The number of observations per year that were acceptable for analysis of trends in food intake ranged from 3,292 to 9,883, except for 1986 and 1990 when only 1,515 and 1,549 observations, respectively, were available. The proportion of women ranged between 49.4% and 53.7% in the various study years. Due to the removal of a mandatory invitation to 30-year olds in VIP, the numbers for 30-year-olds in 2000, 2001, 2003, 2006, 2007, 2008 and 2010 ranged between 38 and 70 observations, but in other years the numbers ranged from 310 to 1,861. The 30-year-olds were kept in the data analyses as they were within the original inclusion age range. Filled symbols (means) in figures indicate years where the numbers exceed or are equal to 310. The numbers of observations per year used for nutrient intake evaluations were slightly fewer than those for food items in each year for both genders and all 10-year age groups.
Changing intake patterns for fat and carbohydrate 1986 to 2010
In 1986, mean reported fat intake, adjusted for age and BMI, was 39.2% of the men’s total reported energy intake (E%). Carbohydrates made up 45.9 E% and protein 13.6 E%. For women the corresponding levels were 35.5 E%, 49.2 E% and 14.3 E% for fat, carbohydrates and protein, respectively, in the same year (Figrue ). From 1986 to 2010 two significant trend breaks in reported fat intake were identified for both men and women. A decrease from 1986 to 1992 resulted in a reduction of reported fat intake by 2.9 E% in men and 4.4 E% in women. These levels stayed largely stable until 2002–2004, and thereafter a significant increase occurred, and reported fat intake reached levels above those in 1986. Thus, in 2010 men got 39.9% and women 37.7% of their reported total energy intake from fat. The trends were similar in 10-year age groups (Additional file 1
: Figure S1). Intake of saturated fat correlated highly with total fat, i.e. Spearman correlation coefficients were 0.86 for men and 0.87 for women. Reported intake of saturated fat followed a similar pattern as total fat, and the correlation coefficients were virtually identical each year (data not shown). In the same period reciprocal trend shifts were seen for reported carbohydrate intake (Figure ). The fraction of energy originating from protein was virtually unchanged over the 25-year period, i.e. a slight increase by 0.9 E% was seen for both men and women but no significant trend break was identified (Figure ).
Figure 2 Mean intake of fat, protein and carbohydrate expressed as energy from each nutrient in per cent of total energy intake. Mean intakes, adjusted for age and BMI for the period 1986 to 2010 for men and women. Information was not available for 1987 to 1990 (more ...)
Time trends for foods associated with high fat intake Fats used for spreading on bread and cooking, dairy products, oil for salad dressing or cooking, various types of meats and sausages as main dish or on sandwiches, pizza, deep- fried potato chips (French fries), and non-sweet snacks (including potato and maize crisps (chips), cheese-flavoured puffed products, popcorn, and peanuts) were identified to be associated with high fat intake (fatE%) in the study population by PLS. These foods were analysed for trends in intake from 1986 to 2010 for items where the question for the specific food/food aggregate had remained identical over the entire 25-year period.
In Figure , age and BMI adjusted mean reported intakes of fats used as bread spread or for cooking are shown. By far the most common type of fat used as bread spread in northern Sweden in 1986 was a butter-raps seed oil blend (brand name Bregott) with 80% fat until 2004 when different variants holding 80 to 43% fat were introduced (Figure upper panel). Reported intake of the butter-raps seed oil blend spread for bread showed a time trend curve characterized by several changes in the 25 year period, starting with a sharp decrease between 1986 and 1991, followed by an increase to 1994, a slowly progressing decrease until 2005, and thereafter a sharp increase. This pattern was consistent in 10-year age groups (Additional file 2
: Figure S2). The opposite was seen for low-fat spread alternatives (Figure upper panel). A linear increase was reported for use of butter and oil for cooking, whereas use of margarine decreased at a similar rate (Figure lower panel and Figure .). Largely the increasing trend for use of butter for cooking was similar for men and women and 10-year age groups, although the sharp increase in use of butter for cooking in 2006 was most pronounced among 25–35 year old men and especially 35–45 year old women (Additional file 3
: Figure S3).
Figure 3 Reported mean intake of various types of fats used for spreading on bread or cooking. Reported weekly mean intake frequencies, adjusted for age and BMI for the period 1986 to 2010 for men and women. Information was not available for 1987 and 1988 since (more ...)
Figure 4 Reported mean intake of various types of non-fermented milk. Reported weekly mean intake frequencies, adjusted for age and BMI for the period 1986 to 2010 for men and women. Information was not available for 1987 and 1988 since the VIP FFQ was not fully (more ...)
Intake of 3% fat milk decreased sharply from 1986 to 1991, and then remained virtually stable until 2008 when a break occurred, and a slightly increasing trend was identified (Figure ). Use of a medium-fat alternative (1 or 1.5% fat) increased sharply from 1986 to 1991 to a level that was maintained throughout the study period, whereas the low-fat alternative (0.5% fat) was similar from 1986 to 2008 after which a decreasing trend occurred (Figure ). Use of cream (including regular cream, crème fraiche and sour cream), oils in salad dressings, and non-sweetened snacks (including potato and maize crisps, cheese-flavoured puffed products, pop corn, and peanuts) increased linearly over the 25-year period for men and women (Figure ). For the other foods identified to contribute to high fat intake, i.e. intake of bacon, hamburgers, sausages, minced meat dishes, steak, stews, pizza and fried potato chips (French fries), reported intakes remained virtually stable over the 25-year period (data not shown).
Figure 5 Reported mean intake of various types of oils used for salad dressing or cooking, cream and cream products, and non-sweet snacks. Reported weekly mean intake frequencies, adjusted for age and BMI for the period 1986 to 2010 for men and women. Information (more ...)
Among remaining foods or food aggregates, the most striking changes in the 25-year period were sharp, linear decreases in consumption of boiled potato and whole grain crisp bread (data not shown). These changes were balanced by increasing intake of rice and pasta and whole grain soft bread (data not shown). Further, a slight increase in fatty fish intake occurred from around 2000, whereas intake of lean fish was unaltered over the study period (data not shown).
Alcoholic beverage consumption 1986 to 2010
The most striking time trend in intake of alcoholic beverages over the 25-year period was a continuous sharp increase in reported wine consumption (Figure ). This was especially evident in women. In year 2010 women reported a higher wine intake than men. Over the study period, men also increased their intake of export beer (>3.5 vol% alcohol). Reported intake of spirits (both genders) and export beer in women remained unchanged (Figure ).
Figure 6 Reported mean intake of various types of alcohol containing products. Reported weekly mean intake frequencies, adjusted for age and BMI for the period 1986 to 2010 for men and women. Information was not available for 1987 and 1988 since the VIP FFQ was (more ...)
25-year trends in two potential markers for diet
Age-adjusted mean BMI and the proportions with a BMI
27 increased continuously from 1986 to 2010 in the studied Northern Sweden cohort with parallel trend curves for men and women (Figure A, upper panel). The increase went from a mean BMI of 25.5 to 27.1 in men and from 24.8 to 25.9 in women. Increases for 10-year age groups are shown in Additional file 4
: Figure S4.
Figure 7 (A) Mean body mass index (BMI) by study year and proportions with BMI>27; (B) mean total cholesterol in serum by study year and proportions reporting intake of cholesterol lowering medication by study year. Means, adjusted for (more ...)
In contrast, total cholesterol levels in serum decreased continuously from 1986 to 2004, remained virtually unchanged a few years and then increased after 2007 (Figure B). The trend curves were parallel in men and women and in 10-year age groups (Additional file 5
: Figure S5. During the 25-year study period use of cholesterol-lowering medication was introduced in the study population. Self-reported use of cholesterol-lowering medication increased linearly from less than 1% of the participants in 1992 to 6.5% in 2010 (Figure B, lower right panel). To evaluate if inclusion of participants taking cholesterol-lowering medication affected the trend curves for cholesterol significantly, age adjusted means were compared when these subjects were included or excluded. Age adjusted means for non-medicated subjects only differed in the second decimal digit with no additional effect on the trend breaks compared with when medicated subjects were retained.
Foods associated with high serum cholesterol levels in men and women in Northern Sweden
We next searched for foods associated with having a high serum cholesterol level by multivariate PLS modelling of energy-providing nutrients/alcohol and foods on cholesterol as a continuous variable in 10-year age groups. In both genders and all age groups models with one significant component were obtained. The explanatory capacities of the models typically were between 4.1 and 2.3% (R2 ranged from 0.041 to 0.023). The models remained stable after cross validation (Q2 ranged from 0.039 to 0.011).
High consumption of boiled coffee, total fat (E%), saturated fat (grams/day), butter-based spread or butter on bread, margarine for cooking, salted fish, sweet buns and crisp bread rolls, and boiled potato characterised subjects with high versus low levels of cholesterol in serum in six of eight gender/age strata. Other items characterizing subjects with high versus low serum cholesterol levels in at least two gender/age strata were high consumption of total fat (grams/day), butter for cooking, 3% and 1.5% fat milk, medium fat cheese (typically 28% fat), whole grain crisp bread, white bread, sweet fruit soups, and alcohol intake (E%, grams/day, beer and liquor). Some of these associations were gender specific, such as alcohol for men. Mean PLS loading correlations in gender and age group strata are summarized in Additional file 6
: Table S1.