Energy and Metabolism Note PDF

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15.ENERGY & METABOLISM1. ENERGY EXPENDITURETotal Energy Expenditure (TEE) A. The total energy expenditure (number of calories needed per day) is composed of three primary factors: i. Resting Energy Expenditure or basal metabolic rate ii. Thermic effect of food (Rough estimation: TEF = Total ...

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15.02.2019

ENERGY & METABOLISM 1. ENERGY EXPENDITURE Total Energy Expenditure (TEE) A. The total energy expenditure (number of calories needed per day) is composed of three primary factors: i.

Resting Energy Expenditure or basal metabolic rate

ii.

Thermic effect of food (Rough estimation: TEF = Total calories consumed/day x 0.1)

iii.

Activity - Activities of daily living (ADL) - physical activity. (PA)

2. RESTING ENERGY EXPENDITURE – WHAT USES ALL THIS ENERGY? A. Organs with high energy needs total only 5% of body weight, yet use 58% of REE: i.

Liver = 21% of total REE; brain 20%; heart 9%; kidneys 8% (heart and kidneys=highest EE/g)

B. Muscle EE is only 3% of heart’s EE/g at rest, but in total comprises 22% of RMR at rest C. Adipose tissue is even lower EE/g, and is always at rest: 4% of RMR in lean, up to 10+% in obese people D. Remaining 16% is from skin, GI, lungs, bones, etc.

3. THERMIC EFFECT OF FEEDING TEF (OR FEEDING/DIET INDUCED THERMOGENESIS, FIT/DIT) A. TEF is the energy cost of digestion, absorption, processing and storage of nutrients B. Comprises about 10% of TEE in sedentary individuals C. There are no significant differences in between ages or gender D. Lower TEF is often seen in obese individuals E. This graph shows the effect of 1 large meal and 6 small meals in the same individuals (same total energy content) F.

The overall increase in metabolic rate was greater after one large meal

G. This may be due to the smaller insulin response that occurs after each of the 6 small meals H. Another idea is that gastric emptying is faster after a large meal, resulting in a sudden large increase in blood nutrient level.

4. ESTIMATING ENERGY EXPENDITURE A. There are several equations that can be used to estimate energy expenditure; the original one was the Harris– Benedict equation B. The one below is the current Institute of Medicine Equation for Estimated Energy Requirement (EER) i.

EER = 354 - (6.91 x age [y]) + PA x {(9.36 x weight [kg]) + (726 x height [m])}

ii.

EER = 662 - (9.53 x age [y]) + PA x {(15.91 x weight [kg]) + (539.6 x height [m])}

5. BMI – ADVANTAGES AND DISADVANTAGES

6. ESTIMATION OF BODY FAT – WAIST TO HIP RATIO A. Ratio of smallest waist measurement to widest hip measurement B. World Health organisation defines obesity as WHR > 0.85 in women and WHR > 0.90 in men

7. EFFECTS OF INADEQUATE ENERGY INTAKE A. In children: reduced growth B. In both children and adults:

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i.

Reduced body mass

ii.

Reduced metabolic rate

iii.

Loss of protein (muscle) and bone mass

8. EFFECTS OF EXCESS ENERGY INTAKE

9. INCREASED HEALTH RISKS ASSOCIATED WITH OBESITY A. Obstructive sleep apnea B. Osteoarthritis C. Cardiovascular disorders D. Gastrointestinal disorders E. Metabolic disorders F.

Endometrial, prostate and breast cancers

G. Complications of pregnancy H. Menstrual irregularities I.

Psychological disorders

J.

Diabetes type II

10.

HYPERTENSION A. Blood pressure is often increased in overweight individuals due to increased length of blood vessels and therefore increased total peripheral resistance B. Increased blood pressure means that the heart needs to work harder, leading to ventricular atrophy. C. Ventricular atrophy causes stiffening of the ventricular walls and inefficient emptying, leading to heart failure i.

11.

Blood pressure = cardiac output * total peripheral resistance

ISCHEMIC STROKES A. Ischemic strokes occur when an artery to the brain is blocked. B. Risk of ischemic stroke is increased in overweight and obesity. C. With increasing BMI, the risk of ischemic stroke increases progressively and is doubled in those with a BMI greater than 30 kg/m2 when compared to those having a BMI of less than 25 kg/m2. 3

12.

CORONARY ARTERY DISEASE A. Increased blood lipid levels increase the risk of formation of fatty plaques in blood vessels. B. Hypertension also increases this risk as it causes damage to arterial endothelium, triggering an inflammatory response. C. Small blood vessels such as those supplying heart muscle are particularly at risk. D. As the lumen of coronary blood vessels decreases, the blood flow to sections of the cardiac muscle is progressively reduced. E. Early symptoms are those of angina; later can result in myocardial infarction.

13.

GALLSTONES A. Obesity appears to be associated with the development of gallstones. B. Approximately 20 mg of additional cholesterol is synthesized for each kg of extra body fat, resulting in higher blood cholesterol levels in obese individuals. C. High cholesterol concentrations relative to bile acids and phospholipids in bile increase the likelihood of precipitation of cholesterol gallstones in the gallbladder. D. Normally, a balance of bile salts, lecithin, and cholesterol keep gallstones from forming. However, if there are abnormally high levels of bile salts or, cholesterol, then stones can form. E. The formation of gallstones is called Cholelithiasis.

14.

TYPE II DIABETES MELLITUS A. Type II diabetes is strongly associated with overweight and obesity in both genders and in all ethnic groups. B. The risk for Type II diabetes increases with the degree and duration of overweight in individuals. C. The risk for Type II diabetes also increases in individuals with more visceral (abdominal) fat.

15.

RELATIONSHIPOE BETWEEN BMI AND RISK FOR TYPE 2 DIABETES MELLITUS

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16.

HOW DOES OBESITY CAUSE TYPE II DIABETES? A. An increase in abdominal fat causes visceral fat cells to release inflammatory mediators. B. Fat cells also release lipids into the blood stream. C. These two factors are thought to cause a reduction in sensitivity of target cells to insulin. D. Less glucose is transported into the target cells, leaving more in the blood. E. Despite increased insulin release, blood glucose level remains high. F.

The beta-cells in the pancreas may eventually become fatigued and stop producing insulin.

G. Losing body fat may partially or completely reverse the condition.

17.

CONTROL OF ENERGY INTAKE A. A very complex process involving the interaction between homeostatic pathways and ‘brain reward’ pathways B. It has been suggested that there is a ‘biological defence’ of body fat level both in lean and obese individuals (Guyanet & Schwartz, 2012) C. Eating is not as simple as a response to hypoglycaemia (there has been little correlation found between blood glucose level and eating initiation).

18.

FACTORS THAT MAY CONTRIBUTE TO CONTROL OF ENERGY INTAKE It is though that we have centres in the hypothalamus that control the desire to eat, which are influenced by a variety of factors. The amount eaten is determined by satiation (feeling of fullness) and satiety (reduced interest in food). A. Stretch receptors in the stomach initiate neural signals to the satiation centre. B. Cholecystokinin released from mucosa in small intestine in the presence of protein and fat; triggers reduction in food intake via vagal afferent nerves. C.

Leptin (hormone) secreted by adipocytes when fat is stored; acts as a negative feedback regulator of adiposity via leptin receptors in the hypothalamus.

D. Ghrelin (a peptide) is secreted from the gastric mucosa; known to increase feeding behaviour but blood levels not always correlated with initiation of feeding so role uncertain. E.

Reward signals – e.g. palatability, association, energy density. Cause release of dopamine in the brain which result in positive reward sensation; reduces amount of food eaten.

F.

Overeating and consequent obesity may be a result of leptin resistance (so the feedback signals are not received).

G. Reduced sensitivity of D2 receptors (for dopamine) may also contribute to overeating, causing individuals to eat more/more energy dense food in order to achieve the same reward.

19.

EFFECT OF ENERGY-RESTRICTED DIET AND EXERCISE ON RMR 5

A. May be due to reduction in thyroid hormone level (although there was no significant difference between the two groups B. Providing there is no loss of lean body mass (muscle), RMR returns to normal following a restricted diet C. The exercise may be important in order to maintain the lean body mass

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