Q & A Thursday: revisiting soy
Posted by kathryn in Myths
Next question is from Joanne:
What is your opinion of soy? I’m a fan of soy and have at least two serves a day of soy products. To me, it is a valuable source of complete protein and, in its fortified forms, of calcium and B12. However, some sources are critical of soy; among their claims is that soy contains anti-nutrients and dangerous levels of phyto-oestrogens!
Soy is one of those topics that keeps on coming up. I’ve blogged about it before, so I’m largely going to answer this question by pointing to other posts.
Briefly, I’m a big fan of soy myself and see no problem with it being part of a healthy diet . There is information about the link between soy and breast cancer here , while I’ve also looked at the question of how much soy to eat here .
The Sally Fallon article you mention has been very influential. Any internet search on soy invariably brings up links to this. The article contains some extreme opinions and quite shocking health claims against the use of soy, most of which I completely disagree with . I think it’s over-the-top, biased and makes faulty claims. The most comprehensive rebuttal I have seen is by John Robbins (thanks again to Andrew for sending this to me).
Soy has at times been promoted as a miracle cure, almost as much as it’s been criticised for being dangerous to our health. In reality it’s neither of these things, but can be eaten regularly as part of a healthy diet.
12 July, 2007
Comments
“To me, it is a valuable source of complete protein”
The claim of a “complete protein” always confuses me. I thought a food needed all 20(?) amino acids to be considered ’complete"? If that is so, do you need to have the missing amino acid from another food source in the same meal or within a certain time frame to use the protein in the body? My vegetarian friends have varying opinions on this, hence the confusion.
“Complete” proteins only need to have all of the essential amino acids.
The old thinking was that you needed to have all eight in the same meal, which lead to the “food combining” idea of eating a grain and a legume together at the same meal (because most of these are incomplete proteins but together make up complete protein).
But current thinking is that you don’t need to consume all amino acids (complete protein) at the same meal. I’m not sure what the time period would be though – a day? Several days?
I agree that the term “complete” is somewhat confusing. All foods contain all 20 amino acids, including the eight essential ones. However, we humans need amino acids in a certain ratio, to match our needs. Animal based foods more closely match our amino acid requirements, while plant based foods are all low in one or more of the essentials.
To counter-act this and ensure an adequate intake of all the essential amino acids, vegetarians need to eat a variety of protein containing foods. Different plant sources are low in different amino acids, so eating a variety ensures you are maximising the overall protein value of your meal, with an amino acid spectrum that much more closely matches your body’s needs.
Varying your protein over the course of a day is fine, it doesn’t have to all happen in one meal.
There’s more on vegetarians and protein here and here.
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