The soya bean has been part of the human diet for thousands of years and the Ancient Chinese believed it to be one of the five sacred grains vital for life (alongside rice, wheat, barley and millet.) This high regard has been carried through time and has been supported by scientific investigation in more recent years. Soya is now recognized as a ‘functional food’ (meaning that it has health-promoting properties) and is one of an elite group of foods, to obtain approval by the U.S. FDA for a health claim. (The FDA currently recommends 25g of soya protein per day for adults to potentially reduce the risk of heart disease.) (1)
However, despite it being a longstanding natural source of nutrition and an established ‘functional food,’ there are elements of controversy regarding soya consumption.
The first point to establish in this debate is that different sources of soya may have different nutritional implications. Like the current carbohydrate controversy, (which ultimately boils down to carefully choosing high fibre, whole grains over refined, high sugar varieties), the type of soya consumed should also be closely examined. The widespread genetic modification of agricultural soya has been associated with negative health and environmental consequences, but this must not be confused with soya that has been naturally farmed.
There are many areas of health, where natural soya foods are recommended as a part of nutritional therapy. These include heart disease, menopause, hormone dependant cancers (breast, prostate and endometrial) and bone health.
What makes soya a healthy choice?
- Soya is a high-quality ‘complete’ protein! Soya is particularly important in a vegan diet, as it is one of the few plant products which provides protein that is nutritionally equivalent to meat. The nutritional quality of protein foods varies according to the amino acid profile of each. (Amino acids are the building blocks of protein and although the body can make some amino acids, there are certain ‘essential amino acids’ which are required from dietary sources.) ‘Complete’ proteins are those which contain all of the essential amino acids. All animal proteins are considered complete whereas plant proteins are generally incomplete (containing some, but not all of the essential amino acids.) However, soya is one of the few plant exceptions, which is recognized as a complete protein! Looking even more closely at protein quality, the WHO and U.S. FDA established the protein digestibility corrected amino acid score (PDCAAS) as the official assay for evaluating protein quality. Proteins that after correcting for digestibility provide amino acids equal to or in excess of human requirements receive a PDCAAS score of 1.0. Soya has been successfully rated as such, meaning that it meets the protein needs of human adults, when consumed as a sole source of protein. (2)
- Soya is cholesterol-free! Cholesterol is only found in animal products, thus although soya protein has been classed as a protein equivalent to meat, chicken and fish, it has the added benefit of providing a cholesterol-free alternative.
- Soya is a good plant source of Iron! There are different chemical forms of iron, some of which have a greater absorption potential than others. Although the general assumption is that plant-based sources of iron have a lower bioavailability than iron obtained from animal proteins, recent research has shown that most of the iron contained within soya, is of the well-absorbed form, ferritin! (3)
- Soya protein is a wise choice for sports nutrition! The importance of protein in the diet of athletes (for muscle development during training,) is well known. What remains misunderstood on this topic, is the actual amount and preferred sources of dietary protein recommended to achieve muscle building. Protein needs are dependent on the type of sport and the total energy intake of athletes and whole food sources are usually recommended above supplements. Excessive protein consumption can result in compromising of glucose levels, dehydration and kidney strain. (2) However, there is evidence that suggests soya protein puts less of a strain on the kidneys compared with intakes of animal protein. (4) Furthermore, high intakes of animal protein (which also contain fat), often result in a higher fat diet. This is not recommended for sportsmen and women due to the associated influence on body fat percentage. Soya can thus be embraced as a good protein source for athletes, being high in protein, but low in fat.
- Soya contains isoflavones! Soya contains healthy phytochemicals (plant compounds) called isoflavones. There are various types of isoflavones, but two specifically (genistein and daidzein) have been studied closely and found to be very similar in structure to the hormone estrogen. These so-called ‘plant hormones’ are much weaker than true hormones, yet seem to have a positive influence on estrogen balancing in the body and have been shown to reduce LDL (bad) cholesterol levels. Phytoestrogens found in soya foods are also able to act as antioxidants, carcinogen blockers and tumor suppressors and may exert a protective effect against hormone-related cancers by binding at estrogen receptor sites.Further studies suggest that plant-based estrogens may reduce the incidence of vasomotor symptoms (hot flashes) of menopause and lastly that they may protect women against osteoporosis by the action of genistein, which stimulates osteoblasts (bone-forming cells). (2)
Are there side effects to soya?
As long as you are choosing good quality soya, which has not been genetically modified, there is little reason to avoid it, with the obvious exception being soya allergy.
As far as the food hormone hype is concerned, soya does not have any mistrustful mechanisms! Dietary estrogens are at least 1000 times weaker when compared to the strength of circulating estrogens in most mammals. (5)
Commonly asked questions allude to various eccentric theories including the effect of plant estrogens on men. However, evaluation of the clinical evidence concludes that isoflavones do not have feminizing effects on men at intakes even higher than are typical in the diet of Asian males. (6) Further, results of a meta-analysis (which is a summary study of previous studies) show no effect of soya protein on the reproductive hormones in men. (7)
There have also been propositions in the literature linking soya foods to gout. (All protein foods contain substances called purines, which yield uric acid as a by-product of metabolism, and could thus supposedly aggravate acid build-up and the symptoms of gout.) However, although soya (being a protein) does have a moderate purine content, it is much lower than that of many high purine animal proteins. It is also worth noting that improvements in the efficacy of gout medication have largely replaced the need for rigid dietary restriction of purines in recent times.
What about supplements?
There is a big difference between soya-based foods and soya supplements, which contain a much higher concentration of isoflavones. There is no scientific evidence to support the practice of mega-dosing with soya and like most other healthy nutritional elements, soya is recommended as part of a balanced diet, where preference is always given to food sources over supplements.
Clinical studies indicative of the health benefits associated with soya, have typically used between 50 and 100mg of soya-derived isoflavones. This is equivalent to 15-20g soya protein (3). Fry’s products generally contain 8-10g soya protein per serving, which is reflectively a perfectly moderate level in accordance with the current science for safe and regular consumption.
Fry’s products incorporate a blend of vegetable proteins, including, but not limited soya. We’ve done our research and we believe in balance, moderation and variety.
Adding to this, we strongly recommend choosing soya products that are GM-free! (which is the start of another story, altogether ?)
(1) Hasler CM. Position of the American Dietetic Association: Functional foods. Journal of the American Dietetic Association. 2004;104(5): 814-26.
(2) Mahan LK and Escott-Stump S; Krause’s Food, Nutrition and Diet Therapy; WB Saunders Company; 2000; pg58,548,275-6.
(3) Messina, M; Insights gained from 20 years of soy research; The Journal of Nutrition. 2010; 140(12) 2289S-2295S
(4) Messina, M; A Brief Historical Overview of the Past Two Decades of Soy and Isoflavone Research; The Journal of Nutrition. 2010; 140(12) 2289S-2295S
(5) Setchell KD, Phytoestrogens: the biochemistry, physiology, and implication for human health of soy isoflavones; The American Journal of Clinical Nutrition.1998;68(6)1333S-1346S.
(6) Setchell KD; Fertil Steril. 2010 May 1;93(7):2095-104. doi: 10.1016/j.fertnstert.2010.03.002. Epub 2010 Apr 8.
(7) Setchell KD; Fertil Steril. 2010 Aug;94(3):997-1007. doi: 10.1016/j.fertnstert.2009.04.038. Epub 2009 Jun 12.