SOY – Is it GOOD or BAD for YOU ?*
Soy and soy products have been consumed as food since soy was first used in China at least 3,000 years ago.
In recent years, questions about the safety and health benefits of soy and its derivatives have been raised. For example:
· The Hippocrates Centre in Australia strongly recommend against the use of soy products. In her book ‘Take Control of Your Health and Escape the Sickness Industry’, chapter 9 ‘Soy – The Abominable Bean’, Elaine Hollingsworth, the Director, sets out very convincing arguments for their stand.
· The Weston A. Price Foundation (a non-profit nutrition education foundation), in a submission to the Food and Drug Administration (USA), claim that “Soy is no health food.”.
· Dr Joseph Mercola, in ‘The World’s Most Popular Natural Health Newsletter’, regularly raises concerns re soy. One such newsletter is entitled ‘Think Soy is Healthy? Here’s Why it’s Not as Good as You Think’.
· Other authors such as Sally Fallon and Mary G. Enig also make a strong case to avoid soy products.
This newsletter looks at what soy is, what are its products and its uses. The arguments for and against the various health claims will be briefly reviewed. With this information, you will be able in make an informed decision as to whether you will chose to eat soy foods, limit their intake or avoid them.
What is Soy?
The term ‘soy’ is commonly used to refer to foods, or food ingredients, derived from the soybean (USA) or soya bean (UK), a type of legume. Other legumes include chickpeas, lentils and broad beans. Soybeans are also classified as ‘oilseeds’.
Soy foods include traditional Asian foods such as tofu, tempeh and miso. More recently however, a greater variety of soy foods, such as soy beverages, yoghurts, soy cheese, breads, breakfast cereals and meat alternatives like burger patties, soy sausages and many foods containing textured vegetable protein (TVP), are routinely found on the supermarket shelves and in food outlets.
The fruit of the soy plant, Glycine max, is a pod that grows in clusters of 3-5. Each pod is 3-8 cm long and usually contains 2-4 ‘seeds’.
The chemical composition of soybeans (dry by weight) is approximately:
· 40% protein
· 20% oil
· 35% carbohydrate
· 5% ash.
The majority of soy protein is a relatively heat-stable storage protein. This heat stability enables soy food products requiring high temperature cooking, such as tofu, soymilk and TVP, to be made.
Since soluble soy carbohydrates are found mainly in the whey and are broken down during fermentation, soy concentrate, soy protein isolates, tofu, soy sauce and sprouted soybeans are without flatus activity.
The insoluble carbohydrates in soybeans consist of the complex polysaccharides cellulose, hemi-cellulose and pectin which can be classified as dietary fibre.
Soybeans are an important global crop, providing oil and protein. The bulk of the crop is solvent-extracted for vegetable oil and the defatted soymeal is used for animal feed. Only a small proportion of the crop is consumed directly by humans.
In 2006, the world total of soybean grown was 221.5 million metric tons (including 87.7 from the USA, 52.4 from Brazil and 40.4 from Argentina).
Soybeans are one of the ‘biotech food’ crops that have been genetically modified, and GM soybeans are being used in an increasing number of products. In 1995, Monsanto introduced Roundup Ready (RR) soybeans that allow the transgenic plant to survive being sprayed with the non-selective herbicide Roundup (Glyphosate). RR soybeans allow a farmer to widely spray Roundup without affecting the crop. In 1997, about 8% of all soybeans cultivated for the commercial market in the USA were genetically modified. By 2006, the figure was 89%.
Soybean is an oilseed. It has a high oil content (20%). Soybeans are the leading agricultural export of the USA, and the bulk of the crop is grown for oil production.
To produce soybean oil, the soybeans are cracked, adjusted for moisture content, rolled into flakes and solvent-extracted with commercial hexane. The oil is then refined, blended for different applications and sometime hydrogenated. Soybean oils, both liquid and partially hydrogenated, are sold as ‘vegetable oil’, or end up in a wide variety of processed foods. The remaining soybean husks are used mainly as animal feed.
The major unsaturated fatty acids (see my October 2008 newsletter ‘Trans Fats’) in soybean oil are linolenic acid (7%), linoleum acid (51%) and oleic acid (23%). It also contains the saturated fatty acids stearic acid (4%) and palmitic acid (10%).
Soybean meal, the material remaining after solvent-extraction of the oil, with 50% protein content, is used to grow farm animals such as poultry and swine on an industrial scale, and more recently is used in the aquaculture of catfish.
Soy flour refers to the defatted soybeans and is used in extruder texturising, giving textured vegetable protein (TVP). It is the starting material for the production of soy concentrate and soy protein isolate.
Soybeans as a Substitute for Other Foods
Soybeans are the primary ingredient in many processed foods, including:
· Dairy product substitutes such as soy margarine, soy ice cream, soy milk, soy yoghurt, soy cheese and soy cream cheese.
· Soybean oil or ‘vegetable oil’
· Veggie burgers
· Soynut butter
· Soy crisps.
Soybeans are processed to produce a texture and appearance similar to other foods, eg butter, ice cream, milk, yoghurt, cheese, lard, olive oil, ground beef, peanut butter, potato chips etc.
Soy milk does not contain significant amounts of calcium, since the high calcium content of soybeans is bound to the insoluble constituents and remains in the pulp.
Other Soy Products
Soybeans are also used in industrial products including oils, soap, cosmetics, resins, plastics, inks, crayons, solvents and clothing. Soybean oil is the primary source of biodiesel in the USA.
The Active Ingredients in Soybeans that Give Health Benefits
The active ingredients in soybeans include:
· Soy protein.
It is considered by some that this is complete protein, one that contains all the essential amino acids that must be provided to the human body because of the body’s inability to synthesise them.
· Dietary fibre, with a range of benefits.
· Omega-3 fatty acids.
These plant (vegetable) fats are an essential nutrient in the diet, and they are not found in significant amounts in other plant foods.
· Phytochemicals. These include:
Ø isoflavones, which have been considered to add to the beneficial effects of soy protein
Ø plant sterols, which are well known to lower blood cholesterol
Ø saponins, which may lower cholesterol and stimulate the immune system.
Health Benefits Claimed for Soy and Soy Products
The following are the health benefits claimed for soy and soy products. They are presented as typically promoted by the commercial industries which market these products. Included are the reasons for the health claims.
· Soy and heart disease.
Cardiovascular disease is a major cause of death worldwide. High levels of blood cholesterol represent a major risk factor for coronary heart disease. Clinical studies with humans have confirmed the ability of soy protein to lower levels of LDL cholesterol (the ’bad’ form) without affecting the ‘good’ HDL cholesterol. The isoflavones act as antioxidants protecting against LDL cholesterol oxidation, and they also reduce the formation of plaques inside the artery.
· Soy and Cancer.
It is well recognised that there is a lower incidence of certain cancers, such as breast and prostate cancer, in populations consuming soy as a regular part of their diet. Other cancers with a decreased incidence in Asian studies include lung, stomach, endometrial and colorectal cancers. In one American study, consuming soy drinks, on two or more occasions per day, was linked with up to 70% reduction in prostate cancer risk in Seventh-day Adventist males.
Animal and test tube studies have shown that soy isoflavones can protect against the development of cancers. Isoflavones inhibit the action of key enzymes and growth factors required for cancer cell growth.
Other components of soy that could act as anti-carcinogens include phytic acid, trypsin inhibitors and saponins. These natural phytochemicals are also found in other plant foods such as whole grain, nuts and legumes.
· Soy and Osteoporosis.
When animal protein (acid forming food) is replaced with soy protein (vegetable protein is less acid forming), less calcium is lost from the body. Calcium loss can lead to negative calcium balance, which is associated with osteoporosis and increased risk of hip fractures.
· Soy and Diabetes.
Studies in Chinese women found that, among post-menopausal women, a regular intake of tofu and other soy products was strongly protective against type 2 diabetes. This is supported by a 20-year follow-up in the Seven Countries Study, which showed that a high intake of legumes protects against type 2 diabetes.
· Soy and Menopausal Symptoms.
There is some evidence that the phytochemicals in soy may have a beneficial effect on menopausal symptoms.
Soy - Fermented or Precipitated?
Whether soy is good or bad for you revolves around the techniques used to produce the soy products:
· Fermentation, eg tempeh and miso
· Precipitation, eg tofu and bean curd
Soybeans come to us from the Orient. During the Chou Dynasty (1134-246BC) the soybean was designated as one of the five sacred grains, along with barley, wheat, millet and rice. The soy plant was not originally used as food, but was used in crop rotation as a method of fixing nitrogen.
Soybean became a food after the discovery of fermentation techniques, sometime during the Chou Dynasty. Thus the first soy foods were fermented products like tempeh, natto, miso and shogu (soy or tamari sauce).
At a later date, possibly in the 2nd century BC, Chinese scientists discovered that a puree of cooked soybeans could be precipitated with calcium sulphate or magnesium sulphate to make a smooth pale curd - tofu or bean curd.
It is the bland precipitated products that are most frequently used, accounting for approximately 90% of the processed soybeans consumed in Asia today.
Why Soy is Not Good
· Enzyme Inhibitors
Soy contains potent enzyme inhibitors which block the action of trypsin and other enzymes needed for protein digestion. These are not completely deactivated during ordinary cooking and can produce serious gastric distress, reduced protein digestion and chronic deficiencies in amino acid uptake.
The soybean also contains haemagglutinin, a clot promoting substance that causes red cells to clump together.
Trypsin inhibitors and haemagglutinin are deactivated during the process of fermentation.
However in precipitated products, enzyme inhibitors concentrate in the soaking liquid rather than the curd. Thus in tofu and bean curd, these enzyme inhibitors are reduced in quantity, but not completely eliminated.
· Phytic Acid or Phytates
Soybeans are high in phytic acid (or phytates). This is an organic acid, present in the bran or hulls of all seeds. It blocks the uptake of essential minerals, in particular calcium, magnesium, iron and especially zinc, in the intestinal tract. The soybean has a higher phytate content than any other grain or legume. It is highly resistant to phytate reducing techniques such as long, slow cooking. Only a long period of fermentation will significantly reduce the phytate content of soybeans.
Thus fermented products such as tempeh and miso provide nourishment that is easily assimilated.
The nutritional value of tofu and bean curd, both high in phytates, is questionable.
When precipitated soy products are consumed with meat, the mineral blocking effects of the phytates are reduced. The Japanese traditionally eat tofu as part of a mineral-rich fish broth.
Vegetarians who consume tofu and bean curd as a substitute for meat and dairy products risk severe mineral (calcium, magnesium, iron and zinc) deficiencies.
Nitrosamines, which are potent carcinogens, are often found in soy protein foods, and are greatly increased during the high temperature drying process.
Soy Protein Isolate
Most soy products that imitate traditional food items (as listed above) are made with soy protein isolate (by precipitation techniques). This is the soy protein isolated from the carbohydrate and fatty acid components that naturally occur in the beans.
Soybeans are firstly ground and subjected to a high-temperature and solvent extraction process to remove the oils. The resultant defatted meal is then mixed with an alkaline solution and sugars in a separation process to remove fibre. Then it is precipitated and separated using an acid wash. Finally the resultant curds are neutralised in an alkaline solution and spray dried at high temperatures to produce protein powder.
Some trypsin inhibitors remain, even after such extreme refining.
Textured Vegetable Protein
High-temperature, high pressure extrusion processing of soy protein isolate produces textured vegetable protein (TVP).
Numerous artificial flavourings, particularly monosodium glutamate (MSG – 621, an additive that has adverse effects in many people), are added to TVP products to mask their strong ‘beany’ taste, and impart the flavour of meat.
The production of soy milk is relatively simple. The beans are first soaked in an alkaline solution to remove as much of the trypsin inhibitor content as possible. The pureed solution is then heated to about 115 degrees Centigrade in a pressure cooker. This method destroys most (but not all) of the enzyme inhibitors, but also denatures the proteins so that they become difficult to digest and much reduced in effectiveness. The phytate content remains in soy milk to block the uptake of essential minerals. The alkaline soaking also reduces the cystine content, which is already low in soybeans.
Fermented soy products, such as tempeh and miso, are recommended.
Precipitated soy products, such as tofu, bean curd, soy protein isolate products such as TVP, and soy milk should be avoided.
*Copyright 2009: The Huntly Centre.
Disclaimer: All material in the Huntlycentre.com.au website is provided for informational or educational purposes only. Consult a health professional regarding the applicability of any opinions or recommendations expressed herein, with respect to your symptoms or medical condition.
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