Secular Trends in Dietary Macronutrient Intake in Minneapolis-St. Paul, Minnesota, 19801992
Donna K. Arnett,
Blong Xiong,
Paul G. McGovern,
Henry Blackburn and
Russell V. Luepker
From the Division of Epidemiology, School of Public Health, University of Minnesota, Minneapolis, MN.
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ABSTRACT
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Trends in dietary macronutrient intake were evaluated in population-based surveys conducted in adults aged 2574 years in 19801982, 19851987, and 19901992 in the seven-county Minneapolis-St. Paul metropolitan area. A 24-hour dietary recall (n = 6,499) was completed by a random 50% sample. The authors obtained energy intake for each macronutrient (protein, carbohydrate, fat, saturated fat, monounsaturated fat, polyunsaturated fat, and alcohol). Tine trends for percentage of total energy were analyzed using a generalized linear mixed model. While energy intake remained stable over time, macronutrient composition changed substantially. In 19801982, the caloric distribution for men comprised 15.8% protein, 39.4% fat, 40.9% carbohydrate, and 3.9% alcohol; similar findings were observed in women (15.7% protein, 38.9% fat, 43% carbohydrate, and 2.4% alcohol). From 1980 to 1992, total fat intake decreased 4.7% in men and 4.9% in women (p < 0.001). The decline was greatest for monounsaturated fat, although saturated and polyunsaturated fat intake also fell. During this same period, carbohydrate intake increased 5.7% and 5.8% in men and women, respectively (p < 0.001). Alcohol intake decreased in men and women (p < 0.01), while protein intake remained stable. In summary, the Minneapolis-St. Paul metropolitan area diet shifted substantially during the 1980s toward more carbohydrate and lower fat and alcohol intake. Am J Epidemiol 2000;152:86873.
diet; diet surveys; food habits; population characteristics
Abbreviations:
BMI, body mass index; CSFII, Continuing Survey of Food Intakes by Individuals; NHANES, National Health and Nutrition Examination Survey.
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INTRODUCTION
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Coronary heart disease mortality rates in the United States have declined steadily since the mid-1960s (1




7
). During this same period, they also decreased in the Minneapolis-St. Paul, Minnesota, metropolitan area, even though its rates were lower compared with US rates (1


5
). The decline in coronary heart disease mortality has been attributed to both improved medical care and changes in lifestyle, such as a reduction in smoking prevalence and increased physical activity (1
3
, 5


9
). Favorable changes in composition of the diet are also thought to have played an important role (1
, 9


13
). According to national dietary surveys of individual intakes, for which various dietary assessment methodologies have been used, food group consumption since the mid-1960s has shifted in the United States toward a lower intake of meats and eggs and an increased intake of fruits and vegetables, low-fat dairy products, bread, cereals, and grain products (1
, 6
, 10
, 14
16
). These changes in food consumption likely influenced dietary macronutrient intake. This study assessed trends in dietary macronutrient intake (protein, carbohydrate, fat, saturated fat, monounsaturated fat, polyunsaturated fat, and alcohol) for men and women aged 2574 years in the Minneapolis-St. Paul, Minnesota, metropolitan area from 19801982 to 19901992 as part of the Minnesota Heart Survey.
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MATERIALS AND METHODS
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Study population
Cross-sectional risk factor and health behavior surveys of adults aged 2574 years in the Minneapolis-St. Paul metropolitan area were conducted in 19801982, 19851987, and 19901992. The population in this area is predominantly White and has a slightly higher level of education and employment than the US population overall. According to the 1990 US Census, the population was 2.29 million.
Detailed descriptions of the Minnesota Heart Survey study design have been published previously (13
, 17

20
). To summarize briefly, a two-stage cluster sampling was performed using a sampling frame created from census maps. The seven-county metropolitan area was first divided into 704 clusters of about 1,000 households, and 40 clusters were randomly selected without replacement and were used for each survey. A proportion of the households was then randomly selected from these clusters (510 percent across the three surveys). Once a household was selected, it was removed from the sampling frame for future surveys.
Selected households received a letter introducing the study. Trained interviewers subsequently visited the household to conduct an enumeration and home interview. In the 19801981 survey cycle, all residents of a household aged 2574 years were asked to participate, while only one person was randomly selected from the household during all subsequent surveys. The data collection methods were the same for all three surveys. The home interview obtained information on sociodemographic characteristics; cigarette smoking status; medication use; and health attitudes, beliefs, and knowledge as well as a brief medical history. The interview was followed by a visit by participants to a local clinic, where physiologic measurements were made, including height, weight, heart rate, blood pressure, and serum cholesterol. In addition, smoking history, diet, and leisure time physical activity were assessed. Weight was measured without shoes and heavy clothing. Home interview response rates were 8291 percent and clinic participation rates 6768 percent for each survey period. Respondents were more likely to be married, employed, better educated (i.e., education beyond high school), and nonsmokers.
Dietary assessment
Diet was assessed during the clinic visit by using a 24-hour dietary recall for a 50 percent systematic sample of participants. Participation rates for the dietary recall ranged from 92 to 100 percent across the three surveys. Interviews were conducted by nondietitians trained and certified by the Nutrition Coordination Center at the University of Minnesota (Minneapolis, Minnesota). The interviewers were retrained and recertified every 6 months to assure collection of high-quality data, and most were employed in all three surveys. Emphasis was given to foods and preparation methods that influence intakes of fat, cholesterol, and sodium. Food models were used to help participants estimate portion size. Because intake was assessed for the preceding day, recall of dietary intake included all days of the week except Friday and Saturday (i.e., the clinic did not operate on weekends). Participants who completed the 24-hour dietary recall were similar in age, sex, and educational level to those who did not.
The Nutrition Coordination Center coded the dietary recall information, conducted quality control procedures, and maintained the nutrient database. Nutrients were assigned to the dietary recalls from all surveys using version 11 of the Nutrition Coordination Center food table; version 11 contains 42 nutrient fields plus fields for the percentage of calories consumed from protein, fat, carbohydrate, and alcohol. The nutrient database was updated to allow for the addition of those foods recently introduced into the marketplace and the "deactivation" of food codes no longer available. Deactivated entries were kept in the database since they contained the values for foods recorded during earlier surveys. Persons with a total intake of more than 10,000 kcal were excluded from the analysis.
Analysis
Analyses were sex specific and age adjusted and were conducted using the SAS software package, version 6.1 (21
). The percentage of total energy for each macronutrient was calculated for men and women separately. Total energy was defined as the sum of energy from total fat, protein, carbo-hydrate, and alcohol consumed from food and drinks and was measured in kilocalories. Fat intake was subdivided into saturated, monounsaturated, and polyunsaturated fat; the trend was assessed as the percentage of total energy contributed by each type of fat. A generalized linear mixed model was used to analyze the change in the percentage of total calories for macronutrient intake across the three surveys.
Gender, age, education, current smoking status, regular physical activity, body mass index (BMI) (kg/m2), and antihypercholesterolemic medication use were examined as possible effect modifiers or confounders of the macronutrienttime trend relation. Interaction terms between the potential effect modifier and survey period were included in the generalized linear mixed model and were retained if the p values were <0.10. Age and BMI were measured as continuous variables. Gender, education, current smoking status, regular physical activity, and antihypercholesterolemic medication use were coded as binary variables. Education was composed of two levels: high school and less versus vocational school or college education. Current smoking status and antihyper-cholesterolemic medication use were determined by self-report during the home interview. Physical activity was assessed during the home interview by asking participants whether they routinely engaged in regular physical activity.
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RESULTS
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Population characteristics of study participants are listed in table 1. A total of 6,499 men and women completed the 24-hour dietary recall. Age and racial composition were similar in the three surveys. The percentage of the sample that had some college education or graduated from college increased over time for both men and women but was higher for men (p < 0.001 for women only). Current smoking declined significantly for both men (p < 0.01) and women (p < 0.01), while upward trends were observed for physical activity, BMI, and use of medication for high cholesterol.
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TABLE 1. Age-adjusted population characteristics of men and women aged 2574 years studied to assess trends in macronutrient intake, Minneapolis-St. Paul, Minnesota
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Trends in macronutrient intake (computed as the percentage of total energy intake) are summarized in table 2. There were no significant changes in total energy intake from 19801982 to 19901992 for men or women, although men had higher intakes than women did. Protein intake was unchanged (15.615.8 percent) across the three surveys. In contrast, statistically significant changes occurred in the percentage of total energy from carbohydrate, alcohol, and fat consumption from 1980 to 1992. As shown in table 2, carbohydrate intake increased from 40.9 to 46.6 percent in men (p < 0.001) and from 43.0 to 48.8 percent in women (p < 0.001) from 19801982 to 19901992. Fat consumption decreased from 39.4 to 34.7 percent (p < 0.001) in men and from 38.9 to 34.0 percent (p < 0.001) in women during the same time period. Alcohol intake declined from 3.9 to 3.0 percent (p < 0.01) in men but represented a small percentage of energy intake; similar trends were observed for women.
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TABLE 2. Age-adjusted trends in macronutrient intake for men and women aged 2574 years, Minneapolis-St. Paul, Minnesota
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Trends for the different types of fat were also examined (table 3). Saturated and monounsaturated fat consumption decreased steadily from 19801982 to 19901992 for both men and women. Saturated fat intake decreased from 14.4 to 12.5 percent (p < 0.001) in men and from 14.0 to 12.3 percent (p < 0.001) in women, and monounsaturated fat intake declined from 15.8 to 13.4 percent (p < 0.001) in men and from 15.2 to 12.9 percent (p < 0.001) in women during this same period. Polyunsaturated fat consumption increased slightly from 19801982 to 19851987 but decreased in 19901992 for both men and women; the 19801982 to 19901992 decrease for women (from 7.0 to 6.3 percent) was statistically significant (p < 0.05).
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TABLE 3. Age-adjusted percentage of energy from intake of saturated, polyunsaturated, and monounsaturated fat in men and women aged 2574 years, Minneapolis-St. Paul, Minnesota
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Macronutrient intake trends were evaluated to assess whether patterns in the trends were consistent across subgroups, such as men or women, sedentary or physically active, young or old, obese or not obese, and so forth. Interaction terms were modeled for study period by gender, age (<45 or
45 years), education, current smoking status, BMI (<30 or
30 kg/m2), and antihypercholesterolemic medication use. Two modest but statistically significant interactions were detected for men, although the pattern of association was similar for men and women. As shown in table 4, carbohydrate intake increased more from 1980 to 1992 in men who regularly engaged in physical activity (7.4 percent) than in those who were sedentary (3.6 percent) (p < 0.05 for interaction). A similar trend of greater increases in carbohydrate intake in physically active compared with sedentary women was also observed, although it was not statistically significant (p = 0.22). This greater increase in carbohydrate intake in physically active versus sedentary participants was accompanied by a greater reduction in fat intake in these corresponding active and sedentary groups (-6.2 vs. -3.6 percent in men; -5.9 vs. -4.0 percent in women, respectively).
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TABLE 4. Age-adjusted percentage of total energy from intake of carbohydrate and fat, by sex, survey period, and sedentary lifestyle, Minneapolis-St. Paul, Minnesota
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DISCUSSION
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Data from the Minnesota Heart Survey indicate significant reductions in dietary fat and alcohol intakes from 19801982 to 19901992. This reduction was offset by an increase in carbohydrate intake, while total caloric intake and protein consumption remained constant. The levels of and trends in protein, carbohydrate, and alcohol intake for Minneapolis-St. Paul metropolitan area men and women were similar to estimates from national studies conducted during approximately the same time period. The National Health Interview Survey (22
, 23
), the Nationwide Food Consumption Survey (14
), and the Continuing Survey of Food Intakes by Individuals (CSFII) are all national surveys designed to obtain food and nutrient intake data representative of the US civilian, noninstitutionalized population. These studies found the range of protein intake to be 16.016.7 percent of total energy from 1977 to 1992 (24
, 25
). Data from CSFII suggest that carbohydrate intake increased from 41 to 45.346 percent of total energy intake for men and women aged 1950 years from 1977 to 1985 (25
, 26
). Comparison of the 1987 and 1992 National Health Interview Surveys found an increase in carbohydrate consumption from 43.2 to 45.8 percent of total energy (an increase of 2.6 percent over 5 years). The National Health Interview Survey reported that alcohol intake, as a percentage of energy, fell from 4.3 to 4.0 percent in this same period (22
, 27
). However, the National Health and Nutrition Examination Survey (NHANES) III, phase 1 (19891991) reported a rate of alcohol consumption (6 percent of total energy) that was two times higher than that observed for the Minneapolis-St. Paul metropolitan area population (
).
The dietary fat intake levels observed in this population are consistent with other population-based findings. NHANES I (19711974); NHANES II; NHANES III, phase I; the Nationwide Food Consumption Survey (19771978 and 19871988); and CSFII (19851986) reported declines in fat intake for US adults (14
). Steven and Wald conducted a meta-analysis of dietary studies (10
) in which energy and fat intake were obtained from individual records of all age and sex groups. They reported that fat intake, as a percentage of energy, declined from the mid-1960s to 1984, supporting the decline in fat intake over time and the absolute fat level obtained by the Minnesota Heart Study in the early and mid-1980s (10
, 14
). While NHANES II found that fat intake was 36 percent of total energy in 19761978 (29
, 30
), NHANES III, phase I and the 19891991 CSFII observed total fat intake to be 34 percent (8
, 29
, 31
). The National Health Interview Survey estimated that fat consumption decreased from 38 percent in 1987 to 36 percent of total energy in 1992 (22
). These reported values are nearly identical to the percentage of fat intake in the Minneapolis-St. Paul metropolitan area adult population in 19801982 to 19901992 (39 and 34 percent, respectively). The estimated saturated, monounsaturated, and polyunsaturated fat intake in this population is also comparable to national dietary surveys. From 1987 to 1992, national saturated fat intake fell approximately 1.6 percent (from 14.3 to 12.7 percent) for those more than age 2 years compared with 1.9 percent (from 14.4 to 12.5 percent) in the Minneapolis-St. Paul metropolitan area population from 1985 to 1992 (8
, 19
, 22
, 25
, 31
). Nationally, monounsaturated and polyunsaturated fat intakes fell by about 2 percent during this same period; monounsaturated fat consumption constituted 14 percent of energy intake in 1985, while polyunsaturated fat intake was about 77.5 percent of energy intake in 1985 (10
, 14
, 19
, 22
, 25
). Comparable levels were observed for monounsaturated and polyunsaturated fat in the Minnesota Heart Survey in 19901992.
One advantage of the Minnesota Heart Survey compared with some other dietary studies is the ability to link dietary data with simultaneous measures of blood cholesterol. Changes in serum total cholesterol levels appeared to accompany changes in the composition of macronutrient intake in the Minneapolis-St. Paul population. Based on the Keys score, in the Minnesota Heart Survey, the reduction in dietary fat would translate to a 7 mg/dl decrease in serum total cholesterol. The Keys score takes into account lipid components of the diet that affect total blood cholesterol and serves as an index of dietary cholesterol and fat intake (17
, 19
, 32
). A high Keys score indicates a higher blood-cholesterol-raising effect of the diet. The observed decrease in serum cholesterol in Minneapolis-St. Paul was 8 mg/dl in women and 6.8 mg/dl in men, similar to that predicted by the Keys score.
NHANES data showed a consistent increase in the prevalence of obesity in American adults from the early 1960s to 19881991 and an increase in BMI during the last decade (28
). BMI also increased in the Minneapolis-St. Paul metropolitan area population, even though self-reported total energy intake remained the same while self-reported physical activity increased in the early 1980s and remained at the same level during the most recent survey. The causes of this paradox are unknown. It may be partially accounted for by measurement error regarding physical activity and diet, which may have been differential over time (i.e., the frequency of obese participants who may have overreported physical activity and/or underreported dietary intake grew over time). Irregular and/or modest physical activity may not be measured accurately by self-report. It could also be that total physical activity (e.g., occupational activity, non-leisure-time activities such as walking to turn off the television) declined but is not captured by using tools that measure physical activity (28
). The 24-hour dietary recall may also be subject to measurement error, although this error is likely to be nondifferential by time (most interviewers worked in all three survey periods, and probes and probing techniques were identical in all three periods). The social desirability of reporting low fat intakes also may have increased over time. This paradox requires more research to fully understand the unique contributions of measurement error and reporting bias to trends in dietary intake.
An interaction between physical activity level and carbohydrate and fat intake time trends from 19801982 to 19901992 was observed, suggesting that those participants claiming to be physically active on a regular basis were more likely to report favorable dietary trends compared with those who were physically inactive. It may simply be that physically active persons consume more carbohydrate and less fat because they are more health conscious. Alternatively, athletes may need to consume more carbohydrate during training programs that require a lot of energy (33

36
). Westerterp et al. conducted a 6-month randomized clinical trial to assess the activity level of those who consumed a reduced-fat, high-carbohydrate diet versus those who consumed a full-fat, low-carbohydrate diet; they found that participants involved in more physical activity consumed more carbohydrate compared with those who were less physically active (33
).
The Minnesota Heart Survey used 24-hour dietary recall methodology to assess intake. At the population level, the 24-hour recall yields reliable dietary intake estimates and changes in intake over time (12
, 34



39
). A validation study of the 24-hour recall found that group means of dietary intake do not change significantly from day to day (35
, 37
). With larger samples, the estimates are more accurate: the Minnesota Heart Survey included a relatively large sample, with more than 1,600 participants in each study period. The high response rate minimized possible response biases. Another strength of the 24-hour dietary recall is its open-ended format, allowing for greater individual variation in foods reported compared with a food frequency questionnaire (12
, 19
). The major disadvantage of the dietary recall is that accurate and reliable estimates for individual persons are lacking because individual intake fluctuates from day to day (12
, 34

37
, 39
). However, our interest was in the population level of dietary macronutrient intake; therefore, the 24-hour recall was appropriate for our study. Nevertheless, reporting of a "socially desirable" dietary intake or inaccuracies in self-reports may have biased observed findings (38
, 39
).
National dietary intake recommendations formulated by the US Department of Agriculture and the US Department of Health and Human Services, the National Cholesterol Education Program, and the National Health Objective involved an overall reduction in dietary fat intake to 30 percent or less for persons aged 2 years or older; specific recommendations were to lower saturated fat intake to 10 percent or less, increase both monounsaturated and polyunsaturated fat intake to 10 percent, and maintain protein intake at 1020 percent and carbohydrate at 5060 percent of total energy (14
, 31
, 40
42
). In 19901992, the Minneapolis-St. Paul metropolitan area population fell short of meeting dietary recommendations. Fat and saturated fat intakes were higher than the recommended levels (4.04.7 percent and 2.42.5 percent higher, respectively); 71.2 percent of this population met the fat intake (<30 percent) recommendation in 19901992. Monounsaturated fat intake was also higher than the recommended level, while carbohydrate and polyunsaturated fat intakes were below recommended levels.
In summary, public health programs focusing on nutritional education and intervention, health promotion, and disease prevention are apparently producing significant favorable trends in macronutrient intake composition. Progress is being made toward a diet lower in fat and higher in carbohydrate intake in the Minneapolis-St. Paul metropolitan area population. However, the majority of the national dietary recommendations remained unmet. This finding suggests a need for increased public health education. Further studies are needed to aid in setting nutrition objectives, policies, and interventions and to monitor achievement of those objectives. Improved dietary assessment tools are essential for valid future studies.
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NOTES
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Reprint requests to Dr. Donna K. Arnett, Division of Epidemiology, School of Public Health, University of Minnesota, 1300 South Second Street, Suite 300, Minneapolis, MN 55454-1015 (e-mail: arnett{at}epi.umn.edu).
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Received for publication April 30, 1999.
Accepted for publication January 27, 2000.