ORIGINAL ARTICLE
Physical Activity and Dietary Behavior in US Adults and Their Combined Influence on Health Paul D. Loprinzi, PhD; Ellen Smit, PhD, RD; and Sara Mahoney, PhD Abstract Objective: To examine the association between objectively measured physical activity and dietary behavior and their combined effect on health. Patients and Methods: Data for this study were obtained from the 2003-2006 National Health and Nutrition Examination Survey cycles. The data were evaluated between September 9, 2012, and August 14, 2013. As part of the national survey, participants wore an accelerometer for 4 or more days to assess physical activity, blood samples were obtained to assess various biological markers, and interviews were conducted to assess dietary behavior. We selected a sample of 5211 participants and categorized them into 4 groups: (1) healthy diet and active, (2) unhealthy diet and active, (3) healthy diet and inactive, and (4) unhealthy diet and inactive. Results: A total of 16.5% of participants (weighted proportions) were classified as consuming a healthy diet and being sufficiently active. After adjustments, participants were 32% more likely to consume a healthy diet if they met physical activity guidelines. For nearly all biomarkers, those who consumed a healthy diet and were sufficiently active had the most favorable biomarker levels. Compared with those who consumed a healthy diet and were active, participants who consumed an unhealthy diet and were inactive were 2.4 times more likely to have metabolic syndrome. Conclusion: Our findings indicate a relationship between objectively measured physical activity and dietary behavior and that participating in regular physical activity and eating a healthy diet are associated with better health outcomes when compared with diet or physical activity alone. ª 2014 Mayo Foundation for Medical Education and Research From the Department of Exercise Science, Donna and Allan Lansing School of Nursing and Health Sciences, Bellarmine University, Louisville, KY (P.D.L., S.M.); and Program in Epidemiology, School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis, OR (E.S.).
190
B
oth dietary and physical activity behavior are independent predictors of numerous health outcomes among adults.1-3 However, we have a limited understanding of the potential combined influence of dietary and objectively determined physical activity behavior among US adults. It is plausible to suggest that individuals who consume a healthy diet and are sufficiently active may have more favorable health outcomes than those who consume an unhealthy diet and are inactive. Along these lines, the association between physical activity and dietary behavior is not clearly understood. Studies have examined this association,4-9 but they are limited in the extent that they have exclusively used self-reported physical activity methodology, which is prone to considerable measurement error,10 with some also only examining a single nutrient or limiting their examination to certain populations. Measurement error associated with self-reported physical activity creates serious challenges in
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Mayo Clin Proc. 2014;89(2):190-198
delineating any potential combined dietary and physical activity effect. Specifically, this increased measurement error associated with self-reported physical activity likely creates bias in the estimated relative risk and may reduce statistical power to detect physical activity and dietedisease associations.11 To bridge these gaps in the literature, the present study employed a nationally representative sample of US adults and an objective measure of physical activity. The 2 objectives of the study were (1) to examine the association between physical activity and dietary behavior and (2) to examine the potential combined effect of physical activity and dietary behavior on biological (eg, total cholesterol) and health (eg, waist circumference) markers. PATIENTS AND METHODS Study Design and Participants Data for this study were obtained from the 2003-2006 National Health and Nutrition
Mayo Clin Proc. n February 2014;89(2):190-198 n http://dx.doi.org/10.1016/j.mayocp.2013.09.018 www.mayoclinicproceedings.org n ª 2014 Mayo Foundation for Medical Education and Research
PHYSICAL ACTIVITY AND DIET
Examination Survey (NHANES). The data were evaluated between September 9, 2012, and August 14, 2013. The NHANES is an ongoing survey conducted by the Centers for Disease Control and Prevention that uses a representative sample of noninstitutionalized US civilians, selected by a complex, multistage, stratified, clustered probability design. The multistage design consists of 4 stages: the identification of (1) counties and (2) segments (city blocks), (3) random selection of households within the segments, and (4) random selection of individuals within the households. Briefly, participants were interviewed in their homes and then subsequently examined in mobile examination centers by NHANES personnel. Further details about the NHANES can be found elsewhere.12 The NHANES study procedures were approved by the National Center for Health Statistics ethics review board, with informed consent obtained from all participants before data collection. In the 2003-2006 NHANES cycles, 20,470 participants were examined. For our study, the following participants were excluded: insufficient data or ineligible for the activity monitoring component, 10,718; missing dietary behavior, 358; less than 20 years old, 3500; pregnant, 236; and missing data on the covariates, 447. The remaining 5211 participants composed the analytic sample.
accelerometer can be found elsewhere.13 Estimates for moderate to vigorous physical activity were summarized in 1-minute intervals. Activity counts of 2020 or more were classified as moderate to vigorous physical activity intensity.14 For our analyses, and to represent habitual physical activity patterns, only participants with activity patterns of 10 or more hours per day for at least 4 days of monitoring data were included in the analyses.14 To determine the amount of time the monitor was worn, nonwear was defined by a period of a minimum of 60 consecutive minutes of zero activity counts, with the allowance of 1 to 2 minutes of activity counts between 0 and 100.14 Participants were classified as meeting physical activity guidelines if they engaged in 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity physical activity per week or some combination of the two.15 To account for the combination of moderate and vigorous physical activity, vigorous intensity was multiplied by 2 before being added to moderate intensity.16 Therefore, participants could meet guidelines if they engaged in at least 150 minutes of moderate plus 2 vigorous intensity physical activity per week. SAS statistical software version 9.2 (SAS Institute Inc) was used to reduce the accelerometry data using the SAS code provided by the National Cancer Institute. Using the SAS code, each participant’s average time per day spent in physical activity from valid individual data were analyzed in this study.
Measurement of Physical Activity While attending the mobile examination center, participants were asked to wear an ActiGraph 7164 accelerometer during all activities except water-based activities and while sleeping. The accelerometer measured the frequency, intensity, and duration of physical activity by generating an activity count proportional to the measured acceleration. The accelerometer output is digitized using an analog-to-digital converter, and once digitized, the signal passes through a digital filter that detects accelerations ranging from 0.05 to 2.00g in magnitude with frequency responses ranging from 0.25 to 2.5 Hz to filter motion outside normal human movement. The filtered signal is then rectified and summed over a predetermined epoch period. After the activity count is sorted into an epoch, it is stored in the internal memory, and the integrator is reset to zero. Detailed information on the ActiGraph
Measurement of Dietary Behavior/Healthy Eating Index Two 24-hour recalls were collected during the visit to the mobile examination center. Dietary intake may differ by weekday, especially weekend days. To capture intake on all days of the week, the 24-hour recalls were collected on every day of the week. The dietary interviewers used the NHANES III Dietary Data Collection system, which is an automated standardized interactive dietary interview and coding system. The Healthy Eating Index (HEI)-2005 was developed by the US Department of Agriculture as an indicator of dietary quality.17 The HEI consists of 12 components (total fruit; whole fruit; total vegetable; dark green, orange vegetables and legumes; total grain; whole grain; milk; meat and beans; oil; saturated fats; sodium; and calories from solid fats, alcoholic beverages, and added sugars), with a maximum score of
Mayo Clin Proc. n February 2014;89(2):190-198 www.mayoclinicproceedings.org
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http://dx.doi.org/10.1016/j.mayocp.2013.09.018
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MAYO CLINIC PROCEEDINGS
100 and a higher score reflecting closer adherence to the dietary guidelines for Americans. The HEI was derived for each of the 24-hour recall days using the MyPyramid Equivalents Database and following the methods and SAS code established by the US Department of Agriculture Center for Nutrition Policy and Promotion.18-21 Using the average of the 2-day HEI scores, participants at or above the 60th percentile (ie, top 40%) of HEI scores in the population were categorized as adhering to the dietary guidelines or consuming a healthy diet.22 Measurement of Lifestyle Groups Consistent with other studies,23 4 mutually exclusive lifestyle groups were created: (1) healthy diet and active, (2) unhealthy diet and active, (3) healthy diet and inactive, and (4) unhealthy diet and inactive. Having a healthy diet included those at or above the 60th percentile of the HEI,22 and participants were considered to be active if they met current physical activity guidelines.15 Measurement of Biological and Health Markers The following biological and health markers that have previously been found to be associated with physical activity and/or diet were assessed: body mass index (BMI; calculated as the weight in kilograms divided by the height in meters squared), waist circumference, mean arterial pressure ([diastolic blood pressure 2] þ systolic blood pressure), C-reactive protein (CRP), white blood cell count, high-density lipoprotein (HDL) cholesterol, fasting low-density lipoprotein (LDL) cholesterol, total cholesterol, fasting triglycerides, fasting glucose, fasting insulin, cotinine (marker of active or passive smoking), and homocysteine (marker of endothelial function). Details on the assessment of these markers can be found elsewhere.24,25 Cut Points for Elevated Biological and Health Markers Normal weight was considered a measured BMI of less than 25 kg/m2, overweight as between 25.0 and 29.9 kg/m2, and obese as 30 kg/m2 or higher. Elevated waist circumference was considered as 102 cm or more for men and 88 cm or higher for women.26 Hypertension was considered as systolic blood pressure of 140 192
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mm Hg or higher or diastolic blood pressure of 90 mm Hg or higher or self-reported use of antihypertensive medication.27 Elevated CRP was considered as a level of more than 0.3 mg/dL.28 Elevated total cholesterol was considered as more than 240 mg/dL (to convert to mmol/L, multiply by 0.0259) or use of cholesterol-lowering medication. Elevated LDL cholesterol was considered as 160 mg/dL or higher (to convert to mmol/L, multiply by 0.0259) or taking cholesterol-lowering medication.29 Elevated triglycerides was considered as 200 mg/dL or more (to convert to mmol/L, multiply by 0.0113).29 Elevated glucose was considered as 126 mg/dL or higher (to convert to mmol/L, multiply by 0.0555) or selfreported use of insulin or pills for diabetes.30 Lastly, elevated homocysteine was considered as more than 10.4 mmol/L for women and more than 11.4 mmol/L for men.31 Consistent with the American Heart Association/National Heart, Lung, and Blood Institute guidelines,26 participants were classified as having metabolic syndrome if they had 3 or more of the following criteria: (1) high waist circumference (102 cm for men and 88 cm for women), (2) elevated levels of triglycerides (150 mg/dL), (3) low level of HDL cholesterol (
Physical Activity and Dietary Behavior in US Adults and Their Combined Influence on Health Paul D. Loprinzi, PhD; Ellen Smit, PhD, RD; and Sara Mahoney, PhD Abstract Objective: To examine the association between objectively measured physical activity and dietary behavior and their combined effect on health. Patients and Methods: Data for this study were obtained from the 2003-2006 National Health and Nutrition Examination Survey cycles. The data were evaluated between September 9, 2012, and August 14, 2013. As part of the national survey, participants wore an accelerometer for 4 or more days to assess physical activity, blood samples were obtained to assess various biological markers, and interviews were conducted to assess dietary behavior. We selected a sample of 5211 participants and categorized them into 4 groups: (1) healthy diet and active, (2) unhealthy diet and active, (3) healthy diet and inactive, and (4) unhealthy diet and inactive. Results: A total of 16.5% of participants (weighted proportions) were classified as consuming a healthy diet and being sufficiently active. After adjustments, participants were 32% more likely to consume a healthy diet if they met physical activity guidelines. For nearly all biomarkers, those who consumed a healthy diet and were sufficiently active had the most favorable biomarker levels. Compared with those who consumed a healthy diet and were active, participants who consumed an unhealthy diet and were inactive were 2.4 times more likely to have metabolic syndrome. Conclusion: Our findings indicate a relationship between objectively measured physical activity and dietary behavior and that participating in regular physical activity and eating a healthy diet are associated with better health outcomes when compared with diet or physical activity alone. ª 2014 Mayo Foundation for Medical Education and Research From the Department of Exercise Science, Donna and Allan Lansing School of Nursing and Health Sciences, Bellarmine University, Louisville, KY (P.D.L., S.M.); and Program in Epidemiology, School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis, OR (E.S.).
190
B
oth dietary and physical activity behavior are independent predictors of numerous health outcomes among adults.1-3 However, we have a limited understanding of the potential combined influence of dietary and objectively determined physical activity behavior among US adults. It is plausible to suggest that individuals who consume a healthy diet and are sufficiently active may have more favorable health outcomes than those who consume an unhealthy diet and are inactive. Along these lines, the association between physical activity and dietary behavior is not clearly understood. Studies have examined this association,4-9 but they are limited in the extent that they have exclusively used self-reported physical activity methodology, which is prone to considerable measurement error,10 with some also only examining a single nutrient or limiting their examination to certain populations. Measurement error associated with self-reported physical activity creates serious challenges in
n
Mayo Clin Proc. 2014;89(2):190-198
delineating any potential combined dietary and physical activity effect. Specifically, this increased measurement error associated with self-reported physical activity likely creates bias in the estimated relative risk and may reduce statistical power to detect physical activity and dietedisease associations.11 To bridge these gaps in the literature, the present study employed a nationally representative sample of US adults and an objective measure of physical activity. The 2 objectives of the study were (1) to examine the association between physical activity and dietary behavior and (2) to examine the potential combined effect of physical activity and dietary behavior on biological (eg, total cholesterol) and health (eg, waist circumference) markers. PATIENTS AND METHODS Study Design and Participants Data for this study were obtained from the 2003-2006 National Health and Nutrition
Mayo Clin Proc. n February 2014;89(2):190-198 n http://dx.doi.org/10.1016/j.mayocp.2013.09.018 www.mayoclinicproceedings.org n ª 2014 Mayo Foundation for Medical Education and Research
PHYSICAL ACTIVITY AND DIET
Examination Survey (NHANES). The data were evaluated between September 9, 2012, and August 14, 2013. The NHANES is an ongoing survey conducted by the Centers for Disease Control and Prevention that uses a representative sample of noninstitutionalized US civilians, selected by a complex, multistage, stratified, clustered probability design. The multistage design consists of 4 stages: the identification of (1) counties and (2) segments (city blocks), (3) random selection of households within the segments, and (4) random selection of individuals within the households. Briefly, participants were interviewed in their homes and then subsequently examined in mobile examination centers by NHANES personnel. Further details about the NHANES can be found elsewhere.12 The NHANES study procedures were approved by the National Center for Health Statistics ethics review board, with informed consent obtained from all participants before data collection. In the 2003-2006 NHANES cycles, 20,470 participants were examined. For our study, the following participants were excluded: insufficient data or ineligible for the activity monitoring component, 10,718; missing dietary behavior, 358; less than 20 years old, 3500; pregnant, 236; and missing data on the covariates, 447. The remaining 5211 participants composed the analytic sample.
accelerometer can be found elsewhere.13 Estimates for moderate to vigorous physical activity were summarized in 1-minute intervals. Activity counts of 2020 or more were classified as moderate to vigorous physical activity intensity.14 For our analyses, and to represent habitual physical activity patterns, only participants with activity patterns of 10 or more hours per day for at least 4 days of monitoring data were included in the analyses.14 To determine the amount of time the monitor was worn, nonwear was defined by a period of a minimum of 60 consecutive minutes of zero activity counts, with the allowance of 1 to 2 minutes of activity counts between 0 and 100.14 Participants were classified as meeting physical activity guidelines if they engaged in 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity physical activity per week or some combination of the two.15 To account for the combination of moderate and vigorous physical activity, vigorous intensity was multiplied by 2 before being added to moderate intensity.16 Therefore, participants could meet guidelines if they engaged in at least 150 minutes of moderate plus 2 vigorous intensity physical activity per week. SAS statistical software version 9.2 (SAS Institute Inc) was used to reduce the accelerometry data using the SAS code provided by the National Cancer Institute. Using the SAS code, each participant’s average time per day spent in physical activity from valid individual data were analyzed in this study.
Measurement of Physical Activity While attending the mobile examination center, participants were asked to wear an ActiGraph 7164 accelerometer during all activities except water-based activities and while sleeping. The accelerometer measured the frequency, intensity, and duration of physical activity by generating an activity count proportional to the measured acceleration. The accelerometer output is digitized using an analog-to-digital converter, and once digitized, the signal passes through a digital filter that detects accelerations ranging from 0.05 to 2.00g in magnitude with frequency responses ranging from 0.25 to 2.5 Hz to filter motion outside normal human movement. The filtered signal is then rectified and summed over a predetermined epoch period. After the activity count is sorted into an epoch, it is stored in the internal memory, and the integrator is reset to zero. Detailed information on the ActiGraph
Measurement of Dietary Behavior/Healthy Eating Index Two 24-hour recalls were collected during the visit to the mobile examination center. Dietary intake may differ by weekday, especially weekend days. To capture intake on all days of the week, the 24-hour recalls were collected on every day of the week. The dietary interviewers used the NHANES III Dietary Data Collection system, which is an automated standardized interactive dietary interview and coding system. The Healthy Eating Index (HEI)-2005 was developed by the US Department of Agriculture as an indicator of dietary quality.17 The HEI consists of 12 components (total fruit; whole fruit; total vegetable; dark green, orange vegetables and legumes; total grain; whole grain; milk; meat and beans; oil; saturated fats; sodium; and calories from solid fats, alcoholic beverages, and added sugars), with a maximum score of
Mayo Clin Proc. n February 2014;89(2):190-198 www.mayoclinicproceedings.org
n
http://dx.doi.org/10.1016/j.mayocp.2013.09.018
191
MAYO CLINIC PROCEEDINGS
100 and a higher score reflecting closer adherence to the dietary guidelines for Americans. The HEI was derived for each of the 24-hour recall days using the MyPyramid Equivalents Database and following the methods and SAS code established by the US Department of Agriculture Center for Nutrition Policy and Promotion.18-21 Using the average of the 2-day HEI scores, participants at or above the 60th percentile (ie, top 40%) of HEI scores in the population were categorized as adhering to the dietary guidelines or consuming a healthy diet.22 Measurement of Lifestyle Groups Consistent with other studies,23 4 mutually exclusive lifestyle groups were created: (1) healthy diet and active, (2) unhealthy diet and active, (3) healthy diet and inactive, and (4) unhealthy diet and inactive. Having a healthy diet included those at or above the 60th percentile of the HEI,22 and participants were considered to be active if they met current physical activity guidelines.15 Measurement of Biological and Health Markers The following biological and health markers that have previously been found to be associated with physical activity and/or diet were assessed: body mass index (BMI; calculated as the weight in kilograms divided by the height in meters squared), waist circumference, mean arterial pressure ([diastolic blood pressure 2] þ systolic blood pressure), C-reactive protein (CRP), white blood cell count, high-density lipoprotein (HDL) cholesterol, fasting low-density lipoprotein (LDL) cholesterol, total cholesterol, fasting triglycerides, fasting glucose, fasting insulin, cotinine (marker of active or passive smoking), and homocysteine (marker of endothelial function). Details on the assessment of these markers can be found elsewhere.24,25 Cut Points for Elevated Biological and Health Markers Normal weight was considered a measured BMI of less than 25 kg/m2, overweight as between 25.0 and 29.9 kg/m2, and obese as 30 kg/m2 or higher. Elevated waist circumference was considered as 102 cm or more for men and 88 cm or higher for women.26 Hypertension was considered as systolic blood pressure of 140 192
Mayo Clin Proc.
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mm Hg or higher or diastolic blood pressure of 90 mm Hg or higher or self-reported use of antihypertensive medication.27 Elevated CRP was considered as a level of more than 0.3 mg/dL.28 Elevated total cholesterol was considered as more than 240 mg/dL (to convert to mmol/L, multiply by 0.0259) or use of cholesterol-lowering medication. Elevated LDL cholesterol was considered as 160 mg/dL or higher (to convert to mmol/L, multiply by 0.0259) or taking cholesterol-lowering medication.29 Elevated triglycerides was considered as 200 mg/dL or more (to convert to mmol/L, multiply by 0.0113).29 Elevated glucose was considered as 126 mg/dL or higher (to convert to mmol/L, multiply by 0.0555) or selfreported use of insulin or pills for diabetes.30 Lastly, elevated homocysteine was considered as more than 10.4 mmol/L for women and more than 11.4 mmol/L for men.31 Consistent with the American Heart Association/National Heart, Lung, and Blood Institute guidelines,26 participants were classified as having metabolic syndrome if they had 3 or more of the following criteria: (1) high waist circumference (102 cm for men and 88 cm for women), (2) elevated levels of triglycerides (150 mg/dL), (3) low level of HDL cholesterol (
