Vegetable consumption and promotion among school-age children and adolescents in West Africa: a systematic review and narrative synthesis

Abstract

Low vegetable consumption among school-age children and adolescents puts them at risk of micronutrient malnutrition and non-communicable diseases. There is a dearth of synthesised literature on vegetable intake and interventions to promote increased consumption among this age group in West Africa. This study pooled evidence on vegetable consumption and interventions to promote vegetable consumption among school-age children and adolescents (6–19 years) in West Africa. Quantitative and qualitative studies from 2002 to 2023 were electronically searched in PubMed, African Journals Online (AJOL) and Google Scholar databases. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses system was adhered to in reporting this review (PROSPERO ID: CRD42023444444). The Joanna Briggs Institute critical evaluation tool was used to appraise the quality of studies. Forty (40) studies met the search criteria out of n 5080 non-duplicated records. Meta-analysis was not possible due to high heterogeneity. Low vegetable consumption expressed in frequency or amounts was recorded among school-age children and adolescents in the reviewed studies. Intervention studies were mostly among adolescents; the most common type of intervention was the use of nutrition education. Insufficient evidence and high heterogeneity of studies reflect the need for more high-quality interventions using globally identified standards but applied contextually. School-age children appear to be an under-served population in West Africa with regard to nutrition interventions to promote vegetable consumption. There is a need for multi-component intervention studies that encourage vegetable consumption as a food group. Gardening, parental involvement, gamification and goal setting are promising components that could improve the availability, accessibility and consumption of vegetables.

School age represents an important developmental stage of life and the second window of opportunity to consolidate the health and nutrition gains made after early childhood for growth, psychosocial development and establishing lifelong dietary and lifestyle habits and preparation for pubertal life (adolescence)⁽¹⁾. Good nutrition during this phase is essential to ensuring optimal growth and development as well as improving short and long-term health outcomes. Children’s nutrition is particularly important, not only because many eating habits that are formed in childhood will persist into adulthood but also because nutrition plays a role in preventing chronic diseases⁽²⁾. In order to maximise long-term health outcomes, it is also crucial to support children in developing good eating habits, as this is pivotal to support the adoption of healthy eating behaviours at this stage⁽³⁾. There is an increasing awareness that children’s eating behaviours are influenced by environmental factors: home environment and parental influence, as well as the school environment, are recognised as major contributors to the eating habits of children^(4,5) .

Due to the dynamic nature of their growth and development, school-age children (SAC) and adolescents have an increased need for nutrients⁽⁶⁾. This should include nutrients needed to support physical and cognitive growth and development, offer sufficient energy reserves for illnesses and pregnancy and avoid the adult onset of nutrition-related diseases⁽⁷⁾.

Several population groups particularly SAC and adolescents appear to be excluded in most global and regional data related to nutrition, with only under-5 children, women of reproductive and adults prominently captured⁽⁸⁾. This gap results in limited insights into the food consumption habits of these overlooked age groups, despite the existence of various national interventions aimed at addressing their nutritional needs⁽⁹⁾.

Low fruit and vegetable (FV) consumption increases the risk of micronutrient deficiencies and non-communicable illnesses, which are known to be major causes of death globally^(10,11) . For example, childhood overweight and obesity are associated with low consumption of certain nutrient-rich foods and excessive consumption of nutrient-poor, high-calorie foods⁽¹²⁾. The number of children and adolescents who are overweight or obese has more than doubled over the past 50 years^(13,14) . Thus, SAC and adolescents’ diets low in FV may deprive them of micronutrients essential for growth, development and bodily functions, which increase their risk of developing non-communicable diseases later in life⁽¹⁵⁾. Hence promoting increased consumption of FV among SAC and adolescents is of public health importance.

Western Africa is one of the youngest populations in the world with more than a tenth of its population estimated to be below 15 years of age⁽¹⁶⁾. In this region like other low- and middle-income countries, many SAC do not meet dietary recommendations for FV^(17–20). Sub-Saharan Africa has been found to be the region with one of the highest levels of micronutrient deficiencies in under-5 children and women comparable only to South Asia⁽²¹⁾. Although intake levels of FV for all age groups in Africa except North Africa are well below the recommended standards⁽²²⁾, Western Sub-Saharan Africa has the highest age-standardised prevalence rates of dietary iron deficiency than other regions in Africa, which fruits and vegetables are the primary plant-based sources⁽²¹⁾. These global and regional evidence are also supported by studies within different locations in the Western African region where insufficient amounts of fruits and vegetables were reported^(17,23,24) . It is probable that most of the poor/low intake may be more for vegetables, as studies have shown that children’s preferences for vegetables in particular are consistently lower than for fruits⁽²⁵⁾.

The period of school age and adolescence are critical stages where attitudes, knowledge and skills acquired can influence their behaviour in adulthood⁽²⁶⁾. This then offers a window of opportunity for interventions to build their capacity to acquire healthy eating habits and improve their vegetable intake, to prevent micronutrient malnutrition and the onset of diet-related chronic diseases in later life, associated with poor and unhealthy dietary patterns and practices earlier in life. Hence there is a need to take a critical look at the vegetable intake of the target population and also intervention studies to promote their consumption. However, when compared with other lifecycle stages, limited research and intervention studies have focused on the health and nutrition of SAC⁽²⁷⁾. For adolescents, there is a lot of focus on their reproductive health. There are very few interventions to address the poor intake of vegetables and fruits among SAC and adolescents. To the best of the authors’ knowledge, a comprehensive review of the literature specifically studying vegetable intake and interventions to promote health-related behaviour to improve vegetable intake among SAC and adolescents to support these assumptions in the West Africa sub-region, where regional evidence suggests priority attention is needed, has not been undertaken.

Therefore, the purpose of this study was to perform a comprehensive systematic review and provide an up-to-date summary to answer the following questions: (1) What is the vegetable intake and consumption pattern of SAC and adolescents in West Africa, including the methodologies/assessment tools employed? (2) What are the common interventions that have been used to promote health-related behaviour to improve vegetable intake among SAC and adolescents in West Africa? (3) What are the barriers and facilitators to vegetable consumption and promotion among SAC and adolescents in West Africa? It is hoped that the results from this review may be used to guide future research and inform intervention studies for promoting increased vegetable consumption among SAC and adolescents.

Methods

A systematic review of the literature of qualitative and quantitative studies was conducted according to a pre-specified protocol that was registered with the International Prospective Register of Systematic Reviews (PROSPERO record with the ID CRD42023444444). The Preferred Reporting Items for Systematic Reviews and Meta-Analyses system was adhered to in the reporting of this review.

Search strategy

The search took place between 16 December 2022 and 28 March 2023. For primary research publications published between the years 2002 and 2022, three databases were used: PubMed, African Journals Online (AJOL) and Google Scholar. We did not conduct a search of the grey literature since we preferred to include only works that had been peer-reviewed, published and available online. The following keyword combinations were used in each of the various databases advanced search features: (Vegetable OR micronutrient) AND (Intake OR consumption OR diet OR dietary OR eating OR nutrition) AND (Primary school children OR Adolescent OR school-age children OR secondary school student OR teen OR pupil) AND (Nigeria OR Benin OR Burkina Faso OR Cabo Verde OR Cote d’Ivoire (Ivory Coast) OR Gambia OR Ghana OR Guinea OR Guinea-Bissau OR Liberia OR Mali OR Mauritania OR Niger OR Senegal OR Sierra Leone OR Togo).

Inclusion and exclusion criteria

Studies were considered eligible for inclusion if they met the following criteria:

Population: SAC and adolescents in the West African region between the ages of 6 and 19 years were included. Studies published in English were included.

Outcomes: Studies were included if they reported vegetable consumption, promotion of vegetables or the role of micronutrients from vegetables.

Study design: Experimental (intervention studies) and observational (cross-sectional, cohort and case control) were eligible.

Systematic reviews, unpublished theses, case studies, conference abstracts, special population studies (participants characterised with an illness or a problem), population studies involving children under 6 and those involving adults aged 19 and older and studies with low risk of bias or written in another language other than English were all excluded. Studies whose conclusions did not take into account vegetable intake, promotion of vegetables or the role of micronutrients were excluded.

Study selection

The article titles were screened to find publications that were pertinent. The paper’s alignment with the necessary inclusion and exclusion criteria was then verified by reading the abstract of pertinent articles by two of the researchers. The articles whose abstracts either satisfied these requirements or fell short of effectively describing the specifics were then downloaded and reviewed in their entirety.

Data collection/extraction

Utilising tables, the data were individually retrieved and recorded using Microsoft Excel by two of the researchers. Missing information was noted as unavailable. The following information was included in the data that were extracted: title, author(s), country, city or location, sample population, methodology (sample size, study design, sampling techniques, variables and study instruments), data analysis, important findings and conclusion. All discrepancies were discussed and resolved by all three researchers.

Quality assessment/appraisal

The risk of bias assessment for the included studies was independently conducted by two of the researchers. The Joanna Briggs Institute critical evaluation tools that were appropriate for this review’s eligible study designs were applied to each included document to help determine whether to include, exclude or request more information on a particular study⁽²⁸⁾. The Joanna Briggs Institute checklist, which consists of eight questions, was used to assess the methodological quality of research by identifying the number of potential biases in the design, conduct, analysis and write-up based on the range of our eligible designs. The eight questions focus on (1) study based on random/pseudo-random sample, (2) clear definition of study inclusion criteria, (3) description of study subjects and settings, (4) outcomes/exposures measured in a valid and reliable way, (5) identification of co-founding factors and strategies, (6) sufficient descriptions for comparison groups, (7) follow-up done for a sufficient time period and (8) appropriate statistical analysis ⁽²⁸⁾. There are four possible responses to each question: ‘yes’, ‘no’, ‘unclear’ and ‘NA’ (non-applicable). Owing to the varying design of the studies reviewed, the researchers focused on identifying criteria common across all of them. These studies were rated positive for inclusion when at least 50 % of each of the five common criteria – 1, 2, 3, 4 and 8 – were met. However, fulfilling all the criteria would result in a total score of 8 (1 point per criterion). The risk of bias was categorised into three levels: low quality (0–2), medium quality (3–5) and high quality (6–8).

Similar to the screening, the methodological quality of the eligible studies was evaluated, and all disagreements were resolved by consensus of the researchers or consultation of a third reviewer.

Data analysis and synthesis

Data were deductively grouped and analysed according to the relevant research questions: (i) vegetable intake and consumption pattern of SAC and adolescents in West Africa (outcome variables, measurement tools, study outcome/frequency of vegetable consumption), (ii) interventions that have been used to promote vegetable intake among SAC and adolescents and (iii) barriers and facilitators of vegetable consumption.

Results

A total of 11 380 possibly relevant articles were found in three (3) databases after the literature search (Fig. 1). 5080 articles remained after duplicate records were removed. 4970 records were eliminated after those articles’ eligibility was checked for the title and abstract. The remaining 110 documents were evaluated and scrutinised in their entirety. Full-text screening resulted in the exclusion of seventy articles. Thus, forty articles in all were finally included in this review.

Figure 1. Flow chart of article selection based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Description of study characteristics

In total, 24 391 SAC and adolescents recruited mostly from schools in five different countries were included in this review. Most of the studies were mainly reported from the population of Nigeria (n 26). Sample size ranged from 18 to 2786 participants with more than 75 % (30 out of 40) of the included studies recruiting between 101 and 1000 participants. The outcomes of each study varied, but the majority primarily focused on the frequency of vegetable consumption. An overview of the included studies is presented in Table 1, while the summary of study characteristics is presented in Table 2.

Table 1. Overview of the included studies

Table 2. Summary of characteristics of studies

Quality assessment of included studies

The quality assessment/appraisal using Joanna Briggs Institute critical appraisal checklist for descriptive/case studies as presented in Fig. 2 showed that 80 % of the reviewed studies were based on random/pseudo-random sample and had clear definition of study inclusion criteria, respectively. All studies had a clear description of the study subjects and setting, 90 % had their outcomes measured in a valid and reliable way, while 12·5 % identified other confounding factors and strategies. For the reviewed qualitative studies, 10 % gave sufficient description for comparison of groups, while follow-up done for a sufficient time period was 7·5 %. Almost all (95 %) of the studies were analysed appropriately. In general, six (15 %) were assessed as high-quality, thirty-four records (85 %) as medium quality and none for low quality, indicative of reliable evidence and low risk of bias. Detailed quality appraisal of each study is reported in the online Supplementary material Table 1.

Figure 2. Quality assessment of included studies using the Joanna Briggs Institute checklist.

Dietary assessment methodologies

Assessment tools in the included studies primarily consisted of FFQ (n 14). The number of items in the FFQ included 4-item FFQ⁽³⁷⁾, 54-item FFQ^(34,43) , 12-item FFQ⁽⁴⁵⁾, 11-item FFQ⁽⁴⁹⁾, 81-item FFQ⁽⁵⁷⁾, 6-item FFQ⁽⁶¹⁾ and 100-item FFQ⁽⁶⁴⁾. In addition, a 24 h dietary recall was used in twelve of the studies. In six studies, FV consumption data were merged together^{(42,47,48,56,61,66)} . Three of the studies used the Global School-based Student Health Survey questionnaire^(58,61,62) , and eight used validated and acceptable questionnaires/tools for national surveys^{(38,41,45,48,51,55,56,67)} . One of these studies⁽⁴⁵⁾ used an online questionnaire (KoBo Collect) to collect data. Questionnaire piloting was reported in nineteen of the studies. In comparison, six studies did not report the type of dietary assessment measured (quantity, frequency, etc.). The WHO-recommended five servings of fruits and vegetables were used as the adequacy cutoff point in two of the studies^(42,43) reporting the percentage of SAC and adolescents meeting the recommendation. Nonetheless, other cutoff points were used in a few studies. One of the studies⁽⁵⁴⁾ defined inadequacy as intake of < 1 slice of fruit or < 1 portion of raw or cooked vegetable per d. Another study⁽³⁶⁾ established their cutoff mark as two servings of FV, while another⁽⁵⁵⁾ used the WHO recommendation of 25 g of fibre.

Dietary outcome (vegetable consumption pattern)

Vegetable consumption data were presented in means, percentage of students consuming regularly or irregularly and those meeting the recommendations and frequencies. Mean consumption was recorded among four countries. A study by Giguère-Johnson et al. ⁽⁵⁵⁾ conducted in Senegal reported mean vegetable consumption as 32 ± 44 g/d, while a study conducted in Benin⁽⁵⁶⁾ reported a mean consumption of 97 g/d. In Burkina Faso⁽⁶²⁾, vegetable consumption was reported to be 2·3 times/week and 1·68 servings/week as observed by Owusu et al. ⁽⁵⁷⁾ in Ghana.

Interventions that promote vegetable intake

Five of the reviewed studies^{(40,45,52,65,68)} evaluated interventions that promote vegetable intake among SAC and adolescents as shown in Table 3. These include school garden and complementary education, nutrition education, gamification, school-based fruit stall and health education. Two of the reviewed studies^(29,50) found an increase in vegetable consumption and dietary habits among the respondents due to their parents owning a home garden.

Table 3. Interventions that promote vegetable intake among school-age children and adolescents

Barriers/facilitators of vegetable consumption

Three of the reviewed studies implemented in a school environment assessed the barriers/facilitators influencing vegetable consumption, while one study looked at the behavioural determinants of healthy food consumption (FV). Three studies reported on facilitators only, and two of them were studies from Nigeria^(32,41) and the third one from Burkina Faso⁽⁶²⁾. One study from Nigeria⁽⁴²⁾ reported both facilitators and barriers. The general observation from the reviewed studies was that vegetable consumption was facilitated by availability and accessibility at home and in school; consumption by parents, siblings and peers; and its health benefits. Specific comments captured were ‘it being served at home, siblings like vegetable, like the taste of vegetables and like for home-made stew’.

‘her mum loves taking fruits and she joins her; that’s how she developed the habit of taking fruits and vegetables’. Barriers to vegetable consumption reported were preparation time lack of taste and attractiveness as well as not making one feel full after consuming it.

Discussion

In this review, studies on vegetable promotion and consumption among SAC and adolescents in West Africa were comprehensively examined. The review included forty studies in total, and these publications included information on the frequency of vegetables consumed by country as well as interventions that support increasing vegetable consumption among different age groups. Due to the high heterogeneity of the reported studies consulted, a meta-analysis was not possible. The results of this systematic review reveal that most studies lumped the intake of fruits and vegetables together, and within the vegetable group, the types were not disaggregated either. This has implications for providing accurate results on the adequacy or lack thereof of vegetable consumption among the age group studied.

Vegetable intake/consumption pattern of school-age children and adolescents

The observed disparities in data assessment tools and techniques for vegetable consumption in different studies have been previously mentioned by several authors and expert groups^(69–71). These reports posited that the unavailability of harmonised dietary assessment indicators poses a critical gap in the comparability of findings and pooling of evidence to compensate for this missing global evidence for the target population in question. The varied FFQ items ranging from 4 to 100 further strengthen the case for more standardisation/harmonisation of FV dietary indicators. However, this is more challenging as other studies have affirmed that the reproducibility of FFQ varies between the FFQ items and age groups, and lower reproducibility is often found among children and adolescents than among adults and the elderly⁽⁷²⁾.

The low consumption of vegetables (at least one portion/d), which ranged from 0·04 to 26·8 % is not surprising, as it corroborates with evidence that Western Africa is far from meeting their recommended five portions (400 g) of fruits and vegetables per d^(20,73) . Similarly, another study also reported that adolescents in forty-nine low-income countries did not consume as many fruits and vegetables as recommended⁽⁷⁴⁾. The inadequacy of vegetable consumption suggests that West African countries are at a higher risk of non-communicable diseases and increased prevalence of micronutrient malnutrition.

Interventions that promote vegetable intake

Nutrition and health education interventions delivered in various forms particularly with visual aids were the dominant vegetable intake interventions given to the SAC and adolescents. Interventions that had additional hands-on/practical components like gardening and gamification were less prominent. This corroborates the report from a systematic review on school-based health and nutrition interventions addressing the double burden of malnutrition and educational outcomes of adolescents in low- and middle-income countries⁽⁷⁵⁾. The study reported a higher prevalence of nutrition education alone compared with having nutrition education along with other hands-on/practical intervention components that will actually facilitate positive dietary outcomes.

Although traditional nutrition education methods reportedly show good promise in these studies, there are still concerns regarding the extent to which this method achieves impactful outcomes among the age group in question if not combined with other practical components/activities⁽⁷⁶⁾. The authors suggest that the design of nutrition and health education for young people should incorporate hands-on practical components within the environment⁽⁷⁷⁾. School feeding is the largest social safety net for young people, with increasing institutional and political commitment in West Africa targeted for young people, while home gardening on the other hand is being advocated as a sustainable approach to improve food security in low-income settings⁽⁸⁾. Thus, integrating additional components like practical gardening sessions will not only promote behavioural change but also increase availability and accessibility and offer some additional fresh FV for consumption in a sustainable way.

Virtually, all nutrition-focused game interventions in literature were directed at children and adolescents, as they are important stakeholders in the game industry^(25,78) . Integrating nutrition and health education into this youth-dominated industry is an innovation that will likely garner the interest of consumers⁽⁷⁹⁾. Several nutrition incentive-based behaviour change interventions in literature were structured as a reward for positive behaviours^(80,81) . It will be interesting to see how much evidence evolves to support the translation of points in nutrition education games into values usable in real life to influence behaviour changes as reported in our studies.

Barriers and facilitators of vegetable consumption

Family (parental intake) and home environment (accessibility and availability) were the dominant factors influencing vegetable consumption among SAC and adolescents. This corresponds with reports from a systematic review on determinants of FV consumption among children and adolescents^(82,83) . Another study reported that parental participation, when combined with digital interventions, improved teenagers’ dietary and physical activity behaviours⁽⁸⁴⁾. Evaluation of the factors that affect children and adolescents’ intake of fruits and vegetables in various parts of the world has shown that parental intake and home accessibility and availability were consistently positively associated with intake^(82,85) . A study among Tehrani teenagers revealed that motivation was significantly influenced by verbal encouragement, supervision and instructions from parents, family, relatives and friends⁽⁸⁶⁾.

Limitations of the study

There are limitations to this systematic review. First, it is difficult to compare results since different research employed different methods to measure vegetable consumption (e.g. some used a 24 h dietary recall, while others used an FFQ). Selection of appropriate risk of bias tool was challenging as studies on vegetable consumption employed distinct research designs. Furthermore, the reference period and response categories varied even among articles that used the same technique. Second, data heterogeneity was noted, which made comparing research challenging. Furthermore, the consumption indicators used in the various papers differed (some studies gave means, others percentages and yet others frequencies). In cases where fruits and vegetables were lumped together, it was difficult to ascertain the consumption of vegetables and also in those studies that assessed vegetable consumption; most of them grouped the various types of vegetables together, while few studies disaggregated them. Finally, not all countries in the West African sub-region had published records of studies on vegetable consumption among these age groups. Hence our review is limited to the results of the studies from the countries where we found published studies.

Conclusion

This review indicates an inadequate intake of vegetables among SAC and adolescents in countries located in West Africa. Inadequate vegetable intake may contribute to poor health outcomes, especially micronutrient inadequacies, and other nutritional problems associated with low intake of vegetables. Therefore, it is crucial to discover the most effective programmes that can early on influence children and adolescents’ healthy eating habits and in particular their vegetable intake. The interventions found in the articles reviewed include the use of nutrition education, gamification, school-based fruit stall and school gardens and complementary nutrition education. These interventions seemed to influence vegetable consumption and nutrition knowledge of the SAC and adolescents. More empirical multi-component and innovative studies to improve vegetable consumption as a food group are urgently needed in the West Africa sub-region. Such studies should include food system factors that will make vegetables more available, accessible and desirable for children and adolescents. For example, parental participation (related to home food environment), vegetable gardening (production at home and/or school), food demonstrations (cooking/recipe development) and school meals, all linked to interactive nutrition education lessons among others, are important factors to consider in such studies. Gamification of nutrition education as a means to promote better dietary habits among this age group seems to also be a promising strategy to explore as well.

It is also important that the types of vegetables studied should be disaggregated, to identify the types of vegetables (leafy and non-leafy) that are commonly and less commonly consumed among the target group. Studies that focus on quantification of different types of vegetables consumed are also needed. In countries where studies have been carried out, it is encouraged that they are published so that the progress made in regions/countries is updated.