Download Obesity is essentially an excessive accumulation of triacylglycerols

clinical Biochemistry 2nd stage college of medicine Dr.Thanaa Alsewedy
Obesity
Obesity is essentially an excessive accumulation of triacylglycerols in
fatty tissue that is the net result of excessive energy intake compared to
energy usage.
Accumulation of fat, or triacylglycerol, is essentially the only way that
body weight can become excessive, as other energy stor(e.g.carbohydrate
glycogen or protein in liver and muscle) does not have the potential of
adipose tissue to exceed the limits of requirement.
ASSESSMENT OF OBESITY by THE ‘BODY MASS INDEX (BMI)
BMI Is defined as body mass (in kg) divided by the square of the height
(in metres) (weight in kg) / height in meters)2
Classification of body weight according to BMI
Principal cut-off
points
Classification
Underweight
<18.50
Normal range
18.50 - 24.99
Overweight
≥25.00
Obese
≥30.00
Causes of obesity
Essentially obesity results from an imbalance between calorie intake and
expenditure and the main causes of obesity are Many factors contribute
towards obesity. Some of the most prominent factors are assorted below:
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clinical Biochemistry 2nd stage college of medicine Dr.Thanaa Alsewedy
1-Genetics
2-Diet high in carbohydrates and Overeating
3-Lack of physical exercises
4-Psychological factors
5- Medical reasons In some patient who develops obesity, the following:
ENDOCRINE FACTORS INFLUENCING OBESITY
1. Cortisol is a well-described enhancer of fat deposition as in Cushing’s
syndrome
2. Hypothalamic damage ( due to trauma, post-meningitis, tumor)
3. Hypothyroidism
4. Polycystic ovarian syndrome (PCOS)
Adepoce cell secret hormones
There is recent evidence showing that. rather than simply a passive fuel
store, adipose tissue is an active endocrine organ, secreting peptide
hormones which included
1-Leptin is an adipocyte-derived hormone that acts to reduce food intake
and increase energy expenditure . Leptin acts within the CNS to inhibit
food intake and increase energy expenditure
2-Adiponectin Adiponectin is an adipocyte-secreted protein that
circulates in high concentrations in the serum and acts to increase insulin
sensitivity.
3- Resistin is another hormone secreted by adipocytes and acts on
skeletal muscle myocytes, hepatocytes and adipocytes.
Opposite in directional effects to adiponectin, higher resistin may
decrease insulin sensitivity
CONTROL OF APETITE
The appetite centre located in hypothalamus, where various influences are
integrated to regulate food intake. These include central (brain-derived)
signals, such as:
1. Neuropeptide-Y (NPY)
2. Melanocyte stimulating hormone (MSH)
3. Cocaine and amphetamine-related transcript (CART)
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clinical Biochemistry 2nd stage college of medicine Dr.Thanaa Alsewedy
. as well as peripheral (body-derived) signals, including:
1. Leptin (ex-adipose tissue)
2. Insulin (ex-β-cells)
3. Cholecystokinin (CCK) (ex-small bowel)
4. Ghrelin (ex-stomach)
Signal regulation of appetite
A. Long-term signals.
1. Leptin:
(Greek Leptos, "thin") is is a hormone made by adipose cells that helps
to regulate energy balance by inhibiting on reaching the brain, acts on
receptors in the hypothalamus to curtail appetite Leptin the "satiety.
Leptin is opposed by the actions of the hormone ghrelin, the "hunger
hormone". Both hormones act on receptors in the arcuate nucleus of the
hypothalamus to regulate appetite to achieve energy homeostasis. In
obesity, a decreased sensitivity to leptin occurs, resulting in an inability to
detect satiety despite high energy stores
Leptin acts on receptors in the lateral hypothalamus to inhibit hunger and
the medial hypothalamus to stimulate satiety
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In the lateral hypothalamus, leptin inhibits hunger by
o counteracting the effects of neuropeptide Y, a potent hunger
promoter secreted by cells in the gut and in the
hypothalamus
In the medial hypothalamus, leptin stimulates satiety by
o promoting the synthesis of α-MSH, a hunger suppressant
so net action of Leptin inhibits neuropeptide Y (NPY) and activates αmelanocyte-stimulating hormone (α-MSH).
Obesity has serious long-term medical complications which include:
• Type 2 /Non-insulin-dependent diabetes
• Hypertension
• Hyperlipidaemia & coronary heart disease
• Osteoarthritis of weight-bearing joints
• Cancer (esp endometrium, breast, colon)
• Earlier onset of puberty
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clinical Biochemistry 2nd stage college of medicine Dr.Thanaa Alsewedy
HOW DOES OBESITY CAUSE INSULIN RESISTANCE AND
GLUCOSE INTOLERANCE?
1. In obesity, abundance of circulating fatty acids and liver-derived
triglyceride (VLDL) provide an excellent fuel for muscle, decreasing
their requirement for glucose
2. Exercise stimulates glucose transport into skeletal muscle (via
induction of the glucose transporter GLUT-4). Obese subject tend to be
sedentary, and thus muscle consumes less glucose
3. Increased delivery of fatty acids to liver (as in visceral obesity)
enhances gluconeogenesis i.e. hepatic glucose output. In lean individuals,
this only happens in during starvation, where it is appropriate.
4. Increased FFAs cause insulin resistance directly by activating enzymes
that decrease the response to insulin, thereby aggravating the pre-existing
insulin resistance
Reduce the obesity by
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At the individual level, people can:
limit energy intake from total fats and sugars;
increase consumption of fruit and vegetables, as well as legumes,
whole grains and nuts;
engage in regular physical activity (60 minutes a day for
children and 150 minutes per week for adults).
Individual responsibility can only have its full effect where people
have access to a healthy lifestyle. Therefore, at the societal level it is
important to:
support individuals in following the recommendations above,
through sustained political commitment and the collaboration of many
public and private stakeholders;
make regular physical activity and healthier dietary choices
available, affordable and easily accessible to all - especially the poorest
individuals.
The food industry can play a significant role in promoting healthy diets
by:
reducing the fat, sugar and salt content of processed foods;
ensuring that healthy and nutritious choices are available and
affordable to all consumers;
practicing responsible marketing especially those aimed at children
and teenagers;
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clinical Biochemistry 2nd stage college of medicine Dr.Thanaa Alsewedy
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ensuring the availability of healthy food choices and supporting
regular physical
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activity practice in the workplace.
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