BOD L2 Introduction to Obesity Flashcards
Understand the definition and context of obesity. Describe models used to study obesity. Understand how obesity contributes to chronic non-communicative diseases.
How is obesity defined?
Overweight and obesity are defined as excessive fat accumulations that present a risk to health.
Measured by Body Mass Index (BMI)
What are the strengths and limitations to BMI?
It is easy to measure and inexpensive and has a strong correlation with body fat levels.
The limitations are it is indirect and does not distinguish between body fat and mean body mass (muscle).
Not as accurate in elderly as it is in younger/middle aged.
Doesn’t discriminate between gender and racial norms (asians on average have more body fat than caucasians).
How is abdominal obesity simply measured?
Using waist circumference, it is cheap and inexpensive with strong correlation to fat and predictive of disease and death.
But measurement has not been standardised and not applicable for children, or individuals with BMI of 35 or higher (severely obese).
Can also use waist to hip ratio, but has similar drawbacks.
What is bioelectric impedance (BIA)?
Small safe electric current passed through body, and resistance is measured. Current faces more resistance passing through fat than it does through lean body mass and water. Equations used to estimate body fat percentage.
Why is underwater weighing (densitometry) good for measuring body fat %?
It is very accurate. Individuals weighed in air and again when submerged in water. Calculations used to calculate body fat percentage as fat is more buoyant than water, so higher body fat will ‘weigh’ less underwater (per volume).
What are limitations to densitometry?
Time consuming requiring individuals to be submerged under water.
Not good option for children or elderly or patients with BMI of 40+
What is Air displacement plethysmography?
Relies on similar principles to densitometry, but air is used instead of water. Overcomes issues with densitometry.
Only limitation is expensive.
Dual Energy X-ray Absorptiometry (DEXA) can be used to determine % body fat. What is the principle upon which it works?
X-ray beams pass through fat-free mass and body fat at different rates, so two low level X-ray beams are used to develop estimates of % body fat.
CT and MRI are considered to be the most accurate methods for measuring different body fat compositions. What are there strengths and limitations?
They are very accurate and allow for measurement of specific body fat such as abdominal or subcutaneous fat.
but the equipment is very expensive and immobile. CT scans cannot be done on pregnant women or children.
Some scanners may not accomodate patients with BMI of 35 or higher.
How does obesity contribute to T2 diabetes?
Obesity increases beta cell proliferation and therefore insulin secretion, attempting to compensate for insulin resistance. Eventually fails and results in impaired glucose tolerance and T2D.
Obesity also contributes to neurological disorders, briefly how?
Obesity reduces synaptic plasticity and neurogenesis, increases the chance of neurological diseases such as multiple sclerosis and Alzheimers.
How does obesity affect the liver?
Leads to Non-alcoholic fatty liver disease (NAFLD). Induces fat accumulation and insulin resistance in the liver.
Damage leads to inflammation and scarring of liver tissue, which develops into cirrhosis and cancer.
A link has been seen between obesity and cancer but is complex, what putative mechanisms drive this?
Inflammation, oestrogen excess (from fat). Insulin changes, endocrine signals and changes to critical growth factors (mTOR and AMPK).
What is leptin?
Hormone secreted by adipose tissue. Binds to leptin receptors in the hypothalamus telling the brain the body has had enough food.
What is the role of pPARy in obesity?
It is the master regulator of adipogenesis. TF causes synthesis of TNF-alpha, link between obesity, inflammation, insulin resistance and fat tissue.
