Mark Kern
San Diego State University
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Medicine and Science in Sports and Exercise | 1996
Dorothy Teegarden; William R. Proulx; Mark Kern; Darlene A. Sedlock; Connie M. Weaver; C. Conrad Johnston; Roseann M. Lyle
Exercise may increase accretion of bone, potentially reducing the risk of osteoporosis. Previous physical activity was assessed in 204 minimally active young women (18-31 yr). Bone mineral content (BMC) and bone mineral density (BMD) for the total body, femoral neck, and spine were assessed by a dual x-ray absorptiometer, and the radius by a single photon absorptiometer. Self-reported occupation and leisure activity for the 5 yr before enrollment in the study, as well as high school and college sports participation, were assigned energy expenditure (EE) values. From this information, EE variables were created as follows: 1) occupation EE + leisure EE + high school sport and/or college sport EE if within prior 5 yr (5-yr EE); 2) occupation EE + leisure EE (occupation + leisure EE); and 3) high school sport EE (high school EE). These variables were correlated with bone mineral measures and significant results follow (P < 0.05). Five-year EE and occupation + leisure EE correlated with all measures of bone health (r from 0.13 to 0.39). High school EE correlated with total body BMD (r = 0.25) and BMC (r = 0.28), femoral neck BMD (r = 0.28), radius BMC (r = 0.20), as well as spine BMD (r = 0.20) and BMC (r = 0.27). When weight was controlled, 5-yr EE and occupation + leisure EE remained correlated with all BMC measures (r from 0.14 to 0.22). When controlled for weight, high school EE remained associated with femoral neck BMD (r = 0.24), total body BMD (r = 0.20) and BMC (r = 0.26), and spine BMC (r = 0.17). To partially control for selection bias, data were also controlled for total body BMD. Five-year EE and occupation + leisure EE remained positively correlated with all measures of BMC. High school EE remained correlated both with femoral neck BMD and total body BMC. In multiple regression analyses, 5-yr EE or occupation + leisure EE were significant predictors of all measures of bone health, except femoral neck BMD. High school EE was a significant predictor for total body BMD and BMC, femoral neck BMD, and spine BMC.
Medicine and Science in Sports and Exercise | 2001
Connie M. Weaver; Dorothy Teegarden; Roseann M. Lyle; George P. McCabe; Linda D McCabe; William R. Proulx; Mark Kern; Darlene A. Sedlock; David D. Anderson; Ben M. Hillberry; Munro Peacock; C. Conrad Johnston
PURPOSEnThe effect of quantified resistance and high impact exercise training on bone mass as modified by age and oral contraceptive (OCont) use in young women was studied.nnnMETHODSnWomen were categorized by age (18-23 vs 24-31 yr) and OCont use, and were then randomized into either three sessions of resistance exercise plus 60 min.wk-1 of jumping rope or a control group for 24 months. Total body, spine, femoral neck, greater trochanter, Wards area, and radial bone mineral density (BMD) and/or content (BMC), biochemical markers of bone turnover, dietary intake of calcium, lean body mass, maximal oxygen uptake, and strength were determined at baseline and every 6 months.nnnRESULTSnTotal body (TB) BMC percent change from baseline was higher in exercisers compared with nonexercisers at 6 and 24 months. OCont users had lower bone turnover at baseline and a decrease in TBBMC from baseline compared with non-OCont users at 24 months. Spine BMC and BMD decreased in the exercise and OCont group at 6 months and remained significantly below nonexercisers who used oral contraceptives at 2 yr. Femoral neck BMD also decreased in the exercise and oral contraceptive group at 6 months.nnnCONCLUSIONSnExercise prevented a decline in TBBMC seen in the nonexercisers. On the other hand, exercise in oral contraceptive users prevented the increase observed in the spine of the nonexercise plus OCont group.
The American Journal of Clinical Nutrition | 2006
Michelle Braun; Berdine R. Martin; Mark Kern; George P. McCabe; Munro Peacock; Zhen Jiang; Connie M. Weaver
BACKGROUNDnNational calcium requirements in the United States for boys are based on data from girls. On average, boys develop larger skeletons than do girls, yet it is unknown whether the additional skeletal accretion in boys requires additional dietary calcium intake.nnnOBJECTIVEnThe objective was to determine calcium retention in adolescent boys in response to a range of controlled intakes and to compare the intake needed for maximal retention in boys with that needed in adolescent girls studied under the same conditions.nnnDESIGNnThirty-one boys aged 12-15 y participated in 3-wk metabolic balance studies testing a range (700-2100 mg/d) of calcium intakes in a crossover study design with a 2-wk washout period. Calcium intake was varied by using a beverage fortified with calcium citrate malate. After a 1-wk equilibration period, calcium retention was calculated as dietary calcium intake minus the calcium excreted in the feces and urine over the following 2 wk. The dietary intake at which maximal calcium retention occurred was determined by using a nonlinear regression model. The results in boys were compared with those obtained in 35 adolescent girls previously studied under the same protocol.nnnRESULTSnMaximal calcium retention in boys was achieved at an intake of 1140 mg/d. Calcium retention was higher (by 171 +/- 38 mg/d) in boys than in girls at all calcium intakes studied.nnnCONCLUSIONnThe higher calcium retention in boys than in girls was attained through higher net calcium absorption and lower urinary excretion than in girls.
Appetite | 2009
Mary Huey-Yu Cheng; Darcy Bushnell; Daniel T. Cannon; Mark Kern
This study assessed the effect of exercise timing relative to meal consumption on appetite and its hormonal regulators (i.e., PYY(3-36), ghrelin and leptin) in moderately active young men. Twelve men performed three trials in a random order: (1) meal consumption, (2) exercise 2h after a meal, (3) exercise 1h before a meal. The test meal provided 16.5 kcal kg(-1) with 70% fat, 26% carbohydrate and 4% protein. Exercise was performed at a work rate eliciting 60% of VO(2max) for 50 min. Hunger ratings and plasma leptin concentrations were measured at baseline and hours 1, 3, 5, and 7 post-meal, and plasma concentrations of ghrelin and PYY(3-36) were measured at baseline and 1, 3, and 7h after meal consumption. Exercise performed 2h after meal consumption extended the appetite suppressing effect of food intake. Furthermore, plasma PYY(3-36) concentration tended to be elevated by exercise after meal consumption. Exercise prior to food intake decreased appetite and increased plasma ghrelin concentrations. No response to timing of exercise relative to food intake on plasma leptin concentration was detected. These data indicated the timing of exercise to meal consumption may influence appetite and its hormonal regulators. Post-meal exercise may extend the suppressive effects of meal consumption on appetite.
The Journal of Clinical Endocrinology and Metabolism | 2008
Kathleen M. Hill; Michelle Braun; Mark Kern; Berdine R. Martin; James W. Navalta; Darlene A. Sedlock; Linda D McCabe; George P. McCabe; Munro Peacock; Connie M. Weaver
CONTEXTnThe relationship between calcium (Ca) intake and Ca retention in adolescent boys was recently reported.nnnOBJECTIVEnThis study evaluated the influence of Ca intake, serum hormone levels, biomarkers of bone metabolism, habitual physical activity, habitual Ca intake, and physical fitness on Ca retention in the same sample.nnnDESIGNnThis study was a randomized, cross-over design that consisted of two 3-wk metabolic balance periods.nnnSETTINGnThe study took place on a university campus as a summer camp.nnnPATIENTS OR OTHER PARTICIPANTSnA total of 31 American white boys (13-15 yr) participated in the study.nnnINTERVENTIONSnEach subject consumed a controlled diet with one of five high-low Ca intake pairs that ranged from 670-2003 mg/d, which was manipulated utilizing a fortified beverage.nnnMAIN OUTCOME MEASURESnCa retention was determined by Ca intake minus urinary and fecal Ca excretion during each balance period.nnnRESULTSnCa intake explained 21.7% of the variability in Ca retention, and serum IGF-I concentration explained an additional 11.5%. Other serum hormone levels did not significantly add to the model. Biomarkers of bone metabolism, habitual physical activity, habitual Ca intake, and physical fitness were not significant predictors of Ca retention in adolescent boys.nnnCONCLUSIONSnIGF-I, a regulator of growth during puberty, is an important predictor of Ca retention in adolescent boys. However, dietary Ca intake is an even greater predictor of Ca retention during this period of growth.
Nutrition Research | 2011
Tricia Nemoseck; Erin G. Carmody; Allison Furchner-Evanson; Marsa Gleason; Amy Li; Hayley Potter; Lauren Rezende; Kelly J. Lane; Mark Kern
Various dietary carbohydrates have been linked to obesity and altered adipose metabolism; however, the influences of honey vs common sweeteners have not been fully explored. We hypothesized that in comparison with sucrose, a honey-based diet would promote lower weight gain, adiposity, and related biomarkers (leptin, insulin, and adiponectin) as well as a better blood lipid profile. Thirty-six male Sprague-Dawley rats (228.1 ± 12.5 g) were equally divided by weight into 2 groups (n = 18) and provided free access to 1 of 2 diets of equal energy densities differing only in a portion of the carbohydrate. Diets contained 20% carbohydrate (by weight of total diet) from either clover honey or sucrose. After 33 days, epididymal fat pads were excised and weighed, and blood was collected for analyses of serum concentrations of lipids, glucose, and markers of adiposity and inflammation. Body weight gain was 14.7% lower (P ≤ .05) for rats fed honey, corresponding to a 13.3% lower (P ≤ .05) consumption of food/energy, whereas food efficiency ratios were nearly identical. Epididymal fat weight was 20.1% lower (P ≤ .05) for rats fed honey. Serum concentrations of triglycerides and leptin were lower (P ≤ .05) by 29.6% and 21.6%, respectively, and non-high-density lipoprotein cholesterol was higher (P ≤ .05) by 16.8% for honey-fed rats. No significant differences in serum total cholesterol, high-density lipoprotein cholesterol, adiponectin, C-reactive protein, monocyte chemoattractant protein-1, glucose, or insulin were detected. These results suggest that in comparison with sucrose, honey may reduce weight gain and adiposity, presumably due to lower food intake, and promote lower serum triglycerides but higher non-high-density lipoprotein cholesterol concentrations.
Journal of Strength and Conditioning Research | 2007
Mark Kern; Christopher J. Heslin; Robert S. Rezende
Research suggests that pre-exercise sources of dietary carbohydrate with varying glycemic indexes may differentially affect metabolism and endurance. This study was designed to examine potential differences in metabolism and cycling performance after consumption of moderate glycemic raisins vs. a high glycemic commercial sports gel. Eight endurance-trained male (n = 4) and female (n = 4) cyclists 30 +/- 5 years of age completed 2 trials in random order. Subjects were fed 1 g carbohydrate per kilogram body weight from either raisins or sports gel 45 minutes prior to exercise on a cycle ergometer at 70% V(.-)O2max. After 45 minutes of submaximal exercise, subjects completed a 15-minute performance trial. Blood was collected prior to the exercise bout, as well as after the 45th minute of exercise, to determine serum concentrations of glucose, insulin, lactate, free fatty acids (FFAs), triglycerides, and beta-hydroxybutyrate. Performance was not different (p > 0.05) between the raisin (189.5 +/- 69.9 kJ) and gel (188.0 +/- 64.8 kJ) trials. Prior to exercise, serum concentrations of glucose and other fuel substrates did not differ between trials; however, insulin was higher (p < 0.05) for the gel (110.0 +/- 70.4 microU x ml(-1)) vs. raisin trial (61.4 +/- 37.4 microU x ml(-1)). After 45 minutes of exercise, insulin decreased to 14.2 +/- 6.2 microU x ml(-1) and 13.3 +/- 18.9 microU x ml(-1) for gel and raisin trials, respectively. The FFA concentration increased (+0.2 +/- 0.1 mmol x L(-1)) significantly (p < 0.05) during the raisin trial. Overall, minor differences in metabolism and no difference in performance were detected between the trials. Raisins appear to be a cost-effective source of carbohydrate for pre-exercise feeding in comparison to sports gel for short-term exercise bouts.
Journal of The American Dietetic Association | 2010
Leslie S. Howarth; Yumi Petrisko; Allison Furchner-Evanson; Tricia Nemoseck; Mark Kern
Because appropriate snacking can promote a healthy body weight and serve as an important contributor to a healthy diet for women, identification of suitable foods for incorporation between meals is essential. We investigated the influence of short-term (2 weeks) incorporation of 100-kcal servings of snacks of dried plums vs low-fat cookies twice daily on total energy and nutrient intake, biochemical parameters, and bowel habits in a randomized crossover design of two 2-week trials separated by a 2-week wash-out period in 26 women aged 25 to 54 years with a body mass index between 24 and 35. Incorporation of dried plums or low-fat cookies into the diet did not alter energy intake or weight; however, compared to cookies, dried plums promoted greater (P< or =0.05) intake of fiber, potassium, riboflavin, niacin, and calcium. Total fat intake tended (P=0.094) to decrease with dried plum consumption, as did cholesterol intake (P=0.098). Plasma triglyceride concentration remained unchanged (P>0.05) by dried plum consumption and was 17.0+/-29.2 mg/dL (0.19+/-0.33 mmol/L) higher (P< or =0.05) after consumption of low-fat cookies vs dried plums at the end of 2 weeks. Dried plums promoted a softer (P< or =0.05) stool consistency vs usual intake and in comparison to intake of low-fat cookies. These results suggest that relative to a commercially processed low-fat cookie snack, dried plums promote more favorable plasma triglyceride responses, improved dietary quality, and slightly improved bowel function.
Comprehensive Reviews in Food Science and Food Safety | 2016
Roger Clemens; Julie Miller Jones; Mark Kern; Soo Yeun Lee; Emily J. Mayhew; Joanne L. Slavin; Svetlana Zivanovic
Overweight and obesity are global health problems that affect more than 1.9 billion adults who are overweight, and of these 600 million are obese. In the United States, these problems affect 60% of the population. Critical to these statistics is the association with increased risk of cardiovascular disease, type 2 diabetes, and metabolic syndrome among other noncommunicable diseases. Many factors, including sugars, have been charged as potential causes. However, obesity and overweight and their attendant health problems continue to increase despite the fact that there is a decline in the consumption of sugars. Sugars vary in their types and structure. From a food science perspective, sugars present an array of attributes that extend beyond taste, flavor, color, and texture to aspects such as structure and shelf-life of foods. From a public health perspective, there is considerable controversy about the effect of sugar relative to satiety, digestion, and noncommunicable diseases. This comprehensive overview from experts in food science, nutrition and health, sensory science, and biochemistry describes the technical and functional roles of sugar in food production, provides a balanced evidence-based assessment of the literature and addresses many prevalent health issues commonly ascribed to sugar by the media, consumer groups, international scientific organizations, and policy makers. The preponderance of the evidence indicates that sugar as such does not contribute to adverse health outcomes when consumed under isocaloric conditions. The evidence generally indicates, as noted by the 2010 Dietary Guidelines Advisory Committee, that sugar, like any other caloric macronutrient, such as protein and fat, when consumed in excess leads to conditions such as obesity and related comorbidities. More recently, the 2015-2020 Dietary Guidelines for Americans recommended limiting dietary sugar to 10% of total energy in an effort to reduced the risk of these noncommunicable diseases.
Appetite | 2010
Allison Furchner-Evanson; Yumi Petrisko; Leslie S. Howarth; Tricia Nemoseck; Mark Kern
The effect of different snack foods on satiety and plasma glucose and hormone responses was assessed. Nineteen fasted adult women (mean age: 39.2 + or - 0.7 years, mean BMI: 26.1 + or - 0.8 kg/m(2)) consumed test foods including dried plums, low-fat cookies, white bread and water only on separate days. The test foods (with the exception of water) provided 238 kcal and were similar in total carbohydrate, fat and protein content but differed in fiber and sugar content. Subjects rated their feelings of hunger using satiety index scales prior to snack consumption and again every 15 min for 2h following initiation of intake. Blood samples were collected at baseline and 15, 30, 45, 60, 90, and 120 min following intake. At the end of the 120-min test period, subjects were presented with a meal to be consumed until satisfied. The satiety index AUC was greater for the dried plum trial versus the low-fat cookie trial (p < or = 0.05). There was no difference in post-snack consumption between the dried plums and cookie trials. The dried plums trial elicited lower plasma glucose and insulin AUC than the low-fat cookie trial (p < or = 0.05) and tended to promote a greater plasma ghrelin AOC (p = 0.056). These results demonstrate that consuming dried plums as a snack suppresses hunger relative to a low-fat cookie as evidenced by lower glucose and/or satiety-regulating hormone concentrations.