Soybean product may be of benefit in preventing Alzheimer’s disease

Scientists in Taiwan have published a paper in the February 2009 edition of the Journal of Agricultural and Food Chemistry indicating that an enzyme, nattokinase, which is found in a fermented soybean product called natto, has powerful ability in lab experiments to prevent formation of the clumps of tangled protein (amyloid fibrils) observed in Alzheimer’s disease.

More than 20 unrelated proteins can form amyloid fibrils in the body, which are related to various diseases, such as Alzheimer’s disease, prion disease, and systematic amyloidosis.  Enhancing amyloid clearance is one of the targets of the therapy of these amyloid-related diseases. Although there is debate on whether the toxicity is due to amyloids or their precursors, research on the degradation of amyloids may shed light on the prevention or alleviation of these diseases.

In this Taiwanese study, nattokinase degraded several kinds of amyloid fibrils suggesting its possible use in the treatment of amyloid-related diseases.

natto

Natto is a traditional Japanese food made from fermented soybeans and is a popular breakfast dish.  For some, natto is an acquired taste due to its powerful smell, strong flavour and sticky consistency.

Natto is made from soybeans, typically a special type called natto soybeans.  Smaller beans are preferred as the fermentation can progress to the centre of the bean more easily.  The beans are washed and soaked in water for 12 to 20 hours, which causes the beans to swell.  Next, the soybeans are steamed for 6 hours, although a pressure cooker can be used to reduce the time.  The beans are then mixed with the bacterium Bacillus subtilis natto, known as natto-kin in Japanese.  From this point on, care has to be taken to keep the ingredients away from impurities and other bacteria.  The mixture is fermented at 40°C for up to 24 hours.  Afterwards the natto is cooled, then aged in a refrigerator for up to one week to add stringiness.  During the ageing process at a temperature of about 0°C, the bacteria develop spores, and enzymes break down the soybean protein into its constituent amino acids.  For this reason, the high protein content of the soybean is in a very digestible form. 

In addition to its high protein content, natto is rich in fibre, vitamin C, vitamin K, calcium, iron, potassium, phosphorus and magnesium.  In common with other soybean products, natto contains significant quantities of the isoflavone phytonutrients including genistein and daidzein, which are believed to have cancer-protective properties.

Natto is believed to have numerous health benefits and there is some medical research to support this.  The enzyme nattokinase is a serine protease which may reduce blood clotting by direct fibrinolysis of clots and inhibition of the plasma protein plasminogen activator inhibitor 1[i].  Clinical trials are needed to confirm laboratory studies.  An extract from natto containing nattokinase is available as a dietary supplement.

Vitamin K, which is present in significant amounts in natto, is involved in the formation of calcium-binding groups in proteins, assisting the formation of bones and preventing osteoporosis.  Vitamin K1 is found naturally in seaweed, liver and some vegetables, while vitamin K2 is found in fermented food products such as cheese and miso.  Natto has very large amounts of vitamin K2, approximately 870 mg per 100 g natto.

Natto is reported to contain substantial levels of a natural product called pyrroloquinoline quinone, which has been shown to stimulate DNA synthesis in cultured human fibroblasts, modulate immune response, and reduce liver injury, cataract formation and lipid peroxidation[ii].   

 A study reported in 1996 suggested that natto may have benefits in reducing cholesterol levels in people whose cholesterol and triglyceride levels are high[iii].

In January 1997, a Japanese television programme called Revealed! Encyclopaedia of Living recommended two portions of natto per day as a means of losing weight in only two weeks.  With the Japanese struggling with overweight and obesity this hit a nerve, and by lunchtime the next day national stocks of natto had sold out.    Whilst it is the case that natto has a relatively low number of calories per g of protein and a high nutrient density, it will only contribute to weight loss if consumed as part of a healthy diet, high in whole grains, vegetables, fruits and unsaturated fats, and low in saturated fats, salt and sugar, combined with plenty of exercise.

The most popular way to eat natto is to put it in a small bowl, add a little soy sauce and some finely-chopped spring onion and/or some mustard, mix the ingredients together and serve on some steamed rice.  Natto can also be added to miso soup to create a rich and nourishing dish, which smells a little like capuccino.

Natto can be purchased in the UK from specialist suppliers of Japanese food, such as the Japan Centre  and Japanese Kitchen.

Learn how to cook with natto and other soybean products such tempeh and tofu at popular Cooking for Health classes  held throughout the year in Somerset, UK .

Jane Philpott

 

References

[i]  Fujita M et al (December 1993). “Purification and characterization of a strong fibrinolytic enzyme (nattokinase) in the vegetable cheese natto, a popular soybean fermented food in Japan”. Biochemical and Biophysical Research Communications 197 (3): 1340–1347.

[ii] Kumazawa, T.  et al. Levels of pyrroloquinoline quinone in various foods.  Biochem J. (1995) 307: 331-333

[iii] National Cardiovascular Center, Osake, Japan (April 2006). “Examining the effects of natto consumption on lifestyle-related disease prevention

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