Obesity , diet and physical activity

P.Myles

Puja.myles@nottingham.ac.uk

Learning outcomes

You should be able to:

• describe how obesity, diet and physical activity impact on population health

• Recognise the various factors that influence individual behaviour

• discuss various public health approaches to tackling obesity

Lecture outline

• What is obesity?

• Who is at risk?

• Is obesity a population health issue?

• What influences individual behaviour?

• Public health approaches to tackling obesity

What is obesity?

Disease, risk factor or lifestyle choice?

“ A disease in which excess body fat has accumulated to such an extent that health may be adversely affected”

-(WHO)

Measuring obesity-1

• Body mass index (BMI): measures relative weight for height

• Calculated by dividing weight in kilograms by height in metres squared (kg/m2)

• Limitations:– Does not take into account factors like age

and gender (particularly an issue in children)– Does not distinguish between weight

associated with muscle mass and fat

Measuring obesity-2

WHO classification of obesity

WHO classification BMI (kg/m2)Underweight <18.5

Normal weight (healthy weight) 18.5-24.9

Pre-obese (overweight) 25-29.9

Obese class 1 (moderately obese) 30-34.9

Obese class 2 (severely obese) 35-39.9

Obese class 3 (morbidly obese) 40 and above

Measuring obesity-3

• Waist-hip ratio

• Rationale: overweight people with central fat distribution are at greater risk of developing heart disease and diabetes

• Apple-shaped ( higher/lower WHR?) versus pear-shaped ( higher/lower WHR?)

Who is at risk?

Causes of obesity

Energy intake> energy expenditure

• Behavioural factors: physical activity, diet, eating patterns

• Genetic factors

• Medical factors: endocrine disorders (hypothyroidism), medication (corticosteroids)

• Others: ageing, smoking, pregnancy

Susceptible groups

• Children where one of both parents are overweight or obese

• Socially deprived groups or those on low income

• Ethnic minority groups

• Those with low levels of education

• People with learning difficulties

Is Obesity a Public Health problem?

Relative risk of health problems associated with obesity

• Greatly increased (RR >3): NIDDM, gall bladder disease, dyslipidaemia, insulin resistance, breathlessness, sleep apnoea

• Moderately increased (RR 2-3): CHD, hypertension, osteoarthritis (knees), hyperuricaemia and gout

• Slightly increased (RR 1-2): Cancers (breast, endometrial, colon), polycystic ovary syndrome, impaired fertility, back pain

Nutrition transition

• Obesity rates associated with economic development of a country

• In poor societies, the more affluent have a higher prevalence of obesity

• As societies develop, more affluent groups have lower obesity

We live in increasingly obesogenic environments…

“…resulting from a multitude of genetic, biological, psychological, sociocultural, and environmental factors that affect both sides of the energy balance equation…”

-(US Food and Nutrition Board, 2005)

Obesogenic environments

• Energy intake (dietary behaviours and patterns)• affordability of food• eating out• convenience foods• food deserts

• Energy expenditure (physical activity)• Cars• desk jobs• TV• internet

Passive obesity

“The epidemic of ‘passive obesity’ is a normal response of our innate biology when confronted with modern living in ‘obesogenic’ environments so everyone, except the genetically very resistant, are guaranteed to put on weight except in unusual social circumstances”

-Foresight report (2007). Tackling obesity: future choices

Small errors in energy balance and biological maintenance

• An average discrepancy of 10-20 kcal/day between energy intake and energy expenditure = 0.5-1kg of weight gain/year in early adult life

• Biological maintenance of obesity: as weight gain occurs, ‘resetting’ of neuroregulatory system so the extra weight is the new ‘normal’ default weight setting

Is it all about individual behaviours?

• Not all individuals are obese even if they live in an obesogenic environment

• Can energy imbalance be rectified by more physical activity and healthy diets?

• Is obesity a manifestation of poor will power?

• Should the individual be responsible entirely?

Factors influencing behaviour

• Health Belief Model (Rosenstock et al)

• A person’s behaviour is a determinant of their health beliefs: threat perception and behavioural evaluation (benefits vs. costs of action)

• Cues to action e.g. mass media campaign, legislation

• Self-efficacy

Achieving lifestyle change: The Three Es model

Public health approaches to tackling obesity

Changing Physical Environments

Physical changes in design of environment for physical activity involving:– play areas– safe pedestrian and cycling friendly streets– Food availability in shops (especially in

deprived areas)

Economic measures

• Refers to costs associated with food and physical activity

• Could include incentives or taxes at either local or national level:– Subsidising healthy food– Penalties for providing unsafe or unhealthy

food– Finance new public transport systems

Political measures

• Refers to rules associated with physical activity and diet including laws, regulations, policies and institutional rules:– Food labelling with appropriate

understandable health-related information– Regulation of food advertising aimed at

children– Town planning policies which prioritise active

transport (walking and cycling)

Changing Sociocultural Environments

• Refers to a community’s/society’s attitudes, beliefs and values towards diet and physical activity

• Measures could include:– Promoting physical activity in the workplace– ‘Health-promoting schools’ with an ethos of

nutritious healthy school dinners – Using role models (like celebrities) to

influence healthy diet (Jamie Oliver) and physical activity (Dame Kelly Holmes)

Summary

• What is obesity?

• Who is at risk?

• Is obesity a population health issue?

• What influences individual behaviour?

• Public health approaches to tackling obesity

Key Reading

• Chapter 5:Obesity

In Ewles (2005). Key topics in Public Health: Essential briefings on prevention and health promotion. Elsevier

• Chapter 9.5: Obesity

In Detels et al (2009). Oxford Textbook of Public Health. Oxford University Press