Study protocol for the evaluation of long-term effects of the school-based obesity prevention program Lekker Fit! (‘enjoy being fit’): a retrospective, controlled design

Abstract

Introduction
Preventive interventions to reduce overweight and obesity in childhood and adolescence are studied on their effectiveness worldwide. A number with positive results. However, long-term effects of these interventions and their potentially wider influence on well-being and health have been less studied. This study aims to evaluate the long-term effects of a multicomponent intervention in elementary school children targeting individual behaviour as well as environment (Lekker Fit!). The primary outcomeis body mass index and the secondary outcomes are waist circumference, weight status, physical fitness, lifestyle, psychosocial health and academic performance.

Methods and analysis
In a naturalistic effect evaluation with a retrospective, controlled design adolescents in secondary schools, from intervention and non-intervention elementary schools, will be compared on a wide set of outcome variables. Data will be collected by questionnaires and through anthropometric and fitness measurements by trained physical education teachers and research assistants. Baseline data consist of measurements from the adolescents at the age of 5 years old and are gathered from preventive youth healthcare records, from before the intervention took place. Multilevel regression models will be used and adjusted for baseline measurements and potential confounding variables on the individual and environmental level. Furthermore, propensity scores will be applied.

Ethics and dissemination
The study has been approved by the Medical Research Ethics Committee of the Erasmus Medical Centre, Rotterdam, The Netherlands (permission ID: MEC-2020-0644). Study findings will be disseminated in peer-reviewed journals and by conference presentations.

Trial registration number
NL8799. Pre-results.

Full text

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SmitMS, etal. BMJ Open 2021;11:e046940. doi:10.1136/bmjopen-2020-046940
Open access
Study protocol for the evaluation of
long- term effects of the school- based
obesity prevention program Lekker Fit!
(‘enjoy being t’): a retrospective,
controlled design
Michel Sebastiaan Smit ,1 Hein Raat ,1 Famke Mölenberg ,1
Mireille Eleonore Gabriëlle Wolfers,2 Rienke Bannink,3 Wilma Jansen 1,2
To cite: SmitMS, RaatH,
MölenbergF, etal. Study
protocol for the evaluation
of long- term effects of the
school- based obesity prevention
program Lekker Fit! (‘enjoy
being t’): a retrospective,
controlled design. BMJ Open
2021;11:e046940. doi:10.1136/
bmjopen-2020-046940
►Prepublication history for
this paper is available online.
To view these les, please visit
the journal online (http:// dx. doi.
org/ 10. 1136/ bmjopen- 2020-
046940).
Received 17 November 2020
Accepted 30 July 2021
1Public Health, Erasmus MC,
Rotterdam, The Netherlands
2Social Development, Gemeente
Rotterdam, Rotterdam, The
Netherlands
3Policy and Research, CJG
Rijnmond, Rotterdam, The
Netherlands
Correspondence to
Dr Wilma Jansen;
w. jansen@ Rotterdam. nl
Protocol
© Author(s) (or their
employer(s)) 2021. Re- use
permitted under CC BY- NC. No
commercial re- use. See rights
and permissions. Published by
BMJ.
ABSTRACT
Introduction Preventive interventions to reduce
overweight and obesity in childhood and adolescence
are studied on their effectiveness worldwide. A number
with positive results. However, long- term effects of these
interventions and their potentially wider inuence on well-
being and health have been less studied. This study aims
to evaluate the long- term effects of a multicomponent
intervention in elementary school children targeting
individual behaviour as well as environment (Lekker
Fit!). The primary outcomeis body mass index and the
secondary outcomes are waist circumference, weight
status, physical tness, lifestyle, psychosocial health and
academic performance.
Methods and analysis In a naturalistic effect evaluation
with a retrospective, controlled design adolescents in
secondary schools, from intervention and non- intervention
elementary schools, will be compared on a wide set of
outcome variables. Data will be collected by questionnaires
and through anthropometric and tness measurements
by trained physical education teachers and research
assistants. Baseline data consist of measurements from
the adolescents at the age of 5 years old and are gathered
from preventive youth healthcare records, from before
the intervention took place. Multilevel regression models
will be used and adjusted for baseline measurements
and potential confounding variables on the individual and
environmental level. Furthermore, propensity scores will
be applied.
Ethics and dissemination The study has been approved
by the Medical Research Ethics Committee of the
Erasmus Medical Centre, Rotterdam, The Netherlands
(permission ID: MEC-2020-0644). Study ndings will be
disseminated in peer- reviewed journals and by conference
presentations.
Trial registration number NL8799. Pre- results.
INTRODUCTION
The prevalence of overweight and obesity in
children has been a growing health concern
for many years worldwide.1–3 Recent estima-
tion from the WHO European Childhood
Obesity Surveillance Initiative (COSI) indi-
cates an overweight prevalence of 9%–43%
for boys and 5%–43% for girls, with numbers
varying across countries.4 5 Furthermore, an
obesity prevalence of 2%–21% for boys and
1%–19% for girls was reported by the COSI.4 5
Although a recent stabilisation in the trend
of the overweight and obesity prevalence in
children has been demonstrated in high-
income countries, the overall prevalence of
overweight in childhood remains high.2 6 In
2019 in the Netherlands, 12.0% of the chil-
dren (aged 4–12 years old) were overweight,
including 2.0% obese children.7 For adoles-
cents (aged 12–16 years old), overweight
prevalence was 14.7% of the population,
including 1.9% obese adolescents.7
Childhood overweight and obesity have
been associated with numerous adverse
health consequences, like cardiovascular
disorders, type 2 diabetes and psychosocial
health problems.8–13 Furthermore, children
with overweight or obesity are at higher risk
for obesity in adulthood than their normal
weight peers.14 15 In addition, individuals with
Strengths and limitations of this study
►Studies regarding the sustainability of effects of
school- based obesity prevention programmes are
needed.
►Effects on a broad set of outcome variables will be
assessed.
►A controlled study design will be used with retro-
spective collection of baseline data and adjust-
ment for the non- randomised design by a range of
confounders.
►Study population will be diverse in age, socioeco-
nomic background, ethnic background, grade and
school level.
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obesity pose a substantial financial burden on the global
healthcare systems as their individual medical costs are
30% higher.16 The combination of the economic conse-
quences, health consequences and high prevalence
warrants the implementation of effective interventions to
prevent and reduce overweight and obesity in children.6 17
Physical acitivity and diet, being factors associated with
the development of overweight and obesity,18 19 often
form important entry points for those interventions. A
recent Cochrane review, addressing interventions for the
prevention of obesity, reported that combined diet and
physical activity interventions do reduce body mass index
(BMI) z- scores for children aged 6–12 years old, although
the level of evidence is low.20 Schools have been suggested
to be the optimal place to deliver the interventions due
to continuous contact with children,21 and reaching chil-
dren with a wide range of different backgrounds.22 Two
recent reviews provide evidence that school- based inter-
ventions are generally effective in the reduction of chil-
dren’s weight gain.17 23 However, little is known about the
sustainability of effects by obesity prevention interventions
as long- term studies are scarce.24 25 The authors of the
Cochrane review indeed suggest that interventions and
strategies to prevent obesity in children should include
follow- up measurements over several years.20 Further-
more, the wider effects of school- based interventions
including a physical acitivity component on health and
well- being have been less studied, although the associa-
tion between physical activity and both academic perfor-
mance26 27 and psychosocial health and well- being28–30 in
children and adolescents have been well documented.
The multicomponent obesity prevention programme
Lekker Fit! (translated as ‘enjoy being fit’31) for
schoolaged children was developed and implemented in
2005 via elementary schools in Rotterdam, the Nether-
lands, targeting children aged 6–12 years old. The results
of a randomised controlled trial (RCT) performed in
2006–2007 demonstrated positive intervention effects on
overweight prevalence, waist circumference and aerobic
fitness among elementary school children in grades 3–5
after 1 year of intervention.32 The long- term effects of
Lekker Fit! (after leaving elementary school) as well as
the wider effects on psychosocial health and academic
performance have not been studied yet. This knowledge
is important to determine whether beneficial effects of
Lekker Fit! sustain into adolescence and whether wider
effects are present. To the authors’ knowledge, no studies
are available for the assessment of the long- term effective-
ness of multicomponent school- based interventions on a
set of outcome variables including weight status, fitness,
lifestyle, psychosocial health and academic performance.
Therefore, the main objective of this study is to eval-
uate the long- term effects of Lekker Fit! on (a) the
primary outcome BMI, and (b) the secondary outcomes
waist circumference, weight status, physical fitness, life-
style and lifestyle determinants, psychosocial health
and academic performance. In subgroup analysis, we
will explore if any encountered effects are different for
gender, socioeconomic status and time since interven-
tion. Moreover, dose–effect assocations will be explored
if the data provide sufficient variability in the amount of
intervention years. Finally, on an exploratory basis, we will
investigate the participants’ appreciation of the Lekker
Fit! intervention and similar components from regular
school programmes.
Our hypothesis is that adolescents who have attended
a Lekker Fit! elementary school exhibit healthier scores
than their peers who have attended a regular elementary
school on the set of primary and secondary outcome vari-
ables. However, we do not know the relationship between
longer follow- up and the intervention effects, due to the
scarce literature on the sustainability of such interven-
tion effects into adolescence. Furthermore, we hypoth-
esise that more years of Lekker Fit! intervention on an
elementary school leads to better scores on the set of
outcome variables, due to the prolonged exposure to this
behavioural changing intervention.
METHODS AND ANALYSIS
Lekker Fit! intervention and regular school program
In 2005, to halt the rise in obesity among children, the
City of Rotterdam, the Netherlands has developed and
implemented the intervention programme Lekker Fit!
(translated as ‘enjoy being fit’).31 This programme has
been implemented in collaboration with elementary
schools in Rotterdam targeting children aged 6–12 years
old and at a later stage with day care organisations. In the
Dutch school system, children attend elementary school
for 8 years (4–12 years old) and start secondary school at
age 12. In 2020, about half of all elementary schools (94)
in Rotterdam have adopted Lekker Fit! into their educa-
tion programme.33
Although the Lekker Fit! programme has no direct
focus on reducing overweight, the contribution of the
programme to reducing overweight is expected to be
the consequence of a healthy diet and active lifestyle.
The intervention entails multiple components (table 1).
In comparison with regular school programmes, these
include an additional third physical education (PE)
lesson per week, professional PE teachers instead of
regular classroom teachers providing the PE lessons,
voluntary additional physical activities outside school
hours, the promotion of drinking water and the promo-
tion of a healthy diet and lifestyle.33
Besides targeting individual behaviours of children,
Lekker Fit! targets the obesogenic environment of the chil-
dren and involves parental engagement.31 32 The strategy
for behavioural change is mainly based on the theory of
planned behaviour (TPB),31 while several components of
Lekker Fit! are based on specific theories such as social
marketing.34 The TPB states that a behaviour is being
influenced by the intention towards that behaviour.
The intention itself is being influenced by the individ-
ual’s attitude, social norm and self- efficacy.35 36 Lekker
Fit! primarily targets children in the socioeconomically
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disadvantaged neighbourhoods, because of a higher prev-
alence of overweight and obesity and therefore a higher
risk at metabolic diseases in those neighbourhoods.37 38
Study design
In order to determine the long- term effects of the Lekker
Fit! intervention, a naturalistic effect evaluation39–41 with
a retrospective, controlled design will be conducted
(figure 1). We will recruit adolescents aged 12–18 years
old on secondary schools for participation in the study.
This allows for a follow- up period of up to 6 years. Due to
the COVID-19 pandemic, a prolonged recruitment and
data collection period is applied in this study. The recruit-
ment period ranges from September 2020 up to and
including September 2021. The data collection period
continues until December 2021.
We will compare the adolescents who attended Lekker
Fit! elementary schools—the intervention group—
with adolescents who attended regular non- Lekker
Fit! elementary schools—the control group. Given the
naturalistic non- randomised design, correction for
confounding variables will be applied. Correction for
available pre- intervention baseline measurements around
the age of 5 years old will be applied by obtaining data
from the regional preventive youth healthcare provider
(CJG Rijnmond). Furthermore, available measurements
at the age of 9 years old will be obtained to serve as an
additional control measurement. Thus, the set of baseline
Table 1 Components (and their year of introduction) of the Lekker Fit! intervention on elementary schools in comparison with
the regular elementary school programme
Since Lekker Fit! intervention components Regular school programme
2005 Three PE lessons per week Two PE lessons per week
2005 A trained PE teacher provides all the PE lessons and coordinates the
implementation of the intervention on school
The classroom teacher provides all
the PE lessons
2005 Three 1.5- hour sessions of special themed education per year by the
classroom teacher. Themes of special education are healthy diet, physical
activity and making healthy choices
Schools are free to use education
programmes on specic themes
2005 A PE lesson for several different sports by an external PE teacher, as a rst
step towards a sportsclub membership (an after school hours component)
Regular schools are given the same
non- obligatory opportunity for these
PE lessons
2006 The school sports clubs provide four trainings of different sports on a weekly
basis (an after school hours component)
Regular schools are given the same
non- obligatory opportunity for these
trainings
2005 Annual weight and height measurements –
2007 Additionally the PE teachers monitor the motor development of children in
accordance with the Dutch basic protocol for PE
–
2005 An information meeting for parents on annual basis regarding the themes fruit,
water, breakfast and physical activity
–
2005 The school dietitian signals overweight and obesity, based on the weight and
height measurements, and provides parents with information
–
2012 Extension of the Lekker Fit! intervention to classes 1 and 2 (children aged 4
and 5 years old)
2013 The water campaign with community involvement; Children drink water at least
two times per day during school hours
–
2013 The ‘enjoy fruit’ component; children only eat fruit or vegetables during their
morning break
–
2015 The ‘treats’ component; In the Netherlands it’s a habit that children share
treats among their peers on their birthday. This component presents guidelines
regarding thse birthday treats. Guidelines say that one treat is enough and that
a small treat is okay!
–
PE, physical education.
Figure 1 The naturalistic effect evaluation with a
retrospective, controlled design of this study.
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data ranges from the period 2007–2017, depending
on the current ages of the participating adolescents.
Confounding variables and baseline measurements
will be described in detail below. We used the Standard
Protocol Items: Recommendations for Interventional
Trials checklist (online supplemental file 1) to address all
recommend items in our study protocol.42
Study population and recruitment
We will include 2218 adolescents aged 12–18 years in this
study (see the Power considerations section). We expect
to include 20–25 secondary schools in Rotterdam, from
neighbourhoods with divergent socioeconomic back-
grounds, in this study. They will receive an informative
letter to explain the nature, relevance, objectives and
measurements of this study. Only after a school has given
consent for its participation, will the adolescents in that
school be approached for participation in close collabo-
ration with the school. We will recruit adolescents from
all different school levels and grades within the age
range. The targeted adolescents and their parents will
receive an information letter. Additionally, all relevant
information about the study will be available on a website
(URL: https://www. rotterdam. nl/ onderzoeklekkerfit).
Comprehensive information will be given about all the
relevant topics regarding the study and the consequences
of participation. Adolescents are asked to give digital
informed consent before they are eligible for partici-
pation in this study. For the adolescents who are under
the age of 16 years old, digital informed consent by one
parent will also be obtained in accordance with Dutch
legislation.
Lekker t! intervention group and control group
For all adolescents in this study, their school career (spec-
ified per school year) will be obtained from the municipal
records in Rotterdam. Specific permission for the collec-
tion and coupling of this data will be asked within the
digital informed consent forms. Combined with informa-
tion from the City of Rotterdam about which elementary
schools implemented Lekker Fit!, we are able to assign
the adolescents to the intervention group or control
group. Adolescents who attended elementary schools
outside Rotterdam were not exposed to Lekker Fit! and
will be assigned to the control group. Children may move
between schools and change between the intervention
condition and the control condition. Based on the accu-
rate year by year school career data from the municipality,
we will be able to determine exposure to Lekker Fit! in
years and years since intervention for all adolescents.
New data collection
Participants are asked to complete a digital questionnaire
using LimeSurvey software during school hours and to
engage in physical measurements during their PE class.
LimeSurvey will also be used by the researchers to manage
the digital consent forms of participants and parents.
Furthermore, we will collect information about possible
confounding variables that might have an influence on
the effect of the Lekker Fit! intervention. In this respect,
measures for age, gender, ethnic background, household
situation and socioeconomic background will be obtained
from participants and environmental measures like the
presence of a healthy school canteen and the presence
of any additional psychosocial or physical interventions
on the secondary schools will be collected. All the instru-
ments that will be used for data collection are described
within the Measurements section.
Retrospective data collection
Retrospective baseline data will be retrieved from the
CJG Rijnmond archives. The CJG Rijnmond is a regional
preventive youth healthcare provider for children in
the larger Rotterdam area. The CJG Rijnmond invites
all children for growth and health monitoring during
childhood. Collected baseline data will involve measures
of anthropometrics, BMI and psychosocial health data.
The data consist of measurements from the participants
around the age of 5 years old and 9 years old (figure 1).
Baseline data around the age of 5 years old will provide
information about participants before the Lekker Fit!
intervention is entered (Lekker Fit! starts in grade 3
of elementary school). Baseline data around the age
of 9 years old will be obtained as an additional control
measurement. Furthermore, the child records consist of
information about any additional professional guidance
that participating adolescents received for being over-
weight during childhood.
Measurements
Primary and secondary outcome variables
The primary outcome variable in this study is BMI.
The secondary outcome variables in this study are waist
circumference, weight status, physical fitness, lifestyle and
lifestyle determinants, psychosocial health and academic
performance.
Trained PE teachers and research assistants will
measure body weight, body length and waist circum-
ference. Body weight will be measured to the nearest
0.1 kg and body length and waist circumference will be
measured to the nearest 0.1 cm. A fixed protocol will be
used in which the adolescents will be measured (apart
from their peers) with light clothing, without shoes. BMI
will then be calculated and BMI- for- age z- scores (zBMI)
will be determined based on international growth stan-
dards for school- aged children and adolescents.43 44 Based
on BMI- for- age z- scores, adolescents’ weight status will be
categorised as underweight (zBMI<−2), normal weight
(−2≤zBMI≤1), overweight (zBMI >1) or obese (zBMI >2)
using common cut- offs according to WHO standards.43 45
Physical fitness will be measured by the 20m- Shuttle Run
test according to a standardised protocol under guid-
ance of the PE teacher in which the outcome will be the
number of stages completed.46 The 20m- Shuttle Run test
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is an acceptable, feasable and reliable method for deter-
mination of cardiorespiratory fitness in youth.47
The LimeSurvey questionnaire will be used to obtain
information on the outcome variables lifestyle and life-
style determinants, psychosocial health and academic
performance. The Short Questionnaire to Assess Health-
enhancing physical activity (SQUASH) will be used to
assess adherence to physical activity guidelines.48 The
SQUASH is being used by Dutch government agencies
to monitor individuals concerning physical activity guide-
lines.49 The SQUASH was validated using the doubly
labelled water method. The SQUASH was found to be a
valid self- report tool for measuring physical activity energy
expenditure for adolescents.49 Furthermore, participants
will be asked if they currently have a membership at a
sportclub and if they had a sportclub membership during
elementary school.
Psychosocial health will be assessed by the Dutch version
of the Strengths and Difficulties Questionnaire (SDQ).50
The SDQ contains 25 items which are evenly distributed
over the domains of emotional symptoms, behavioural
problems, hyperactivity/inattention, problems with peers
and pro- social behaviour. The SDQ leads to a total score
as well as five domain scores. Its Dutch version is classified
as a valid and reliable instrument for the first identifica-
tion of psychosocial problems in adolescents.51
Determinants of a healthy lifestyle are measured using
items based on the TPB.35 Questions are included for
healthy behaviours that are promoted by the Lekker Fit!
intervention using the guidelines by Ajzen.52 The healthy
behaviours, for which determinants will be measured,
include53 54:
1. 1 hour of moderate intensely exercising every day.
2. Three times per week muscular and bone strengtening
exercises.
3. Consciously making healthy choices in diet.
4. Two pieces of fruit every day.
5. 250 g of vegetables every day (approximately four serv-
ing spoons).
6. Limiting sugar- sweetened beverage consumption.
Participants are asked to rate their attitude, social
norm, self efficacy, intention and actual behaviour (TPB
items) towards these standards of healthy behaviour to
derive the determinants for a healthy and active lifestyle
(example illustrated in table 2).
Academic performance is measured by the question
‘how well is your academic performance as judged by
your teacher in comparison with the academic perfor-
mance of your classmates?’. This item, derived from the
International Health Behaviour in School- aged Children
Study, was confirmed to be valid and useful to distinguish
respondents who get good grades from respondents
who do not get good grades.55 Furthermore, academic
performance will be captured by the school level (prepa-
ratory vocational secondary education or senior general
secondary education or university preparatory educa-
tion) of the adolescent.
Possible confounders
Possible confounding variables that we will collect are
participant’s current age, gender, ethnic background,
household situation, socioeconomic background and
professional guidance for overweight during childhood.
Within the questionnaire, the adolescent’s, mother’s
and father’s country of birth will be asked. According to
Statistics Netherlands, adolescents will be classified for
ethnic background based on their mother’s country of
birth (to take into consideration the cultural background
of the most frequent primary caregiver), unless it is the
Netherlands. In that case, adolescents will be classified
for ethnic background based on their father’s country of
birth (55).
Regarding household situation, we assess whether the
participant lives alone, in a two parent or single parent
household.
Socioeconomic background will be assessed by ques-
tions on parents’ financial difficulties (Did you experi-
ence any financial burden in expenses in your household
in the last 12 months?) and unemployment payments
(Did one of your parents receive an unemployment
Table 2 Example of questions to asses the outcome measure determinants of a healthy and active lifestyle following the
guidelines of Ajzen according to the theory of planned behaviour
Healthy behaviour
Eating two pieces of fruit every day
TPB items Question asked Rating
Attitude If I eat two pieces of fruit every day for the next 3 months, that
would be …
Bad 1/2/3/4/5/6/7 Good
Perceived norm Most people who are important to me approve that I eat two
fruits every day for the next 3 months
Disagree 1/2/3/4/5/6/7 Agree
Self- efcacy I am condent that I can eat two pieces of fruit every day for the
next 3 months
False 1/2/3/4/5/6/7 True
Intention I intend to eat two pieces of fruit every day for the next 3 months Unlikely 1/2/3/4/5/6/7 Likely
Past behaviour In the past 3 months, I have eaten two pieces of fruit every day False 1/2/3/4/5/6/7 True
TPB, theory of planned behaviour.
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payment in the last 12 months?). Furthermore, socio-
economic neighbourhood indicators will be obtained for
adolescents based on their postal code and/or elemen-
tary schools attended.
Other possible confounding variables that are
embedded within the questionnaire include measure-
ments for pubertal development. Pubertal development
is measured with the Dutch version of the self- report
Pubertal Development Scale.56 57 These items are used
to determine pubertal status of the participants and
will be used to adjust weight status measures. For male
participants, questions on pubertal development include
growth spurt, body hair, facial hair, voice change and
skin changes, whereas for female participants, questions
include growth spurt, body hair, breast development,
menstruation and skin changes.
On a school level, we will collect the following informa-
tion from secondary schools:
1. The number of PE lessions per week.
2. The presence of dietetic programmes (for instance a
healthy school canteen programme).
3. The presence of preventive mental health and
well- being programme (for instance anti- bullying
programmes).
Appreciation of the intervention or similar components on regular
elementary schools
Within the questionnaire adolescents are asked to evaluate
on several components of the Lekker Fit! intervention
(or evaluate on similar components in regular elemen-
tary schools for the control group). Adolescents are asked
to evaluate the quantity and quality of their PE lessons
and quality of their PE teachers on elementary school.
Furthermore, they are asked to rate their attendance and
the quality regarding organised physical activites outside
school hours. These items allow us to analyse the subjec-
tive experiences of participants during elementary school
and allow us to compare appreciation of the Lekker Fit!
intervention with the regular school programme.
Power considerations
A statistical a priori power analysis was performed for
the estimation of sample size.58 With an alpha=0.05,
power=0.80 and taking into account the cluster design,
we need a sample size of n=2218 in total to find an abso-
lute BMI difference of 0.3 kg/m2 between the interven-
tion and control group.58 Hereby assuming an SD of
3.0, clustering within schools accounting for 4% of the
variance (Intraclass correlation 0.04), a correlation of
0.75 for baseline and follow- up measurements.59 Further
assuming a 30% participant loss to non- response, we aim
to invite 3169 adolescents for participation in the study.
Statistical analysis
Descriptive statistics will be used to describe the charac-
teristics of the participants in the total study population
and separately for the intervention group and the control
group. To study the effects of Lekker Fit!, we will use
logistic and linear regression models to evaluate the long-
term effects of the Lekker Fit! intervention for all primary
and secondary outcome variables. Multilevel analyses will
be used to correct for the clustering within secondary
schools. The exposure to the Lekker Fit! intervention
(intervention/control group) forms the independent
variable. All baseline measurements and confounding
variables will be added to the models as covariates. Inter-
action terms for intervention and the variables gender,
ethnic background, educational level and time since inter-
vention will be tested. Depending on results, exploratory
subgroup analysis will be performed. Moreover, if the
data provide sufficient variability in the amount of inter-
vention years for participants, further exploratory anal-
ysis will be performed to evaluate possible dose–response
associations (using years of intervention exposure). We
anticipate that adolescents in the intervention group
and control group may differ regarding several baseline
characteristics. These baseline characteristics may have
had an influence on the chance of receiving the Lekker
Fit! intervention or not. Therefore, we will also perform
propensity score adjusted comparisons of effects between
intervention and control groups, by using propensity
scores as a covariate in the model, to account for these
possible bias due to the non- randomised design of this
naturalistic study. The propensity score will be calculated
using a model based on all baseline and confounding
variables that will be used as covariates in the analysis on
intervention effects. Multiple imputation techniques will
be used to handle missing baseline and covariate data.
Patient and public partnership
No participants were involved in the creation and design
of this study. A sample of the study population was first
involved in this study by testing the questionnaires on
quality and feasibility. Individual data may be dissemi-
nated to participants who are interested in their personal
outcome variables. Participating secondary schools will
receive data on school level, which can be used for their
school policies. They will be encouraged to share the
results with their students.
DISCUSSION
In this article the study protocol for a naturalistic effect
evaluation with a retrospective, controlled design is
described. The aim of this study is to evaluate the long-
term effects of the Lekker Fit! intervention on (a) the
primary outcome BMI and (b) the secondary outcomes
waist circumference, weight status, physical fitness, life-
style and lifestyle determinants, psychosocial health and
academic performance.
Earlier studies have demonstrated a number of positive
intervention effects for the Lekker Fit! intervention.32 60
An RCT on the effectiveness of Lekker Fit! was conducted
a decade ago.32 Findings included positive intervention
effects for weight status, waist circumference and physical
fitness for 6–9 years old children in elementary schools,
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although no positive effects on BMI were found. The
Lekker Fit! intervention programme has been updated
with several additional components since then (table 1);
among others a water campaign component which incor-
porated multiple stakeholders in the neighbourhood of
the school. The effectiveness of the water campaign was
studied in a controlled design and provided evidence for
the reduction of children’s sugar- sweetened beverages
consumption.60
Weihrauch- Blüher and colleagues recommended to
combine behaviour- oriented intervention programmes,
that were found to have only limited effects, with
community- oriented components in order to reach
sustainable effectiveness of obesity prevention interven-
tions for children and adolescents.61 The Lekker Fit!
intervention is such a multicomponent school- based
intervention targeting the individual child and its envi-
ronment.31–33 Lekker Fit! is thereby primarily targeting
children in the socioeconomically disadvantaged neigh-
bourhoods, because those children are at higher risk for
the development of overweight and obesity.37 38
The recent Cochrane review on obesity prevention
interventions included 64 studies on school- based inter-
ventions, and 3 studies on school- based interventions
with a community element for children aged 6–12 years
old.20 They indicate that most of the evidence in their
review is based on interventions of 12 months or less.
They emphasise that research on long- term effects of
completed studies would provide important information
on the sustainability of behaviour change and impact on
weight.20 Since long- term studies are scarce, little is known
about the sustainability of effects24 25 or about the deter-
minants that explain whether results are sustainable or
not. Furthermore, little is known about the wider benefits
that these interventions have on health and well- being of
children and adolescents, although associations between
physical activity and both academic performance26 27 and
psychosocial health and well- being28–30 in children and
adolescents have been reported.
To the authors’ knowledge, no studies are yet conducted
for the measurement of the long- term effectiveness of
multicomponent school- based interventions on the broad
set of outcome variables including weight status, fitness,
psychosocial health and academic performance. The
Lekker Fit! intervention in elementary schools targets
children up to 12 years old. As this study includes adoles-
cents aged 12–18 years, long- term effects up to 6 years
will be assessed. Additional subgroup analysis will provide
insight in the interaction effects between intervention
and follow- up length. The current study will therefore
contribute to this field of scarce knowledge and expand
the insights in the long- term effects of multicomponent
school- based interventions and into the sustainability
of intervention effects. Adding to this knowledge helps
policymakers and intervention developers to decide on
further implementation and intervention development.
RCTs are considered the gold standard for effective-
ness evaluations of an intervention.62 Choosing for a
randomised controlled design, with the length of the
follow- up period we employ, would be almost impossible
as it would be unethical to withhold schools from imple-
menting an intervention programme that was already
proven at least partly effective. The non- randomised
design of our study can be regarded as the main limita-
tion. We acknowledge that the assessment of the long-
term effects of Lekker Fit! by a naturalistic evaluation
design39–41 is potentially subject to selection bias, which
could arise by the fact that schools are not randomly
chosen for implementation of the Lekker Fit! interven-
tion. This limitation is accounted for by using propensity
scores in the analysis63 to reduce selection bias. We also
acknowledge there are factors that possibly influence our
outcome measures besides the Lekker Fit! intervention
on elementary school. Therefore, we will include pre-
intervention baseline measurements and a broad spec-
trum of possible confounding variables on the individual
and environmental level. The retrospective, controlled
design with the application of propensity score analysis
we choose seems best suited to overcome this limitation.
Further, the self- report for physical activity can be regarded
as a limitation. However, the SQUASH questionnaire was
found to be a valid self- report tool for measuring phys-
ical activity energy expenditure for adolescents and is less
costly than direct measurements.49 Self- report items may
also manifest recall bias. To minimise recall bias for the
items in our questionnaire, the items are easy to under-
stand and sometimes provided with additional explana-
tion or relatable examples.
On the other hand, we do not rely on self- report
regarding anthropometric measurements or fitness. This
can be regarded as a strength. Further, the naturalistic
effect evaluation design of this study also allows us to
observe subjects in ‘a real world’ setting instead of in a
highly controlled experimental setting. A second strength
of this practice- based design is therefore that it provides
strong external validity of the results by providing a real-
istic representation of the ‘practice- based’ setting.39 40
This study hereby measures a broad set of outcome vari-
ables for a wide picture of the effects of Lekker Fit! on
health in youth. The fact that we include a large sample
size of participants with different socioeconomically back-
grounds might be considered a strength of this study. It
provides us with the opportunity to further generalise our
findings to several populations characterised by apparent
socioeconomic inequalities.
In conclusion. this paper describes the design of a
study to determine the sustained effects of the school-
based Lekker Fit! intervention, a multicomponent inter-
vention targeting overweight and physical inactivity in
children. This study will provide insight in the long- term
intervention effects and will extend insights in a variety of
outcome measures including BMI, waist circumference,
weight status, physical fitness, lifestyle and lifestyle deter-
minants, psychosocial health and academic performance.
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8SmitMS, etal. BMJ Open 2021;11:e046940. doi:10.1136/bmjopen-2020-046940
Open access
ETHICS AND DISSEMINATION
Ethical statement
The Medical Research Ethics Committee of the Erasmus
Medical Centre, Rotterdam, The Netherlands decided
that the regulations from the Dutch Medical Research
Involving Human Subjects Act (Dutch abbreviation
WMO) do not apply to this research protocol. Therefore
permission was granted by the committee for the execu-
tion of this study and for publications in a later stage of
the study (permission ID: MEC-2020-0644). The research
proposal has been registered in the Dutch trial register
NTR, in which effect- studies are registered that are
conducted in the Netherlands.
Dissemination statement
The project team will disseminate the findings from this
scientific study by conference presentations and scientific
peer- reviewed journals.
Twitter Hein Raat @heinraat and Famke Mölenberg @FamkeMolenberg
Acknowledgements The authors would like to thank all the involved advisors for
their role in the setup of this study.
Contributors MSS, HR, FM, MEGW, RB and WJ contributed to the design of the
study and the development of the protocol for this study. MSS mainly wrote the
manuscript and HR, FM, MEGW, RB and WJ contributed to the manuscript by critical
revisions and giving comprehensive feedback on multiple drafts. MSS, HR, FM,
MEGW, RB and WJ read and approved the nal manuscript.
Funding This study is made possible by funding of the City of Rotterdam Sports
Department.
Competing interests None declared.
Patient and public involvement Patients and/or the public were involved in the
design, or conduct, or reporting, or dissemination plans of this research. Refer to
the Methods section for further details.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Open access This is an open access article distributed in accordance with the
Creative Commons Attribution Non Commercial (CC BY- NC 4.0) license, which
permits others to distribute, remix, adapt, build upon this work non- commercially,
and license their derivative works on different terms, provided the original work is
properly cited, appropriate credit is given, any changes made indicated, and the use
is non- commercial. See:http:// creativecommons. org/ licenses/ by- nc/ 4. 0/.
ORCID iDs
Michel SebastiaanSmit http:// orcid. org/ 0000- 0003- 4231- 3972
HeinRaat http:// orcid. org/ 0000- 0002- 6000- 7445
FamkeMölenberg http:// orcid. org/ 0000- 0002- 5305- 9730
WilmaJansen http:// orcid. org/ 0000- 0002- 4453- 9054
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