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
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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)
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affordability of food
eating out
convenience foods
food deserts
• Energy expenditure (physical activity)
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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
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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