Obesity

1. Obesity Dr. Sumbul Fatma

2. Overview • Definition • Prevalence • Consequences of Obesity • Assessment of Obesity • Causes of obesity

3. Definition • Obesity is a disorder of body weight regulatory systems characterized by an accumulation of excess body fat usually 20 percent or more over an individual's ideal body weight. • A combination of abundance of food with reduced activity levels found in industrialized societies, has resulted in a tendency for the sustained deposition of fat

4. Prevalence • The prevalence of obesity increases with age. Particularly alarming is the explosion of childhood obesity, which has shown a three fold increase in prevalence over the last two decades. • As adiposity has increased so has the risk of developing associated diseases, such as diabetes, hypertension, and cardiovascular disease.

5. Prevalence of Obesity • Childhood and adolescent obesity increased from 5% to 16% in the last 20 years • Adulthood obesity increased from 12% to 21% in 10 years. • 16 million US adults with BMI over 35 • 60 million US obese adults (BMI > 30)

6. Assessment • Body mass index (BMI)— is an indirect measure of obesity and correlates with the amount of body fat in most individuals. (exceptions are athletes who have large amounts of lean muscle mass) • The BMI gives a measure of relative weight, adjusted for height. This allows comparisons both within and between populations.

7. Calculating BMI • Calculate Body Mass Index (BMI) = weight (kg) height squared (meters) Or… weight (pounds) x 703 height squared (inches)

8. Definition of Overweight & Obesity • Using BMI

10. Anatomic differences in fat deposition It has a major influence on associated health risks. Android, “apple-shaped,” or upper body obesity is the excess fat located in the central abdominal area of the body • is associated with a greater risk for hypertension, insulin resistance, diabetes, dyslipidemia, and coronary heart disease • waist to hip ratio of more than 0.8 for women and more than 1.0 for men.

11. Anatomic differences in fat deposition Gynoid, “pear-shaped,” or lower body obesity - Fat distributed in the lower extremities around the hips or gluteal region. • waist to hip ratio of less than 0.8 for women and less than 1.0 for men. • The pear shape is relatively benign healthwise, and is commonly found in females • Waist-to-hip ratio is a better predictor of myocardial infarction than BMI

12. Biochemical differences in regional fat depots Abdominal fat cells are much larger and have a higher rate of fat turnover than lower body fat cells Hormonally more responsive than adipocytes in the legs and buttocks As men tend to accumulate the readily mobilizable abdominal fat, they generally lose weight more readily than women do Substances released from abdominal fat are absorbed via the portal vein and, thus, have direct access to the liver Gluteal fat- free fatty acids from gluteal fat enter the general circulation, and have no preferential action on hepatic metabolism

13. Number of fat cells • When triacylglycerols are deposited in adipocytes, the cells increase in size and when the ability of a fat cell to expand is limited, and when its maximal size is reached, it divides • Obesity involves an increase in both the number and size of adipocytes • Fat cells, once gained, are never lost • An obese individual, with increased numbers of adipocytes, will have to reduce the size of those fat cells in order to normalize fat stores. These individuals will be in the doubly abnormal state of having too many, too small fat cells. • Formerly obese patients have a particularly difficult time maintaining their reduced body weight

15. Body weight regulation • The body weight of most individuals tends to range within ten percent of a set value • This observation prompted the theory that each individual has a biologically predetermined “set point” for body weight

16. ‘Set Point’ Theory • The body attempts to add adipose tissue when the body weight falls below the set point, and to lose weight when the body weight is higher than the set point Weight loss weight gain Appetite increases Appetite falls Energy Exp. Falls Increases

17. Strict set point model does not explain why some individuals fail to revert to their starting weight after a period of overeating, or • the current epidemic of obesity

18. Body weight, rather than being irrevocably set, seems to drift around a natural “settling point,” which reflects a balance between factors that influence food intake and energy expenditure • Body weight is stable as long as the behavioral and environmental factors that influence energy balance are constant.

20. Factors predispose to obesity • Genetic – familial tendency • Environmental and behavioral • Sex – women more susceptible • Activity – lack of physical activity • Psychogenic – emotional deprivation, depression • Social class – poorer classes • Alcohol – problem drinking • Smoking – cessation smoking • Prescribed drugs – tricyclic derivatives

21. Genetic contributions to obesity • Despite the widely held belief that obesity is a result of uncontrolled, gluttonous eating behavior, it is now evident that genetic mechanisms play a major role in determining body weight • Obesity is often observed clustered in families. If both parents are obese, there is a 70–80% chance of the children being obese. In contrast, only 9% of children were fat when both parents were lean

22. The inheritance of obesity is not simple Mendelian genetics as would be expected if the condition were a result of a defect in a single gene. Rather, obesity behaves as a complex polygenic disease involving interactions between multiple genes and the environment • The importance of genetics as a determinant of obesity is also indicated by the observation that children who are adopted usually show a body weight that correlates with their biologic rather than adoptive parents • Furthermore, identical twins have very similar BMI, whether reared together or apart, and their BMI are more similar than those of nonidentical, dizygotic twins.

23. The epidemic of obesity occurring over the last decade cannot be explained by changes in genetic factors, which are stable on this short time scale • Environmental factors, such as the ready availability of palatable, energy-dense foods, play a role in the increased prevalence of obesity • Furthermore, sedentary lifestyles enhance the tendency to gain weight • When Japanese or Chinese populations migrate to the United States, their BMI increases. For example, men in Japan (aged 46–49 years) are lean, with an average BMI of 20, whereas Japanese men of the same age living in California are heavier, with an average BMI of 2 • Eating behaviors, such as snacking, portion size, variety of foods consumed, an individual's unique food preferences, and the number of people with whom one eats also influence food consumption and the tendency toward obesity

24. Weight Gain: How Does It Happen? • Energy imbalance • calories consumed not equal to calories used • Over a long period of time • Due to a combination of several factors • Individual behaviors • Social interactions • Environmental factors • Genetics

25. Weight Gain: Energy In 3500 calories = 1 pound • 100 calories extra per day • = 36,500 extra per year • = 10.4 lbs weight gain • Question: How much is 100 calories? • Answer: Not very much! • 1 glass skim milk, or • 1 banana, or • 1 slice cheese, or • 1 tablespoon butter

26. Evolving Pathology • More in and less out = weight gain • More out and less in = weight loss • Hypothalamus • control center for hunger and satiety • Endocrine disorder • where are the hormones?

27. Reference • Lippincott’s Illustrated Reviews of Biochemistry 4th Edition

28. Thank You!