Last year, I got it in my head that I wanted to write an article for a very prestigious scientific journal. I submitted an article not really knowing a whole lot about scientific writing (that's really my amazing brother Brad's specialty-- and he is really, really good at it). Shockingly, upon peer review, it wasn't rejected. It was returned to me with a list of comments and corrections I was to make before re-submitting. And I meant to make those corrections. I really did. I would sit, staring at that paper for upwards of 30 minutes at a time, and making nary a dent in it. Because what I learned from this experience was this:
I hate scientific writing.
I suck at it.
I might get better at it with practice, but I don't honestly really have a whole lot of desire to practice.
I love writing, but the type of writing I do in this blog is way more my style. It's just as informative (I think), and way more fun to read (in my very humblest of opinions).
That having been said, I have this article I wrote, just sitting there, and it seems to me that it should at the very least be read. It is deeply flawed, from a scientific journal point of view, but it was decent enough to not be rejected. And so, with all that said, here is my very poorly written scientific journal submission. I hope it is informative to you.
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THE EFFECTS OF SOY CONSUMPTION ON LIPOGENESIS, MINERAL ABSORPTION, HORMONE BALANCE, AND MENTAL STATE
Melody L. Schoenfeld, CSCS
ABSTRACT
The consumption of soy has been demonized by many popular health professionals. The purpose of this article is to review non-biased, peer-reviewed, human-based studies on soy to determine whether or not there is a basis to avoid it in the human diet. Subjects covered include whether or not soy contributes to mental decline, lipogenesis, mineral deficiencies, and changes in hormone levels.
Keywords: Soybeans, soy, phytoestrogens, mineral deficiencies, vegetarians, vegans, protein sources, daidzein, isoflavones, ferritin, lipogenesis
INTRODUCTION
In recent years, there has been much argument against soy of any kind in the diet. Allegations of ani-soy proponents include claims that consumption causes mental decline in elderly adults and may lead to mineral deficiencies.16 In addition, it has been purported that soy acts like estrogen in the body, promoting weight gain, infertility, and other disruptions of the endocrine system in both men and women.16 Given the controversy, the purpose of this article is to examine whether there is a research basis to support a negative impact of soy consumption.
In order to keep the contents of this review as accurate as possible, studies that appear to be subsidized by corporations with a financial interest in the research have been eliminated.
SOY CONSUMPTION AND LIPOGENESIS
There is surprisingly little data available regarding soy consumption and lipogenesis. The data that is available, however, seems to indicate that dietary soy may actually decrease lipogenesis. Vigna, et. al.15 demonstrated that soy protein alone seemed to actually lowered the rate of lipogenesis, whereas its active components had no effect on serum lipid levels or lipogenesis.15 In this, double-blind, parallel, placebo (caseinate) controlled study, 77 postmenopausal women (44 dyslipidemic) were assessed for serum total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, apo A-I, apo B, and lipoprotein (a) both before and after the 12-week diet modification. Although both groups showed a significant reduction in total cholesterol, only the group given isolated soy protein showed a significant lowering of both apo B and LDL/HDL ratio. Additionally, the dyslipidemic women with higher concentrations of LDL showed a greater improvement in their lipid profile with isolated soy protein than with placebo.15
Azadbakht, et. al.3performed a crossover clinical trial on 42 women with metabolic syndrome. In this study, participants were randomly assigned to either a DASH (Dietary Approaches to Stop Hypertension) diet including red meat, an isolated soy protein diet (in which the soy protein replaced the red meat in the DASH diet), or a soynut (whole, dried, baked soybeans) diet (in which soynuts replaced the red meat in the DASH diet) for eight weeks each.3 The soynuts performed the best in this study, decreasing the homeostasis model of assessment-insulin resistance score significantly in comparison to isolated soy protein (percentage change –7.4% ± 0.8; P < 0.01) and control (-12.9 ± 0.9; P < 0.01) diets.3 Soynuts also reduced fasting plasma glucose more significantly than did the soy protein or control diets, and significantly reduced serum C-peptide concentrations in comparison to control diet, while isolated soy protein consumption did not.3 Based on this study, soynut consumption clearly seems to have a beneficial effect on the glycemic index and lipid profiles for postmenopausal women with metabolic syndrome.
Wu, et. al.19 showed a significant reduction in both fat mass and bone mineral density in postmenopausal women given soy isoflavones, provided that they also were able to produce equol (a product of daidzein, an active component of soy isoflavones).19 In this one-year long double-blind, randomized study, 54 healthy, postmenopausal (>1 year) women between the ages of 45 and 60 were given either 75mg of isoflavote conjugates (38.3 mg daidzein, 0.2 mg genistein, 24.4 glycitin with glycitein) with dextrin or a placebo containing only dextrin. Of the 29 women in the placebo group, 15 were equol producers, and in the isoflavone group, there were also 15 equol producers. In the isoflavone group, equol producers had a significantly lower mass change than did the nonproducers.19 This was not the case for the placebo group, however. In addition, there was a lower percent of bone loss change in the equol producers (P < 0.05) than in the nonproducers (-2.28 and 2.61%, respectively). 19 While soy isoflavone consumption definitely seems to play a role in lower body fat and higher bone mass, the extent of this may depend on one’s ability to produce equol in the intestinal flora.
In cases in which an individual is concerned about excess adipose tissue, it can be concluded from current research that it is not only safe, but likely a good idea to include moderate amounts of soy in the diet. Of course, the total number of calories consumed, with or without soy, is a key factor in lipogenesis. Soy products tend to have fewer calories than most meat products of the same weight, so soybeans can be a good way to help lower the total number of calories eaten per day when used as a substitute for red meat, pork, and lamb.
SOY CONSUMPTION AND HORMONE LEVELS
Another common concern regarding soy is the fact that it contains phytoestrogens. The claim is that these phytoestrogens lower testosterone and increase estrogen in the body. The majority of the available research on this subject indicates that, particularly in low to moderate amounts, soy does not appear to affect estrogen or testosterone levels in the body.
Maskarinec, et. al. performed a randomized crossover study which showed a direct correlation between soy consumption and lower prostate-specific antigen levels in men, while not affecting testosterone levels . In this study, 24 men ages 58.7 +/- 7.2 years were given a low or high soy diet, randomly. Compliance was determined via self-reporting, soy calendars, 24-hour dietary recalls, and urinary excretion of isoflavones. Compliance was high for all participants. Of these men, 23 completed the study. In the high soy diet, the men consumed two servings of soy per day, while the low soy diet participants maintained their usual diet. Prostate-specific antigen (PSA) levels were 14% lower in the high-soy group, but there was no change in testosterone between the high-soy and the low-soy groups. This indicates a lower risk of prostate cancer for the high-soy-consuming group without affecting testosterone levels.
Allen, et. al. performed a cross-sectional analysis of 696 men with varying degrees of soy consumption. The consumption of soymilk was determined using a validated semiquantitative food frequency questionnaire, while serum hormone levels were measured via immunoassay. The study authors used multiple regression techniques to examine links between soy milk consumption, an index of isoflavone intake, and hormone levels. It was determined that soy milk intake was not associated with serum levels of testosterone, free testosterone, androstanediol glucuronide, sex hormone-binding globulin, or leutinizing hormone.
In a meta-analysis of fifteen placebo-controlled treatment groups with baseline and ending measures plus 32 reports involving 36 treatment measures, Hamilton-Reeves, et. al. found no notable effects of soy protein or isoflavone intake on male sex hormones, regardless of the statistical model used.
It would appear that concerns about hormonal changes as a result of soy consumption are unfounded. Unless an individual is having adverse effects from soy consumption, it is not necessary to eliminate soy based on concerns about soy-induced hormonal alterations.
SOY AND MINERAL DEFICIENCIES
Anti-soy proponents commonly claim that soy consumption leads to mineral deficiency in humans.16 There does not appear to be any scientific research performed on humans to support this claim. One study did, however, show an association between high levels of soy consumption and increased bone density in post-menopausal women. In this study, Somewaka, et. al.12estimated daily isoflavone intake of 478 postmenopausal Japanese women who reported soy consumption. Their bone mineral density was measured between L2 and L4 using dual energy x-ray absorptiometry. The women were divided into groups based on how long they had been postmenopausal, and each of those groups was subcategorized based on isoflavone intake amount. The mean estimated isoflavone intake of these women was 54.3mg per day. Using stepwise regression analysis, it was discovered that weight and postmenopausal time were both predictors of bone mineral density.12 Because of this, bone mineral densities were adjusted to years since menopause and weight. It was found that bone mineral density were significantly different in the highest isoflavone intake group compared to the lowest intake group (P < .001) within the early and late postmenopausal groups.12 In addition, within the early postmenopausal group, the researchers found significant differences in palpation and in back pain between the high isoflavone intake groups and the low isoflavone intake groups, but this statistic was not significant in the late postmenopausal group. It was concluded that a high consumption of soy products had a positive association with increased bone mass in postmenopausal women.12
In a controlled, double-blind study, Anderson, et. al.2set out to prove that bone mineral density could be improved in healthy, menstruating young adult females. Anderson and his team were testing the hypothesis that bone mineral content and density could be improved in young, menstruating women of any ethnic background based on evidence from other scientific studies showing beneficial effects of isoflavone consumption on the bone mineral content and densities of peri- and post-menopausal women.2 Anderson studied the women for 12 months, assessing them at baseline, 6 and 12 months. The findings were that neither the isoflavone-consuming group nor the control group showed changes in bone moneral density and conentration.2 Menstrual patterns and other factors also did not change. This study demonstrated that consumption of isoflavones does not influence bone mass, either for better or worse.
Although vegetarian diets do not generally contain sources of heme iron, which tends to be more readily absorbed by the body, nonheme iron is abundant in many vegetarian sources such as lentils, green, leafy vegetables, and molasses. Soybeans are also a source of nonheme iron. Some research does indicate that the phytates in soy can inhibit iron absorption. For instance, Lynch, et. al.9measured iron absorption in 34 individuals using an extrinsic radioiron label in liquid meals containing corn starch, corn oil, and either egg white or a series of soy protein derivatives. The findings in this study showed that unmodified soybean protein isolate markedly inhibited protein absorption, but that a hydrolized version with minimal phytate content showed 19 times more iron absorption.9 The glycinin and conglycinin content of soy were found to be inhibitory to iron absorption in this case.9
However, other studies demonstrate that the iron found iron from soy in the form of ferritin is utilized just as well as ferritin from other sources, and has a great potential for providing a plant-based iron source to deficient individuals. Murray-Kolb, et. al.11gave meals with intrinsically labeled (55Fe) soybeans (hydroponically grown and unnodulating) as soup or muffins, and a reference dose of 59Fe as ferrous sulfate in acsorbate solution. They then measured radioactivity in red cells 14 and 28 days later. The researchers discovered that the mean 55Fe absorption in both forms was absorbed at 27%, and that the reference dose was absorbed at 61%.11 The iron was distributed more or less equally between protein and phytate. An inverse correlation (r = -0.793, P < 0.001) existed between red cell radioactivity and serum ferritin concentration. It was concluded that soybeans appear to be a good source of iron in marginally iron-deficient individuals, and that nodulation may be a factor in whether or not iron is properly absorbed from soybeans.11
Lönnerdal, et. al.8performed a randomized, crossover study in which 16 healthy, non-anemic women were fed a bagel, cream cheese, and apple juice containing 1 1 µCi 59Fe/meal as FeSO4, or as iron-free soy ferritin reconstituted with the high-phosphate characteristic of plant ferritin (iron:phosphorus = 4:1). Iron-free, apo-soybean ferritin was prepared from purified ferritin. Another meal, containing FeSO4 or ferritin, was given after four weeks. Whole body and blood cell iron was measured after 28 days, before and after dosing. There appeared to be no difference between the absorption of soy ferritin and FeSO4 in whole-body iron or in iron absorption calculated from red blood cell incorporation.8 The evidence suggested that sensors regulating iron absorption responded similarly to both types of iron.
SOY AND MENTAL DECLINE
Another claim made is that soy consumption “shrinks the brain.”16 This claim is based on the Honolulu-Asia Aging Study, which found that elderly men who consumed tofu twice per week or more were more prone to cognitive impairment compared with those who rarely or never ate tofu.17 However, a followup study performed by Hogervorst, et. al.5on older adults in Indonesia found that tofu and tempeh consumption was associated with better immediate recall in older adults up to age 80, after which positive or negative association between soyfoods and memory was no longer statistically significant.5 In this study, cognitive performance data was available on 142 Central Javanese participants between the ages of 56 and 97 covered by the Borobudur Health Centers. The results of this study showed a significant positive linear association between consuming tofu and tempeh weekly and immediate recall in those with an average age of 67 years.5 In those with an average age of 80 years, the previously reported negative association of soy consumption with negative recall was no longer significant. It was suggested that lifestyle changes (i.e. reduction of tofu consumption after results had been disseminated) or “healthy survivor effects” may have been the cause of this finding. 5
The SOPHIA (SOy and Postmenopausal Health In Aging) study, performed by Kritz-Silversetin, et. al.6was a 6-month, randomized, double-blind, placebo-controlled clinical trial examining the cognitive effects of soy on post-menopausal women. The study analyzed 56 healthy, post-menopausal (min. 2 years) between the ages of 55 to 74 years who were not taking estrogen therapy. In the active treatment group, 27 women took two pills per day containing 55mg of soy-extracted isoflavones. The 26 women in the placebo group took two identical-looking pills with inert ingredients. All women took at least 85% of their pills.6 Cognitive tests included Trails A and B, category fluency, logival memory, and recall. All of the women had a similar cognitive baseline and were cognitively intact. The women in the isoflavone group showed significant improvement over their baseline, and also in comparison to the placebo group at the six month mark.6 The isoflavone group showed significant improvement in category fluency (P = 0.02), and nonsignificant improvement on the other two test of verbal memory and Trails B.6 This demonstrated that, particularly in the case of verbal memory, isoflavone supplementation appears to be of benefit to cognitive function in healthy postmenopausal women.
Thorp, et. al.13 performed a twelve-week, double-blind, placebo-controlled, randomized, crossover trial on 34 healthy men to test soy’s effect on memory-related tasks. The men in the active group were given four capsules containing 116mg isoflavone equivalents per day, consisting of 68mg daidzein, 12mg genistein, and 36mg glycitin for 6 weeks, while the placebo group was given an inert supplement. The alternate treatment was given for the following six weeks.13 The mental assessments given at baseline and after each treatment period included verbal episodic, auditory, working, planning, attention, mental flexibility, and visual-spatial processing. Isoflavone supplementation had a significant positive correlation with improved spatial working memory (P = 0.01).13 Isoflavones did not have an effect, either positive or negative, on auditory and episodic memory, executive function, or on visual-spatial processing.13 As women tend to perform better than men on tests of spatial working memory, it was concluded that isoflavone supplementation in healthy men may benefit cognitive functions that appear to be more dependant upon estrogen activation.13
The World Heath Organization notes that East Asian countries such as Japan and China, where tofu consumption tends to be highest, have significantly lower rates of dementia than Western countries.18 In addition, Japanese Americans living in Washington and Hawaii had much higher rates of Alzheimer’s Disease than their counterparts living in Japan.18 This would indicate that there is likely more at work than tofu consumption in the mental decline of residents of Hawaii.
CONCLUSION
Science simply does not support many popular claims against soy consumption. It does not appear that one needs to be concerned with mineral deficiencies or cognitive issues as a result of soy consumption, and there is no conclusive evidence linking soyfood consumption to lower testosterone levels. For those who hope to reduce adipose tissue while maintaining muscle mass, soy can be an excellent replacement for some animal proteins in the diet. While dietary soy does not seem to affect strength or performance in athletes, in cases in which muscle mass is a concern, a mixed protein intake is recommended for ideal anabolism. Whey protein appears to be ideal for this particular aspect, but for those wishing to avoid it, soy protein can be supplemented with pea, rice, and hempseed proteins.
1. Allen, N, Appleby, P, Davey, G, Key, T. Soy Milk Intake in Relation to Serum Sex Hormone Levels in British Men. Nutr. Cancer, 41:41-46, 2001
4. Hamilton-Reeves, J, Vazquez, G, Duval, S, Phipps, W, Kurzer, M, Messina, M, Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis. Fertil. Steril., 3:997-1007, 2010
7. Kurzer, M, Hormonal Effects of Soy in Premenopausal Women and Men. J. Nutr. 132:570S-573S, 2002
10.Maskarinec, G. Morimoto, Y, Hebshi, S, Sharma, S, Franke, AA, Stanczyk, FZ. Serum prostate-specific antigen but not testosterone levels decrease in a randomized soy intervention among men. Eur J Clin Nutr. 60:1423-1429, 2006
17. World Health Organization http://www.searo.who.int/en/Section1174/Section1199/Section1567/Section1823_8066.htm
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