Elsevier

Metabolism

Volume 62, Issue 2, February 2013, Pages 244-254
Metabolism

Clinical Science
The effects of sex, metabolic syndrome and exercise on postprandial lipemia

https://doi.org/10.1016/j.metabol.2012.08.003Get rights and content

Abstract

Objective

Exercise has been suggested to have cardioprotective benefits due to a lowering of postprandial triglycerides (PPTG). We hypothesized that a morning exercise bout would significantly lower PPTG measured over a full day, in response to moderate fat meals (35% energy) in men more so than women, and in metabolic syndrome (MetS) relative to normal weight (NW) individuals.

Materials/Methods

Participants completed two randomized study days; one control and one exercise day (60 min of morning exercise, 60% VO2peak). Meals were consumed at breakfast, lunch and dinner with the energy expended during exercise replaced on the active day. The areas (AUC) and incremental areas (IAUC) under the curve were calculated for total triglycerides, total cholesterol and other metabolites.

Results

Exercise did not significantly change the PPTG AUC & IAUC overall, or within, or between, each sex or group (NW and MetS). Exercise induced a 30% decrease in total cholesterol IAUC (p = 0.003) in NW subjects. Overall, women had a lower IAUC for PPTG compared to men (p = 0.037), with the greatest difference between MetS women and MetS men, due to a sustained drop in TG after lunch in the women. This suggests that PP, rather than fasting, lipid analyses may be particularly important when evaluating sex differences in metabolic risk.

Conclusions

With energy replacement, moderate morning exercise did not result in a significant decrease in PPTG excursions. Exercise did elicit a significant decrease in PP cholesterol levels in NW subjects, suggesting a potential mechanism for the cardioprotective effects of exercise.

Introduction

Cardiovascular disease (CVD)is the leading cause of death in the United States and most developed countries, and dyslipidemia is a major treatable risk factor for CVD. While it is standard practice to evaluate serum lipid levels in the fasted state, the majority of individuals spend most of each day in a fed or postprandial (PP) state. It has been suggested that 40% of all patients with premature coronary artery disease have normal fasting plasma lipids, but impaired clearance of PP lipoproteins [1], [2] a response that appears to be exaggerated in obese subjects [3].

The association of elevated PP triglycerides (PPTG) with increased risk of CVD [4], [5], has led to a search for interventions that might minimize the PPTG response, including exercise. Participation in regular exercise has been shown to reduce CVD risk in a wide range of individuals [6], [7], and there are data to suggest that a single, acute bout of exercise can reduce PPTG levels [8], [9]. Although certain studies report a significant decrease in PPTG with prior exercise [10], [11], [12] others report varying effects on PPTG response based on exercise intensity, duration, and time relative to meal ingestion [13], [14].

Most studies to date have evaluated PPTG following an acute bout of moderate exercise, performed 12–14 h before a single high fat test meal. The fat content of these test meals has not been typical of the intake in the general population [15] with both the absolute (grams) and relative (percentage of total kilocalories) fat intake being much greater than would be normally consumed in a single meal. Moreover, as there is evidence of a “second meal” effect on cumulative post prandial lipemia(PPL) for a day [16], it would be prudent to study PPTG in response to multiple meals. Indeed, while TGs were significantly increased in men with > 3 components of the metabolic syndrome at baseline and after a single meal, the separation between those with 1–3 components was not obvious until after consumption of a second meal [17].

Habitual diet, physical activity patterns, sex and estrogen status (i.e. menstrual cycle phase & menopause) are also critical variables that have not always been controlled in previous studies of PPL. Healthy, premenopausal women are generally believed to have a lower PPTG response [18], and a lower incidence of CVD relative to age-matched men [19] and postmenopausal women [20].Whether or not exercise lowers PPTGs to the same extent in women as compared to men has not been directly tested within a single study.

Individuals characterized as having metabolic syndrome (MetS) have been reported to have an exaggerated PPTG response relative to normal weight subjects (reviewed in [21]). This is relevant as individuals with MetS have a significantly increased risk of mortality from CVD, as well as increased incidences of CVD, coronary heart disease and stroke [22]. Elevated PPL could contribute to the increased CVD risk of MetS individuals, therefore, evaluating the ability of interventions such as exercise, to lower PPL in these high risk individuals is relevant. Notably, women with MetS have never been tested with regard to the effects of exercise on PP lipemia.

The main aim of this study, was to address the effect of exercise on PPL under conditions that more closely resemble normal daily living, that is, after a single bout of moderate morning exercise, followed by the consumption of 3 moderate fat meals over an entire day. This was evaluated in normal weight and MetS, men and pre-menopausal women to address the effects of sex and/or CVD risk status on the PPTG response.

The primary hypotheses were that a) exercise would significantly decrease PPTG AUC and IAUC in all groups b) women would have a lower PPTG response than men, and c) subjects with MetS would have a greater PPTG response than NW subjects and that a moderate exercise bout would ‘normalize’ the MetS PPTG response to a level similar to that seen in NW subjects on a rest day.

Section snippets

Subjects and methods

The study was approved by the Colorado Multiple Institution Review Board , and subjects were studied at the Clinical Translational Research Center (CTRC) at the University of Colorado Denver. Written informed consent was obtained from all subjects before participation in the study.

Subject demographics

Table 1 displays subject characteristics. The NW women were significantly older than the NW men (p = 0.04), whereas no sex difference in age was observed for the MetS group. As a group, the MetS subjects were significantly older than the NW subjects (p < 0.001).

MetS subjects had a higher BMI than NW subjects (p < 0.001), and NW men had a higher average BMI than NW women (p = 0.01), but there was no sex difference in the MetS group. MetS subjects had significantly greater percent body fat (p < 0.05) than

Discussion

In contrast to what was hypothesized, in this population of NW and MetS men and women, a single bout of moderate, morning exercise did not significantly decrease the cumulative PPTG response to mixed meal feeding, measured over an entire day. Possible explanations for the lack of effect include the composition of the diet; timing, length and/or intensity of the exercise bout; and/or the replacement of the energy expended during exercise.

As discussed, data are equivocal in the limited number of

Author contributions

Dr. Cox-York: manuscript writing, data collection, analysis and interpretation. Dr. Sharp: data collection and analysis. Sarah Stotz: data collection. Dr. Pagliassotti: technical assistance and mentoring. Dr. Bessesen data collection and interpretation, manuscript writing, mentoring. As the primary investigator, Dr. Horton: study design, funding, provided mentoring, and data collection, analysis and interpretation.

Funding

American Heart Association Grant-in-Aid #0355429Z, NIH DK071155, The Colorado Nutrition Obesity Research Center NIH P30-DK048520 and the Colorado Clinical Translational Research Center, NIH MO1-RR000051.

Conflict of interest

Authors have no conflicts of interest or financial disclosures.

Acknowledgments

We thank the study participants and their families, UC Denver Clinical and Translational Research Center (CTRC), Metabolic Kitchen and Core Laboratory, and the Energy Balance Laboratory of the Colorado Nutrition Obesity Research Center.

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