WEEK 3: Overweight and obesity

Question 1

what is energy balance?

Answer 1

*it is when the energy output is equal to the energy input
*the state at which the number of calories eaten equals the number of calories used.

Question 2

State the first law of thermodynamics

Answer 2

Energy cannot be created nor destroyed but it can be converted from one form to another

Question 3

What is energy input?

Answer 3

Chemical energy locked in bonds that hold the atoms together in nutrient molecules which is released when these molecules are broken down in the body
all energy used by cells derived from the food we eat

Question 4

State the two types of energy expenditure (output)

Answer 4

internal work
external work

Question 5

define external and internal work

Answer 5

External work: energy expended when skeletal muscles contract to move external object or to move the body in relation to the environment
internal work: All other forms of biological energy expenditure that do not accomplish mechanical work outside the body

Question 6

what is the percentage ratio of energy in nutrient transferred to ATP and the nutrient energy lost as heat energy?

Answer 6

50:50

Question 7

75% of energy output is converted to heat. What are the proportions of the sources?

Answer 7

50% : from nutrient breakdown
25% : from cellular processes

Question 8

Describe the 3 possible states of energy balance.

Answer 8

Positive energy balance: input is more than output
Negative energy balance: input is less that output
Neutral energy balance: (input = output)

Question 9

What is metabolic rate?

Answer 9

The rate at which energy is expended by the body during both internal and external work.
Energy expenditure per unit time

Question 10

State the formula for calculating metabolic rate

Answer 10

Metabolic rate= energy expenditure/ unit of time (kJ/s)

Question 11

What is basal metabolic rate(BMR) ?

Answer 11

It is the metabolic activity required to maintain basic body functions
It is the minimal waking rate of internal energy expenditure

Question 12

Describe the direct method of measuring BMR

Answer 12

A person sits a closed chamber with water circulating through the walls. The difference in temperature of the water entering and leaving the chamber reflects the amount of heat liberated by the person and picked up by the water as it passes the chamber

Question 13

Describe the indirect method of measuring BMR

Answer 13

*Indirectly through oxygen consumption measure

Food + O2 →CO2 + H2O + energy (mostly heat)

*Amount of O2 is proportional to the amount of heat

E.g., For a mixed diet, 1L of O2 will yield about 5Kcal/hr. of energy as heat (a known standard)

Thus, a measure of 12L of O2 will yield an energy output of 60Kcal/hr.

Question 14

State factors that influence BMR

Answer 14

HORMONES: Thyroid hormone, epinephrine increases BMR)
sleep; decreases BMR.

Question 15

State the conditions necessary when measuring BMR

Answer 15

Be at physical rest
Be at mental resting state
Not eat 12hr before determining BMR: to avoid diet-induced thermogenesis
Comfortable room temperature to avoid shivering

Question 16

State the three components of total energy expenditure

Answer 16

*Resting metabolic rate (RMR); energy requirement of an awake resting person measured after 8-12hr (70% of TEE)

*Thermic effect of food (TEF): energy required to digest and absorb food.

*Physical activity energy expenditure (PAEE).

NOTE: Physical activity (PA) and energy expenditure (EE) are therefore 2 separate measures

PHYSICAL ACTIVITY: Any bodily movement that requires energy expenditure.

Question 17

State the formula for calculating TEE

Answer 17

TEE= RMR+TEF+PAEE

Question 18

How do we measure what people are eating?

Answer 18

Diet history
Written food diary (Diet record)
24hr recall
Food frequency questionnaire (FFQ)

Question 19

What is BMI?

Answer 19

The body mass index (BMI) is a measure that uses your height and weight to work out if your weight is healthy.

Question 20

State the formula for calculating BMI.

Answer 20

BMI is defined as weight in kg / (height in m)2.

Question 21

Although increasing BMI is widely interpreted to indicate an increasing proportion of body fat (and vice versa), this is not always the case, and you should be aware of possible exceptions.

State the inconsistencies with BMI.

Answer 21

*Some sportsmen, particularly from games such as rugby, or American football, and body builders, may have a BMI high enough to put them in the ‘obesity’ range, even though they have very little body fat.

-This is because their training gives them abnormal amounts of skeletal muscle.

*Conversely some people, especially the elderly, may have apparently normal or nearly normal BMIs, but a high proportion of body fat, because they have a lower-than-normal skeletal muscle mass.

*Some malnourished individuals may develop oedema, and the increased body weight produced by water may push their apparent BMI towards the normal range even though they are severely undernourished.

*Children cannot be assessed on the normal adult scales. ‘Normal’ BMI ranges for children of different ages have been determined (Webb pp 192 – 3) but there are no internationally agreed standards.

Question 22

Describe the ranges for the following:

1.Underweight
2.Healthy
3.Overweight
4.Obese
*Obese class I
*Obese class II
*Obese class III

Answer 22

below 18.5 – Underweight range
18.5 -24.9 – Healthy weight range
25 -9.9 – Overweight range
30+ = Obese range

OBESE CLASSES
*Obese class I: 30-34.9
*Obese class II: 35-39.9
*Obese class III: 40+

Question 23

Outline other methods of measuring body fat.

Answer 23

*Skinfold thickness: this is the traditional direct method of body fat estimation. Thickness of a fold of skin is measured in several places using calipers. Tables can be used to convert the values obtained to percentage of body fat.

*Electrical impedance: fatty tissue conducts electricity much less well than lean tissue, and this principle can be used in instruments which measure body fat directly. This method is now being used in gyms and health clubs to give a fairly reliable and almost instant estimate of body fat.

*Body water content: fatty tissue contains little water, so measurement of body water content by the standard physiological dye dilution methods can give an estimate of the lean tissue mass of the body.

-Subtraction of this figure from total body mass will give an estimate of body fat.

*Mid –arm muscle circumference: this is a simple and fairly reliable method used in immobile or unconscious hospital patients and children being assessed for malnourishment. Measurements need standards for interpretation, but it is possible to set up a rapid, simple and reliable measurement technique.

Question 24

What is the normal waist hip ratio for men and women?

What is the normal waist circumference for men and women?

Answer 24

*A waist/hip ratio higher than 0.95 in men and 0.85 in women is regarded as indicating increased health risk.

*Waist circumference of 102 cm in men and 88cm in women is taken as the upper limit of normality.

Question 25

What is obesity?

Answer 25

*A disease

*Associated with increased risk to many other diseases

*Defined by relationship between body weight & height

Question 26

What happens to fat cells earlier and later in obesity?

Answer 26

*Earlier, fat cells become large (hypertrophy)
*Later, fat cells multiply (hyperplasia)

Question 27

Outline factors involved in weight loss and obesity.

Answer 27

*Family history and heredity (genetics)

*Family habits and culture

*Race or Ethnicity

*Age (older age associated with weight gain but this weight tends to settle at 60-65)

*Sex (females tend to gain more weight than men; however, women tend to gain weight around their hips and buttocks while men gain weight around the abdomen (belly fat)).

*Eating habits (e.g. eating food at night, eating food high in calories, sugar & fat, drinking beverages containing high sugar content etc.)

*Composition of bacterial colonies

*Physical activity habits (eg lack of exercise or physical activity)

*Stress

*Certain medical conditions (binge eating disorders, some endocrine disorders such as hypothyroidism)

*Certain medications

*Too little sleep (recommended 7 to 9hrs per day for 18 to 65yr-olds)

Question 28

Define the following terms;
*food
*diet
*nutrients
*balanced diet

Answer 28

food: substances we eat that contains nutrients

diet; a selection of food eaten by an individual

balanced diet; a diet consisting of all essential nutrients in the appropriate amounts and portions

nutrients; substances that are absorbed and used to promote cellular function.

Question 29

Define macronutrients and micronutrients

Answer 29

Macronutrients are the nutrients we need in larger quantities that provide us with energy: These are carbohydrates, proteins, fats, vitamins, minerals, fibre and water.

Micronutrients: are equally important but consumed in very small amounts.

Question 30

Name the sites in the body where energy balance is regulated

Answer 30

Hypothalamus
Brain stem

Question 31

What are the functions of hunger and satiety signals.

Answer 31

Feeding or hunger signals give rise to the sensation of hunger, stimulates the desire to eat.

Satiety is the feeling of being full; satiety signals serve to suppresses the desire to eat.

Question 32

What is the Hypothalamus’ role in body weight?

Answer 32

(a) Long-term control of energy balance and body weight

(b) Short-term control of food intake from meal to meal.

Question 33

Name the part of the hypothalamus involved in energy balance and body weight control.

Answer 33

Arcuate Nucleus of the Hypothalamus is part of the structures involved in energy balance and body weight control.

Question 34

State the two components of the arcuate nucleus of hypothalamus that are involved in long term energy balance and body weight.

Answer 34

*Has 2 sub-sets of neurons, functioning in opposing fashion (1st Order neurons).

-Neuropeptide Y (NPY) secreting neurons
-Melanocortinin-secreting neurons

NOTE:
*Pro-opiomelanocortins (POMC) is the precursor alpha-melanocyte stimulating hormone (MSH) in this case. Others are endorphin & ACTH.

Question 35

Describe the functions of the components of the arcuate nucleus involvement in long term energy balance and body weight.

Answer 35

(a) NPY secreting neuron
*a potent appetite stimulator
*Inducing a +ve energy balance & increased food intake & possibly weight gain

(b) Melanocortin (specifically, alpha-MSH)-secreting neurons
a potent appetite suppressor
Inducing a -ve energy balance & decreased food intake

Question 36

State other cells in the hypothalamus that are involved in long term energy balance and body weight control.

What are they collectively known as?

Answer 36

*(a) Lateral hypothalamic area (LHA)
Secrete OREXINS
Appetite stimulants

(b) Paraventricular neurons (PVN)
Secrete corticotropin releasing hormone (CRH)
Appetite suppressants

*Collectively called 2nd order neurons

NB! The 1st order neurons act to influence the activity of 2nd order neurons.

Question 37

What is the largest hormone-secreting organ in the body called?

Answer 37

An endocrine gland.

Question 38

What is the role of adipose tissue in the long-term energy balance regulation?

Answer 38

*Contains adipocytes which secrete a group of hormones called adipokines.

*Also plays a role in homeostasis and metabolism.

Question 39

State the adipokines produced in the adipocytes.

What are their functions?

Answer 39

Examples includes leptin, tissue necrosis factor, interleukin-6 (IL-6), adiponectin, visfatin, resistin

*Leptin:

(a) Inhibits the action of NPY- releasing neurons
-Thus, suppressing appetite
(b) Stimulates alpha MSH cells
-Thus, suppressing appetite

NB! The greater the fat stores, the higher the [plasma leptin]
Leptin- an appetite suppressor

Adiponectin:
-Increase sensitivity to insulin

*Resistin:
-Results in insulin resistance

*Visfatin :
-Associated with heart diseases as it is released from visceral fat

*Tumor necrosis factor and Interleukin 6:
-Contribute to low grade inflammation in excessive fat stores

Question 40

Differentiate Ghrelin and Peptide YY3-36 (PYY 3-36) in the short-term control of eating behavior or food intake by the GIT.

Answer 40

*G: Produced in the stomach
P: Produced in the small and large intestines and pancreas

*G: Appetite STIMULANT
P: Appetite SUPPRESANT

*G: Stimulates NPY- secreting neurons
P: Inhibits NPY-secreting neurons

*G; Signify hunger
P:Signify fullness (satiety)

Question 41

Insulin is also involved in the long-term control of energy balance.

Describe its function.

Answer 41

*Inhibits the action of NPY- releasing neurons.
Thus, suppressing appetite.

Insulin- also an appetite suppressor

Question 42

Short-term control of eating behavior by the Satiety Center

Where is the satiety center found?

What signals does it process?

Where do the signals arise from?

Answer 42

*Located at the Nucleus Tract Solitarius (NTS) of the brain stem

*Processes signals critical in the feeling of being full

*Signals arising from:
The hypothalamus
The stomach (distension) & small intestines (increased CCK)
The result is a signal of fullness = satiety

Question 43

State the energy composition for 1g of each major nutrients.

Answer 43

1g of FAT: 38kJ (9kcal)
1g of PROTEINS: 17kJ (4kcal)
1g of CARBOHYDRATES: 17kJ (4kcal)

Question 44

What is the conversion factor between calories and kilojoules?

Answer 44

1kcal = 4.184kJ

Question 45

What is the basal metabolic rate for females and males?

Answer 45

FEMALES; 6000- 8000kJ/day
MALES: 8000- 10 000kJ/day
ATHLETES AND LABOURERS; 25 000- 30 000kJ/day

Question 46

how many g of proteins are degraded per day to produce other body chemicals?

Answer 46

20-30g/day

Question 47

what are the WHO recommendations for fats ,proteins and carbohydrates and dietary fiber?

Answer 47

PROTEINS: 10-15% (30-50g)
CARBOHYDRATES:55-75%
FATS:15-30%
DIETARY FIBRE: 27-40g

Question 48

What is the set point concept?

Answer 48

The idea that body weight mechanisms seem to operate to maintain a fixed level of body fat stores. Over a long period of time, the body weight remains constant

Question 49

Outline the hunger signals.

Answer 49

*GHRELIN

-Is the main hormone producing feeding behavior, and the only hunger signal known to be produced peripherally.

-It is secreted mostly by the oxyntic cells of the stomach, but to a much lesser extent by the intestine.

-It is produced during fasting, and its production rapidly stops when the stomach fills.

*The neurotransmitters NPY and AGRP promote feeding behavior as already noted.

*The stress hormones cortisol and endorphins promote feeding behavior.

*A number of other neurotransmitters including the amino acid glutamate and g-amino butyrate (GABA).

Question 50

Outline the satiety signals.

Answer 50

*Gut filling: nerve signals which indicate gut filling probably affect the hypothalamus, but hormonal signals may be more important.

*Cholecystokinin is released when food enters the intestine and inhibits feeding behavior.

*Two peptides with similarities to NPY, called pancreatic peptide (PP) and Peptide YY (PYY) reduce food intake.
-PP is produced by the pancreas and PYY by endocrine cells of the gut.

*Glucagon like peptide (GLP) and oxyntomodulin

-Are released into the blood by the small intestine and the colon after eating and have appetite suppressing effects.

*High blood glucose together with insulin

-Have appetite suppression effects, though the exact mechanism for this remains unclear. It is nevertheless an important factor and was at one time proposed to be the major appetite suppression signal.

*Leptin

-Leptin is produced by the adipose tissue cells and the amount produced is directly proportional to the amount of adipose tissue.

*Leptin appears to have a central role in the regulation of energy balance. In starvation and weight loss leptin production from adipose tissue falls.

Question 51

How does low leptin levels result in infertility or delayed puberty?

Answer 51

*Low leptin levels produce increased food intake if food is available, reduced energy expenditure, including reduced body temperature, reduced production of pituitary hormones including gonadotrophins, leading to infertility or delayed puberty.