Application of the Indicator Amino Acid Oxidation
Technique for the Determination of Metabolic Availability of Sulfur Amino
Acids from Casein versus Soy Protein Isolate in Adult Men.
Research Institute, Hospital for Sick Children, Toronto, ON, Canada M5G 1X8;
4Department of Nutritional Sciences, University of Toronto, Toronto, ON
Canada M5S 2Z9 5Department of Agricultural, Food and Nutritional Science,
University of Alberta, Edmonton, Alberta, Canada T6G 2P5.
Our objective was to determine the metabolic availability (MA) of sulfur
amino acids in dietary proteins using the indicator amino acid oxidation (IAAO)
technique. Five to seven men received graded levels (20, 40, 60, and 70%) of
the mean total sulfur amino acid (TSAA) requirement of 13 mg . kg(-1) .
d(-1) as a crystalline AA mixture, casein, and soy protein isolate (SPI)
(40, 50, 60, and 70%), respectively. Five of these subjects received 40% of
TSAA requirement from SPI supplemented with methionine to the level of 40%
of requirement. These 5 subjects also repeated the level of 60% TSAA
requirements from both casein and SPI to assess repeatability. The mean MA
of TSAA from SPI (71.8 +/- 3.6%) was lower than from casein (87.4 +/- 3.8%,
P < 0.05). Supplementation of SPI with methionine decreased the IAAO (11.5
+/- 0.3% administered dose) compared with unsupplemented SPI (12.8 +/- 0.5%
administered dose, P < 0.05). IAAO was similar for repeated measurements of
casein and SPI, respectively, at the 60% TSAA intake level (10.8 +/- 1.0 vs.
10.7 +/- 1.2% for casein; 12.7 +/- 1.3 vs. 12.9 +/- 2.6% for SPI). In
conclusion, the IAAO technique can be used to determine the MA of AA for
protein synthesis in test proteins for humans.
PMID: 17634258 [PubMed - as supplied by publisher]
Departamento de Fisiología de la Nutrición, Instituto Nacional de Ciencias
Médicas y Nutrición, Mexico.
The worldwide increase in degenerative diseases is in part due to
modifications in the lifestyle including the diet. Epidemiological, clinical,
and experimental evidence shows that soy protein may prevent lipotoxicity in
non-adipose tissues during obesity. The molecular mechanism by which soy
protein prevents lipotoxicity involves a reduction in the insulin/glucagon
ratio, resulting in a down-regulation of lipogenic genes mediated by the
transcription factor sterol regulatory element-binding protein (SREBP)-1,
and up-regulation of SREBP-2 to reduce serum cholesterol. In addition, soy
protein maintains the functionality of adipose tissue-liver axis to prevent
hepatic steatosis during the development of obesity.
Nutrition and Toxicology Research institute Maastricht (NUTRIM), Department
of Human Biology, Maastricht University, P.O. Box 616, 6200 MD Maastricht,
The Netherlands.
High-protein diets are beneficial in weight maintenance because of their
satiating and thermogenic effects. These effects may be partly mediated by
the hormonal effects of proteins. This study investigated the effect of soy
protein hydrolysate (SPH) with and without a carbohydrate pre- and afterload
on energy metabolism and hormonal secretion in 8 healthy nonobese subjects.
In an additional trial, pea protein hydrolysate was compared to SPH, both
with a carbohydrate afterload. The study had a single-blind crossover
design. In all cases, 0.4g protein and/or carbohydrate per kilogram of body
weight was tested. Diet-induced thermogenesis (DIT) was measured by
ventilated hood measurements, and postprandial blood samples were drawn over
3 hours. Soy protein hydrolysate consumption induced a higher DIT than a
carbohydrate (CHO) load. Both conditions induced similar insulin responses.
Soy protein hydrolysate induced a glucagon, but no glucose, response;
whereas CHO induced a glucose, but no glucagon, response. Soy protein
hydrolysate with a CHO pre- or afterload induced similar DIT and insulin
responses. No glucose response was found when SPH preceded the CHO load.
Total glucagon responses were similar with CHO as pre- and afterload, but
time courses were different. Pea protein hydrolysate with a CHO afterload
induced both higher insulin and glucagon responses (area under the curve)
than SPH with CHO afterload, but DIT was similar in both conditions. In
conclusion, this study shows that the larger DIT after protein than after
CHO may be related to the glucagon response that is induced by protein but
not by CHO; that the protein-induced DIT and glucagon response are not
influenced by a CHO pre- or afterload; and that protein ingestion can fully
prevent the plasma glucose increase associated with CHO when CHOs are
ingested after proteins.
Institute for Cancer Prevention, Valhalla, NY, USA. Lac65@earthlink.net
BACKGROUND: Soy isoflavones may lower breast cancer risk through altered
hepatic estrogen metabolism, leading to increased urinary excretion ratios
of 2-hydroxyestrone (20HE1) to 16a-hydroxyestrone (16alphaOHE1). MATERIALS
AND METHODS: Urinary excretion of 20HE1/16alphaOHE1 was measured in 36
healthy, pre-menstrual women before and after ingestion of a soy-protein
formula containing 120 mg of isoflavone daily for one month. Since
isoflavone absorption and metabolism depends on intestinal bacteria, effects
of co-administration of Lactobacillus GG (2 x 10(12)) on estrogen ratios and
isoflavone excretion were studied. Urinary isoflavone excretion measurements
assessed compliance. RESULTS: Soy isoflavone ingestion induced quantitative
differences in urinary excretion of estrogen metabolites and isoflavones but
failed to alter 20HE1/16alphaOHE1 ratios. Co-administration of Lactobacillus
GG with soy reduced excretion of total and individual isoflavones by 40%
(p=0.08), without altering 2OHE1/16alphaOHE1 ratios. CONCLUSION:
Isoflavone-rich soy protein administration alone, or with probiotic
supplement, did not alter urinary excretion of estrogen metabolites in
premenopausal women. However, adding concentrated probiotics may alter
isoflavone bioavailability.
Isoflavone-rich soy protein isolate suppresses androgen
receptor expression without altering estrogen receptor-beta expression or
serum hormonal profiles in men at high risk of prostate cancer.
Department of Food Science and Nutrition, University of Minnesota,
Minneapolis, MN 55455, USA.
The purpose of this study was to determine the effects of soy protein
isolate consumption on circulating hormone profiles and hormone receptor
expression patterns in men at high risk for developing advanced prostate
cancer. Fifty-eight men were randomly assigned to consume 1 of 3 protein
isolates containing 40 g/d protein: 1) soy protein isolate (SPI+) (107 mg/d
isoflavones); 2) alcohol-washed soy protein isolate (SPI-) (<6 mg/d
isoflavones); or 3) milk protein isolate (0 mg/d isoflavones). For 6 mo, the
men consumed the protein isolates in divided doses twice daily as a partial
meal replacement. Serum samples collected at 0, 3, and 6 mo were analyzed
for circulating estradiol, estrone, sex hormone-binding globulin,
androstenedione, androstanediol glucuronide, dehydroepiandrosterone sulfate,
dihydrotestosterone, testosterone, and free testosterone concentrations by
RIA. Prostate biopsy samples obtained pre- and postintervention were
analyzed for androgen receptor (AR) and estrogen receptor-beta expression by
immunohistochemistry. At 6 mo, consumption of SPI+ significantly suppressed
AR expression but did not alter estrogen receptor-beta expression or
circulating hormones. Consumption of SPI- significantly increased estradiol
and androstenedione concentrations, and tended to suppress AR expression (P
= 0.09). Although the effects of SPI- consumption on estradiol and
androstenedione are difficult to interpret and the clinical relevance is
uncertain, these data show that AR expression in the prostate is suppressed
by soy protein isolate consumption, which may be beneficial in preventing
prostate cancer.
Can the combination of flaxseed and its lignans with soy
and its isoflavones reduce the growth stimulatory effect of soy and its
isoflavones on established breast cancer?
Department of Nutritional Sciences, University of Toronto, Toronto, Ontario,
Canada. Fax: +1-416-978-5882.
Consumption of phytoestrogen (PE)-rich foods (i. e., soy and flaxseed (FS))
is increasing because of their suggested health benefits. However, recent
studies raise concern over the safety of soy and its isoflavones,
particularly genistein (GEN), for postmenopausal breast cancer (BC), due to
their potential stimulatory effects on human breast tissue and on the growth
of existing tumors in rodents. FS, rich in PE lignans, which is metabolized
to the mammalian lignans enterolactone (ENL) and enterodiol (END), has
consistently been shown to have tumor inhibitory effects in a human clinical
trial as well as rodent BC models. Using the preclinical athymic mouse
postmenopausal BC model, combining FS with soy protein or GEN with END and
ENL, was found to negate the tumor stimulatory effects of soy protein or GEN
alone. The mechanism may be related to the modulation of estrogen receptor
and MAPK signaling pathways. If these studies can be confirmed in clinical
trials, then consumption of combined soy and FS, or their PEs, may reduce
the tumor growth stimulatory effect of soy or GEN. This may indicate that if
soy is consumed with lignan-rich foods, it may continue to induce its other
beneficial health effects, without inducing adverse effect on postmenopausal
BC.
PMID: 17579892 [PubMed - in process]
7:
Nutrition.
2007 Jul-Aug;23(7-8):551-6. Epub 2007 Jun 15.
School of Nutrition and Health Sciences, Taipei Medical University, Taipei,
Taiwan, Republic of China.
OBJECTIVE: This study investigated the effects of a soy-based low-calorie
diet on weight control, body composition, and blood lipid profiles compared
with a traditional low-calorie diet. METHODS: Thirty obese adults (mean body
mass index 29-30 kg/m(2)) were randomized to two groups. The soy-based
low-calorie group consumed soy protein as the only protein source, and the
traditional low-calorie group consumed two-thirds animal protein and the
rest plant protein in a 1200 kcal/d diet for 8 wk. A diet record was kept
everyday throughout the study. Food intake was analyzed before and after the
study. Anthropometric data were acquired every week, and biochemical data
from before and after the 8-wk experiment were compared. RESULTS: Body
weight, body mass index, body fat percentage, and waist circumference
significantly decreased in both groups (P < 0.05). The decrease in body fat
percentage in the soy group (2.2%, 95% confidence interval 1.6-2.8) was
greater than that in the traditional group (1.4%, 95% confidence interval
-0.1 to 2.8). Serum total cholesterol concentrations, low-density
lipoprotein cholesterol concentrations, and liver function parameters
decreased in the soy-based group and were significantly different from
measurements in the traditional group (P < 0.05). No significant change in
serum triacylglycerol levels, serum high-density lipoprotein cholesterol
levels, and fasting glucose levels was found in the soy or traditional group.
CONCLUSION: Soy-based low-calorie diets significantly decreased serum total
cholesterol and low-density lipoprotein cholesterol concentrations and had a
greater effect on reducing body fat percentage than traditional low-calorie
diets. Thus, soy-based diets have health benefits in reducing weight and
blood lipids.
Preventive Medicine Research Institute, 900 Bridgeway, Sausalito, CA 94965,
USA. antonella.dewell@pmri.org
High levels of insulin-like growth factor 1 (IGF-1) are associated with
increased risk of prostate cancer, whereas increased levels of some of its
binding proteins (IGFBPs) seem to be protective. High intakes of dietary
protein, especially animal and soy protein, appear to increase IGF-1.
However, soy isoflavones have demonstrated anti-proliferative and apoptotic
effects both in vitro and in vivo. We evaluated dietary intakes of total
protein and soy isoflavones in relation to the IGF axis in prostate cancer
patients making comprehensive lifestyle changes including a very low-fat
vegan diet supplemented with soy protein (58 g/day). After one year,
intervention group patients reported significantly higher intakes of dietary
protein and soy isoflavones compared to usual-care controls (P < 0.001). IGF-1
increased significantly in both groups, whereas IGFBP-1 rose in the
experimental group only (P < 0.01). Increases in vegetable protein over one
year were associated with increases in IGFBP-1 among intervention group
patients (P < 0.05). These results suggest that dietary protein and soy
isoflavones, in the context of comprehensive lifestyle changes, may not
significantly alter IGF-1. However, given the recent literature indicating
that high intake of protein rich in essential amino acids (animal or soy
protein) may increase IGF-1, it may be prudent for men with early stage
prostate cancer not to exceed dietary protein recommendations.
Carbohydrate and mineral removal during the production of
low-phytate soy protein isolate by combined electroacidification and high
shear tangential flow ultrafiltration.
Department of Chemical Engineering, University of Waterloo, 200 University
Avenue West, Waterloo, Ontario, Canada N2L 3G1.
In this work, soy protein isolates were produced by a combination of
electroacidification and high shear tangential flow hollow fiber
ultrafiltration with a 100 kDa membrane under constant pressure. The
filtration performance was evaluated by comparing the filtration time and
the final product composition for an electroacidified (pH 6) and a
non-electroacidified (pH 9) soy protein extract. The removal of
carbohydrates during the filtration was always consistent with the
theoretical predictions (based on free permeability assumption) for both the
electroacidified and the non-electroacidified feeds. A higher removal of
calcium, magnesium, and phytic acid was achieved during the filtration of
the electroacidified feed compared to the non-electroacidified feed. However,
the electroacidification pretreatment had a negative impact on the permeate
flux and resulted in more significant membrane fouling with correspondingly
longer filtration times. A discontinuous diafiltration enhanced the removal
of carbohydrates and minerals, thus yielding a product with higher protein
content but was unable to improve the permeate flux for the electroacidified
feed.
Karolinska Institute, Stockholm, Sweden. hoie@nutripharma.com
This study was undertaken to compare the effects on plasma cholesterol
concentration of a new isolated soy protein in which the protein structure
is kept in its native, nondenaturated form (verum 1) versus a conventional
isolated soy protein (verum 2) and milk protein (placebo). This prospective,
randomized, double-blind, placebo-controlled study was conducted in an
outpatient clinical study center in Berlin, Germany. Over 8 wk, 120 patients
(total cholesterol, 5.2-7.8 mmol/L) were given verum 1, verum 2, or placebo
at a dosage of 25 g protein daily. At the end of the treatment period, total
cholesterol levels were significantly reduced by 10.7% in the verum 1 group
compared with placebo (P<.001), and levels were reduced by 5.8% in the verum
2 group (P=.008). The difference between the 2 verum groups was
statistically significant (P=.008). Low-density lipoprotein cholesterol
levels were significantly reduced with nondenaturated isolated soy protein
only: levels were reduced by 9.4% in the verum 1 group (P=.002) and by 4.9%
in the verum 2 group (P=.107). Again, the difference between the verum
groups was significant (P=.05). The results of this study confirm that
supplementation with isolated soy protein can lead to significant reductions
in plasma concentrations of total and low-density lipoprotein cholesterol.
These reductions are significantly more pronounced with an isolated soy
protein that maintains the native protein structure than with a commercially
available reference isolated soy protein.
[1] 1Clinical Nutrition & Risk Factor Modification Center, St Michael's
Hospital, Toronto, ON, Canada [2] 2Department of Medicine, Division of
Endocrinology and Metabolism, St Michael's Hospital, Toronto, ON, Canada [3]
3Department of Nutritional Sciences, University of Toronto, Toronto, ON,
Canada [4] 4Department of Medicine, Faculty of Medicine, University of
Toronto, Toronto, ON, Canada.
Objective:To determine the effect on blood pressure of dietary advice to
consume a combination of plant-based cholesterol-lowering foods (dietary
portfolio).Methods:For 1 year, 66 hyperlipidemic subjects were prescribed
diets high in plant sterols (1.0 g/1000 kcal), soy protein (22.5 g/1000
kcal), viscous fibers (10 g/1000 kcal) and almonds (22.5 g/1000 kcal). There
was no control group. Seven-day diet record, blood pressure and body weight
were monitored initially monthly and later at 2-monthly intervals throughout
the study.Results:Fifty subjects completed the 1-year study. When the last
observation was carried forward for non-completers (n=9) or those who
changed their blood pressure medications (n=7), a small mean reduction was
seen in body weight 0.7+/-0.3 kg (P=0.036). The corresponding reductions
from baseline in systolic and diastolic blood pressure at 1 year (n=66
subjects) were -4.2+/-1.3 mm Hg (P=0.002) and -2.3+/-0.7 mm Hg (P=0.001),
respectively. Blood pressure reductions occurred within the first 2 weeks,
with stable blood pressures 6 weeks before and 4 weeks after starting the
diet. Diastolic blood pressure reduction was significantly related to weight
change (r=0.30, n=50, P=0.036). Only compliance with almond intake advice
related to blood pressure reduction (systolic: r=-0.34, n=50, P=0.017;
diastolic: r=-0.29, n=50, P=0.041).Conclusions:A dietary portfolio of
plant-based cholesterol-lowering foods reduced blood pressure significantly,
related to almond intake. The dietary portfolio approach of combining a
range of cholesterol-lowering plant foods may benefit cardiovascular disease
risk both by reducing serum lipids and also blood pressure.European Journal
of Clinical Nutrition advance online publication, 25 April 2007; doi:10.1038/sj.ejcn.1602768.
PMID: 17457340 [PubMed - as supplied by publisher]
Studies on persisting effects of soy-based compared with
amino acid-supplemented casein-based diet on protein metabolism and
oxidative stress in juvenile pigs.
Research Institute for the Biology of Farm Animals (FBN), Research Unit
Nutritional Physiology 'Oskar Kellner', Dummerstorf, Germany. junghans@fbn-dummerstorf.de
Juvenile growing pigs were studied to explore whether a soy-based diet can
induce persistent physiological alterations, especially in protein and
energy metabolism, nutrient oxidation and redox homeostasis. In former
studies we have shown that in juvenile pigs chronically fed protein diets
based on either casein (CAS) or soy protein isolate (SPI), the SPI diet
significantly decreases growth rate and increases oxidative stress
responsiveness as compared to CAS. In addition, here we show that chronic
feeding of SPI vs. CAS diet decreases whole body protein synthesis (WBPS) (p
= 0.007) and hepatic gene expression associated with protein synthesis. To
study persistent SPI effects, a three-period feeding experiment was designed:
In the test group 18 pigs received the CAS diet for 24 days (period 1),
followed by 31 days on the SPI diet (period 2) and further 31 days on the
CAS diet (period 3). In the control group 18 pigs were fed the CAS diet
throughout the three periods (86 days). Temporary consumption of SPI diet
results in persistent changes of protein metabolism and oxidative stress
responsiveness. After switching back from SPI to CAS diet the decrease of
WBPS of the test group vs. control group was of borderline significance (p =
0.061), transcript levels of hepatic gene expressions of leucine
aminopeptidase, endopeptidase 24.16, glutathione-S-transferase and peptide
methionine sulfoxide reductase were increased. In liver tissue, total
glutathione was increased and thiobarbituric acid reactive substances were
decreased in the test vs. control group. In conclusion, results suggest that
SPI-induced changes in protein and amino acid metabolism as well as in redox
homeostasis and antioxidative potential in growing pigs persist 4 weeks
after the cessation of SPI feeding.
Division of Cardiology, Beth Deaconess Medical Center, Boston, Massachusetts
02215, USA. fwelty@bidmc.harvard.edu
BACKGROUND: Epidemiological studies suggest a low incidence of hot flashes
in populations that consume dietary soy. The present study examined the
effect of soy nuts on hot flashes and menopausal symptoms. METHODS: Sixty
healthy postmenopausal women were randomized in a crossover design to a
therapeutic lifestyle changes (TLC) diet alone and a TLC diet of similar
energy, fat, and protein content in which one-half cup soy nuts divided into
three or four portions spaced throughout the day (containing 25 g soy
protein and 101 mg aglycone isoflavones) replaced 25 g of nonsoy protein.
During each 8-week diet period, subjects recorded the number of hot flashes
and amount of exercise daily. At the end of each 8-week diet period,
subjects filled out the menopausal symptom quality of life questionnaire.
RESULTS: Compared to the TLC diet alone, the TLC diet plus soy nuts was
associated with a 45% decrease in hot flashes (7.5 +/- 3.6 vs. 4.1 +/- 2.6
hot flashes day, respectively, p < 0.001) in women with >4.5 hot flashes/day
at baseline and 41% in those with <or=4.5 hot flashes/day (2.2 +/- 1.2 vs.
1.3 +/- 1.1, respectively, p < 0.001). Soy nut intake was also associated
with significant improvement in scores on the menopausal symptom quality of
life questionnaire: 19% decrease in vasomotor score (p = 0.004), 12.9%
reduction in psychosocial score (p = 0.01), 9.7% decrease in physical score
(p = 0.045), and a trend toward improvement in the sexual score, with a
17.7% reduction in symptoms (p = 0.129). The amount of exercise had no
effect on hot flash reduction. CONCLUSIONS: Substituting soy nuts for nonsoy
protein in a TLC diet and consumed three or four times throughout the day is
associated with a decrease in hot flashes and improvement in menopausal
symptoms.
Department of Medicine, University of Medicine and Dentistry of New
Jersey/Robert Wood Johnson Medical School, New Brunswick, NJ 08903-2681,
USA. goodin@umdnj.edu
PURPOSE: To determine if a commonly used soy protein supplement exhibits
biological activity in vivo and in vitro, we evaluated an over-the-counter
soy protein powder supplement using blood from healthy male volunteers and
in an estrogen receptor in vitro assay. SUBJECTS AND METHODS: We recruited
healthy male volunteers 18 years of age or older that were in good health.
Treatment consisted of consuming two scoops (56 g) of pure soy protein
powder (Puritan's Pride, Oakdale, NY) daily for 28 days. Serum testosterone
and luteinizing hormone (LH) levels were collected on days -7, 0, 14, and 28
of therapy, and day 42. A reporter estrogen receptor (ER) assay was used to
determine the effect on ER-beta and ER-alpha in vitro. RESULTS: Twelve
subjects were enrolled with a mean age of 32.25 years (range 25 to 47).
Serum testosterone decreased 19%(+/-22%) during the 4-week use of soy
protein powder (P = 0.021) and increased within 2 weeks after we
discontinued soy protein powder. Serum LH concentrations decreased during
the 4-week use of soy protein powder then increased within 2 weeks after we
stopped the soy protein powder, but the changes did not reach statistical
significance (P = 0.20). Soy protein powder was found to induce agonist
activity to ER-beta using a reporter estrogen receptor assay in yeast.
CONCLUSION: Soy protein powder decreases serum testosterone levels in
healthy men and acts as an ER-beta agonist; the significance of this
biological effect with respect to cancer prevention needs further study.
Consumption of fluid skim milk promotes greater muscle
protein accretion after resistance exercise than does consumption of an
isonitrogenous and isoenergetic soy-protein beverage.
Exercise Metabolism Research Group, Department of Kinesiology, McMaster
University, Hamilton, Canada.
BACKGROUND: Resistance exercise leads to net muscle protein accretion
through a synergistic interaction of exercise and feeding. Proteins from
different sources may differ in their ability to support muscle protein
accretion because of different patterns of postprandial hyperaminoacidemia.
OBJECTIVE: We examined the effect of consuming isonitrogenous, isoenergetic,
and macronutrient-matched soy or milk beverages (18 g protein, 750 kJ) on
protein kinetics and net muscle protein balance after resistance exercise in
healthy young men. Our hypothesis was that soy ingestion would result in
larger but transient hyperaminoacidemia compared with milk and that milk
would promote a greater net balance because of lower but prolonged
hyperaminoacidemia. DESIGN: Arterial-venous amino acid balance and muscle
fractional synthesis rates were measured in young men who consumed fluid
milk or a soy-protein beverage in a crossover design after a bout of
resistance exercise. RESULTS: Ingestion of both soy and milk resulted in a
positive net protein balance. Analysis of area under the net balance curves
indicated an overall greater net balance after milk ingestion (P < 0.05).
The fractional synthesis rate in muscle was also greater after milk
consumption (0.10 +/- 0.01%/h) than after soy consumption (0.07 +/- 0.01%/h;
P = 0.05). CONCLUSIONS: Milk-based proteins promote muscle protein accretion
to a greater extent than do soy-based proteins when consumed after
resistance exercise. The consumption of either milk or soy protein with
resistance training promotes muscle mass maintenance and gains, but chronic
consumption of milk proteins after resistance exercise likely supports a
more rapid lean mass accrual.
Department of Medicine, George Washington University Medical Center,
Washington, DC, USA.
Soy protein is an important component of soybeans and provides an abundant
source of dietary protein. Among the dietary proteins, soy protein is
considered a complete protein in that it contains ample amounts of all the
essential amino acids plus several other macronutrients with a nutritional
value roughly equivalent to that of animal protein of high biological value.
Soy protein is unique among the plant-based proteins because it is
associated with isoflavones, a group of compounds with a variety of
biological properties that may potentially benefit human health. An
increasing body of literature suggests that soy protein and its isoflavones
may have a beneficial role in obesity. Several nutritional intervention
studies in animals and humans indicate that consumption of soy protein
reduces body weight and fat mass in addition to lowering plasma cholesterol
and triglycerides. In animal models of obesity, soy protein ingestion limits
or reduces body fat accumulation and improves insulin resistance, the
hallmark of human obesity. In obese humans, dietary soy protein also reduces
body weight and body fat mass in addition to reducing plasma lipids. Several
potential mechanisms whereby soy protein may improve insulin resistance and
lower body fat and blood lipids are discussed and include a wide spectrum of
biochemical and molecular activities that favorably affect fatty acid
metabolism and cholesterol homeostasis. The biologic actions of certain
constituents of soy protein, particularly conglycinin, soyasaponins,
phospholipids, and isoflavones, that relate to obesity are also discussed.
In addition, the potential of soy protein in causing food allergy in humans
is briefly discussed.
New York Obesity Research Center, St Luke's/Roosevelt Hospital, New York, NY
10026, USA. ms2554@columbia.edu
The objective of this study was to determine whether a weight-loss diet high
in soy-protein-rich foods leads to greater weight loss and reductions in
waist circumference, fat mass, and cardiovascular disease risk factors than
a control diet. Groups of overweight women (body mass index [calculated as
kg/m(2)] of 28 to 33, aged 25 to 49 years) were counseled to decrease their
caloric intake by 500 kcal/day for a period of 12 weeks; in addition, the
soy-protein-rich group was counseled to consume 15 g soy protein/1,000 kcal
daily. Soy-protein-rich foods were provided to subjects. Body weight, waist
circumference, percent body fat, fat-free mass, lipids, glucose, and insulin
were measured at repeated intervals. Forty-seven women completed the study.
Both groups lost a similar amount of weight both when a completers only
(-3.18%+/-0.63% vs -4.04%+/-0.95% for soy-protein-rich and control diets,
respectively) and a last-observation-carried-forward analysis
(-1.93%+/-0.50% vs -2.50%+/-0.67%, for soy-protein-rich and control diets,
respectively) were performed. There was no difference between groups in
change in percent fat mass (-5.31%+/-1.50% for soy-protein-rich diet vs
-3.94%+/-1.68% for control diet), percent fat-free mass, and waist
circumference. There was no dietary assignment-by-group interaction on lipid,
glucose, and insulin concentrations when analyses were done on completers
only or on all subjects using a last-observation-carried-forward approach.
Percent change in any of the biochemical parameters studied over the 12-week
period was not significantly different between groups. Our results do not
lend support to the emerging notion that soy-protein-rich foods could be
considered potential functional foods for weight management, in the
quantities consumed in this study.
Food Futures National Research Flagship, CSIRO Human Nutrition, Adelaide,
Australia.
Feeding higher levels of dietary animal protein (as casein or red meat)
increases colonic DNA damage and thins the colonic mucus barrier in rats.
Feeding resistant starch (RS) reverses these changes and increases large
bowel SCFA. The present study examined whether high dietary dairy (casein or
whey) or plant (soya) proteins had similar adverse effects and whether
dietary RS was protective. Adult male rats were fed diets containing 15 or
25 % casein, whey or soya protein with or without 48 % high amylose starch
(as a source of RS) for 4 weeks. DNA damage was measured in isolated
colonocytes using the comet assay. Higher dietary casein and soya (but not
whey) increased colonocyte DNA damage. DNA damage was highest with soya when
fed at 15 or 25 % protein without RS. Dietary RS attenuated protein-induced
colonocyte DNA damage in all groups but it remained significantly higher in
rats fed 25 % soya compared with those fed 15 % protein. Dietary protein
level did not affect colonic mucus thickness overall but the barrier was
thinner in rats fed high dietary casein. This effect was reversed by feeding
RS. Caecal total SCFA and butyrate pools were higher in rats fed RS compared
with digestible starch. Caecal and faecal SCFA were unrelated to genetic
damage but correlated with mucus thickness. The present data confirm that
higher dietary protein affected colonocyte DNA and colonic mucus thickness
adversely but that proteins differ in their effects on these indices of
colon health. The data show also that these changes were reversed by RS.
K risten M ontgomery is an assistant professor in the College of Nursing at
the University of South Carolina in Columbia, South Carolina.
Soy protein comes from soybeans and offers multiple health benefits, some of
which are just beginning to be discovered. This column reviews the health
benefits of soy products with a special focus on women and children's health.
To date, little has been written or researched that is directly related to
perinatal health. Thus, the column has a more broad focus so that childbirth
educators have a general resource to gain knowledge related to the use of
soy-based foods.
Department of Internal Medicine, University of Kentucky, Lexington, KY
40504, USA. jwandersmd@aol.com
Recent studies suggest that obese individuals lose weight more rapidly and
lose more total weight with soy protein than with animal protein as a major
diet component. The purpose of the present study was to evaluate the
weight-loss efficacy and changes in body composition, waist circumference,
blood pressure, and levels of plasma glucose, insulin, serum lipids,
C-reactive protein, and homocysteine from consumption of either 3 soy shakes
or 3 casein shakes daily as part of a 16-week, energy-restricted diet for
obese women. Forty-three women with body mass index values of 30 to 40
kg/m(2) were randomized to intensive dietary interventions using either
casein (n = 21) or soy (n = 22) shakes. Subjects were instructed to consume
3 shakes, 1 prepackaged entrée, and 5 servings of fruits or vegetables daily
to achieve an energy intake of 4.5 to 5.0 MJ/d. Subjects attended classes
weekly or biweekly. Weight, body fat, lipid, and glucose measurements were
obtained at baseline and at 8 and 16 weeks. For both groups combined,
subjects lost 8.1% of initial body weight (7.7 kg) at 8 weeks and 13.4%
(12.7 kg) at 16 weeks. Weight loss from baseline did not differ
significantly by group and, for completing subjects, was 14.0% +/- 1.2% (mean
+/- SE) for casein and 12.8% +/- 1.4% for soy. With the intention-to-treat
analysis, weight losses at 16 weeks were 12.5% +/- 1.4% for casein and 11.3%
+/- 1.2% for soy. Body fat losses were 23.7% +/- 2.0% for casein and 21.8%
+/- 2.4% for soy and did not differ significantly. Both study groups lost
significant amounts of weight with a highly structured behavioral program
incorporating 4 meal replacements and vegetables and fruits. Differences in
weight loss and body composition changes between casein and soy treatments
were not significant.
Department of Thoracic Surgery, University of L'Aquila, G. Mazzini Hospital,
Teramo, Italy. duilio.divisi@virgilio.it
The aim of our study is to evaluate the relationship between diet and cancer
development. It has been estimated that 30-40% of all kinds of cancer can be
prevented with a healthy lifestyle and dietary measures. A low use of fibres,
the intake of red meat and an imbalance of Omega-3 and Omega-6 fats may
contribute to increase the risk of cancer. On the other hand, the assumption
of lots of fruit and vegetables may lower the risk of cancer. Protective
elements in a cancer-preventive diet include selenium, folic acid, vitamin
B12, vitamin D, chlorophyll and antioxidants such as carotenoids (alpha-carotene,
beta-carotene, lycopene, lutein, cryptoxanthin). Ascorbic acid has limited
benefits if taken orally, but it effective through intravenous injection. A
supplementary use of oral digestive enzymes and probiotics is also an
anticancer dietary measure. A diet drawn up according to the proposed
guidelines could decrease the incidence of breast, colon-rectal, prostate
and bronchogenic cancer.
Karolinska Institute, Stockholm, Sweden. hoie@nutripharma.com
A randomized, placebo-controlled, double-blind clinical study was performed
to investigate the dose-dependent response of serum cholesterol after
consuming an ultra-heat-treated milk containing a soy protein preparation.
Eighty hypercholesterolemic subjects were assigned to one of four study
groups receiving 12.5 or 25 g soy protein (active treatment) or casein
(placebo) daily over a period of 4 weeks. The trial substances were provided
as ready-made, ultra-heated milk preparations. Before and after the
treatment, serum concentrations of total, low-density lipoprotein, and
high-density lipoprotein cholesterol were determined. Unexpectedly, at the
end of the study, low-density lipoprotein cholesterol concentrations were
significantly increased compared with baseline in all study groups. The
magnitude of this increase (17-19%) was similar in all active and placebo
study groups. Soy protein supplements previously shown to be effective in
reducing serum cholesterol had in this study no such lipid-lowering effect
after ultra heat treatment.
Institute of Nutritional Sciences, Martin-Luther-University Halle-Wittenberg,
Halle/Saale, Germany.
OBJECTIVE: We assessed the effect of dietary proteins isolated from beef,
pork, and turkey meat on concentrations of cholesterol and triacylglycerols
in plasma, lipoproteins, and liver and the composition of the microsomal
membrane (fatty acids, phosphatidylcholine/phosphatidylethanolamine ratio)
compared with that of casein and soy protein in rats. METHODS: Five groups
of 12 rats each were fed semisynthetic diets for 20 d that contained 200
g/kg of proteins isolated from beef, pork, or turkey meat or, as controls,
casein or soy protein. RESULTS: Rats fed beef, pork, or turkey proteins did
not differ in cholesterol concentrations of plasma, lipoproteins, and liver
and in composition of microsomal membrane from rats fed the casein diet. All
groups fed a protein from an animal source had higher very low-density
lipoprotein (VLDL) and liver cholesterol concentrations than did rats fed
soy protein. However, rats fed pork protein had lower concentrations of
triacylglycerols in liver, plasma, and VLDL and lower mRNA concentrations of
sterol regulatory element binding protein-1 and glucose-6-phosphate
dehydrogenase than did rats fed casein. However, concentrations of plasma
and VLDL triacylglycerols in rats fed pork protein were not as low as those
observed in rats fed soy protein. CONCLUSION: Proteins isolated from beef,
pork, or turkey meat do not differ from casein in their effects on
cholesterol metabolism. Pork protein decreases plasma triacylglycerol
concentrations compared with casein but not compared with soy protein. The
triacylglycerol-lowering effect of pork protein compared with casein is
suggested to be caused by decreased hepatic fatty acid synthesis.
School of Human Kinetics, Laurentian University, Sudbury, Ontario, Canada.
The purpose was to compare changes in lean tissue mass, strength, and
myofibrillar protein catabolism resulting from combining whey protein or soy
protein with resistance training. Twenty-seven untrained healthy subjects
(18 female, 9 male) age 18 to 35 y were randomly assigned (double blind) to
supplement with whey protein (W; 1.2 g/kg body mass whey protein + 0.3 g/kg
body mass sucrose power, N = 9: 6 female, 3 male), soy protein (S; 1.2 g/kg
body mass soy protein + 0.3 g/kg body mass sucrose powder, N= 9: 6 female, 3
male) or placebo (P; 1.2 g/kg body mass maltodextrine + 0.3 g/kg body mass
sucrose powder, N = 9: 6 female, 3 male) for 6 wk. Before and after
training, measurements were taken for lean tissue mass (dual energy X-ray
absorptiometry), strength (1-RM for bench press and hack squat), and an
indicator of myofibrillar protein catabolism (urinary 3-methylhistidine).
Results showed that protein supplementation during resistance training,
independent of source, increased lean tissue mass and strength over
isocaloric placebo and resistance training (P < 0.05). We conclude that
young adults who supplement with protein during a structured resistance
training program experience minimal beneficial effects in lean tissue mass
and strength.
Toxicology Research Division, Reproductive Biology Unit, and University of
Ottawa, Department of Cellular and Molecular Medicine, Sir Frederick G.
Banting Research Centre, Ottawa, ON, K1A 0L2, Canada. Gerard_Cooke@hc-sc.gc.ca
This review considers the recent literature in which animal models were used
to investigate the purported health benefits of soy isoflavones. The main
conclusions are that our animal models demonstrate minimal effects in breast,
prostate, and colon cancer prevention, and that, while some cancers may
respond to isoflavones, it would appear that isoflavones do not prevent
further development once cancer has become established. Regarding
cardiovascular health, the lipid-lowering effects of isoflavones have been
established, but their efficacy may be less than original research purported.
However, it may be considered a bonus of habitual soy consumption that blood
cholesterol levels would be reduced somewhat. With respect to osteoporosis
and menopausal symptoms, animal models do not show any consistent benefit of
isoflavones in preventing osteoporosis, and calcium fortification or the use
of prescribed medications are likely much better approaches to combat bone
loss. However, our animal models of osteoporosis and menopausal symptoms may
not be entirely representative of the human situation. Perhaps the benefit
of isoflavones in cognitive skills and in delaying Alzheimer's disease is an
area where they can be of some advantage. However, this field is very recent
and requires much more research in both humans and animal models before any
definitive benefit can be propounded. On the other hand, isoflavones in
moderation are probably not dangerous, as few studies have indicated adverse
effects. However, large doses have been shown to increase apoptosis and cell
degeneration, and in some cancer regimes, once the cancer has progressed
beyond the hormone-dependent stage, high doses of isoflavones may be
contraindicated. The prospect of mega-dosing from isoflavone supplements
opens a new chapter in the risk assessment of isoflavone consumption.
Centro de Investigación Bioquímica y Biología Molecular, Hospital Vall
d'Hebron, Barcelona, Spain. mfarriol@ir.vhebron.net
The aim was to determine in what areas the therapeutic application of soy
predominates in clinical trials and to assess the emerging fields of its use
by means of an analysis of bibliographic resources. A search was performed
in the MEDLINE database up to 31 december 2004, limited to the Title/Abstract
field, and Clinical Trials as the type of publication. The abstracts from
the publications selected (n=86) were reviewed and different variables were
assessed. A total of 3280 subjects were included: 15% men and 59% women (71%
postmenopausal). The studies were performed basically in healthy individuals
(71%). Twenty five percent of the studies investigated plasma levels of
different metabolites and 21% determined hormone or lipid profiles. After
the year 2000 a new population focus was detected, with the publication of
two studies in elite gymnasts and judoists, with positive results. The
present observations indicate that soy supplementation in the competitive
sports elite may be an emerging application.
Yale New Haven Hospital, New Haven, CT, USA. jane.kerstetter@uconn.edu
We showed that increasing dietary protein from omnivorous sources increases
intestinal calcium absorption and urinary calcium, whereas a low-protein
diet decreases calcium absorption and lowers urinary calcium. To assess the
effect of soy protein on this relation, we substituted soy for meat in high-
and low-protein diets fed to healthy women. The study consisted of a 2-wk
adjustment period followed by a 4-d experimental period in which 20 healthy
women consumed, in random order, the following 4 diets: high-protein
soy-based, low-protein soy-based, high-protein meat-based, low-protein
meat-based. Measures of calcium homeostasis were evaluated at baseline and
after 4 d of the experimental period. At 24 h, net acid excretion was higher
during the high- compared with the low-protein intervention (P < 0.05), and
during the meat compared with the soy intervention (P < 0.05). The
high-protein diets increased 24-h urinary calcium (P < 0.001), but urinary
calcium did not differ due to the type of protein. Serum concentrations of
parathyroid hormone and calcitriol, and urinary nephrogenous cAMP were
higher during the low- compared with the high-protein intervention and
during the soy compared with the meat protein (P < 0.05). In a subset of
subjects, intestinal calcium absorption tended to be lower (P = 0.1) when
they consumed the soy diets rather than the meat diets. These data indicate
that when soy protein is substituted for meat protein, there is an acute
decline in dietary calcium bioavailability.
