Socio-economic differences in health have been reported in many countries [1–3]. It is well known that health inequalities depend on economic, cultural, psychosocial, environmental and lifestyle factors. Diet is one such factor, playing an important role in the development of chronic non-communicable diseases (NCD), such as cardiovascular diseases (CVD), some cancers, and obesity; therefore, social differences in nutrition habits may partly explain social inequalities in morbidity and mortality from NCD [4–6]. Many studies have shown that people of higher socioeconomic status tend to have healthier diets than lower-status groups [7–9]. Social and economic changes in a country may impact nutrition habits, socio-demographic differences in diet, and other health behaviours of populations [10, 11].

In Lithuania, the transition period from a centralized-communist to a market-oriented economy was characterized by a widening gap between social strata [12]. Mortality rates decreased among the highly educated but increased among those with lower levels of education [13]. Life expectancy of rural population was shorter compared to urban population [14]. During the post-communist transition period, food prices increased dramatically [14]. People with lower socio-economic position were more vulnerable to inflation and subsequent declines in real income. Meanwhile, the availability and variety of foods increased considerably in Lithuania. Different kinds of vegetable oil and margarine, as well as fresh fruits and vegetables, became easily accessible. Furthermore, health promotion programmes and new food legislation were introduced. However, relatively little is known about how these changes influenced social inequalities in Lithuanian nutritional habits.

Since 1994, health behaviour monitoring has been carried out among the Lithuanian adult population. The monitoring data provide an opportunity to study the changes of socio-economic differences in health behaviours during the post-communist transition period. This study focused on dietary behaviours. Specifically, the use of vegetable oil in cooking and daily consumption of fresh vegetables were chosen as examples of healthy dietary habits, while the use of butter on bread and drinking high-fat milk were considered as unhealthy food habits.

The aim of the study was to evaluate trends in selected food habits by the level of education and place of residence from 1994 to 2010.

Our study has demonstrated some positive changes in the food habits of the Lithuanian adult population during the post-communist transition period. The use of vegetable oil in cooking and the frequency of consumption of fresh vegetables both increased. Conversely, the use of butter on bread decreased and the proportion of women drinking high-fat milk declined.

Several factors could explain these trends in food habits. Great changes occurred within the Lithuanian food market during this study period. Trade was liberalized; healthier food products, such as vegetable oils, soft margarines, low-fat dairy products, and a variety of fruits and vegetables became available. Affordable prices and good quality contributed to increases in consumption of these foods. Lithuanian food behaviours may have also been affected by health promotion campaigns and new health policies that emphasized the role of healthy nutrition in NCD prevention. For example, targets for healthy nutrition were included in the Lithuanian Health Programme (1998) [17]. In 2003, the Republic of Lithuania approved the State Food and Nutrition Strategy and Action Plan for 2003-2010 [18]. The main goal of this strategy was to reduce the prevalence of diet-related diseases and to improve the population's overall health. Among its priorities was increasing the accessibility and affordability of healthy food for all social groups. Food-based dietary guidelines were published to help the population make healthier choices [19]. These guidelines encouraged reduced fat consumption, especially from animal fat sources, limited consumption of meat products, and promotion of fruit and vegetable consumption.

Recently, the national diets of European countries became less distinct [20]. Mediterranean countries increased their consumption of meat, milk and sugar; meanwhile, some Northern countries decreased their intake of such foods and increased their fruit and vegetable consumption [21–26]. Dietary trends observed elsewhere in Central and Eastern European countries are similar to those found in Lithuania [10, 11, 27, 28]. The increase in the availability of vegetable oils, margarines, fresh fruits and vegetables - even when out of season - was followed by rise in the consumption of healthier foods. Stimulated by the initiative of the WHO European Regional Office, many European countries developed their own policies on food and nutrition that contributed to favourable changes in nutrition habits of their populations [24, 29, 30].

Our study revealed that trends in nutrition habits varied between various socio-demographic groups. The increase in the use of vegetable oil was more evident among less educated people and those living in villages compared to the highly educated and urban residents. Increased availability of vegetable oils stimulated widespread replacement of lard-based cooking technique, which was traditionally used in food preparation, particularly among lower socio-economic groups. In 1987, 52.0% of the Lithuanian rural population used mostly lard in cooking [31]. During the study period, social differences in use of vegetable oil in cooking have diminished.

Our findings showed that trends in the type of fat spread on bread also differed by socio-demographic group. A greater proportion of less educated people and rural inhabitants replaced butter with margarine. Such trends might be explained by the increase in the price of butter over time. When margarines, which are considerably cheaper than butter, became available, the use of butter decreased among those with lower incomes. Data from previous studies illustrated that food prices influence food choice and that people of lower socio-economic position are the most susceptible to price fluctuation [32, 33]. Moreover, cultural factors and the food-related beliefs of consumers are also important contributors to food choice [32, 34]. For example, in Lithuania butter is considered an organic, healthy food. People are sceptical of replacing butter with margarine, which is seen as a processed, 'artificial' food, with negative impacts on health. The media supports such attitudes by providing misleading information about the health benefits of butter produced by Lithuanian farmers. The Lithuanian media may have a greater impact on highly educated people who use butter more often than the less educated. Similar educational patterns were observed in Russia, Latvia, Poland, and other countries with transition economies [10, 11, 35]. Meanwhile, the opposite association was found in Estonia and the Nordic countries [11, 35]. Health education campaigns warning against butter as source of saturated fatty acids and recommending unsaturated fats might have influenced the behaviours of the highly educated in those countries.

According to our data, less educated and rural populations consumed high-fat milk most often. Social differences in milk consumption did not change over time. Such results are in line with other studies that reported an inverse association between consumption of high-fat milk and education level [36–38].

During the study period, daily consumption of fresh vegetables increased in all educational groups. However, this increase was most evident among the highly educated. In Lithuania, fresh vegetables and fruits are inexpensive in summer, but in spring and winter, when most fresh vegetables and fruits are imported, their prices rise. Our surveys were carried out in April and May, when availability of local vegetables was limited and prices were high. In order to increase consumption, the Lithuanian Government reduced VAT rate on fruits and vegetables in 2008; one year later, the VAT rate was restored because of the global economic crisis. According to comparison of surveys from nine European countries, a positive association between education level and vegetable consumption was related to the availability of vegetables [9]. This positive association was observed in countries with low availability and high prices for fruits and vegetables (Nordic and Baltic countries), whereas in countries where the availability and affordability were higher (France, Italy, Spain), the association was opposite. Northern countries do not have a tradition of consuming vegetables regularly. In those countries, consumption of fruits and vegetables is considered a 'modern' food habit. Higher socioeconomic groups are typically the first to choose these 'modern' foods [9].

In general, our study indicated beneficial dietary changes within the Lithuanian adult population. However, food habits of a large proportion of the Lithuanians do not meet healthy nutrition recommendations [19]. Therefore, Lithuanian Food and Nutrition Policy need renewal and supplementation to achieve the desired change in nutrition habits. The Ministry of Health, in collaboration with other government sectors, is developing the new Intersectorial Food and Nutrition Action Plan for 2012 - 2014 that aims to harmonise all activities dealing with nutritional problems of Lithuanians.

Several limitations of our study should be considered when interpreting our results. Our questionnaire included food-related questions that were used to identify the groups of people with different food habits. However, we were not able to measure amounts of consumed food or to calculate the nutrient content of respondent's diet. Validation studies of the questionnaire, using the 24-hour dietary recall as a reference method, revealed that data obtained by the two methods correlated well and simple food questions could be used to estimate 'high' and 'low' users of certain foods [39].

We used education and place of residence to characterize socio-economic groups. The level of education within a population increases over time; therefore, a comparison of educational differences in food habits over a period of 16 years may be biased. In Lithuania, the system of primary-secondary-higher education developed between the two world wars. In Soviet times, the education system was rather uniform. The development of Lithuania's current system started in the 1990s. Since 2003, it covers preschool, general, secondary, vocational, and higher (college and university) education. After reform of the vocational education system, college, as a higher education institution, was established. We grouped all respondents with college and vocational educations into one category, in order to maintain comparable educational categories throughout the study period. We were unable to study the effects of income on food habits; however, previous studies carried out in a Lithuanian population showed that educational level was directly associated with income [40]. The question about income appeared to be very sensitive to our respondents and was not included in the most surveys.

Furthermore, people belonging to higher social classes are more likely to be conscious of socially desirable eating habits and this might affect the reporting of nutrition habits [41]. Moreover, our findings may not be entirely representative, since non-response is often associated with unhealthy behaviours. The response rate tended to decrease in the most recent surveys. Therefore, it is possible that our results show a more favourable picture than if all selected samples were examined. We did not have data on non-respondents, but comparison of early and later respondents found only slight differences [42].

Despite the limitations described above, several major strengths of our study can be emphasized. First, it provides long-term trends in nutrition habits of Lithuanian adult population covering almost two decades of economic transition. Second, all cross-sectional surveys were carried out on nationally representative samples following the same methodology. Response rates were relatively high. Finally, to obtain maximal comparability, the questions regarding foods were asked in the same way in all surveys.

The Health Behaviour Monitoring has offered reliable data for the planning and evaluation of Lithuanian Food and Nutrition Policy. The future actions should be aimed at the increase of fresh vegetables consumption and reduction of high-fat dairy products intake targeting the most vulnerable groups of society.

Our study showed an improvement in food habits of the Lithuanian adult population during the period 1994-2010. The consumption of animal fat declined, while the use of vegetable oil in cooking and consumption of fresh vegetables increased. In general, those with a higher level of education had healthier food habits than those with low education. The educational gradient in analyzed food habits, except the use of vegetable oil, enlarged. A higher proportion of the rural population compared to urban reduced their usage of butter on bread. However, drinking of high-fat milk was most prevalent in the rural population. These results highlight the need for future food and nutrition policies and health promotion programmes targeting the whole population, particularly those with lower education and living in rural areas.