Nora Gedgaudas

No beans about it!

No beans about it!

At their most benign, legumes might just be the most socially awkward food produced by the agricultural revolution.  In the wild, legumes contain some of the highest levels of toxic compounds of any plants.  In fact, they would never have been consumed in any meaningful way by our ancestors. Certainly no evidence of their consumption by us exists via stable isotopic analysis of human fossilized remains throughout innumerable periods of human history studied.

At their most benign, legumes might just be the most socially awkward food produced by the agricultural revolution.  In the wild, legumes contain some of the highest levels of toxic […]

Anyone having taken a wild edible plant class knows that you don’t touch these with a 10-foot pole under any circumstances (raw OR cooked).  I find it interesting that humans ever would have thought to cultivate these otherwise toxic plant foods as something to eat.  All I have to say is that someone must have been desperate.

We likely observed wild ruminants occasionally foraging upon them at certain times of the year and (being both hungry and enterprising) made the assumption there must be a way of making them work for us.  After a few millennia now of hybridization efforts we have created something widely perceived as benevolent and promoted as healthy.  But are they really?

All of our efforts at plant hybridization have certainly created something quite a bit more edible– but by no means entirely benign.  Numerous toxic compounds continue to remain in modern-day cultivated varieties of legumes and may represent a significant dietary compromised human health when consumed in significant amounts.[1] [2]  Soy is another particularly problematic example of a legume known to generate a wide variety of health-related compromises, even in the rare absence of industrial genetic modification (GMO’s).[3]  –See my more extensive article regarding the pitfalls of soy foods elsewhere on this website (deserving an article all on its own).

Vegetarians and dietitians alike enjoy lauding the presence of minerals such as zinc, calcium, magnesium and iron in legumes. Unfortunately, the truth is that these minerals, although certainly potentially present to varying degrees (depending on the health of the soil they were grown in) are by-in-large quite poorly bio-available due to the presence of compounds such as phytates, saponins, tannins and fiber.  Not only this, but these very substances have the potential to actually deplete your own mineral stores if you eat enough of them![4] [5] [6] [7]

Legumes are in fact especially rich in phytates (also known as phytic acid).  This substance effectively binds minerals in a way that makes them extremely difficult to absorb. Distinct deficiencies, in particular can become particularly pronounced in those eating a diet high in whole grains and legumes— with soy by far having the most phytic acid content.  Despite what might look like a decent amount of iron and zinc in beans on paper, for instance, these plant-based minerals may only be 25% bio-available, at best.[8] [9] [10] This can become particularly problematic in vulnerable populations such as the elderly and nutritionally-compromised individuals in Third World nations.[11] [12]

Legumes are also known to contain significant amounts of thyroid-compromising substances known as goitrogens.  In fact, these substances are high enough in soy to generate concern for not only women’s hormonal health[13], but also for developing fetuses during pregnancy—associated with a potentially greater risk of autism (and other adverse issues).[14]  One research study looking at the effects of soy (a legume) consumption in elderly individuals found that just 30 grams of soy a day for only 3 months induced symptoms of depressed thyroid function.  Half of these persons actually developed goiters![15]

Yet another “nasty” found in legumes known as saponins can damage your gut and even your blood cells when exposed to them.  Saponns additionally bind dietary minerals and interfere with protein digestion.

All legumes such as beans, peas, lentils, peanuts and soybeans contain large amounts of other potentially health compromising substances that include concentrated levels of foreign lectins (inflammatory, immune and hormone dysregulating compounds that can also damage your gut—and even your brain).[16] [17] [18] [19] [20] [21] [22] [23] [24] [25]  Although lectins are also present in many foods other than legumes and grains, the ones present in these particular plant foods tend to present uniquely problematic effects for us.  Lectins are basically responsible for protecting plants from foraging predators.   Plants– the absence of teeth, claws or legs with which to discourage or escape predation developed lectins as a potent, toxic defense against the animals (including us) that want to eat them.[26]  One particularly nasty lectin, called phytohemagglutinin, or PHA, is found in all varieties of beans (including black beans, kidney beans, pinto beans, navy beans, etc.) within the Phaseolus vulgaris species.  It is an extremely toxic lectin with damaging cumulative effects.[27] [28] [29]   In short, the more PHA you eat the less healthy you become.  Cooking can help lessen the concentrations of PHA and other anti-nutrients in some legumes but that doesn’t eliminate all of it.  The richest natural source of PHA?  — Soy protein isolate (for all you athletes out there consuming protein powders and all you vegetarians eating so-called “meat substitutes” made from this).  NOT good.

What about beans as a supposedly “healthy” source of plant-based protein?

Much ado is made of the protein value of beans/legumes as some manner of viable alternative to animal protein by government agencies and fans of vegetarian diets. They try to make the nutrient content of legumes look good on paper–but the reality of what happens when we actually consume them is something completely different.

Legumes contain small amounts of poorly utilized, incomplete protein that is without doubt nutritionally inferior to naturally complete and otherwise highly bioavailable, nutrient dense animal source protein.  Legumes are nearly devoid in critical amino acids, methionine and cysteine, which are essential for our health and normal internal protein synthesis.  Also, despite the smattering of amino acids in these foods, legumes tend to be more comprised of starch than anything else (up to 60%).  So trying to compensate for relative deficits of key amino acids in both beans and rice by combining them results in a pretty big bolus of starch, without a whole lot of usable protein.  Note the fact that “complete” by no means suggests “sufficient”, much less bioavailable.  Starchy foods tend to be quite poor in their elicitation of gastric hydrochloric acid— not only essential for the digestion of protein but also for the ionization and assimilation of minerals.  And since zinc is needed also for the very manufacture of hydrochloric acid and zinc tends to be depleted by legume consumption, this is an issue that only tends to be compounded with time. The presence of pancreatic protease inhibitors in legumes (and grains) complicate the digestion and bio-availability of their proteins even further, having the potential to even affect the health of the pancreas over time.[30] [31] [32] [33]

There is not a single nutrient present in legumes (or grains, for that matter) that cannot be found abundantly elsewhere in a quality, Paleo-oriented grain, legume-free diet; and with far fewer potential consequences.  There is literally nothing present in legumes that is “essential” to anyone, but there is quite a bit in them that can cause you some real problem.

[1] Gupta YP (1987) “Antinutritional and toxic factors in food legumes: a review.” Plant Foods for Human Nutrition, vol. 37, pp. 201-228.

[2] Pusztai A et al. (1981) “The toxicity of Phaseolus vulgaris lectins: Nitrogen balance and immunochemical studies.” J Sci Food Agric, vol. 32, pp. 1037-1046

[3] Liener IE (1994) “Implications of antinutritional components in soybean foods.” Crit Rev Food Sci Nutr., vol. 34, pp. 31-67

[4] Hallberg L, Hulthén L. Prediction of dietary iron absorption: an algorithm for calculating absorption and bioavailability of dietary iron. Am J Clin Nutr. 2000 May;71(5):1147-60

[5] Gibson RS, Bailey KB, Gibbs M, Ferguson EL. A review of phytate, iron, zinc, and calcium concentrations in plant-based complementary foods used in low-income countries and implications for bioavailability. Food Nutr Bull. 2010 Jun;31(2 Suppl):S134-46

[6] Couzy F, Mansourian R, Labate A, Guinchard S, Montagne DH, Dirren H. “Effect of dietary phytic acid on zinc absorption in the healthy elderly, as assessed by serum concentration curve tests.” Br J Nutr. 1998 Aug;80(2):177-82

[7] Sandberg AS. Bioavailability of minerals in legumes. Br J Nutr. 2002 Dec; 88 Suppl 3:S281-5

[8] Hallberg L, Hulthén L. “Prediction of dietary iron absorption: an algorithm for calculating absorption and bioavailability of dietary iron.” Am J Clin Nutr. 2000 May;71(5):1147-60.

[9] Hurrell RF, Juillerat MA, Reddy MB, Lynch SR, Dassenko SA, Cook JD. “Soy protein, phytate, and iron absorption in humans.” Am J Clin Nutr. 1992 Sep;56(3):573-8.

[10] Sandberg AS. “Bioavailability of minerals in legumes.” Br J Nutr. 2002 Dec;88 Suppl 3:S281-5

[11] Couzy F, Mansourian R, Labate A, Guinchard S, Montagne DH, Dirren H. “Effect of dietary phytic acid on zinc absorption in the healthy elderly, as assessed by serum concentration curve tests.” Br J Nutr. 1998 Aug;80(2):177-82.

[12] Gibson RS, Bailey KB, Gibbs M, Ferguson EL. “A review of phytate, iron, zinc, and calcium concentrations in plant-based complementary foods used in low-income countries and implications for bioavailability.” Food Nutr Bull. 2010 Jun;31(2 Suppl):S134-46

[13] Pirke KM, Schweiger U, Laessle R, Dickhaut B, Schweiger M, Waechtler M. “Dieting influences the menstrual cycle: vegetarian versus nonvegetarian diet.” Fertil Steril. 1986 Dec;46(6):1083-80

[14] Román GC. “Autism: transient in utero hypothyroxinemia related to maternal flavonoid ingestion during pregnancy and to other environmental antithyroid agents.” J Neurol Sci. 2007 Nov 15;262(1-2):15-26

[15] Ishizuki Y, Hirooka Y, Murata Y, Togashi K.  “The effects on the thyroid gland of soybeans administered experimentally in healthy subjects.” Nippon Naibunpi Gakkai Zasshi. 1991 May 20;67(5):622-9.

[16] Pusztai A, Greer F & Grant G. “Specific uptake of dietary lectins into the systemic circulation of rats.” Biochemical Society Transcations. 1989;17, 527-528

[17] Pusztai A, Ewen  SWB, Grant G, Peumans WJ, Van Damme EJM, Rubio LA, Bardocz S. “Plant (food) lectins as signal molecules: Effects on the morphology and bacterial ecology of the small intestine.”  In Lectin Reviews, Volume I , pp. 1-15 [D.C. Kilpatrick, E. Van Driessche, T.C. Bog-Hansen, editors].  St. Louis: Sigma, 1991

[18] Greer F,  Pusztai A. (1985).  Toxicity of kidney bean (Phaseolus vulgaris) in rats: changes in intestinal permeability. Digestion. 1985 32: 42-46

[19] Pusztai A, Greer F & Grant G. Specific uptake of dietary lectins into the systemic circulation of rats. Biochemical Society Transcations. 1989;17, 527-528

[20] Pusztai A, Ewen SW, Grant G, Brown DS, Stewart JC, Peumans WJ, Van Damme EJ, Bardocz S. “Antinutritive effects of wheat-germ agglutinin and other N-acetylglucosamine-specific lectins.” Br J Nutr. 1993 Jul;70(1):313-21

[21] Pusztai A, Ewen  SWB, Grant G, Peumans WJ, Van Damme EJM, Rubio LA, Bardocz S. “Plant (food) lectins as signal molecules: Effects on the morphology and bacterial ecology of the small intestine.”  In Lectin Reviews, Volume I , pp. 1-15 [D.C. Kilpatrick, E. Van Driessche, T.C. Bog-Hansen, editors].  St. Louis: Sigma, 1991

[22] Wang Q, Yu LG, Campbell BJ, Milton JD, Rhodes JM. “Identification of intact peanut lectin in peripheral venous blood.” Lancet. 1998;352:1831-2

[23] Caron, M. & Steve, A.P. Lectins and Pathology, Taylor & Francis, 2000, London.

[24] Gupta YP. “Anti-nutritional and toxic factors in food legumes: a review.” Plant Foods Hum Nutr 1987;37:201-228.

[25] Liener IE.  “Nutritional significance of lectins in the diet.”  In The Lectins: Properties, Functions, and Applications in Biology and Medicine, pp. 527-52 [I.E. Liener, N. Sharon, I.J. Goldstein, editors]. Orlando; Academic Press, 1986

[26] Chrispeels, M.J. & Raikel, N.V. “Lectins, lectin genes, and their role in plant defense.” Plant Cell 1991. Vol 3, 1-9.

[27] oufassa C, Lafont J, Rouanet J M, Besancon P. “Thermal inactivation of lectins (PHA)isolated from Phaseolus vulgaris.” Food Chem 1986. 20 295-304

[28] Grant G, More LJ, McKenzie NH, Pusztai A. “The effect of heating on the haemagglutinating activity and nutritional properties of bean (Phaseolus vulgaris) seeds.” J Sci Food Agric 1982;33: 1324-1326

[29] Pusztai A, Grant G.  “Assessment of lectin inactivation by heat and digestion.” In: Methods in Molecular Medicine: Vol. 9: Lectin methods and protocols.  J M Rhodes, JM, J D Milton JD (Eds). Humana Press Inc. Totowa, NJ, 1998.

[30] Gilani GS, Cockell KA, Sepehr E. “Effects of antinutritional factors on protein digestibility and amino acid availability in foods.” J AOAC Int. 2005 May-Jun;88(3):967-87.

[31] Grant G. “Anti-nutritional effects of soyabean: a review.” Prog Food Nutr Sci. 1989;13(3-4):317-48

[32] Liener IE (1994) “Implications of antinutritional components in soybean foods.” Crit Rev Food Sci Nutr., vol. 34, pp. 31-67

[33] Losso JN. “The biochemical and functional food properties of the bowman-birk inhibitor.” Crit Rev Food Sci Nutr. 2008 Jan;48(1):94-118

By Nora Gedgaudas

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