Obesity Flashcards
Define obesity, including the BMI cut-offs.
Obesity is an inflammatory disease, characterised by the excessive or abnormal accumulation of fat, that poses a risk to health.
BMI < 18.5 - underweight BMI 18.5-24.9 - healthy BMI 25-29.9 - overweight BMI 30-34.9 - obese class I BMI 35-39.9 - obese class II BMI 40+ - obese class III
Explain the two types of fat distribution, including their relation to cardiometabolic risk.
Visceral fat
- fat stored around the organs
- poses the biggest risk to health even if BMI is healthy
Subcutaneous fat
- fat stored under the skin
- less associated with adverse outcomes
Visceral fat produces a larger inflammatory response that subcutaneous fat, and therefore has a great associated with cardiometabolic risk.
Pro-inflammatory cytokines are involved in the development of insulin resistance, and CVD.
Pro-inflammatory cytokines from visceral fat directly impacts liver metabolism.
Describe adipocytes, including the three types of adipocyte.
Adipocytes are cells that store fat as energy. Adipocytes have a major role in endocrine function.
White adipocyte:
- large lipid droplet
- few mitochondria
- role is energy store
- can signal to the brain to influence feeding behaviour
Beige adipocyte:
- more, smaller lipid droplets
- more mitochondria
Brown adipocyte
- many small lipid droplets
- many mitochondria
- role is heat generation through thermogenesis
Describe adipose tissue, including some functions of adipokines and the difference between lean and obese adipose tissue.
Adipose tissue is the largest reservoir of energy in the body - approx. 100,000kcal energy stored as fat in healthy individual.
It is the largest endocrine organ in the body - secretes thousands of hormones and cytokines.
Adipokines are bioactive peptides synthesised and secreted by adipose tissue. Some functions of adipokines include: - inflammation - appetite and satiety regulation - energy metabolism - energy expenditure - insulin sensitivity
The difference between lean and obese adipose tissue:
Lean adipose tissue has an equal proportion of pro-inflammatory and anti-inflammatory cytokines. Obese adipose tissue has more pro-inflammatory than anti-inflammatory cytokines.
This is why obesity is considered an inflammatory disease.
Explain the fundamental cause of obesity and how obesity has become an issue of epidemic proportion.
Fundamental cause of obesity is an imbalance between energy intake and energy expenditure = calorie surplus.
Globally, there has been an increase in the consumption of calorie dense, processed foods (fast food and takeaway), combined with increasingly sedentary lifestyles (improvements in transport, desk jobs, and urbanisation).
Explain some contributors to obesity.
Metabolic
- low resting metabolic rate
- body composition
- level of physical activity
Hormonal
- ghrelin and leptin levels
Maternal nutrition during pregnancy (FOAD)
- malnutrition
- low birth weight
Infant feeding practices
- baby-led vs spoon fed weaning
Post-absorption of nutrients
- nutrients in blood signal to the brain about their ability and utilisation
- as nutrient availability decreases, satiety diminishes and hunger is induced
Describe the functions of ghrelin and leptin in appetite control.
Ghrelin
- the hunger hormone
- levels of ghrelin increase when fasting/empty stomach
- in animal models, administration of ghrelin stimulates feeding
- ghrelin levels increase around main meal times
Leptin
- the satiety hormone
- synthesised in adipose tissue - levels of leptin correlate with fat mass
- less of an impact on main meal times but more a long-term regulator of food intake.
Explain how genetics can contribute to obesity.
Monogenic obesity
- single gene mutation causes obesity e.g., congenital leptin deficiency caused by mutation in the gene for leptin production.
Syndromic obesity
- multiple gene mutations causing a variety of effects beside obesity, e.g., Prader-Willi syndrome.
Polygenic obesity
- large number of genes involved in the promotion of weight gain/obesity
Describe the effect of maternal malnutrition on the development of obesity, with reference to the Dutch Famine.
Maternal nutrition has lasting effects on infant health (FOAD theory).
Experimental study design based on the unusual situation of the dutch famine, looks at the health outcomes of babies at various stages of gestation during the famine.
Late gestation
- glucose intolerance
Mid gestation
- glucose intolerance and microalbuminuria
Early gestation
- glucose intolerance
- obesity
- atherogenic lipid profile
- CHD
- breast cancer
Describe the role of obesity in the pathophysiology of non-communicable diseases.
Obesity is considered an inflammatory disease as obese adipose tissue (especially visceral white adipose tissue), contains a great proportion of pro-inflammatory cytokines and adipokines
Pro-inflammatory cytokines and hormones regulate functions that are involved in the development of chronic diseases, such as:
- inflammation
- oxidative stress
- insulin resistance (diabetes)
- metabolism
- blood coagulation (atherosclerosis)
Explain some metabolic effects of obesity.
Insulin resistance and impaired glucose tolerance = T2 diabetes
There is a strong link between BMI and T2D - 90% T2 diabetics have BMI > 23
Non-alcoholic fatty liver disease - liver structure and function is disrupted by excess fat.
Dyslipidaemia - obesity is associated with low HDL, high LDL & vLDL, and increased triglyceride level.
Metabolic syndrome - the presence of any 3 of the following:
- increased TG
- raised fasting blood glucose
- raised WC
- elevated blood pressure
Increased risk of cancer
Gynaecological abnormalities e.g., PCOS
