I am no fan of processed foods generally. And many processed foods, I think, masquerade as something quite healthy on the basis of being low or absent in something supposedly unhealthy. Not so long ago, I highlighted the not so nutritional aspects of the mold-organism-taken from-soil-and-fermented-with-sugar-based product that is Quorn.
This food, in a dizzying array of incarnations, portrays itself as a healthy alternative to meat. And some store is made of the fact that, compared to meat, it is lower in supposedly toxic substances such as saturated fat and cholesterol. However, seeing as the evidence suggests these fats are quite benign, then the assumed healthiness of Quorn products looks, in my view, very suspect indeed.
Today, I see, that meat-substitute foods have had a bit of a kicking in the press. See this article in the Daily Mail (UK) as an example. An organisation called Consensus Action on Salt and Health has revealed that many veggie-sausages and burgers are stacked with salt.
This body is keen, it seems, to be aware that just because a food is meat-free, that doesn’t mean it’s automatically healthy. I couldn’t agree more. Firstly, the evidence does not support the notion that meat and its fatty constituents are the killer foods some would have us believe them to be. Also, even if they were, the mere absence of them does not make a highly processed, salty food based on quite unnatural ingredients a ‘healthy’ alternative.
In addition to Quorn, the other major base product used in meat substitute foods is soy. It’s a food that has managed to get itself quite a wholesome, healthy reputation. One angle here, has been for its manufacturers to draw our attention to its ability to reduce cholesterol levels. I don’t know if that’s true or not, and I don’t very much care anyway seeing as taking dietary steps to reduce cholesterol has not been shown to have broad benefits for health.
So, the health claim regarding cholesterol seems to lack substance, But is there anything else about soy that might be positively detrimental to health? Well, for a start, soybeans are also rich in a substance known as phytic acid ” a compound which impairs the absorption of a range of minerals including calcium, magnesium, iron and zinc. Phytic acid is also found in grains, but soybeans seem to be especially rich in this anti-nutrient [1]. Unfortunately, cooking does not seem to destroy phytic acid, though levels of this compound can be reduced (though not necessarily eliminated) by fermentation to make foods such as tempeh and miso.
The food industry has contrived to contrive soya into a huge range of processed foods by converting raw soya beans into something known as soy protein isolate (SPI). Production of SPI takes place in factories where a slurry of soy beans is treated with acid and alkali solutions to get the protein to precipitate out. In this process the product can be tainted with the metal aluminium (aluminium exposure has been linked with an increased risk of degeneration of the nervous system and Alzheimer’s disease). The resultant protein-rich ‘curd’ is spray dried at high temperature to produce a powder. SPI may then be heated and extruded under pressure to make a foodstuff known as textured vegetable protein (TVP). SPI and TVP will often have monosodium glutamate (MSG) added to it to impart a ‘meaty’ flavour before it is fashioned into products such as vegetarian burgers, sausages and mince.
Versatile SPI may be, but it is actually a very heavily processed food. What are its effects on health? Certain toxins found in soy, including substances that inhibit digestion are known to remain in SPI [2]. Animal experiments that suggest that the eating of SPI can lead to a deficiency of a range of nutrients including calcium, magnesium, manganese, copper, iron and zinc [3].
Soy is also rich in hormone-like molecules known as phytoestrogens, and it their presence in soy which has led to the other common claim made for soy: that it can help protect against breast cancer. However, the evidence in this area is very mixed, and there is simply no clear evidence which supports the role of dietary phytoestrogens in the prevention of breast cancer [4].
Also, it is possible that plant compounds that mimic oestrogen may actually have an adverse effect on health. It is known, for instance, that high levels of oestrogen have been associated with an increased rate of mental decline associated with ageing. It is interesting, then, that one study has found a significant statistical relationship between the eating of tofu and accelerated brain ageing [5].
One of the phytoestrogens in soy has been shown to have the potential to poison the thyroid gland. Feeding rats the soy phytoestrogen known as genistein has been found to cause irreversible damage to enzymes that make thyroid hormones in the body [6]. In humans, this effect could conceivably lead to low thyroid function (hypothyroidism), which can cause symptoms which include weight gain, fatigue, depression and constipation.
With all this in mind, does soy really deserve healthy reputation some would have us believe it deserves? I don’t think so.
During the weekend I delivered a lecture in Berlin. One of the questions I got asked after the lecture was about the nutritional attributes (or otherwise) of soy. Sometimes, when asked about a specific food I deliver what might be seen as a verdict first, and then qualify and justify it with some science. I went for this approach at the weekend. My response to the question about soy started: It’s a shite food, really�. Sometimes, it’s best just to say it how you see it.
References:
1. El Tiney AH. Proximate Composition and Mineral and Phytate Contents of Legumes Grown in Sudan Journal of Food Composition and Analysis, 1989;2:67-68
2. Rackis JJ, et al. The USDA trypsin inhibitor study. I. Background, objectives and procedural details,” Qualification of Plant Foods in Human Nutrition, 1985;35
3. Rackis JJ. Biological and physiological Factors in Soybeans,” Journal of the American Oil Chemists’ Society, January 1974, 51:161-170
4. Gikas PD , et al. Phytoestrogens and the risk of breast cancer: a review of the literature. Int J Fertil Womens Med 2005 50(6):250-8
5. White L. Association of High Midlife Tofu Consumption with Accelerated Brain Aging. Plenary Session 8: Cognitive Function, The Third International Soy Symposium, Program, November 1999, page 26
6. Doerge DR. Inactivation of Thyroid Peroxidase by Genistein and Daidzein in Vitro and in Vivo; Mechanism for Anti-Thyroid Activity of Soy presented at the 1999 Soy Symposium in Washington, DC National Center for Toxicological Research, Jefferson
