L9 - Energy Balance And Control Of Body Weight

Question 1

What is the Total Body Weight equal to?

On average in males and females, how much fat contributes to the total body weight?

How much fat is present compared to TBW in obese individuals?

Answer 1

Total body weight = Fat + Fat free mass

In Males: Less than 1/3 is fat
In Females: About 1/2 is fat

For males, if fat mass contributes to more than 1/3 of TBW, they tend to be obese.

Question 2

How is body composition measured?

Answer 2

1) Body density
2) Body water - water only found in lean tissue
3) Total body K - K only in lean tissue
4) Skin fold measurements: Biceps, Triceps, Sub scapular and Supra illiac
5) Mid-arm Circumference

Question 3

What is Bioelectrical Impedance:

Answer 3

Bioelectrical impedance involves passing electrical signals through the body.

These signals tend to go faster in fat free (lean) tissues (as these predominantly contain water - good conductor of electricity).

Signals go slower through fat tissues (poor conductor of electricity).

Allows measurement of % of body fat.

Question 4

What is the bod pod (air displacement plethysmography)?

Answer 4

This involves measuring the volume of chamber when no subject is present and when subject occupies the pod. Can measure % of body fat and fat free mass = body density.

Question 5

How much energy content in lipids, alcohol, protein and carbohydrates?

Answer 5

1) Lipid - 9.2 kcal/g
2) Alcohol - 7 kcal/g
3) Proteins - 5.4 kcal/g
4) Carbohydrates - 4 kcal/g

Question 6

Types of energy present in food?

Answer 6

• Total energy
• Digestible energy - this obtained from the food which is absorbed
• Metabolisable energy - some energy is lost through skin, sweat and urine and 50% is lost as heat. The rest is the metabolisable energy.

Question 7

Energy Requirement Equation:

Answer 7

Energy Intake (requirement) = Energy Expenditure

O2 consumption is proportional to energy expenditure.
Food intake is proportional to energy requirement.

Question 8

Factors which affect energy requirement:

Answer 8

1) Basal metabolic rate - energy expenditure at rest in supine position
2) Diet-induced thermogenesis
3) Physical activity - increase activity = increase energy requirement
4) Environmental Temperature
5) Growth, pregnancy and lactation - would have increased energy requirement in these situations
6) Age - increase in age = reduced BMR and reduced activity

Question 9

What is energy balance?

Answer 9

Energy intake = Energy Expenditure

No changes to body weight.

Most people tend to have constant body weight. Day-to-day regulation of body weight is weak.

Question 10

Energy intake/ Food intake regulation:

Answer 10

1) Hypothalamus - has satiety and hunger centres (regulates appetite in arcuate nucleus)
2) Signals - short and long-term signals released from stomach, intestine, adipocytes and pancreas

Question 11

Long-term signals which promote satiety (leptin, insulin and PYY):

Answer 11

Leptin - this is proportional to adipose fat stores and hence represents the state of fat stores.

Insulin - represents the fullness of carb stores.

Both can act on POMC/CART and NPY/AgRP neurons to stimulate satiety and inhibit hunger pathways.

PYY - inhibits NPY/AgRP - promotes satiety.

Question 12

Long-term signals which promote hunger (NPY and Ghrelin):

What happens to satiety signals (leptin and insulin)?

Answer 12

NPY and ghrelin both act on NPY/AgRP neurons in ARC nucleus of hypothalamus to stimulate hunger and inhibit satiety pathways.

Leptin and Insulin levels are low.

Question 13

Short-term signals:

Answer 13

Have signals released from:

1) GI tract
2) HPV
3) Liver
4) Vagal stimulation inhibits appetite

Not very efficient.

Question 14

What is BMI?

How is BMI categorised?

Answer 14

BMI = weight/(height * height)

BMI Categories:
18.5 - 24.9 = Normal
25.0 - 29.9 = Overweight
30.0 - 34.9 = Obesity Grade 1
35.0 - 39.9 = Obesity Grade 2
≥ 40.0 = Obesity Grade 3

Question 15

Prevalence of obesity in UK:

Answer 15

• about two-thirds (66%) are overweight and obese
• around 23% are obese

Considerable health risk associated to obesity.

Question 16

Causes of Obesity:

1) Genetic
2) Metabolic Rate
3) Socio-economic status
4) Endocrinological
5) Low Physical Activity
6) Viral Infection

Answer 16

1) GENETIC
In ob/ob individuals, leptin deficiency is seen - no inhibition of satiety (hyperphagia) - RARE

Common obesity is associated to leptin resistance rather than deficiency as high leptin levels are seen with high BMI. Giving leptin injections to these won’t improve their outcome.

2) METABOLIC RATE
This was assumed to be lower in obese individuals; however, this is not the case.

3) SOCIO-ECONOMIC STATUS
In developed countries, low socioeconomic status = obese.
In developing countries, high socioeconomic status = obese.

Obesity, preferred size, etc depends on society.

4) ENDOCRINOLOGICAL
Hypothyroidism (low BMR) and adrenal hyperactivity can cause obesity - VERY RARE.

5) LOW PHYSICAL ACTIVITY
FI > EE so more energy is stored as fat than used.

6) VIRAL INFECTION
Some obese individuals have AD36 Ab which causes obesity by increasing production of adipocytes and can affect appetite centres in brain.

Question 17

Risk Factors of Obesity:

Answer 17

1) Lack of education
2) Chronic Disease
3) Low level of activity
4) Excessive alcohol consumption (high calories)
5) Cessation of smoking (eat food instead of smoking)
6) Getting married!

Question 18

Conditions caused by obesity:

Answer 18

1) CVD (Stroke, angina, MI)
2) T2D (T2D is a result of obesity not a cause of obesity)
3) Hypertension
4) Respiratory problems
5) Gall bladder stones (4 F’s)
6) Infertility
7) Cancer (breast, prostate, colon, endometrial)
8) PCOS
9) Osteoarthritis

Question 19

Treatments of obesity:

1) Diet
2) Pharmacological Approach
3) Surgery

Answer 19

1) DIET
Diet which aims to restrict energy intake is ideal. However, difficult to maintain as it is tedious so relapse is common and these individuals tend to have low BMR.

High protein diet is ideal - high satiety value than carbs and fat. Should have wholegrain cereals and fruit and veg in the long-term.

2) PHARMACOLOGICAL APPROACH
Sibutramine - increases 5-HT production to inhibit appetite (NOT USED)
Orlistat - reduces fat absorption (steatorrhea)
Uncouplers - uncouples ETC from ATP synthesis so still metabolise food but no energy produced (lost as heat)
Leptin (not efficient in those who have high leptin (most cases of obesity))

3) SURGERY
Liposuction, resection of intestines, gastric band and gastric stapling. However, complications can occur.

Gastric banding — reduces FI and can help reduce body weight and possibly resolve T2D.