Research articleHabitual consumption of eggs does not alter the beneficial effects of endurance training on plasma lipids and lipoprotein metabolism in untrained men and women
Introduction
Cardiovascular disease (CVD), any of several diseases affecting the heart or blood vessels, is the number one cause of death in America [1]. Coronary heart disease (CHD), atherosclerosis of the coronary arteries specifically, accounted for more than half of CVD deaths in America in 2004 and is the primary killer of American men and women [1]. Major modifiable risk factors for developing CHD are abnormal blood cholesterol levels [i.e., elevated total cholesterol (TC) and LDL cholesterol (LDL-C) and low HDL cholesterol (HDL-C)]. To decrease the risk of developing CHD, the American Heart Association (AHA) and American College of Sports Medicine [2] along with the United States Department of Agriculture (USDA) and the Department of Health and Human Services (DHHS) [3] have established physical activity and dietary guidelines to favorably modify blood cholesterol levels. For healthy adults, these guidelines recommend at least 30 min of moderate-intensity, aerobic activity at least 5 days per week and a decrease in the consumption of foods high in saturated fats, trans-fatty acids and cholesterol.
It is well known that physical activity is associated with a decreased risk of coronary heart disease [1], [4]. Data from cross-sectional studies suggest aerobically trained individuals have blood lipid profiles which place them at lower risk of developing CHD when compared to sedentary controls [5], [6], [7], [8], [9], [10]. However, conflicting data [11], [12], [13], [14], [15], [16], [17], [18], [19] make it unclear what specific changes in lipoprotein profiles occur following endurance exercise training to exert this protective effect [20]. However, in groups regularly expending 1200–2200 kcal of energy per week by briskly walking or jogging, HDL-C typically increases while TG levels decrease [20].
Associations between elevated levels of serum cholesterol and increased risk of CHD [21] and increased dietary cholesterol and elevations in serum lipids [22] were first identified in the 1960s. However, epidemiological, animal and human studies have failed to establish a definitive relationship between cholesterol consumption and CHD development [23], [24], [25], [26]. Nonetheless, the message to avoid high-cholesterol eggs has been ubiquitously recommended by government agencies and health professionals for many years.
One study [24] investigating the dietary intake of 117,000 nurses and health professionals over 14 years reported no differences in the relative risk of CHD development between individuals consuming <1 egg·week−1 vs. >1 egg·day−1. Ballesteros et al. [26] reported that consuming 2 eggs·day−1 by children 10–12 years old did not increase CHD risk as determined by the nonsignificant change in the LDL-C/HDL-C, an important marker of CHD risk [27], [28]. Similarly, in men and premenopausal women consuming 3 eggs·day−1 for 30 days, Herron et al. [27], [28] observed no change in CHD risk as determined by insignificant alterations in LDL-C/HDL-C. Still, in 2000, eggs comprised only 1.3% of total energy consumed by Americans [29].
The purpose of this investigation was to determine how endurance training would influence blood lipids, apoproteins and lipoprotein metabolism in healthy, previously sedentary adults. In addition, we evaluated whether a diet supplying cholesterol primarily from eggs and in excess of the upper limits proposed by the AHA [30], USDA and DHHS [3] and IOM [31] would impact the blood lipid responses observed with training. To achieve this objective, we studied 12 normolipidemic adult men and women over 6 weeks who were assigned to one of two groups: (1) Egg (12 eggs·week−1; 468.5 mg cholesterol·day−1) or (2) No Egg (0 eggs·week−1; 159.2 mg cholesterol·day−1). We hypothesized that 6 weeks of aerobic exercise training would favorably impact blood lipid profiles independent of egg (and hence, cholesterol) intake.
Section snippets
Subjects
Twelve untrained, but otherwise healthy adults (n=12; 7 men, 5 women) ages 18–30 years were recruited from the university community. Eleven subjects (6 men, 5 women) completed the intervention. Prior to selection for the study, participants were asked to provide a complete medical history, activity log and record of dietary intake. Individuals reporting metabolic or cardiovascular abnormalities, gastrointestinal disorders (i.e., lactose intolerance, egg protein allergies), use of
Baseline and post-training subject characteristics
Baseline (Untrained) and post-endurance training (Trained) characteristics for the Egg (n=3 males, 2 females) and No-Egg (n=3 males, 3 females) groups are presented in Table 1. No differences were noted between groups for any of the criterion measures at baseline or post-training. From pre- to post-training, the Egg group experienced an increase in REE and VO2peak (P<.01) and a significant increase in the 3-mile time trial performance (P<.05). The No-Egg group also experienced an increase in VO
Discussion
The present study compared the plasma lipid and apolipoprotein profiles of normolipidemic subjects following 6 weeks of progressive, aerobic exercise training while consuming an egg or no-egg diet for 8 weeks. The major findings were that short-term, aerobic exercise training without weight loss or changes in body composition improved plasma lipid and lipoprotein profiles of subjects regardless of daily egg consumption. More specifically, both diet groups experienced increases in HDL-C,
Acknowledgment
This study was supported in part by the American Egg Board. The authors are grateful to those who willingly participated in these investigations and for the efforts of all the graduate students and staff who helped make this project possible.
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