nutrition

Community Medicine Lec - 11 -

Learning objectives

At the end of this lecture student would be able to : 1-Explain difference between over weight & obesity . 2-Define the ideal body weight . 3-Classify body fats . 4- Determine epidemiological facts about obesity. 5-Enumerate causes of obesity . 6-Illustrate methods of obesity classification . 7-Demonstrate methods of obesity assessment . 8-Mention medical complications of obesity . 9-Discuss possible measures for weight reduction . To a level accepted to the accreditation standard of the College .


Obesity is a medical term for over fatness frequently resulting in a significant ill health . It refers to excess body fat . It is an accumulation of adipose tissues . The body weight increase 20% or more above the IBW . It is considered as a chronic disease associated with illness & death from complications .

Over weight: is the excess wt/ht by standard tables 10% of IBW . In most individuals overweight & obesity are related, except in athletes they are overweight because of their increase in lean body mass, but not obese . On the other hand some of inactive individuals with little muscles may be obese but not overweight. Ideal body weight: is the body wt. for a given ht. that statistically associated with the greatest longevity.

Two kinds of human body fats : 1-Essential fat :vital to health (it cushion &protect body organs),3-8% of B.W. 2-Storage fat: layers& cushion of fat providing stored energy. Gender specific fat: In women breasts& pelvic region. Normal proportion of body weight (as fat) is 15-20% for men& 20-25% for women.

During 20s of age , man has 15% body fat; 3% essential & 12% storage fat. Woman of the same age has 25% body fat; 13% essential & 12% storage fat. Most girls do not begin menstruation unless their bodies have at least 17% body fat, & do not continue regular periods without having a 22% as body fat.

Epidemiology: Prevalence of obesity all over the world is increasing, especially in USA. But the mortality rate has decreased especially in women over 45 years (group of highest prevalence of obesity). Recently the IBW of American population has been increased by 10-15%. Prevalence of obesity in western world begin in infancy, 1/3rd or more of their infants are obese, school children obesity vary between 6-15% . The more the obesity in childhood the more the obesity in adulthood, adolescent obesity 20-30 %, 80% of obese adolescents become obese adults.

Young women are more likely to be obese than young men. The obesity is more risky in young adults than older ones. Epidemiological studies shows a strong association between socioeconomic status & the prevalence of obesity (inversely related) . 30% of low socioeconomic individuals are obese. Higher incidence among ethnic minorities seems to reflect a combined genetic & environmental influences.



Causes of obesity :1-Metabolic causes: excess calories intakethan required to meet the metabolic demandswill result in triglycerides store in adipose tissues.2-Sedentary life style.3-Emotional: impaired self –image &feeling of inferiority, which leads to social isolation.4-Familial cause (genetically predisposed) :Two obese parents have a 73% chance of having obese offspring.One obese parent has 41% chance.Two lean parents have only 9% chance. Strong correlation in identical twins.

5- Brown fat: some people seems to eat more than others without gaining weight due to brown fat hypothesis :Cytochrome –pigmented brown adipose tissues which occur only in certain areas of the body (around neck & chest)& not develop after birth; these tissues are rich in mitochondria & produce heat. It serves as caloric buffer that disposes energy excess when food intake is high & conserves energy when food intake is low. Defect in brown adipose tissues function may be responsible in part for obesity or fewer brown fat cells may be responsible.

6-Lipoprotein lipase: it can potentiate hunger by altering the availability of circulating metabolites. 7-Role of leptin: mutation in a gene Ob causes a severe hereditary obesity in mice, the protein of Ob gene called leptin H, which regulate the amount of body fat through control of appetite & energy expenditure, its secretion is suppressed by feeding & enhanced by starvation. When inject mice with leptin , food intake decrease, thermo genesis increase& weight reduction will result (either inactive gene or no leptin at all) .


Classification of obesity: There are different classifications . 1-Hypertrophic obesity: result from an increase lipid content of adipocytes . It is common in adults (mild to moderate obesity). 2- Hyperplasic- hypertrophic obesity: increase in the fat cells number & lipid content of fat cells . Over feeding during infancy & adolescent lead to permanent abnormality, therefore preventive measures should taken during these age periods .


Other classification; regional fat distribution; *Android =Apple shaped (upper body) obesity: excessive fat located in the central abdominal area which is statistically associated with increased risk of Diabetes , hypertension & CVD (common in males). *Gyroid = pear shaped (lower body) obesity: the fat distributed in the lower extremities around the hips or femoral region, relatively benign (common in females).


Assessment measures of obesity:A-Body weight:The life insurance industry statistics have been used to develop tables of normality which give ideal weight ranges for height, frame size, age& sex. There is generally an increase in body weight&change in body composition with age.The measurement is done by using a leaver balanced –type scale.B-Height:The height is measured by using a horizontal arm that moves vertically on a calibrated scale, in erect position, heels together, against a straight surface with the head level, without shoes.

C-BMI: Is the ratio of weight in kilogram (with minimal clothing) to height (without shoes) in meter square. For both male &female, the degree of obesity is classified as: -BMI 20-24.9 (normal or desirable weight range). -BMI 25-29.9 (over weight) low relative risk. -BMI 30-40 (moderate obesity) moderate risk = grade I&II -BMI > 40 (morbid obesity) high risk =grade III

Relationship between body mass index and mortality rate . The lowest mortality rates are associated with BMIs between 19 and 27 kg/m2



D-Waist to hip ratio: Waist to hip circumference can identify the two types of obesity. A ratio of 0.7 considered as normal. A ratio < 0.7 indicates lower body obesity. A ratio > 0.7 indicates upper body obesity. Fat below the waist is more difficult to lose than above the waist.

E-Skin fold thickness: About half of body fat is deposited under the skin &the rest is around the organs &between muscles fibers. The fat is not distributed equally under the skin throughout the body. Therefore, the measurement should be made at some selected sites.


Compared with reference standards tables to assess the fat thickness. *18mm for men ,>20 means excess fat. *23mm for women, >25 means excess fat. Fatty arms appear to run in families even when the rest of the body have low fat .Therefore not to rely on Triceps SFT alone but other SFT. F-Supra iliac SFT: the top of the hip bone just above the iliac crest. G-Abdominal SFT. H- Sub scapular SFT .

Medical complications:

Obesity is associated with a number of chronic diseases Including: 1-Adult onset diabetes, 2.9 times higher prevalence. F.B.G. incr. about 2mg/dL for each 10% above I.B.W. (the body resist his own insulin). 2-Hypercholesterolemia, high plasma T.G., 2mg/dL for each kg excess of B.W., with incr. VLDL.(relative risk increased 4 folds with obesity) 3-Hypertension & heart disease, there is linear association betw. B.W.& B.P. (relative risk increased 5 folds with obesity). 4-Cancer; higher mortality from cancer of colon& prostate in males, & breast in females.


5-Gall stones (related to increased cholesterol synthesis) 6-Arthritis, & gout. 7-Undesirable social,& psychological consequences . 8-Heavy menstrual blood flow, irregular cycle,& infertility. 9-Decreased life expectancy For 10% increased body weight , the life expectancy decreased by 11% for males & 7% for females . When body weight increase 20% , the life expectancy decreased by 20% or more in males & 10% in females. On the other hand risk of osteoporosis is lower with obesity.

Weight reduction strategies:

Body weight represents the balance between energy intake & energy expenditure. To reduce body weight requires negative energy balance. 1-Diet; to lose 500gm/week , patient should reduce caloric intake by 500Kcal/day i.e. 3500Kcal/week (max. loss 2kg/month). 2-Exercise; increase physical activity which result in expenditure of 500Kcal ( running for 45min., playing tennis 60min., walking 75min. & bicycling 90min.)


3-Behavioral modification: eating when hungry,& stopping with first sign of satiety, small, regular & frequent meals.4-Surgical treatment (for morbid obesity), creating smaller bowel( produce malabsorption of calories), or creating small stomach to reduce the reservoir for food . Note : Dietary treatment is particularly effective for initial weight loss.It is advisable to take multivitamins –mineral pills to prevent essential nutrients deficiencies.


The best approach to lose weight is to follow a balanced mildly hypo-caloric diet (any diet <1000Kcal should be used only under medical supervision). Repeated cycles of weight loss & weight regain called yo-yo dieting which takes longer to lose weight & shorter to regain it when the cycles are repeated. It is not benign, leads to nutritional inadequacies, confused food habits, loss sensitivity to physiological hunger, &diminished self confidence.


Typical outcome of serious attempts to lose weight A comparison of two year weight loss trends in behavioral treatments of obesity (diet , exercise , & combination interventions)