Efficacité des politiques de réduction des acides gras trans alimentaires: une revue systématique des données probantes
La eficacia de las estrategias para reducir las grasas trans en la dieta: examen sistemático de los datos disponibles
Shauna M Downs*; Anne Marie Thow; Stephen R Leeder
Menzies Centre for Health Policy, Victor Coppleson Building (D02), University of Sydney, Sydney, NSW 2006, Australia
OBJECTIVE: To systematically review evidence for the effectiveness of policies, including self-regulation, aimed at reducing industrially produced trans fatty acids (TFAs) in food.
METHODS: The Medline, Embase and Cinahl databases were searched to identify peer-reviewed articles examining the effect of TFA policies. In addition, the first 20 pages of Google searches were examined for articles from the grey literature. A study was included if: (i) it was empirical and conducted in a "real-world" setting (i.e. modelling studies were excluded); (ii) it examined a TFA policy involving, for example, labelling, voluntary limits or bans; and (iii) it examined a policy's effect on TFA levels in food, people's diets, blood or breast milk.
FINDINGS: Twenty-six articles met the inclusion criteria: 5 involved voluntary self-regulation; 8, labelling alone; 4, labelling and voluntary limits; 5, local bans and 4, national bans. Overall, the TFA content of food decreased with all types of policy intervention. In general, saturated fat levels increased or decreased, depending on the product type, and total fat content remained stable. National and local bans were most effective at eliminating TFAs from the food supply, whereas mandatory TFA labelling and voluntary TFA limits had a varying degree of success, which largely depended on food category.
CONCLUSION: Policies aimed at restricting the TFA content of food were associated with significant reductions in TFA levels, without increasing total fat content. Such policies are feasible, achievable and likely to have an effect on public health.
OBJECTIF: Examiner systématiquement la preuve de l'efficacité des politiques, y compris l'autorégulation, visant à réduire les acides gras trans (AGT) industriels dans l'alimentation.
MÉTHODES: Les bases de données Medline, Embase et Cinahl ont été exploitées pour identifier les articles évalués par des pairs, portant sur l'effet des politiques AGT. En outre, on a recherché dans les 20 premières pages de recherches Google des articles de la littérature grise. Une étude était prise en compte si: (i) elle était empirique et conduite dans des conditions «réelles» (c'est-à-dire que les études de modélisation ont été exclues), (ii) elle portait sur une politique AGT impliquant, par exemple, l'étiquetage, les limitations ou interdictions volontaires, et (iii) elle examinait l'effet d'une politique sur les niveaux d'AGT dans les aliments, l'alimentation des personnes, le sang ou le lait maternel.
RÉSULTATS: Vingt-six articles répondaient aux critères d'inclusion: 5 impliquaient l'autorégulation volontaire, 8 l'étiquetage seul, 4 l'étiquetage et les limitations volontaires, 5 des interdictions locales et 4 des interdictions nationales. Dans l'ensemble, la teneur en AGT des aliments a diminué avec tous les types de politique d'intervention. En général, les niveaux de graisses saturées ont augmenté ou diminué, selon le type de produit, et la teneur totale en matières grasses est restée stable. Les interdictions nationales et locales ont été les plus efficaces dans l'élimination des AGT dans l'approvisionnement alimentaire, alors que l'étiquetage obligatoire AGT et les limitations volontaires ont eu un degré de succès variable, qui dépendait en grande partie de la catégorie des aliments.
CONCLUSION: Les politiques visant à limiter la teneur en AGT des aliments ont été associées à des réductions significatives des niveaux d'AGT, sans augmentation de la teneur totale en graisses. Ces politiques sont faisables, réalisables et susceptibles d'avoir un effet sur la santé publique.
OBJETIVO: Examinar sistemáticamente los datos disponibles sobre la eficacia de las estrategias (incluida la autorregulación) dirigidas a reducir los ácidos grasos de tipo trans (AGT) de producción industrial en los alimentos.
MÉTODOS: Se examinaron las bases de datos Medline, Embase y Cinahl para identificar artículos revisados por expertos en los que se estudiara el efecto de las estrategias acerca de las grasas trans. Además, también se buscaron artículos de literatura gris en las primeras 20 páginas de resultados de Google. Los estudios se incluyeron cuando: (i) se trataba de un estudio empírico que se desarrolló en un entorno del «mundo real» (esto es, se excluyeron estudios de modelamiento); (ii) se examinaba una estrategia relacionada con los AGT que incluyera, por ejemplo, etiquetado, límites voluntarios o prohibiciones; y (iii) se examinaba el efecto de una estrategia sobre los niveles de AGT en los alimentos, la dieta de las personas, la sangre o la leche materna.
RESULTADOS: Veintiséis artículos cumplieron con los criterios de inclusión. De ellos, cinco incluyeron una autorregulación voluntaria; ocho, sólo etiquetado; cuatro, etiquetado y límites voluntarios; cinco, prohibiciones locales y cuatro, prohibiciones nacionales. En su conjunto, todas las estrategias redujeron el nivel de AGT en los alimentos. Por regla general, los niveles de grasas saturadas aumentaron o disminuyeron según el tipo de producto, y el contenido total de grasa permaneció estable. Las prohibiciones locales y nacionales resultaron ser las más eficaces a la hora de eliminar los AGT de los alimentos, mientras que el etiquetado obligatorio y los límites voluntarios obtuvieron resultados variados, dependiendo, en su mayor parte, de la categoría de alimento.
CONCLUSIÓN: Las estrategias dirigidas a la reducción del contenido de AGT en los alimentos estuvieron asociadas a reducciones significativas de los niveles de AGT sin un aumento del contenido total en grasas. Estas estrategias son factibles, viables y pueden tener un efecto sobre la salud pública.
Trans fatty acids (TFAs) are unsaturated fats found in foods obtained from ruminants, such as dairy products and meat, and in industrially produced partially hydrogenated vegetable oils.1 Human consumption of naturally occurring TFAs from ruminants is generally low and there is evidence to suggest that it does not adversely affect health.2 In contrast, consumption of industrially produced partially hydrogenated vegetable oils has been associated with an increased risk of cardiovascular disease, infertility, endometriosis, gallstones, Alzheimer's disease, diabetes and some cancers.3,4 In the 1960s, following public health campaigns aimed at decreasing the use of animal fats, the food industry began using substantial amounts of partially hydrogenated vegetable oils in processed food.2 Their use is favoured by industry - and their removal resisted - because: they are cheap; they are semisolid at room temperature, which makes them easier to use in baked products; they have a long shelf-life; and they can withstand repeated heating.2
The removal of partially hydrogenated vegetable oils containing industrially produced TFAs from the food supply has been described as one of the most straightforward public health interventions for improving diet and reducing the risk of noncommunicable disease.2 In fact, the World Health Organization (WHO) has called for the elimination of TFAs from the global food supply.1 In response to the rise in the prevalence of noncommunicable diseases, of which cardiovascular disease is the most common, the United Nations hosted a high-level meeting on the topic in September 2011. The political declaration that resulted from this meeting led to the development, in consultation with Member States, of a WHO global framework for monitoring noncommunicable diseases. This framework stipulates global indicators and targets for monitoring noncommunicable diseases up to 2025,5 including a small number of indicators associated with specific time-dependent targets and core indicators that will be monitored but are not linked to specific targets.5 One core indicator is the "adoption of national policies that virtually eliminate partially hydrogenated vegetable oils in the food supply and replace [them] with polyunsaturated fatty acids".5
Although the removal of TFAs from the food supply has been identified as a "best-buy" public health intervention for low- and middle-income countries,6 WHO Member States that took part in consultations indicated "low (no) support" for including the removal of TFAs as a global monitoring target because of concerns about the feasibility, achievability and public health effect of removing them from the food supply.7 However, both national and local bans of TFAs in foodstuffs have been implemented throughout the world (Fig. 1), which demonstrates that the removal of TFAs is both feasible and achievable. However, there has never been a systematic review of the effect of TFA policies on the amount of TFAs in the food supply. The aim of this study was to review the evidence surrounding the effectiveness of policies aimed at reducing TFAs in food, including those involving self-regulation.
A systematic literature search was conducted using the Medline, Embase and Cinahl databases to identify peer-reviewed articles that examined the effect of a TFA policy. In addition, the first 20 pages of Google searches were examined to identify articles from the grey literature. The main search terms were trans fat and policy. Additional search terms related to trans fat were: trans fatty acids, hydrogenation, vanaspati, elaidic acid and margarine. Additional search terms related to policy were: regulation, nutrition policy, health policy, legislation, ban, intervention, labelling, law, standards and restriction. These terms were used as keywords and in free text searches of titles and abstracts, depending on the database being searched. When a Google search identified a TFA policy that had been implemented but whose effects had not been reported online, one of the study authors (SMD) contacted the government department monitoring the ban to ascertain whether or not an evaluation had been conducted.
A study was included in the review if: (i) it was empirical and conducted in a "real-world" setting (i.e. modelling studies of hypothetical policy interventions were excluded); (ii) it examined a TFA policy involving, for example, labelling, voluntary limits or bans; and (iii) it examined a policy's effect on TFA levels in, for example, food, diet, blood or breast milk. We intended to include only articles published after 1990, when evidence of the health effects of TFA consumption first appeared.8 However, all articles identified were published between 2005 and 2012.
One author (SMD) carried out the initial review of study titles and two authors (SMD and AMT) assessed abstracts using the aforementioned inclusion criteria. The reference lists of the articles were also examined. If the two reviewers disagreed, the full article was reviewed. The main reason for excluding studies was that they did not involve empirical research. The principal reviewer read the full text of 45 articles and subsequently received Google alerts on any new studies that could be included. Ultimately, the review involved 26 studies that were found to meet the inclusion criteria (Fig. 2). Although the majority were published in peer-reviewed journals, four were reported in the grey literature. The quality of the study evidence was ranked from level I (strongest) to level IV (weakest) using a previously published classification that primarily considered study design.9
Table 1 (available at: http://www.who.int/bulletin/volumes/91/4/12-111468) lists the relevant results of the 26 studies included in the review, grouped by TFA policy intervention: 5 involved voluntary self-regulation; 8, labelling alone; 4, labelling and voluntary limits; 5, local bans and 4, national bans. The countries covered were Brazil, Canada, Costa Rica, Denmark, the Netherlands, the Republic of Korea and the United States of America. All policy interventions were associated with a reduction in the availability of TFAs. The majority of studies had either a post-test or a pretest - post-test design, both of which provide level-IV evidence. Although only one study used a case - control design, which provides level-III evidence, three other studies compared TFA levels in the study country with levels in other countries, which acted as "pseudo" control groups. Three studies used an interrupted case series design, which provides level-III evidence. Four of the nine studies of TFA bans did not include detailed descriptions of the study methods.27,29,30,35
Ten studies examined the formulation of food products before and after the TFA policy intervention. Table 2 gives details of the resulting changes in fatty acid composition. For most products, saturated fatty acid levels did not increase as the TFA level decreased. However, after the intervention the level of saturated fatty acids was higher in specific foods, such as bakery products and popcorn. Mono- and polyunsaturated fatty acid levels generally increased with product reformulation and total fat levels remained relatively constant, with a decrease in the combined level of TFAs and saturated fatty acids.
National bans virtually eliminated TFAs from the food supply (Table 3) and local bans were very successful in removing TFAs from fried foods. The effects of mandatory TFA labelling and voluntary limits were more variable and depended largely on the food category. In particular, changes in TFA levels in margarines and bakery products were smaller in countries without a national ban.
Four studies examined TFA intake before and after TFA policy interventions. Each study used a different measure of intake. In Canada, mandatory TFA labelling combined with voluntary limits was associated with a 35% reduction in TFAs in breast milk23 and a 30% reduction in dietary intake in the general population.26 In the United States, mandatory TFA labelling was associated with a 58% reduction in TFA levels in blood plasma.21 Voluntary self-regulation of TFA levels in the Netherlands was associated with a 20% reduction in dietary intake.11 Intake was not measured in studies of countries where national bans virtually eliminated TFAs from the food supply or where local bans removed TFAs from fried fast foods.
Two studies examined the relationship between policy interventions aimed at reducing TFA levels in food and health outcomes. Vesper et al.21 found that mandatory TFA labelling in the United States was associated with a reduction in low-density lipoprotein cholesterol and triglyceride levels and an increase in high-density lipoprotein cholesterol levels. Colón-Ramos et al.36 examined the effect of voluntary self-regulation in Costa Rica on the risk of myocardial infarction and found a significant association between the risk of myocardial infarction and the level of TFAs in subcutaneous fat before the intervention but not after.
Two studies examined the effect of TFA policy interventions on product price.17,24 Both found a significant negative relationship between price and TFA content in margarines and one found a similar relationship in savoury snacks.
The findings of this review show that the policies introduced to decrease TFA levels in the food supply have been effective, regardless of the intervention employed. National and local bans were the most effective. Although significant progress has been made with labelling regulation in countries such as Canada and the United States, TFA levels need to be reduced more, particularly in margarines and bakery products.
Our observation that national and local bans were far more effective than mandatory TFA labelling reflects the Danish Nutrition Council's decision to opt for a ban when considering how to remove TFAs from the food supply.35 Labelling policies have several limitations. First, TFA intake can remain extremely high in pockets of the population.26,37 In Canada, even after mandatory labelling led to 76% of foods meeting voluntary TFA limits, intake in the population still exceeded the WHO recommendation that less than 1% of dietary energy intake should come from consuming TFAs. In particular, intake by teenage boys was double the recommended level.26 Second, some foods with low TFA levels are costlier, which will be felt more by consumers with a low socioeconomic status.17,24,38 Ricciuto et al.24 found that some margarine companies in Canada offered products with a low TFA level while continuing to sell products with a high level at a lower price. Thus, price-conscious consumers would be more likely to consume the less healthy product, thereby increasing their risk of diet-related chronic disease.39 Third, for labelling regulation to be effective, the population must be both aware of TFAs and able to interpret nutrition labels accurately. In high-income countries, where literacy levels are high, labelling is more likely to be effective in reducing TFA intake than in low- and middle-income countries.
Perhaps one of the strongest arguments in favour of mandatory TFA labelling is that it will lead to product reformulation. The impetus for product reformulation often comes from consumers who value and demand products low in TFAs. In countries where awareness of TFAs is low, the food industry may be less likely to reformulate their products. In Brazil, the TFA level in some margarines remained over 50% after regulation,22 perhaps due to a low level of consumer awareness.
Labelling regulation often applies solely to packaged foods and not foods purchased at restaurants and fast-food outlets. None of the national policies on mandatory TFA labelling investigated by studies included in this review applied to non-packaged food. However, many large fast-food companies do provide information on the TFA content of their foods, either in store or on their web sites. Moreover, in many low- and middle-income countries, the main source of TFAs is food purchased from street vendors and the unorganised food sector rather than pre-packaged food,2,40,41 which may further limit the effectiveness of labelling regulation.
During consultations on the global framework for monitoring noncommunicable diseases, some WHO Member States indicated that they preferred a voluntary to a mandatory approach to reducing TFAs.7 Although voluntary regulation may reduce TFA levels in some contexts, mandatory regulation appears to have a greater effect.42 In New York City in the United States, voluntary regulation was tried first to reduce TFA levels in restaurant food. However, the number of restaurants using partially hydrogenated vegetable oils as frying fats did not decrease and the city banned TFAs in restaurants.27 Although the Netherlands succeeded in reducing TFAs through voluntary measures and intake is now below the WHO recommended limit, this outcome was regarded by the authors as "typically Dutch" since the country has a long history of resolving social issues through the engagement of and collaboration between various branches of society.10 Other countries may need mandatory measures to reduce TFA levels in the food supply. Even in countries where there is substantial societal pressure to reduce TFA intake, levels are still high in some foods.33
In North and South America, many large multinational companies signed a declaration to help reduce TFAs in food but few have provided data to show their progress towards this goal.13 However, a voluntary approach may be more effective when the agriculture sector is engaged.12,43 In particular, making the transition from partially hydrogenated vegetable oils to "healthier" oils may be easier for countries that grow crops producing oils rich in mono- or polyunsaturated fatty acids. For example, Argentina was able to shift production to high-oleic sunflower oil to aid product reformulation, whereas similar changes may be more difficult in countries such as India that rely heavily on imports.41,42
Product reformulation that involves the removal of TFAs from food may simply lead to higher levels of saturated fatty acid, thereby limiting the public health effect of TFA policies. However, our findings indicate that reformulation resulted in the removal of TFAs with little change in saturated fatty acid content in the majority of products; bakery products were an exception. Moreover, the fatty acid profile of many reformulated products improved while the total fat content remained constant. The resulting health benefits may exceed those associated with simply removing TFAs from food.44
Nevertheless, all but three studies included in this review were conducted in high-income countries. Many multinational companies have switched sources of fat to reduce TFA levels in products sold in high-income countries but tend to resist making these changes in low- and middle-income countries.45 Moreover, product reformulation may involve replacing partially hydrogenated vegetable oils with palm oil, which increases the level of saturated fatty acids. For example, recently PepsiCo in India switched the frying oil used in producing Lays potato crisps from rice bran oil to palm oil in an effort to cut costs after previously marketing the product as a "smart snack" cooked in healthier oil.46 Progress in low- and middle-income countries will have to be monitored to ensure that partially hydrogenated vegetable oils are not replaced exclusively with palm oil, which is cheap, abundant and high in saturated fatty acid. It may be necessary to provide incentives to oil producers and the manufacturers of food products containing TFAs to dissuade them from replacing oils rich in TFAs with palm oil.
The studies that included information on dietary TFA intake or biomarkers showed that all forms of intervention resulted in significant declines. A study conducted in the United States21 found a 58% reduction in TFA in plasma following mandatory TFA labelling and two Canadian studies observed a 30% decrease in dietary intake26 and a 35% decrease in TFA in breast milk,23 respectively, after the introduction of a more restrictive policy. Although these studies are not directly comparable because the outcome measures were different, since the only source of TFA in plasma and breast milk is from dietary intake, the difference is worth noting. However, it is important to be aware that, in both countries, labelling policy was only one factor influencing TFA intake. Twenty per cent of the United States population live in areas covered by a TFA ban,47 which may help explain why the reduction in plasma TFA was more substantial than the reductions in dietary and breast milk levels observed in Canada, in which only one province, containing approximately 12% of the Canadian population, has a TFA ban.
Political awareness and commitment were important for the success of many of the policy interventions aimed at reducing TFAs in the food supply.48 Although bans proved to be most effective, many countries, states and cities lack the political will to introduce the necessary legislation. Even when the political commitment is there, the prospect of legislation often provokes resistance from food and agriculture industries. In addition, resistance can sometimes come from within other parts of government as well as from individuals who may hold strong libertarian views. For example, the local government in the city of Cleveland in the United States recently introduced legislation to ban TFAs in food but this was later blocked by the Ohio state government.47In response, the city sued the state government and won. When Denmark introduced its ban on TFAs, the country experienced resistance from the European Union, which regarded the legislation as creating a barrier to trade given that all food in the country, including imports, had to abide by the restriction on TFAs.49 Perhaps unsurprisingly, in the months leading up to the United Nations high-level meeting on noncommunicable diseases, many European countries were "furiously watering down" their commitment to reduce TFA levels in food.37 Nevertheless, including the removal of TFAs from the food supply as an indicator in the WHO global monitoring framework is an encouraging step towards reducing TFA levels in food worldwide.
Natural experiments lack the strength of controlled experiments, which are frequently infeasible. This makes it difficult, if not impossible, to determine the direct effect of policy interventions on TFA levels in the food supply. The most conclusive studies examine both TFA intake and its effect on health outcomes; unless these specific outcomes are measured, doubt about an intervention's effectiveness often persists. Consequently, some studies in this review were limited because they used compliance with regulations or the TFA level in blood or breast milk as an intermediate outcome and did not examine TFA intake and its associated disease risk. Nevertheless, the studies reviewed generally supported the view that TFA policies can be effective.
Another limitation is that studies examining TFA policy interventions in a "real-world" setting may overestimate the resulting reduction in TFA levels because of sampling limitations: many studies of product reformulation considered only a small number of foods; some studies examined products cross-sectionally rather than testing the same products before and after reformulation; and some examined foods that had already been reformulated.
In addition, the studies in the review were not directly comparable. For example, labelling policy in the United States allows foods with up to 0.5 g TFA per serving to be labelled TFA-free, whereas all other countries included in this review defined TFA-free as less than 0.2 g TFA per serving.50 Moreover, there are important differences between local and national TFA bans. To date, local bans have focused on foods served in restaurants rather than all foods. Outcomes can also be different. In Denmark, for example, the national ban was applied to all food sold within the country and led to the complete elimination of TFAs from the food supply, whereas in New York City it is still possible to purchase a fast-food meal containing 5 g of TFA despite a local TFA ban.28
This review indicates that TFA policies were associated with significant reductions in TFA levels in the food supply: such policies are feasible, achievable and likely to have an effect on public health. Although product reformulation in high-income countries has improved the fatty acid profile of foods, further research is needed in low-resource settings to identify context-specific challenges and policy responses. Moreover, monitoring TFA levels in the food supply is important for ensuring that progress continues, particularly in low-income settings where little information on consumption is available. Encouraging the agriculture sector to increase the supply of suitable alternative oils may facilitate product reformulation. Finally, it is important to note that reducing the TFA content of food is only one component of a multipronged strategy to improve diet and reduce the risk of diet-related chronic disease. ■
Competing interests: None declared.
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Submitted: 13 August 2012
Revised version received: 19 November 2012
Accepted: 17 December 2012
Published online: 4 February 2013