Why is behaviour change so
difficult to achieve?
Dr Elisabeth Weichselbaum
Nutrition Scientist and Consultant
ewnutrition.net
Knowledge alone is not enough
• Plenty of information about healthy diet and
lifestyle
• It is likely that many people are aware of ‘what
they are supposed to eat’
• Survey in UK
– 99% knew fruit and vegetables very or fairly important
– 94% said eating less salt was important
– 92% said limiting foods high in saturated fat was
important
Food Standards Agency 2010
What factors influence behaviour?
Physical
Psychological
Includes knowledge & skills
Reflective
processes
Automatic
processes
Physical
Social
Michie et al. 2011, Implementation Science 6:42
Why is the healthier choice not always
the easier choice?
Our intentions and plans can only influence
behaviour if they generate sufficiently strong wants
or needs at the relevant moment to overcome
competing wants or needs.
Environmental cues +
power of immediate and
certain pleasure (e.g. of
eating chocolate)
Larger, less certain
and more distant
vs.
rewards (e.g. losing
weight, stay healthy)
Marteau 2011, BMJ 342:263-265; Atkins and Michie, Nutrition Bulletin 38:30-35
Human behaviour shaped by two systems
(Dual Process model)
Reflective, goal oriented system
• Driven by our values and
intentions
• Requires cognitive capacity or
thinking space
• Many traditional approaches to
health promotion target this
system, i.e. designed to alter
beliefs and attitudes
Automatic, affective system
• Requires little or no
cognitive engagement
• Driven by immediate
feelings and triggered by
environments
Strack and Deutsch 2004, Pers Soc Psychol Rev 8:220-47.
Beyond awareness
• Adults typically make more than 200 foodrelated decisions per day…
• …but are aware of 14.4 food-related
decisions.
• Most of our food-related decisions are
beyond conscious awareness
• This is for a good reason
– Would you get much done if you questioned all
of your 200+ food-related decisions?
Wansink and Sobal 2007, Env Behav 39:39-106; Chadwick et al. 2013, Nutrition Bulletin 35:36-42
Consumption norms
• People very easily influenced when it comes
to how much they eat
• Plate size, package size, larger portions in
restaurants, larger kitchen ware…
• They all suggest a certain ‘norm’ or portion
size
• People underestimate this influence and
believe they are immune to them
Wansink 2010, Psychology & Behavior 100:454-463
Are we aware of influence?
• 4 Experiments, intervention:
– A larger serving (double popcorn)
– Same serving, but in larger package
• Intervention groups consumed 32%
more than control group
– Only 8% thought they ate more than usual
– 73% thought they ate about the same
– 19% thought they ate less
Wansink 2010, Psychology & Behavior 100:454-463
Are we aware of influence?
• When told about the intervention and its
effect
– 52% claimed they did not eat more
– 31% said if they did eat more it was because they
were hungry
– 15% gave other reasons (special occasion, it was
free)
– Only 2% acknowledged it was because of the
environmental cue
Wansink 2010, Psychology & Behavior 100:454-463
The power of habit
• Strength of habit has a
strong influence on
behaviour
• Habit can even override
taste (which itself strongly
influences food choice)
• Habitual behaviour is more
dependent on environment
and less under conscious
control
Chadwick et al. 2013, Nutrition Bulletin 35:36-42;
The power of habit
Fresh
Stale
Weak habit of eating popcorn
in cinema
Meeting room context
Cinema
Strong habit of eating
popcorn in cinema
Meeting room context
Ate less when presented with
stale than with fresh popcorn.
Cinema
Ate the similar amount
of fresh and stale
popcorn.
Neal et al. 2011, Pers Soc Psychol Bull 37:1428-37
Nudging – a possible way to change
behaviour
• Nudging means to change
physical or social environment
to make a certain behaviour
more likely
• Mainly operates through the
automatic, affective system
Marteau 2011, BMJ 342:263-265; Thaler and Sunstein: Nudge. Yale University Press 2008.
Does nudging work?
• Nudging works, although currently often used
to drive unhealthy eating behaviour
• Limited evidence on nudges to encourage
healthy behaviour
• Cumulative nudges in a wide range of contexts
may be required to be effective
• Within enabling legislative and policy
environments
Marteau 2011, BMJ 342:263-265.
Healthier choice does not equal healthy
weight
• People tend to think of foods as either ‘good’
or ‘bad’
• Behave as though healthy foods have ‘halos’ –
are perceived to be less likely to promote
weight gain
Chernev 2011, J Cons Psych 21:178-183.
Which promotes more weight gain?
Students and adults were presented with a variety
of ‘healthy’ and ‘unhealthy’ snack options
Chocolate
47 kcal
vs.
+
569 kcal
Oakes 2005, Appetite 44:317-324; Oakes 2005, Food Quality and Preference 16:447-454
The Dieter’s Paradox
+
OR
4000
14%
8%
3000
kJ
2000
Burger
1000
Burger plus celery sticks
0
Weight-concious
individuals
Weight-indifferent
individuals
Chernev 2011, J Cons Psych 21:178-183.
Conclusion
• How can we influence behaviour that lies
outside awareness?
• Could nudging work?
• How can we avoid stereotype thinking about
food?
Obesity is not a rational choice!