Welcome to Session on Obesity

Meera Kaur, PhD, RDAssistant Professor

Department of Family MedicineFaculty of Medicine

kaur@cc.umanitoba.cahttp://home.cc.umanitoba.ca/~kaur

Outline• Learning objectives• Introduction• Classification and diagnosis• Obesity trend• Adipose tissue, adiposity, hypertrophy and hyperplasia• Energy balance• Regulation of body weight• Regulation of food intake and body weight• Regulatory factors in feeding and adiposity• Sound weight loss program• Conclusions• Questions and answers

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Learning Objectives

• To understand – the physiological and metabolic

perspectives of obesity/overweight, and– the regulation of body weight with special

reference to:• Regulatory factors involved in feeding and

adiposity

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Introduction

• Obesity is the disorder of body composition defined by a relative or absolute excess of body fat.

• The WHO and NHLBI have classified obesity as an epidemic• In 2002, ~64% Americans overweight; 32% obese• 16% or 9 million kids were overweight• Thus, a trend towards an ever-fatter America• By 2009, 70% of American expected to be overweight or obese• Obesity contributes to +300,000 deaths a year• From a global perspective, the increase in the prevalence of obesity is

alarming

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Classification and Diagnosis5

Classification BMI (kg/m2) Risk of Co-morbiditiesUnderweight <18.5 increased risk in other areas

Desirable 18.5-24.9 Average

Overweight 25.0-29.9 Mildly Increased

Obese >30.0

Class I Obesity 30.0-34.9 Moderate

Class II Obesity

Class III Obesity

35.0-39.9

>40.0

Severe

Very severe

Classification for Children (<2 Years)

BMI StatusNormal weight for height 10th-90th percentile

At risk for overweight 85th-95th percentile

Overweight >95 percentile

(Centre for Disease Control and Prevention, 2005)

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Assessing Obesity• Waist circumference at level of iliac crest

– Above 40 inches for men and 35 inches for women are indicative of health risk.

• Waist-to-hip ratio: Circumference of the waist at the level of L3 divided by the circumference of the hip at the largest area of the gluteal region. (Helps identify central or android obesity.) – For men waist-to-hip ratio > 1 – For women waist-to-hip ratio > 0.85

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Obesity Trends in US Adults8

1991 1993

1995 1998

< 10%

10% to 15%

> 15%AH, et al. JAMA. 1999

Obesity Trends in US Adults…9

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Obesity Trends in US Adults, 2004

No Data <10% 10%–14% 15%–19% 20%–24% ≥25%

Adipose Tissue, Adipocytes, Hypertrophy and Hyperplasia

• Adipose tissue– White: energy, cushion, insulation– Brown: Key regulator of energy expenditure

• Adipocytes– store 80-90% fat as tryglyceride

• Hypertrophy adipose tissue due to enlarged adipocytes

• Hyperplasia adipose tissue due to number of adipocytes

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Juvenile-Onset Obesity

• Develops in infancy or childhood• Increase in the number of adipose cells• Adipose cells have long life span and need to

store fat• Makes it difficult to lose the fat (weight loss)• Causes

– poor dietary patterns– lack of physical activity

• 43% of adolescents watch 2 hours or more of TV/day

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Adult-Onset Obesity• Develops in adulthood• Fewer (number of) adipose cells• These adipose cells are larger (stores excess

amount of fat)• If weight gain continues, the number of

adipose cells can increase

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Regulation of Body Weight

• Short-term regulation is governed by:– Hunger (postabsorptive), appetite and satiety

(postprandial)– physical trigger for hunger > satiety

• Long-term regulation is governed by:– feedback mechanism– adipocytokines (signaling protein

is released from the adipose mass when normal body composition is disturbed. This mechanism plays a greater role in younger persons than older adults.

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Set-Point Theory• Fat storage in nonobase adult is regulated to preserve the

specific weight.– deliberate effort to starve or overfeed are followed by a rapid return

to original body weight (set-point).– if set-point theory is true, some form of obesity could be due to the

abnormally established set-point.• Can we establish a new settling-point vs. Set-point to treat

obesity? – However, data are not conclusive in this area. We need to do more

research.

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Energy Production16

Energy Balance…• State in which energy intake, in the form of food and

/or alcohol, matches the energy expended, primarily through basal metabolism and physical activity

• Positive energy balance

Energy intake > energy expended

Results in weight gain

• Negative energy balance

Energy intake < energy

Results in weight loss

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Energy Balance 18

Regulation of Energy Intake and Body Weight

• Factors that regulate energy intake and body weights are:– Dietary thermogenesis and the Thermic Effect of

Foods (TEF)/Specific Dynamic Action (SDA) of foods

– Resting/Basal Metabolic Rate (RMR)/(BMR) – Energy expended in voluntary activity– Regulatory neurotransmitters and hormones

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Thermic Effect of Foods• Energy used to digest, absorb, and metabolize food nutrients• “Sales tax” of total energy consumed• ~5-10% above the total energy consumed• TEF is higher for CHO and protein than fat• Less energy is used to transfer dietary fat into adipose stores

– Meal size, meal composition, previous meal, insulin resistance, physical activity and aging influence the TEF.

– Aerobic exercise the TEF

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Resting Metabolic Rate (RMR)

• RMR explains 60-70% of Total Energy expenditure (TEE). When body is deprived of energy– RMR adapts to conserve energy by dropping rapidly

(up to 15% in two weeks).• RMR declines with age• During undernutrition, abnormalities in lipolysis may

cause insulin resistance affecting RMR• The regulation of free fatty acid availability is an important

area of research related to the RMR.

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Activity Thermogenesis (AT)

• Energy expended in voluntary activity – activity thermogenesis (AT) is the most important component of TEE (15-30% normally). Therefore, AT should be when energy is not restricted.

• RMR and Fat free mass (FFM) decrease with age. Hence adjustment between energy intake and AT should be adjusted for preserving normal weight.

• All activity counts including nonexcercise activity thermogenesis (NEAT).

• To reverse obesity standing and ambulatory time should be promoted at least 2.5 hours/day.

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Energy Balance 23

Ultimate Energy Balance24

TEF

REE

NEAT

Physical activity

Dietary

Intake

Macronutrients and Fat Storage

• Body prefers to use CHO as energy source• Only excess intake of CHO and protein will be turned into fat• Fat will remain as fat for storage • Physical activity encourages the burning of dietary fat (Beta-oxidation)

• High CHO diet decreases Beta-oxidation• Most endurance athletes burn fatty acids for energy

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Fat Storage• Fat

– Most fat is stored directly into adipose tissue– Body has ability to store fat (as fat)

• Carbohydrates– Limited CHO can be stored as glycogen Most CHO is used

as a energy source– Excessive CHO will be synthesized into fat (for storage)

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Protein and Fat Storage

• Protein is primarily used for tissue synthesis• Adults generally consume more protein than

needed for tissue synthesis• Excess protein is used as a energy source• Some protein will be synthesized into fat

(for storage)

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Regulatory Factors in Feeding and Adiposity

• Brain Neurotransmitters• Gut hormones• Other hormones

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Brain Neurotransmitters• Norepinephrine and Dopamine

– Released by symphathetic nervous system (SNS)– Fasting & starvation SNS activity, epinephrine that govern

feeding behaviour and subatrate mobilization – Dopaminnergic pathway in the brain play a role in

reinforcement properties of foodds.

• Serotonin In serotonin leads to carbohydrate appetite.

• Corticotrophin-releasing Factor (CRF)– CRF is a potent anorexic agent and weakens the feeding

response produced by norepinephrine and neuropeptide Y.– CRF is released during exercise.

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Gut Hormones…• Incretins is a G-I peptide

insulin release after eating , even before blood glucose level is elevated. Serotonin is a G-I peptide

• Cholecystokinin (CCK)– At brain level inhibits food intake. Stimulates pancreatic

enzymes

• Bombesin Food intake and enhances the release of CCK.

• Enterostatin– Part of pancreatic lipase; satiety following fat consumption

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Gut Hormones• Adiponectin - Adipocytokine secreted by adipose tissue

– Level of this hormone is inversely related to BMI. Plays role in metabolic disorders.

• Glucagon causes hypoglycemia• Glucagon-like-peptide-1 (GLP-1)

– Released in presence of glucose rich food, delays gastric emptying time and promote satiety.

• Leptin is an adipocytokine and regulates appetite.– In obesity it loses the ability to inhibit energy intake.

• Resistin - An adipocytokine that antagonizes insulin action• Ghrelin – Produced in stomach and stimulate hunger. • Peotide YY-3-36 (PYY -3-36 ) is secreted in small bowel in response to

foods.– In obesity it loses the ability to inhibit energy intake.

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Other Hormones• Thyroid hormone – Modulates the tissue

responsiveness to the catecholamines secreted by SNS. A in thyroid hormone lpwers the SNS activity and adaptive thermogenesis.

• Vispatin - An adipocytokine protein that has an insulin-like-effect. Plasma level with adiposity and insulin resistance.

• Adrenomedullin - A new peptide secreted by adipocytesas a result of inflammatory process

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Satiety Regulator

• The hypothalamus– When feeding cells are stimulated, they signal us to eat– When satiety cells are stimulated, they signal us to

stop eating

• Sympathetic nervous system– When activity increases, it signals us to stop eating– When activity decreases, it signals us to eat

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Influences of Satiety…34

Influences of Satiety35

What it Takes to Lose a Pound

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• Body fat contains 3500 kcal per pound

• Fat storage (body fat plus supporting lean tissues) contains 2700 kcal per pound

• Must have an energy deficit of 2700-3500 kcal to lose a pound per week

Do the Math

To lose one pound, you must create a deficit of 2700-3500 kcal

So to lose a pound in 1 week (7 days), try cutting back on your kcal intake and increase physical activity so that you create a deficit of 400-500 kcal per day

- 500 kcal x 7 days = - 3500 kcal = 1 pound of weight loss

day week in 1 week

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Sound Weight Loss Program

• Meets nutritional needs, except for kcal• Slow & steady weight loss • Adapted to individuals’ habits and tastes• Contains enough kcal to minimize hunger and fatigue• Contains common foods• Fit into any social situation• Change eating problems/habits• Improves overall health• See a physician before starting

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Summary and Conclusion

• To treat obesity and/or develop an effective weight loss program, understanding of– the physiological and metabolic perspectives of

obesity/overweight is important– the regulation of body weight with special reference to:

• Regulatory factors involved in feeding and adiposity is crucial

– Energy balance is the key point– Team approach is important in developing a sustainable

weight loss program

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Thank you for gracing the session!

Any question?