Obesity

Question 1

What are the two mechanisms by which body fat accumulates?

Answer 1

• Adipose Hypertrophy

- Adipose Hyperplasia

Question 2

What is the difference between visceral and subcutaneous adipose tissue in terms of where it is located?

Answer 2

Subcutaneous fat is located under the skin, visceral fat is located around the organs

Question 3

What is the role of fat (specifically white adipose tissue) in the body in normal quantities?

Answer 3

It is an energy storage and metabolically regulatory endocrine organ that regulates lipid handling, inflammation and immune function

Question 4

What are the most popular methods of body composition measurement?

Answer 4

• BMI
• Skinfold Calipers
• DEXA *
• Hydrostatic Weighing *
• Air Displacement Plethysmography
• Electrical Bioimpedence

Question 5

What is the gold standard body composition measure, and how does it work?

Answer 5

-Hydrostatic Weighing:

Body density is estimated by submerging the body in water, then the Siri equation is used to estimate bodyfat percentage

Question 6

When is hypertrophy vs hyperplasia more likely to occur?

Answer 6

• Hypertrophy is more likely over small time frames and small amounts of weight gain
• Hyperplasia occurs when a significant amount of weight is gained.

Question 7

What is adipose dysfunction?

Answer 7

-When you accumulate too much adipose tissue, the immune function changes to cause an accumulation of white blood cells in the tissue, and an inappropriate release of hormones such as increased leptin and decreased adiponectin.

Question 8

What are the endocrine functions of adipose tissue?

Answer 8

Secretion of hormones for:

• Control of nutritional intake
• Control of insulin sensitivity and inflammatory process mediators and processes

Question 9

What is the function of leptin? How does it differ in normal vs dysfunctional adiposity?

Answer 9

It is a mediator of long term energy balance (unlike ghrelin which is short term), suppressing hunger/food intake.
Low/normal levels in Normal Adiposity
Very high levels in dysfunctional adiposity, concomitant with leptin resistance
(Klok et al 2007)

Question 10

What is the function of adiponectin?

Answer 10

• Increased fatty acid oxidation and inhibition of hepatic glucose production, leading to improved insulin sensitivity and lower plasma glucose (Lihn et al 2005)
• Anti inflammatory and anti-atherogenic effects

Question 11

What are the hormones released by adipose tissue in relation to regulation of nutritional intake?

Answer 11

• Leptin
• Angiotensin (mechanism is unknown, Yoshida et al., 2012)

Both reduce food intake/hunger

Question 12

What are the hormones released by adipose tissue in relation to regulation of insulin sensitivity and inflammation (adipokines)?

Answer 12

Adiponectin, Resistin, IL-6, Visfatin and TNF alpha, among others

Question 13

What is adipogenesis?

Answer 13

Differentiation of pre-adipocytes into mature fat cells

Question 14

What are the two main phenotypes of macrophage in adipose tissue?

Answer 14

M1 and M2 macrophages

Question 15

What are M1 macrophages?

Answer 15

Macrophages that produce pro-inflammatory cytokines, impact lipid trafficking/metabolism, inhibiting mitochondrial function and increasing ROS.

Question 16

What are M2 macrophages?

Answer 16

Macrophages that enhance lipid handling, mitochondrial function, anti-inflammatory cytokine production and inhibition of ROS

Question 17

How does macrophage activity differ in healthy vs dysfunctional adipose tissue?

Answer 17

M2 predominates in healthy adipose, and M1 predominates in dysfunctional tissue

Question 18

Outline the main differences between dysfunctional and healthy adipose tissue in terms of metabolic/immune/hormonal function:

Answer 18

Healthy: M2 Macrophages predominate, very little M1 activity. Decreased leptin and increased adiponectin
Dysfunctional: M1 macrophages predominate, increased leptin and decreased adiponectin

Question 19

What did Frayn 2018 find about the relationship between BMI and bf%?

Answer 19

reliable relationship between BMI and bf% at a population level

Question 20

Fat people are not necessarily in energy surplus. They could have been in surplus a long time ago and now are in balance. This is a reminder, not a question.

Answer 20

Yes.

Question 21

What is the biggest differentiator between any individuals energy expenditure? Give evidence

Answer 21

Physical activity. According to Thompson et al 2009, there is a difference in over 500,000kcal per year between the most and least active individuals in the sample, which is explained by differences in physical activity

Question 22

What is the primary observational evidence to show that obesity is determined by physical activity rather than energy expenditure?

Answer 22

-Prentice and Jebb 1995 found that there is a correlation between obesity increasing and physical activity decreasing, but energy intake has not changed in the same time. So physical activity is more important than diet

Question 23

What did the systematic review by Franz et al 2007 on intervention studies for obesity?

Answer 23

Exercise least effective both in impact and adherence
Diet alone more effective, Diet and exercise most effective.

Weight loss medication and meal replacements seemingly as effective as diet and exercise in first 12 months.

Question 24

Name a systematic review in opposition to exercise interventions for weight loss

Answer 24

Thorogood et al 2011

Question 25

Name a systematic review giving mixed results for exercise and diet interventions for weight loss, with some detail

Answer 25

Schwingshackl et al 2014: Diet and exercise is moderately supported to be useful for long term obesity management. Diet is slightly more important than exercise

Question 26

Why is it that physical activity interventions may not be effective for obesity? 2 main reasons

Answer 26

• Substitution effect

- PA compensation effect

Question 27

what is the substitution effect and how does it impact the effectiveness of exercise interventions for weight loss?

Answer 27

The effectiveness of a physical activity intervention depends on the level of physical activity that the planned exercise is replacing/substituting. If the exercise is planned for a time when one would normally be active, it will be less effective than if planned for a time where one would usually be totally sedentary, resulting in a lower deficit

Question 28

What is PA compensation and why does it impact the effectiveness of an exercise intervention for weightloss?

Answer 28

Individuals may be less physically active for the rest of the day after exercising, resulting in the same overall energy expenditure

Question 29

What compensation can exist outside of PA compensation that can impact the effectiveness of exercise for weight loss?

Answer 29

Dietary compensation. Eating more after exercising more.

Question 30

How does weight loss impact your BMR? How does this impact energy balance on a diet?

Answer 30

As you lose weight you lose mass, which means you lose total metabolically active mass, so your BMR decreases. With the same energy deficit, your weight loss will eventually plateau,

Question 31

Is there any evidence to suggest that obesity is genetic?

Answer 31

-Stunkard et al 1986 found that BMI of adoptive children are associated with those of their bio-parents, not adoptive parents.

Question 32

Does the environment ‘expose’ the effects of genetic predisposition to obesity? Give evidence.

Answer 32

Walter et al 2016 found that in more recent observational studies, individuals with a higher genetic risk for obesity were more likely to be obese than individuals with the same risk several decades before

Question 33

Is there any evidence to support the concept of ‘fat but fit’?

Answer 33

Francisco B Ortega et al., found that CV fitness can offset the risks of CVD and all cause mortality associated with obesity. A fit obese person may have less risk of CVD than normal weight but unfit people.

Question 34

Is there any evidence to support the concept of ‘fat but fit’?

Answer 34

Francisco B Ortega et al., found that CV fitness can offset the risks of CVD and all cause mortality associated with obesity. A fit obese person may have less risk of CVD than normal weight but unfit people.

Question 35

Which type of white adipose tissue increases the risk of chronic diseases more?

Answer 35

Visceral moreso than subcutaneous.