Role of resistant starch in improving gut health, adiposity, and insulin resistance

The realization that low-glycemic index diets were formulated using resistant starch led to more than a decade of research on the health effects of resistant starch. Determination of the metabolizable energy of the resistant starch product allowed for the performance of isocaloric studies. Fermentation of resistant starch in rodent studies results in what appears to be a healthier gut, demonstrated by increased amounts of short-chain fatty acids, an apparent positive change in the microbiota, and increased gene expression for gene products involved in normal healthy proliferation and apoptosis of potential cancer cells. Additionally, consumption of resistant starch was associated with reduced abdominal fat and improved insulin sensitivity. Increased serum glucagon-like peptide 1 (GLP-1) likely plays a role in promoting these health benefits. One rodent study that did not use isocaloric diets demonstrated that the use of resistant starch at 8% of the weight of the diet reduced body fat. This appears to be approximately equivalent to the human fiber requirement. In human subjects, insulin sensitivity is increased with the feeding of resistant starch. However, only 1 of several studies reports an increase in serum GLP-1 associated with resistant starch added to the diet. This means that other mechanisms, such as increased intestinal gluconeogenesis or increased adiponectin, may be involved in the promotion of improved insulin sensitivity. Future research may confirm that there will be improved health if human individuals consume the requirement for dietary fiber and a large amount of the fiber is fermentable.

Role of resistant starch in improving gut health, adiposity, and insulin resistance

The realization that low-glycemic index diets were formulated using resistant starch led to more than a decade of research on the health effects of resistant starch. Determination of the metabolizable energy of the resistant starch product allowed for the performance of isocaloric studies. Fermentation of resistant starch in rodent studies results in what appears to be a healthier gut, demonstrated by increased amounts of short-chain fatty acids, an apparent positive change in the microbiota, and increased gene expression for gene products involved in normal healthy proliferation and apoptosis of potential cancer cells. Additionally, consumption of resistant starch was associated with reduced abdominal fat and improved insulin sensitivity. Increased serum glucagon-like peptide 1 (GLP-1) likely plays a role in promoting these health benefits. One rodent study that did not use isocaloric diets demonstrated that the use of resistant starch at 8% of the weight of the diet reduced body fat. This appears to be approximately equivalent to the human fiber requirement. In human subjects, insulin sensitivity is increased with the feeding of resistant starch. However, only 1 of several studies reports an increase in serum GLP-1 associated with resistant starch added to the diet. This means that other mechanisms, such as increased intestinal gluconeogenesis or increased adiponectin, may be involved in the promotion of improved insulin sensitivity. Future research may confirm that there will be improved health if human individuals consume the requirement for dietary fiber and a large amount of the fiber is fermentable.

Adult Female Rats Defend “Appropriate” Energy Intake after Adaptation to Dietary Energy

OBJECTIVE

To determine if adult female rats adapt to lower and higher dietary energy density.

RESEARCH METHODS AND PROCEDURES

Study 1 compared high-fat (56%), high-energy density (HD) (21.6 kJ/g) and high-fat (56%), low-energy density (LD) (16.0 kJ/g) diets before surgery (two groups, 2 weeks, n = 16) and after surgery [ovariectomy (O) Sham (S); 2 x 2 factorial, n = 8; 6 weeks]. The second study (no surgery) compared high-fat (60.0%), high-energy (22.0 kJ/g) and low-fat (10.0%), low-energy (15.1 kJ/g) diets (n = 8).

RESULTS

In study 1, food intake was similar for the first 2 weeks, but rats on the LD diet consumed less energy, gained less weight, and had lower nonfasted serum leptin (all p < 0.0001) than rats on the HD diet. After surgery, rats on the LD and HD diets had similar weight gain, but rats on the LD diet consumed more food (p < 0.0001) and less energy (p < 0.009). O rats consumed more food and gained more weight (p < 0.0001) than S rats. Results from study 2 were similar to those from study 1.

DISCUSSION

The results demonstrated that O and S surgery rats and rats with no surgery adjust their food intake to defend a level of energy intake. This defense only occurred after a 2-week adaptation period. The major differences in final body weights and abdominal fat resulted from the initial 2 weeks before adaptation to energy density. Rats fed higher-energy diets seemed to "settle" at a higher level of adiposity, and rats fed lower-energy diets consumed more food to increase energy consumption.

High-amylose resistant starch increases hormones and improves structure and function of the gastrointestinal tract: a microarray study

BACKGROUND/AIMS

Type 2 resistant starch from high-amylose maize (HAM-RS2) is associated with increased fermentation, increased expression of proglucagon (gene for GLP-1) and peptide YY (PYY) genes in the large intestine, and improved health. To determine what other genes are up- or downregulated with feeding of HAM-RS2, a microarray was performed.

METHODS

Adult, male Sprague Dawley rats were fed one of the following three diets for a 4-week study period: cornstarch control (CC, 3.74 kcal/g), dietary energy density control (EC, 3.27 kcal/g), and 30% HAM-RS2 (RS, 3.27 kcal/g). Rat microarray with ∼27,000 genes and validation of 94 representative genes with multiple qPCR were used to determine gene expression in total RNA extracts of cecal cells from rats. The RS versus EC comparison tested effects of fermentation as energy density of the diet was controlled.

RESULTS

For the RS versus EC comparison, 86% of the genes were validated from the microarray and the expression indicates promotion of cell growth, proliferation, differentiation, and apoptosis. Gut hormones GLP-1 and PYY were increased.

CONCLUSIONS

Gene expression results predict improved structure and function of the GI tract. Production of gut hormones may promote healthy functions beyond the GI tract.

Comparative methodologies for measuring metabolizable energy of various types of resistant high amylose corn starch

Energy values of high amylose corn starches high in resistant starch (RS) were determined in vivo by two different methodologies. In one study, energy values were determined according to growth relative to glucose-based diets in rats fed diets containing RS(2), heat-treated RS(2) (RS(2)-HT), RS(3), and amylase predigested versions to isolate the RS component. Net metabolizable energy values ranged from 2.68 to 3.06 kcal/g for the RS starches, and 1.91-2.53 kcal/g for the amylase predigested versions. In a second study, rats were fed a diet containing RS(2)-HT and the metabolizable energy value was determined by bomb calorimetry. The metabolizable energy value was 2.80 kcal/g, consistent with Study 1. Thus, high amylose corn based RS ingredients and their amylase predigested equivalents have energy values approximately 65-78% and 47-62% of available starch (Atwater factor), respectively, according to the RS type (Garcia, T. A.; McCutcheon, K. L.; Francis, A. R.; Keenan, M. J.; O'Neil, C. E.; Martin, R. J.; Hegsted, M. The effects of resistant starch on gastrointestinal organs and fecal output in rats. FASEB J. 2003, 17, A335).

Dietary resistant starch upregulates total GLP-1 and PYY in a sustained day-long manner through fermentation in rodents

Glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) are anti-diabetes/obesity hormones secreted from the gut after meal ingestion. We have shown that dietary-resistant starch (RS) increased GLP-1 and PYY secretion, but the mechanism remains unknown. RS is a fermentable fiber that lowers the glycemic index of the diet and liberates short-chain fatty acids (SCFAs) through fermentation in the gut. This study investigates the two possible mechanisms by which RS stimulates GLP-1 and PYY secretion: the effect of a meal or glycemic index, and the effect of fermentation. Because GLP-1 and PYY secretions are stimulated by nutrient availability in the gut, the timing of blood sample collections could influence the outcome when two diets with different glycemic indexes are compared. Thus we examined GLP-1 and PYY plasma levels at various time points over a 24-h period in RS-fed rats. In addition, we tested proglucagon (a precursor to GLP-1) and PYY gene expression patterns in specific areas of the gut of RS-fed rats and in an enteroendocrine cell line following exposure to SCFAs in vitro. Our findings are as follows. 1) RS stimulates GLP-1 and PYY secretion in a substantial day-long manner, independent of meal effect or changes in dietary glycemia. 2) Fermentation and the liberation of SCFAs in the lower gut are associated with increased proglucagon and PYY gene expression. 3) Glucose tolerance, an indicator of increased active forms of GLP-1 and PYY, was improved in RS-fed diabetic mice. We conclude that fermentation of RS is most likely the primary mechanism for increased endogenous secretions of total GLP-1 and PYY in rodents. Thus any factor that affects fermentation should be considered when dietary fermentable fiber is used to stimulate GLP-1 and PYY secretion.

Effects of resistant starch, a non-digestible fermentable fiber, on reducing body fat

OBJECTIVE

To assess the effects of energy dilution with non-fermentable and fermentable fibers on abdominal fat and gut peptide YY (PYY) and glucagon-like peptide (GLP)-1 expressions, three rat studies were conducted to: determine the effects of energy dilution with a non-fermentable fiber, compare similar fiber levels of fermentable and non-fermentable fibers, and compare similar metabolizable energy dilutions with fermentable and non-fermentable fibers.

RESEARCH METHODS AND PROCEDURES

In Study 1, rats were fed one of three diets with different metabolizable energy densities. In Study 2, rats were fed diets with similar fiber levels using high amylose-resistant cornstarch (RS) or methylcellulose. In Study 3, rats were fed diets with a similar dilution of metabolizable energy using cellulose or RS. Measurements included food intake, body weight, abdominal fat, plasma PYY and GLP-1, gastrointestinal tract weights, and gene transcription of PYY and proglucagon.

RESULTS

Energy dilution resulted in decreased abdominal fat in all studies. In Study 2, rats fed fermentable RS had increased cecal weights and plasma PYY and GLP-1, and increased gene transcription of PYY and proglucagon. In Study 3, RS-fed rats had increased short-chain fatty acids in cecal contents, plasma PYY (GLP-1 not measured), and gene transcription for PYY and proglucagon.

DISCUSSION

Inclusion of RS in the diet may affect energy balance through its effect as a fiber or a stimulator of PYY and GLP-1 expression. Increasing gut hormone signaling with a bioactive functional food such as RS may be an effective natural approach to the treatment of obesity.

Peptide YY and proglucagon mRNA expression patterns and regulation in the gut

OBJECTIVE

Peptide YY (PYY) and glucagon-like peptide-1 are important in the control of energy homeostasis and are both secreted from the gut in response to ingested nutrients. However, more studies are needed on nutrient regulation of their gene expression patterns in specific areas of the gut. This study detailed PYY and proglucagon (the gene that encodes glucagon-like peptide-1) gene expression patterns and regulation in the gut. We further examined the regulation of PYY and proglucagon mRNA by a diet containing fermentation-resistant starch (in vivo) and butyrate (in vitro).

RESEARCH METHODS AND PROCEDURES

Quantitative real time reverse transcriptase-polymerase chain reaction was used to measure PYY and proglucagon gene expression in epithelial cells collected from the duodenum, jejunum, cecum, and colon in normal Sprague-Dawley rats and in rats fed a resistant starch diet for 4 weeks. The same measurements were also performed in primary epithelial cells collected from the cecum and colon of normal rats after the cells were incubated with butyrate for 3 hours.

RESULTS

The gene expression patterns for PYY and proglucagon are similar to their peptide distribution patterns in the gut. Also, PYY and proglucagon mRNA expression were up-regulated in the cecum and colon in resistant-starch-fed rats. Butyrate increased PYY and proglucagon gene expression in a dose-dependent manner in vitro.

DISCUSSION

Our data provide evidence that the distal part of the gut has the ability to sense nutrients such as butyrate, resulting in the up-regulation of PYY and proglucagon gene expression.

L-Carnitine Supplementation does not Promote Weight Loss in Ovariectomized Rats Despite Endurance Exercise

In this five-week study, we tested the hypotheses that free access to a maintenance diet supplemented with L-carnitine (L-C) would reduce body fat in adult, sedentary, ovariectomized (OVX) rats, and that there would be an additive effect of L-C on weight reduction in swim-trained animals. As expected, serum carnitine was higher in rats fed the L-C diet, and the OVX-induced weight gain and abdominal fat were counteracted by swimming. L-C supplementation did not reduce the weight gain or abdominal fat in these adult female rats. Moreover, though not reaching statistical significance, rats that were fed L-C demonstrated a tendency for greater weight gain than their basal-fed counterparts despite no difference in energy intake. If the results of this study on ovariectomized rats can be translated to postmenopausal women, moderate intensity exercise may be recommended, but L-C supplementation, with no energy restriction, may be contraindicated as a weight loss method in this cohort.

Water exercise prevents femur density loss associated with ovariectomy in the retired breeder rat

The effect of non-weight-bearing exercise on skeletal bone remains controversial. The objective of this pilot study was to examine the effects of water exercise training on femur density and serum alkaline phosphatase activity in ovariectomized and sham-operated (ovaries left intact) retired breeder rats. Exercised animals swam at progressively increasing duration from 5 minutes to 75 min.d(-1), 5 d.wk(-1), for a 6-week conditioning period. Exercised rats had greater (p < 0.02) soleus muscle citrate synthase activity than sedentary rats, confirming an aerobic training effect. Femur density (g.cm(-3)) was greater (p < 0.0007) for exercised rats than sedentary rats but lower (p < 0.01) for ovariectomized rats compared to sham rats. Serum alkaline phosphatase activity tended (p < 0.06) to be greater for exercised rats compared to sedentary rats. These results indicate that dynamic water-flotation exercise prevents the femur bone loss associated with ovariectomy in rats. We conclude that this form of exercise could be beneficial in maintaining bone density in hormone-deficient postmenopausal women, especially the elderly who may not be able to perform weight-bearing activities.

Dietary soy protein maintains some indices of bone mineral density and bone formation in aged ovariectomized rats

Hormone replacement therapy (HRT) has been used to prevent osteoporosis in postmenopausal women. However, HRT may increase the incidence of some cancers and has other side effects. There is considerable interest in dietary alternatives that include the consumption of soy and isoflavones derived from soy. The purpose of this study was to determine the effects of dietary soy protein on bone density, formation and resorption in cortical and cancellous bone in aged, ovariectomized rats. Specific emphasis was placed on indices of bone formation. Rats were assigned to the following groups: baseline; sham surgery + casein diet; sham + soy protein diet; ovariectomy (Ovx) + casein diet; Ovx + soy protein diet. The diets were fed for 3 mo. The Ovx Soy group had a greater bone mineral density (BMD) than the Ovx Casein group. There was a trend (P < 0.10) for greater periosteal bone formation rates in the Sham Soy compared with the Sham Casein group. In the Ovx Soy group, indices of endocortical bone formation were greater than those of the Ovx Casein group. There were no significant differences in resorption indices or endochondral growth (bone elongation) rates with soy in either the Sham or Ovx groups. In cancellous bone, the double-labeled surface and bone formation rates were greater in the Ovx Soy group than in the Ovx Casein group. These results show that dietary soy had a beneficial effect on the preservation of BMD associated with estrogen deficiency bone loss in aged rats. These data also show that at the tissue level, soy functions in a manner different from estrogen by increasing or sustaining elevated bone formation rates after ovariectomy.

[Phytoestrogens role in bone functional structure protection in the ovariectomized rat]

Effects of soy protein diet on bone formation and density were evaluated in ovariectomized rats as a model for postmenopausal women. Twenty-seven 9-month-old rats were assigned to 3 treatment groups for the 9-week study: sham-surgery (Sh, n = 9); ovariectomy (Ovx, n = 9); ovariectomy + soy diet (OvxS, n = 9). Rats had free access to an AIN-93 M diet or AIN-93 M diet with 7% soy protein concentration and water. At sacrifice, rear legs were removed, and the right femur and tibia were cleaned manually. Serum alkaline phosphatase, a marker of bone formation, was measured colorimetrically. Bone density was measured using Archimedes' Principle. Alkaline phosphatase activity was greater in OvxS (114 +/- 19 U/L) and Ovx (128 +/- 26 U/L) compared to Sh (110 +/- 22 U/L). Femur bone density was greater for OvxS (1.520 +/- 0.02 g/cc) compared to Ovx (1.510 +/- 0.017 g/cc), but not to Sh (1532 +/- 0.025 g/cc). Tibia bone density was greater for OvxS (1.560 +/- 0.019 g/cc) compared to Ovx (1.553 +/- 0.015 g/cc), but not to Sh (1566 +/- 0.03 g/cc). In conclusion soy protein diet increased the rate of bone formation and bone density in some bones, suggesting that may help prevent bone loss in postmenopausal women.

Swim-trained rats have greater bone mass, density, strength, and dynamics

Weight-bearing exercise is traditionally recommended for improving bone health in postmenopausal women. Effects of swim exercise were studied as an alternative to weight-bearing exercise in ovariectomized rats. Rats in a swim group (Sw, n = 8) swam for 12 wk, 5 days/wk for 60 min per session. A control group (Con, n = 9) engaged in no structured exercise. Femurs were analyzed for bone mineral density and for bone mineral content by dual energy X-ray absorptiometry, biomechanical properties by three-point bending (Instron), and bone structure and formation by histomorphometry. Food intake did not differ among groups. Final body weights were significantly lower in Sw compared with Con (P < 0.05). Swimmers had significantly greater femoral shaft bone mineral density and content (P < 0.05) compared with Con. Femurs of the Sw group had greater mechanical properties (P < 0.05) compared with Con. Histomorphometric data were significantly better in the Sw group compared with Con after the 12-wk intervention (P < 0.05). In conclusion, data from this study demonstrate some beneficial effects of swim exercise on bone structure, turnover, and strength.

Creatine supplementation alters the response to a graded cycle ergometer test

To determine the effects of creatine supplementation on cardiorespiratory responses during a graded exercise test (GXT) 36 trained adults (20 male, 16 female; 21-27 years old) performed two maximal GXTs on a cycle ergometer. The first GXT was done in a nonsupplemented condition, and the second GXT was done following 7 days of ingesting either 5 g creatine monohydrate, encased in gelatin capsules, four times daily (CS, 13 male, 6 female), or the same number of glucose capsules (PL, 7 male, 10 female). CS significantly (P<0.05) improved total test time [pre-CS = 1217 (240) s, mean (std. dev.) versus post-CS = 1289 (215) s], while PL administration had no effect (P>0.05) on total test time [pre-PL= 1037 (181) s. versus post-PL= 1047 (172) s]. In addition, both oxygen consumption (VO2) and heart rate at the end of each of the first five GXT stages were significantly lower after CS, but were unchanged after PL. Moreover, the ventilatory threshold occurred at a significantly greater VO2 for CS [pre-CS = 2.2 (0.4) l x min(-1) or 66% of peak VO2 versus post-CS = 2.6 (0.5) l x min(-1) or 78% of peak Vo2; pre-PL = 2.6 (0.9) l x min(-1) or 70% peak VO2 versus post-PL = 2.6 (1.1) l x min(-1) or 68% of peak Vo2]. Neither CS nor PL had an effect on peak Vo2 [pre-CS = 3.4 (0.7) l x min(-1) versus post-CS = 3.3 (0.7) l x min(-1); pre-PL = 3.7 (1.1) l x min(-1) versus post-PL = 3.7 (1.1) l x min(-1)]. Apparently, CS can alter the contributions of the different metabolic systems during the initial stages of a GXT. Thus, the body is able to perform the sub-maximal workloads at a lower oxygen cost with a concomitant reduction in the work performed by the cardiovascular system.

Swimming eliminates the weight gain and abdominal fat associated with ovariectomy in the retired breeder rat despite high-fat diet selection

The effects of swim-training on choice of dietary fat, carbohydrate or protein, weight gain, energy intake, and energy efficiency were examined in ovariectomized and sham-operated retired breeder rats. After a 3 week training period of increased duration, rats swam for 75 min per session (5 days per week) for 4 weeks. Ovariectomized rats gained more weight than sham rats, while swimming reduced weight gain and abdominal fat. As a percentage of total intake, macronutrient choices (weight and energy) were similar for all groups, ovariectomized animals consumed more food and more energy, compared with sham animals. All rats freely chose the majority of their food (g) as carbohydrate and the majority of energy (kJ) as fat. Results indicate that a moderate intensity training program of swimming prevented the weight gain following ovariectomy in older rats despite their excessive caloric intake of fat.

Ovariectomy fails to modify the cardiac myosin isoenzyme profile of adult rats

Estrogen has been shown to help maintain the elevated expression of the high ATPase myosin isoform, V1, present in the hearts of young rats (< 70 days of age). Because hearts of this age are still undergoing significant maturation, the current study sought to determine if estrogen similarly regulates myosin isoenzyme expression in the mature adult heart. To make this determination, ten month old retired female Sprague-Dawley rats were made estrogen-deficient by ovariectomy (OVAR, n = 8). Sham-operated (CONTR, n = 8) animals served as controls. Nine weeks later, the animals were sacrificed and left ventricular tissue collected. Crude myofibrills were isolated from these samples and electrophoretically separated into the three isoenzymatic forms of cardiac myosin (V1, V2, and V3). OVAR animals were larger than the CONTR group (p < 0.05), but heart weight/body weight ratios were not different between groups. Distribution of myosin among its three isoenzymes was similar between groups (CONTR: V1, 80%, V2, 14%; V3, 6%; OVAR: V1, 77%, V2, 16%, V3, 7%). These data demonstrate that myosin isoenzyme distribution in the adult heart is unaltered by ovariectomy, suggesting that estrogen loses its ability to regulate expression of this protein in the mature heart.

Comparison of bone density measurement techniques: DXA and Archimedes' principle

The standard method for determination of density (g/cm3) of bones from small animals has been the application of Archimedes' principle. A recent development has been software for the determination of "density" (g/cm2) of small animal bones with dual-energy X-ray absorptiometry (DXA). We compared Archimedes' principle and DXA (Hologic QDR-2000) in the measurement of the densities of whole and hollowed femurs of 5- to 6-month-old retired female breeder rats. In an attempt to ensure detectable treatment differences, rats were used from a low-vitamin D Holtzman and a supplemental-vitamin D Sprague-Dawley colony. Whole femur densities were higher for supplemental-vitamin D colony rats than for low vitamin D rats using both techniques (Archimedes' principle, p < 0.002; DXA, p < 0.005), and the densities from the two techniques were highly correlated (r = 0.82, p < 0.0001). Actual density values were higher for Archimedes' principle than for DXA. Other variables such as femur ash weight and calcium content were also highly correlated to densities with both techniques. Hollowed femur density values were higher than whole femur values with Archimedes' principle but lower with DXA. Colony effects for hollowed femur densities were diminished with Archimedes' principle (p < 0.03) and eliminated with DXA (p < 0.53). Investigation of whole bones is more biologically relevant, and both techniques were effective in detecting differences between whole femurs from low-vitamin D and supplemental-vitamin D colony rats.

Maternal consumption of a low vitamin D diet retards metabolic and contractile development in the neonatal rat heart

During the fetal and suckling periods of mammalian development, the mother serves as the sole nutritional source for the offspring. As such, the quality of the maternal diet effects growth and development of the offspring during these periods. This study sought to determine if a maternal vitamin D deficiency altered the well characterized development of the neonatal heart. Weaned rat pups (21-day-old) were obtained from mothers who had consumed either a vitamin D-supplemented diet (3000 IU of vitamin D/kg) or a low vitamin D diet (< 200 IU of vitamin D/kg) prior to becoming pregnant and throughout pregnancy and suckling. These pups were sacrificed, hearts excised, and the hearts biochemically analysed for metabolic and contractile protein properties. The pups of dams fed the low vitamin D diet were slightly hypocalcemic relative to those on the supplemented diet (2.28 v 2.41 mumol/l, P < 0.05), had significantly lower body weights (43 v 55 g), heart weights (143 v 174 mg), citrate synthase activity (106 v 147 mumol g-1 min-1), and 3-hydroxyacyl CoA dehydrogenase activity (59 v 91 mumol g-1 min-1). Hexokinase activity (1.98 v 2.02 mumol g-1 min-1), and the distribution of cardiac myosin among its three isoforms (> 85% V1), were unaffected by this dietary deficiency, however myofibrillar protein content was approximately 15% lower in the experimental hearts. These data demonstrate that maternal consumption of a low vitamin D diet results in a general but significant slowing of neonatal cardiac development.

Effects of dietary boron in rats fed a vitamin D-deficient diet

Although boron has long been known to be a required nutrient for plants, it was not until recently that there was any suggestion of a nutritional requirement for animals and humans. Addition of boron to the diet of vitamin D-deficient chicks indicated that boron may play a role in animal nutrition. Studies with rats have demonstrated that supplemental dietary boron has most marked effects when the diet is deficient in known nutrients. We observed higher apparent-balance values of calcium, magnesium, and phosphorus for rats fed a vitamin D-deprived diet with dietary supplemental boron (2.72 ppm), than for rats fed the same diet without added boron (0.16 ppm). The treatment group with dietary supplemental boron demonstrated a high degree of variability in response to boron. We hypothesize that relatively large and variable vitamin D stores in weanling rats from a colony supplemented with 3000 IU vitamin D/kg diet accounted for the observed variable response. A recent, unpublished study using weanling rats from a low-vitamin D colony appears to support this hypothesis.

Effects of chromium picolinate on beginning weight training students

Changes in body weight (BW), a sum of three body circumferences (sigma C), a sum of three skinfolds (sigma SF), and the one-repetition maximum (1RM) for the squat (SQ) and bench press (BP) were examined in 59 college-age students (37 males [M], 22 females [F]) over a 12-week weight lifting program. Using a double-blind protocol, half of the students were given 200 micrograms/day chromium (Cr) in the form of chromium picolinate (CrPic) while the other half received a placebo (P). Therefore four groups were randomly formed: F-CrPic (n = 12), F-P (n = 10), M-CrPic (n = 18), and M-P (n = 19). All groups had significant increases in sigma C and significant decreases in sigma SF. No treatment effects were seen for the strength measurements, although the males experienced greater absolute increases. The only significant treatment effect found was due to the F-CrPic group gaining more BW (p = 0.0048) than the other three groups. It was concluded that CrPic supplementation had a greater effect on the females than on the males.

Suboptimal levels of dietary copper vary immunoresponsiveness in rats

The effects of severe, moderate, and mild copper deficiencies on cellular and humoral immunity were studied. Fifty male Sprague-Dawley rats, 5 wk of age, were fed diets containing 0.5, 2.0, 3.5, or 5.0 micrograms Cu/g for either 4 or 8 wk. Ten of the rats were fed the control diet, but were pair-fed with the 0.5-micrograms/g treatment group. All rats were immunized once with sheep red blood cells. Mean plasma-copper concentration reflected the dietary levels of copper, and ceruloplasmin activity correlated highly to plasma copper. Rats consuming suboptimal levels of copper responded differently to the deficiencies, so copper status varied among those animals. After 8 wk, cell proliferation, when stimulated by phytohemagglutinin, was dependent on the copper status of the animal. Severely deficient rats had consistently lower lymphocyte stimulation indexes for phytohemagglutinin and concanavalin A, but specific antibody response was not reduced. Immunoglobulin G (IgG) concentrations were variable for all rats, and immunoglobulin M (IgM) concentrations were lower for the severely deficient rats. Suboptimal dietary copper may alter immune function in rats, depending on the ensuing effect on copper status.

Effect of boron on vitamin D deficient rats

The effects of different levels of dietary boron were determined in vitamin D deficient rats. Vitamin D deficient diets containing either 0.158 ppm or 2.72 ppm of boron were fed to rats for 11 w, and calcium, magnesium, and phosphorus apparent absorption and balance were measured in the twelfth week. Higher apparent absorption and balance values for calcium and phosphorus were observed in the rats with higher dietary boron, but very few differences were seen in body wt, organ wt, and bone parameters. Balance measurements represented the present status of the rats after 12 w on the diets, but other measurements represented an accumulation over the lifetime of the rat, including a suckling period with ample vitamin D and boron. The data demonstrated that when rats are vitamin D deficient, as indicated by hypocalcemia, the level of boron in the diet affects mineral balance.

Recovery of rats from vitamin D-deficient mothers

Two separate studies were conducted using weanling rats from either an unsupplemented, low vitamin D colony or a supplemented, adequate vitamin D colony. Severe hypocalcemia, slower increases in body weight gain, and lower apparent calcium, magnesium, and phosphorus balance values occurred in the rats from the low vitamin D colony fed a purified AIN-76A, vitamin D-devoid diet compared to rats from the vitamin D-adequate colony fed the same diet. Apparent calcium, magnesium, and phosphorus balance values, as well as most other measurements, in rats from the low vitamin D colony fed a purified AIN-76a, vitamin D-adequate diet were greater than or equal to those of rats never subjected to low vitamin D. This was suggestive of overcompensation in recovery from low maternal vitamin D. However, rats from the low vitamin D colony fed an unrefined (chow), vitamin D-adequate diet had lower apparent balance and bone values compared with rats from the vitamin D-supplemented colony fed the same diet. Presumably high levels of calcium, magnesium, and phosphorous in the unrefined diet prevented any overcompensation during recovery, as occurred with purified diets, from the earlier vitamin D deficiency. Overall, results indicated weanling rats from a low vitamin D colony had low vitamin D stores and were marginally vitamin D-deficient. In addition, recovery from the marginal deficiency had occurred to a large extent after feeding a purified, vitamin D-adequate diet. The results suggest the use of low vitamin D colony rats as a model for human, marginal vitamin D deficiency.

Anthropometric measurements of white and black southern adolescent girls

Anthropometric measurements of 691 white and 550 black 12-, 14-, and 16-year-old girls from three income groups, residing in the southern United States, were evaluated, Heights, weights, mid-upper arm circumferences, and arm muscle areas of 14-year-old girls were significantly higher than those of 12-year-old girls and significantly lower than those of girls 16 years of age; triceps skinfolds, arm fat areas, and body mass indexes of 12-year-olds were significantly lower than those of older subjects. Blacks had significantly higher weights, body mass indexes, and arm muscle areas than whites. Black 12-year-old girls were significantly taller than white 12-year-old girls but significantly shorter than older girls of either race; white 16-year-old girls were significantly taller than blacks of that age. Body mass indexes of black 12-year-olds and white 14-year-olds were significantly higher than those of white 12-year-olds, and significantly lower than those of black 14- and 16-year-olds. Medium-income blacks and whites of all income levels had lower (usually significantly) weights, body mass indexes, mid-upper arm circumferences, arm muscle areas, and arm fat areas than low- and high-income blacks did. Anthropometric values of white, but not of black, girls were generally similar to those reported in surveys of primarily white girls.

A non-human primate model for the study of oral iron chelators

Recent studies have demonstrated that parenteral deferroxamine can prolong life in patients with iron overload. We have developed a non-human primate model of iron overload and have accurately determined negative iron balance in parenteral and oral studies of deferroxamine and a new chelator, desferrithiocin. Cebus monkeys were loaded with iron dextran (10 mg/kg twice weekly) until their serum contained a transferrin saturation greater than 75%, and (in two animals) liver biopsies showed iron loading. When complete iron balance studies were performed at this time, basal iron balance was -53 +/- 11 micrograms (N = 4), providing a low background for provocative studies. Iron balance was determined for intramuscular (N = 2) and oral (N = 3) deferroxamine, as well as intramuscular (N = 1) and oral (N = 4) desferrithiocin. The pattern of iron excretion after parenteral deferroxamine strongly resembled that of the iron-loaded, transfused human. Desferrithiocin was found to have significant activity as an oral chelator. This Cebus monkey model accurately determines negative iron balance and readily permits precise comparison of iron chelators given parenterally or orally. This model may offer an important step between rodent and human trials of promising new iron chelators.

The effect of bulimia upon diet, body fat, bone density, and blood components

A study was conducted to determine baseline data for dietary intake, percent body fat, bone mineral density, and blood components in women with bulimia. Eight bulimic and 10 control subjects completed the study. Each subject was assessed for a 3-day diet, frequency of purge, menstrual history, percent body fat, bone mineral density, by dual photon absorptiometry, and blood components. Mean age, height, and weight of subjects were similar. Percent body fat was similar for both groups. Vomiting was the predominant method of purge. Folacin intake was found to be significantly (p less than .05) lower in bulimic subjects. Control subjects consumed greater quantities of vitamin/mineral supplements than the bulimic subjects. Bone mineral density (gm/cm2) was found to be lower in bulimic subjects. Mean hemoglobin (gm/L [gm/dL]) levels were found to be significantly (p less than .01) higher in control subject. The data indicate that the method and duration of purge behavior could influence bone mineral density and blood components.

Actual and perceived nutritional knowledge of elderly individuals

The perceived and actual nutritional knowledge of 150 noninstitutionalized elderly individuals was measured using mean scores on a 20 item test. Over 90% of those surveyed knew about the daily dietary need for vitamin C; about the life-long need for calcium; and about sources of fiber coming from whole grain breads and cereals. The elderly who thought they had fair knowledge of nutrition, in fact, did have higher mean scores on the nutritional knowledge test. Data analysis indicated that mean scores on actual nutritional knowledge were higher for those who were white and for those who were in a higher socioeconomic level. Mean scores of elderly men and women were found to be similar.

Factors related to blood pressure in a biracial adolescent female population

Blood pressure levels, anthropometric parameters, and dietary intakes were assessed in 1981 and 1983 in a population of black (n = 236) and white (n = 296) adolescent girls, aged 14 and 16 years in 1983. The 14-year-old black girls exhibited significantly higher mean systolic and diastolic blood pressures than whites in both years. Body weight and Quetelet index were more strongly associated with blood pressure than were height and triceps skinfold thickness. Correcting blood pressures for weight, Quetelet index, 2-year changes in height, and age at menarche decreased in each case (but did not negate) the observed race differences in blood pressure. Dietary calcium and potassium intakes were inversely related to blood pressure, and a race difference in the intake of these nutrients (whites greater than blacks) was observed. Covariate adjustment for calcium, but not for potassium, decreased the magnitude of race differences in blood pressure. Family type (single-parent vs nuclear) and place of residence (urban vs nonurban) appeared to be the most important confounding variables for race differences in blood pressure, since differences largely were eliminated by controlling for these factors. Conflicting reports in the literature regarding the age range during which race differences in blood pressure become apparent may be partially attributed to the complex interrelationships among these factors and the potential influence of other genetic-environmental interactions that may also play a role in blood pressure regulation.

Evaluation of zinc and copper nutritional status and effects upon growth of southern adolescent females

A biracial sample of twenty-nine 14-yr old and thirty 16-yr old females was evaluated for zinc and copper nutritional status. Socioeconomic, demographic, anthropometric and 24-h dietary recall data were collected and plasma zinc and copper and erythrocyte zinc levels determined. Mean plasma zinc was 83 +/- 15 micrograms/dl; racial differences were significant (p less than 0.05) with plasma zinc levels at 87 +/- 3 micrograms/dl for whites and 79 +/- 3 micrograms/dl for blacks. Mean plasma copper was 119 +/- 24 micrograms/dl and was slightly higher for blacks than for whites. Mean erythrocyte zinc was 8.3 +/- 2.7 micrograms/g and represented 10 times the level of zinc in plasma. Plasma copper levels were positively (p less than 0.05) related to body size. Plasma copper was negatively (p less than 0.05) related to dietary fiber. Other dietary and economic factors did not affect mineral status.

Renal acid, urinary cyclic AMP, and hydroxyproline excretion as affected by level of protein, sulfur amino acid, and phosphorus intake

Two 51-day human studies were conducted to investigate the effects of level of protein and phosphorus intake on the various components of renal acid excretion and on urinary sulfate, cyclic AMP and hydroxyproline; the role of the sulfur amino acids (Saa) of the protein was also evaluated. Dietary treatments included: 1) a 50 g protein diet; 2) a 150 g protein diet; and 3) a 50 g protein diet plus Saa to equal that of the 150 g protein diet, each given at 2 levels of phosphorus (1010 and 2525 mg). Calcium intake was 500 mg. Subjects were 16 young adult males. The results are discussed in relationship to calcium data previously reported (1, 2). Changes in renal acid and calcium excretion are not directly related for these reasons: a) the Saa accounted for all of the protein-induced increase in urinary sulfate and acid but for only 43% of the increase in urinary calcium and b) the acid phosphate supplement decreased urinary calcium but increased total acid excretion. The phosphorus supplement increased cyclic AMP but not hydroxyproline excretion. In fact, protein and Saa caused increases in hydroxyproline that were greatly reduced by the phosphorus supplement. Increases in urinary hydroxyproline and calcium were well correlated indicating that, at low calcium intakes, protein or Saa-induced increases in urinary calcium result in increased bone resorption which is reduced by the administration of phosphorus.

Protein-induced hypercalciuria

Under controlled dietary conditions the level of dietary protein has a profound and sustained effect on urinary calcium and calcium retention of man. Young adults achieve calcium balance at low intakes of 500 mg calcium and 700 to 1,000 mg phosphorus when protein intake is 50 g. Large calcium losses occur at the same calcium and phosphorus intakes when the protein intake is increased approximately threefold. The protein-induced hypercalciuria is due mainly to a decrease in fractional renal tubular reabsorption of calcium, although an increase in glomerular filtration rate is also involved. The changes in kidney function appear to result from the catabolism of excess dietary sulfur amino acids to sulfate and the subsequent excretion of sulfate in the urine. An increase in both protein and phosphorus intakes has a much less dramatic effect on urinary calcium and calcium retention than an increase in protein intake alone. An increase in dietary phosphorus greatly reduces urinary calcium by increasing the fractional renal tubular reabsorption of calcium. It appears therefore that high protein intakes may increase the requirements for both calcium and phosphorus.

Role of the sulfur-containing amino acids in protein-induced hypercalciuria in men

A human metabolic study was conducted to determine what part sulfur-containing amino acids play in protein-induced hypercalciuria. The effects on the renal handling of calcium of increasing dietary protein from 50 to 150 g protein were compared with those of increasing the sulfur amino acids to simulate the amounts present in the 150 g protein diet; we also evaluated the effects of adding a 1.5 g supplement of phosphorus to the 50 g protein diet containing the sulfur amino acids. An increase in protein intake caused urinary calcium to double, increased glomerular filtration rate and decreased fractional renal tubular reabsorption of calcium and urinary sodium. Sulfur amino acids added to the low protein diet also caused urinary calcium to increase and fractional tubular reabsorption of calcium and urinary sodium to decrease, but the changes were only 43, 44 and 66%, respectively, those caused by the increase in protein. The phosphorus supplement effectively prevented the hypercalciuria caused by adding the sulfur amino acids to the low protein diet.

Urinary calcium and calcium balance in young men as affected by level of protein and phosphorus intake

Eight young adult males were subjects in a 51-day metabolic study conducted to examine the effects of level of protein and of phosphorus intake on urinary calcium and calcium balance. Two levels of protein (50-150 g) were given at each of two levels of phosphorus intake (1,010 and 2,525 mg). Dietary calcium and magnesium were maintained at 500 and 350 mg, respectively. Raising the protein intake from 50 to 150 g caused a calciuresis at both phosphorus intakes, but the actual increase in urinary calcium was 71 mg/day greater at the low than at the high phosphorus intake and calcium balance was changed from 24 to -116 mg/day at the low phosphorus intake and from 8 to -25 mg/day at the high. When the phosphorus intake was raised, urinary calcium decreased from 156 to 93 mg/day at the low protein intake and from 334 to 200 mg/day at the high protein intake and the markedly negative calcium balance found at the high protein intake was greatly improved. Simultaneous increases in protein and phosphorus intakes caused a 28% increase in urinary calcium whereas the increase in protein intake alone caused a 115% increase.

Long-term effects of level of protein intake on calcium metabolism in young adult women

The long-term effect of level of protein intake on calcium metabolism, renal function and renal acid excretion was determined during a 75-day metabolic study. Six women consumed a diet containing either 46 or 123 g protein for 60 days; they then consumed the alternate diet for 15 days. Calcium, phosphorus and magnesium intakes were maintained constant at 500, 900 and 350 mg, respectively, throughout the 75-day study. Urinary calcium was remarkably constant with time at both levels of protein intake but was approximately twice as high when the 123 g protein diet was consumed. Level of protein intake had no effect on calcium absorption; the increase in urinary calcium found when the high protein diet was given, therefore, caused a markedly negative calcium balance. Glomerular filtration rate (GFR) and renal acid excretion were higher and fractional renal tubular reabsorption of calcium was lower when the high protein diet was given. The hypercalciuria caused by the high protein intake was due primarily to the decrease in fractional tubular reabsorption of calcium and, to a lesser extent, to the increase in GFR. Neither GFR, fractional renal tubular reabsorption of calcium nor any of the components of renal acid excretion exhibited any tendency to change with time over the 60-day experimental period.