How much energy does 1kg of body fat contain?
A ‘classic rule’ states that one kilogram of body fat contains approximately 30 000 kJ of energy
What does the weight gained/lost in the body actually include?
- Quick changes in body weight are not simple changes in fat stores
- Weight gained or lost rapidly includes:
- Over the long term, weight lost is around 75% fat and 25% lean
How does a bomb calorimeter measure food energy?
- Direct measure of food’s energy value (as heat is measured)
- When food burns, the chemical bonds break
- Carbons and hydrogens combine with oxygen to form CO2 and water
- The amount of oxygen consumed = an indirect measure of the amount of energy released
What are the two types of calorimetry?
- Direct calorimetry measures the heat energy released
- Indirect calorimetry measures the amount of oxygen consumed and carbon dioxide expelled
What does physiological fuel value refer to?
- Human body is less efficient and can not completely metabolise all of the energy in food
- Physiological fuel value is the difference between the number of kJs measured with calorimetry and the number of kJs that the human body derives from a food
How much energy does each macromolecule contain?
Why do we eat?
What is hunger controlled by?
- Is controlled by chemical messengers in the brain, particularly the hypothalamus
- Influenced by presence or absence of nutrients in the bloodstream, size and composition of the previous meal, customary eating patterns, climate (heat reduces eating, cold increases), exercise, hormones and physical and mental illness
- Stomach acts as a hopper – around 4 hours after a meal, all the food has left the stomach
What is the difference between satiation and satiety?
- During a meal, hunger diminishes and satiation develop which causes us to stop eating
- Receptors in the stomach stretch, and hormones such as cholecystokinin increase
- Satiety should remind us not to eat again until the body needs food
- Satiation = stop eating
- Satiety = don’t start eating again
What is the cycle of hunger, satiation and satiety?
What are some signals to overeat?
- Eating can be triggered by other signals; e.g. stress or anxiety
- Cognitive influences to overeat might include:
- large portion sizes
- memories
- intellect
- social interactions
How else can hunger be suppressed?
- Hunger can also be suppressed by signals other than satiety, such as:
- stress and how people perceive it
- eating disorders
- enforced discipline
What is the basal metabolic rate?
- About two-thirds of the energy a person expends/day = basal metabolism
- Basal metabolic rate (BMR) is the rate the body expends energy to maintain essential body functions
- e.g. breathing, heart beat, maintaining body temperature, filtering waste
What are some factors affecting the basal metabolic rate?
- Gender – Men generally have a higher BMR
- Growth – BMR is high in people who are growing
- Age – BMR declines as lean body mass decreases
- Physical activity – Activities are clustered by intensity and vary considerably
- Body composition and body size – BMR is higher in people with lots of lean body mass than in those with less
How does physical activity affect the energy expenditure?
- Physical activity (voluntary movement):
- Most variable component of EE
- Significant in weight loss and weight gain
- Duration, frequency and intensity influence energy expenditure
How does the thermic effect of food affect energy expenditure?
- about 10% of total energy intake
- Digestion and absorption require energy (e.g. for contractions, making and secreting digestive juices, active transport during absorption)
- Produces heat
- Greater for high protein foods than high fat foods
What is adaptive thermogenesis?
- Adjustment in energy expenditure related to environmental changes
- E.g. when the body has to adapt to extreme cold, overfeeding, starvation, trauma or other forms of stress
- Physiological adjustments are made (e.g. building tissue, making enzymes) – they require energy
- However, as adaptive thermogenesis is so variable, it is in calculations of energy requirements not included
What is body mass index defined by?
What is the function of body fat?
- provides energy
- insulates against temperature extremes
- protects against physical shock
- forms cell membranes
- makes compounds such as hormones, vitamin D and bile
Where is fat distributed around the body?
- Fat distribution and location is the key to health outcomes
- Fat stored around the organs of the abdomen = central obesity or intra-abdominal fat
- Fat deposited in the abdominal cavity strongly predisposes to metabolic syndrome, type 2 diabetes and heart disease
What is the difference between male and female fat distribution?
- Abdominal fat more common in men than women
- Men tend to have apple-like ‘androidal’ obesity
- Young and middle-aged women tend to have pear- like ‘gynoidal’ obesity
- After menopause women’s fat distribution becomes more androidal
What does weight circumference indicate?
- Waist circumference:
- – >88 cm is considered substantially increased risk for women
- – >102 cm is considered substantially increased risk for men
- Indicator of fat distribution and central obesity
- Sometimes waist-to-hip ratio used, but waist circumference is easier
What are some other measures of body fat?
How does BMI link to mortality?
- BMI and mortality
- J-shaped curve
- Both underweight and overweight are associated with increased risk of premature mortality
What does disorded eating in athletes lead to?
Young athletes/dancers may restrict energy intake to:
a) Improve performance
b) Improve aesthetic appeal of their performance (e.g. gymnastics, ballet)
c) Meet weight guidelines of their sport (e.g. wrestling)
What is anorexia nervosa?
- Diagnosed when someone has distorted body image that overestimates personal body fatness
- Cannot be self-diagnosed After a few months:
- Most people have protein–energy malnutrition (PEM) that is similar to marasmus
- Females suffer from amenorrhoea
What happens to the person in bulimia nervosa?
- Like the person with anorexia nervosa, the person with bulimia nervosa spends much time thinking about body weight and food but bulimia nervosa is the not the same disease as anorexia nervosa
- A bulimic binge is characterised by a sense of lacking control over eating
- A vicious cycle of restricting, binging and purging often accompany this disorder
What is binge eating disorder?
- Diagnosed based on recurring episodes of binge eating, with a marked sense of lack of control
- Can occur in people of normal weight as well as those who are severely overweight
What are the two types of fat in the body?
- Subcutaneous fat
- Found under the skin
- Protective wrap over the body’s surface
- Visceral fat
- Located inside the peritoneal cavity, between the organs
- Contributes to belly fat
- Strong correlation between central obesity and CVD, insulin resistance, type 2 diabetes, inflammatory diseases, high blood pressure and other obesity related diseases
When does the number of fat cells in the body increase?
- Excess energy is stored in fat cells
- Fat cell numbers increase most rapidly in later childhood and early puberty
- After we stop growing, fat cell numbers continue to increase whenever energy balance is positive
- Obesity due to an increase in the number of fat cells is called hyperplastic obesity
How do fat cells change during obesity?
- Obesity due to increase in size of fat cells is called hypertrophic obesity
- Enlarged fat cells stimulate the production of more fat cells
- People with obesity have more fat cells than healthy weight people, and their fat cells are larger
How do fat cells change during negative energy balance?
With negative energy balance, the size of the fat cells decreases, but not the number
How does lipoprotien lipase promote fat storage?
- Lipoprotein lipase (LPL) promotes fat storage in adipose and muscle cells
- People who are obese have more LPL activity in their fat cells than lean people do
What are the gender differences in LPL fat metabolism?
- LPL is regulated by gender-specific hormones: oestrogen in women testosterone in men
- In women, fat cells in the breasts, hips and thighs produce abundant LPL – stimulating fat deposit
- In men, fat cells in the abdomen produce abundant LPL – increasing risk for developing central obesity
How does the set point affect weight loss and regain?
- Weight loss may increase LPL action (promoting fat storage)
- It has been proposed that the body prefers to maintain weight at a ‘set point’
- i.e. after losing weight, the body tries hard to return to the original weight
- The idea is that the ‘set point’ moves gradually over time for long- term weight loss
- Yo-yo Dieting
What are some factors behind the causes of obesity?
What does the mouse leptin experiment show?
- Obesity gene ob codes for the protein leptin which is a hormone produced by fat cells
- Both mice have a defective ob gene
- Neither produced leptin but both became obese
- Mouse on the right received injections of leptin which supressed food intake
- Increased energy expenditure and led to weight loss
What is the difference between white and brown adipose tissue?
- White adipose tissue stores fat for other cells to use
- Brown adipose tissue releases stored energy as heat
- Important for newborns
- Brown fat accounts for less than 1% of fat cells in adults
- Recent research suggests ‘browning’ of fat cells (to brite/beige) increases energy expenditure may reduce obesity
What is the psychology of weight cycling?
What happens in a gastric bypass surgery?
- Limits the amount of food that may be eaten without discomfort
- Dark pink area shows the altered flow of food through the GI tract
- Pale pint area indicates the bypassed section
What happens in gastric banding surgery?
- Limits the amount of food that may be eaten without discomfort
- Dark pink area shows the altered flow of food through the GI tract
- Pale pint area indicates the bypassed section
What happens in a sleeve gastrectomy surgery?
- Limits the amount of food that may be eaten without discomfort
- Dark pink area shows the altered flow of food through the GI tract
- Pale pint area indicates the bypassed section
- For all these surgeries, patients may develop nutritional inadequacies e.g. absorption of nutrients may be reduced
How can people change their eating patterns to achieve weight loss?
- Emphasise nutritional adequacy: Adequate kilojoules are provided by a balanced diet of fruits, vegetables, whole grains, lean meats and alternatives, and lower-fat milk products
- Eat small portions using small plates and utensils
- Lower energy density by eating from five healthy groups and avoiding excessive amounts of nutrient poor energy dense discretionary foods
How have public health programs been suggested to decrease obesity?
