Recommended Blood Tests for Vegans

People on vegan and plant-based diets often ask me 'how often do I need to get blood tests?' and 'what do I need to test for?'

These are valid questions, and are actually quite difficult to answer in general terms, as your nutrient needs and status depends on a number of factors, such as your gender, your medical history, your stage of life (whether you're planning a pregnancy, for example), or whether you're on any medications. 

One thing I can't recommend highly enough is forming a relationship with a good GP who knows you and your medical history, as they will be the one who orders and interprets your blood tests.

To begin with, there’s a lot of confusion about which nutrients tested in the blood are actually reflective of your dietary intake and/or the body's stores. As a prime example of this, many people assume that if their calcium levels in their blood are within the range, that their dietary calcium intake is adequate. This is unfortunately untrue, as the body maintains your calcium levels between narrow limits by way of a mechanism known as homeostasis, so if your dietary calcium intake is low, your body will draw on its calcium stores (i.e. the skeleton) in order to maintain calcium levels in the blood. To some extent, other nutrients are subject to this same regulation, including the minerals zinc and magnesium.

So, how often should you have a blood test? 
If you’re otherwise fit and healthy, I wouldn’t recommend having a blood test any more frequently than once per year.  If you’ve been diagnosed with a condition such as vitamin B12 deficiency or iron deficiency anaemia, your GP will recommend testing more regularly to ensure that the treatment is working. 
 
What to test for:


1. Full blood examination/count  
This provides detailed information about your red and white blood cells, and is usually done with all blood tests. It can be used to detect things such as an anaemia caused by iron and vitamin B12 deficiency.

2. Vitamin B12
As this vitamin is only found in animal products (including meat, dairy and fish), it’s absolutely essential that anyone on a plant-based diet ensure they are taking supplemental vitamin B12 on a regular basis (which you can read more about here).

Your GP will order 'total vitamin B12’, and if this test result is low or borderline low (<260pmol/L), the pathologist will also perform an ‘active vitamin B12’ (holotranscobalamin) test, which measures how much of the biologically active form of the vitamin you have in your blood.

Serum methylmalonic acid (MMA) and homocysteine (HC) are metabolites which can also be used to assess vitamin B12 status, but these are not covered by Medicare bulk-billing, so you'll need to pay out of pocket if you'd like these tests conducted.

3. Iron studies
Firstly, there is no greater risk of iron deficiency if you’re vegan or vegetarian (in fact, most people on plant-based diets actually get more dietary iron), though people on plant-based diets usually have lower ferritin levels, which is a marker of how much iron is stored in the body. 

As low iron is a relatively common problem for women of childbearing age, it's definitely worth keeping an eye on your levels, particularly if you have heavy periods, are a long distance runner, or are feeling tired and depressed. 

If you're interested in reading more about iron and plant-based diets, have a read of this post I published earlier in the year on my blog, or this article published in the Medical Journal of Australia in 2012.

4. Vitamin D
Medicare have recently clamped down on 'unnecessary' vitamin D testing (as it was costing them tens of millions of dollars every year), so under new guidelines, only individuals 'at risk' of vitamin D deficiency are eligible for a bulk-billed blood test, which includes people with Coeliac Disease, Inflammatory Bowel Disease, or a 'chronic lack of sun exposure’ (which just sounds like ‘living in Melbourne’ to me, ha ha).

Vitamin D testing is at the discretion of the GP, so ask them if they think it’s medically necessary for you to have your level tested.

As I (and the majority of my clients) live in Melbourne, I routinely recommend vitamin D supplements through the cooler months (May-September) anyway, so for some people it makes more sense to just start on a supplement rather than go out and have their levels tested. However, if your levels are very low, you will need a much higher dose of vitamin D than I recommend for the general population to correct the deficiency, so please have a chat with your GP to see what they recommend for you. 

In summary: your GP is the best person to determine whether you need additional tests depending on your health status. For example, if you've been feeling tired and gaining weight, your GP may want to test your thyroid function, as an underactive thyroid gland could be causing those symptoms. Your GP may also want to test your cholesterol levels (depending on your age, and family history of heart disease) or your glucose tolerance if you are at risk of type 2 diabetes. 

One final thing: as a dietitian I can’t order blood tests to be bulk-billed through Medicare, so please ask your GP to fill out a pathology request form for you, which you will then present to the pathology collector. 

Is soy bad for you?

Ah, soy. Such a divisive little bean! 

Many clients I see in my clinical practice deliberately avoid soy, with the most common reasons for doing so being:

‘I have heard soy causes breast cancer’

'Soy contains anti-nutrients'

‘I have a thyroid condition and heard soy is bad for the thyroid’

‘Soy is all genetically-modified’

In order to thoroughly dispel all these myths, I’ve waded through the scientific literature on the subject and will address each of these concerns in turn. 

Firstly, soy products include foods made from soybeans, such as soy milk, tempeh, tofu, edamame, soy yoghurt, texture vegetable protein (TVP), isolated soy protein powders (available as protein supplements or in processed foods such as vegetarian sausages), miso paste, soy sauce and tamari.

Does soy contain anti-nutrients?

Anti-nutrients are defined as dietary components that can reduce or inhibit the utilisation of specific nutrients in food. They are naturally-occurring in almost all plant foods, as a defense mechanism against predators. The anti-nutrients in soy including protease (enzyme) inhibitors, saponins, phytates and lectins are increasingly being considered as having numerous health benefits (1), including being protective against cancer (2)

Saponins

Saponins are a broad range of compounds found in a number of plant foods, including soybeans. The name is derived from their ability to form a soap-like foam in liquids (if you’ve ever rinsed quinoa you’ll now know what the foam is!). As some of the saponins have been shown to be highly-toxic, the entire class of compounds known as saponins have all been ‘mistakenly labeled' as toxic (3).

Lucky for soybeans, the saponins found in soybeans have no reported adverse effects in humans, and have are being extensively researched for their antioxidant properties, cholesterol-lowering effect, attenuating (blunting) the blood glucose response to a meal and anti-cancer potential (3).

Phytate

Phytic acid (and its salt, phytate) is a storage form of phosphorous and minerals for the growing grain or seed kernel. Phytate is found in cereals, legumes, oilseeds (including soybeans) and nuts, and can bind to and inhibit the absorption of certain minerals including zinc and iron.  However, it is only thought that this inhibitory effect can lead to mineral deficiencies under ‘non-varied and non-balanced dietary conditions’ (4).

Furthermore, the inhibitory effect of phytate on iron and zinc absorption can be reduced by adding a good source of vitamin C to your meal (such as tomatoes or red capsicum), and adding a good source of beta-carotene to your meal (such as carrot, pumpkin, sweet potato or kale) (4).

Schlemmer et al recently reviewed the available scientific evidence on dietary phytates and human health and found evidence for a blood glucose lowering effect, antioxidant capacity and anticancer activity, and in light of these findings, noted that terms for phytate such as ‘antinutrient’ should ‘belong to the past’ (4). Another author (Shamsuddin, 2002) went so far as to propose that phytic acid should be considered an ‘essential nutrient (perhaps a vitamin)’ (5).

In summary, in well-balanced diets, the inhibitory effect is relatively low and phytate is increasingly being considered a beneficial component of food.

Enzyme inhibitors

Many foods contain enzyme inhibitors, including chicken eggs, potatoes and soybeans. The enzyme inhibitors in question in soy are trypsin inhibitors, which block the action of human the digestive enzymes responsible for breaking down proteins into smaller peptides and amino acids (such as trypsin and chymotrypsin). However, as the majority of these enzyme inhibitors are inactivated by soaking soybeans overnight and heat-treating the soybeans (as per the production of soy milk or tofu), or by fermentation (as per tempeh or miso production). As we don’t eat soybeans raw, they are of no significance to human health .

Lectins

Lectins (also known as haemagglutinins) are widely-distributed in the plant foods, including soybeans (known as soybean agglutinin or SBA). These proteins have been extensively studied since early experiments showed that lab animals (mainly rats) experienced growth problems when fed raw soybeans (6). Further animal studies have shown that lectins from raw soybean withstand digestion in the gastrointestinal tract and can bind to the intestinal epithelium (the cells lining the gastrointestinal tract) and cause a number of adverse effects including increased intestinal permeability (‘leaky gut’) (6). However, studies in animals using raw soy products are of little relevance to human health as the lectins in soy are easily deactivated by 'wet' heat, and hence pose no threat to human health (6)(7).

Does soy contain estrogens?

Soy is rich in a class of phytonutrients known as isoflavones, which are classed as phytoestrogens (‘phyto’ meaning plant-derived). Other plant foods also contain isoflavones, including flaxseeds and whole grains. The isoflavones in soy are structurally similar to human estrogen (a reproductive hormone), but this doesn’t mean that soy products contain estrogen. Isoflavones can bind to estrogen receptors in the body, but they generally exert a much weaker effect than human estrogen, and can have pro- or anti-estrogenic effects in the body. 

There are also two types of estrogen receptors (ER), named ER-alpha and ER-beta, which are found in different locations in the body. Isoflavones have been shown to be ‘selective’ in their binding to these receptors, choosing to bind to ER-beta over ER-alpha, and hence are known as selective estrogen receptor modulators (SERMs). This helps to explain how they can both enhance and block the action of estrogen, depending on the tissue type. They can also reduce levels of circulating estrogen by increasing the level of sex hormone binding globulin (SHBG), which binds and inactivates estrogen.

Soy & Breast Cancer

Many people believe that the phytoestrogens in soy products may increase the risk of breast cancer, however, the majority of the evidence suggests that soy consumption is either neutral or protective against breast cancer. A review in 2010 in the Journal of Nutrition found that women who consumed moderate amounts of soy (1-2 servings per day) throughout their life have lower risk of developing breast cancer risk than women who do not consume soy; however, this protective effect may originate from soy intake early in life (in childhood and adolescence). The authors also concluded that soy consumption does not increase the risk of breast cancer recurrence in women who have previously survived breast cancer (8).

Soy & Men’s Health

Soy products may help to prevent prostate cancer in men. A recent meta-analysis (which pools a number of studies) found that men with the highest intake of soy had a statistically-significant reduction in prostate cancer risk, compared to the men who consumed the least soy (9).

A recent review on the topic found that neither isoflavone supplements nor soy products affected total or free testosterone levels, and there was no evidence to suggest that isoflavone exposure affects estrogen levels (10).

There are a handful of published case reports of men suffering from adverse hormonal effects relating to excessive soy consumption, but these men were all consuming very large quantities of soy (in excess of 12 servings per day). The main effects reported were growth of breast tissue (gynecomastia) and reduced libido.

How much is safe to have each day?

 The use of soy protein for lowering LDL cholesterol levels has been extensively studied, which has resulted in the recommendation to have 25g of soy protein each day (the equivalent of 2-3 servings). This represents a minimum level of intake to reap the cholesterol-lowering benefits, and could be used as a conservative upper limit of intake if you are still concerned soy.

Dr. Michael Greger (of NutritionFacts.org) recommends an intake of 3-5 servings per day to maximise the health benefits and minimse any risk of harm from excessive consumption (13).

1 serve is equal to:

-100g firm tofu

-50g tempeh

-½ cup (120g) shelled edamame

-1 cup soy milk

My Tips for Healthy Soy Consumption

  1. When choosing a soy milk, read the label to make sure it’s made from ‘whole soybean’ rather than from ‘soy protein’ or ‘soy protein isolate’
  2. Choose non-GM (genetically-modified) soy if that it is important to you
  3. Avoid isolated soy protein (also known as soy protein isolate) in protein powders and bars, mock meats and textured vegetable protein (TVP)

References:

1.         Singh J. Non-Nutritive Bioactive Compounds in Pulses and Their Impact on Human Health: An Overview. Food Nutr Sci. 2012;03(12):1664–72.

2.         Mathers JC. Pulses and carcinogenesis: potential for the prevention of colon, breast and other cancers. Br J Nutr. 2002 Dec;88(S3):273.

3.         Shi J, Arunasalam K, Yeung D, Kakuda Y, Mittal G, Jiang Y. Saponins from edible legumes: chemistry, processing, and health benefits. J Med Food. 2004;7(1):67–78.

4.         Schlemmer U, Frølich W, Prieto RM, Grases F. Phytate in foods and significance for humans: Food sources, intake, processing, bioavailability, protective role and analysis. Mol Nutr Food Res. 2009 Sep;53(S2):S330–75.

5.         Shamsuddin AM. Anti-cancer function of phytic acid. Int J Food Sci Technol. 2002 Oct 1;37(7):769–82.

6.         Liener IE. Implications of antinutritional components in soybean foods. Crit Rev Food Sci Nutr. 1994 Jan;34(1):31–67.

7.         Ma Y, Wang T. Deactivation of Soybean Agglutinin by Enzymatic and Other Physical Treatments. J Agric Food Chem. 2010 Nov 10;58(21):11413–9.

8.         Hilakivi-Clarke L, Andrade JE, Helferich W. Is Soy Consumption Good or Bad for the Breast?123. J Nutr. 2010 Dec;140(12):2326S – 2334S.

9.         Yan L, Spitznagel EL. Soy consumption and prostate cancer risk in men: a revisit of a meta-analysis. Am J Clin Nutr. 2009 Apr 1;89(4):1155–63.

10.       Messina M. Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence. Fertil Steril. 2010 May;93(7):2095–104.

11.       Schaafsma G. The protein digestibility–corrected amino acid score. J Nutr. 2000;130(7):1865S – 1867S.

12.       Sathyapalan T, Manuchehri AM, Thatcher NJ, Rigby AS, Chapman T, Kilpatrick ES, et al. The Effect of Soy Phytoestrogen Supplementation on Thyroid Status and Cardiovascular Risk Markers in Patients with Subclinical Hypothyroidism: A Randomized, Double-Blind, Crossover Study. J Clin Endocrinol Metab. 2011 Feb 16;96(5):1442–9.

13.       Michael Greger. How much soy is too much? [Internet]. NutritionFacts.org. [cited 2014 Nov 12]. Available from: www.nutritionfacts.org/2013/02/19/how-much-soy-is-too-much/