THE BLOG
01/14/2015 06:51 pm ET Updated Dec 06, 2017

Beans: Calming the Fears

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In the last installment of this blog, I showed that adding beans to your diet can improve your health in many ways, such as lowering the risk for cancers, improving blood sugar, helping your intestinal flora and slowing the aging process. Yet despite these clearly-documented benefits, many are concerned about beans. These concerns stem mostly from ideas set forth by the paleo community.

The paleo take on beans is that humans did not consume beans until our more recent history, say 8,000-10,000 years ago. The argument continues that this timeframe would not allow us to adapt to beans. They also claim that beans have phytotoxins that can damage our intestinal lining, trigger autoimmune disease and take nutrients out of our bodies. A further problem is that many people who have avoided beans now notice digestive symptoms if they add them back into their diets, even if they never had issues before. Let's look at these concerns one by one.

When Did Humans Start Eating Beans?
Domesticating beans, drying them and cooking them at a later time did likely emerge within the last 8,000-10,000 years. However, human ancestors have eaten large amounts of the types of plants that include grains and beans for at least 1.2 million years. [1]

How Fast Do Humans Adapt to New Foods?
The newest perspectives on human evolution show that measurable genetic change can happen in as little as 200 years. [2] That does not take into account the new science of epigenetics, which shows that diet can modify our genes within a single individual's lifetime. Several thousand years is definitely long enough for adaptation.

Are Beans a Unique Source of Phytotoxins?
Beans do contain many naturally-occurring chemical defenses, such as oxalates, lectins, phytates and saponins. These phytotoxins are there to protect the nutrient-dense seed of a bean plant from being easily eaten by insects or destroyed by fungi. These same phytotoxins, along with many others, are found in higher amounts in foods like kale, chia, parsley, spinach, coconuts, chocolate, almonds, carrots, coffee and broccoli.

If that is not enough, domesticated meat, as well as game meat, also contains phytotoxins based on which plants the animal ate during its lifetime. [3] Beans are not unique and are not even the highest source of phytotoxins. Ironically, the only way to be free of phytotoxins is to eat a diet based on synthetic and processed foods. I would not advise this.

Do Phytotoxins Cause Harm?
Remember the cancer-reducing benefits of beans? The phytotoxin IP6 is likely the source of these good properties. We are healthiest when our diets have a wide variety of plant foods rich in beneficial, naturally-occurring phytotoxins. [4]

Do Antinutrients Create Deficiencies?
Phytic acid is the main antinutrient in legumes, but antinutrients have been misunderstood to be much more insidious than they truly are. They do cause you to absorb less of a nutrient, but they do not take nutrients out of your body. Imagine adzuki beans have 150 mg of magnesium per serving. The antinutrients in them may cause you to absorb only 145 mg rather than the full 150. They do not take magnesium out of your body or even cause you to absorb less magnesium from other foods eaten at the same meal. In fact, a study showed that young boys, who are known to get low in zinc, did not get low in zinc even when eating a diet unusually high in zinc-blocking antinutrients. [5]

"But I Can't Digest Beans"
Our intestinal flora is adaptable, but it does take some time to respond to change. Beans are rich in a compound called stachyose, which is loved by good bacteria like lactobacilli. [6] If you do not consume beans, your good lactobacilli may get crowded out by less-beneficial bacteria. When you start feeding them, they do regrow, but at first, this can cause gas and bloating. If you have avoided beans, just add them into your diet slowly. Try 1 tablespoon daily for a few weeks. Most people can then eat them more freely.

There are many packaged, non-food items that are worth avoiding, but don't be afraid of real foods. Life gives us enough worries we can't avoid.

References:

1. Cerling TE, Manthi FK, Mbua EN, Leakey LN, Leakey MG, Leakey RE, Brown FH, Grine FE, Hart JA, Kaleme P, Roche H, Uno KT, Wood BA. Stable isotope-based diet reconstructions of Turkana Basin hominins. Proc Natl Acad Sci U S A. 2013 Jun 25;110(26):10501-6. doi: 10.1073/pnas.1222568110. Epub 2013 Jun 3. PubMed PMID: 23733966; PubMed Central PMCID: PMC 3696807.

2. Hawks, J., Wang, E. T., Cochran, G. M., Harpending, H. C., and Moyzis, R. K. (2007). Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences 104(52):20753-20758.

3. Improving the Safety of Fresh Meat edited by John N. Sofos pg. 78. CRC Press; 1 edition (August 12, 2005).

4. Urbano G(1), López-Jurado M, Aranda P, Vidal-Valverde C, Tenorio E, Porres J. The role of phytic acid in legumes: antinutrient or beneficial function? J Physiol Biochem. 2000 Sep;56(3):283-94.

5. Mesías M1, Seiquer I, Navarro MP. Is the Mediterranean diet adequate to satisfy zinc requirements during adolescence? Public Health Nutr. 2012 Aug;15(8):1429-36. doi: 10.1017/S1368980011003429. Epub 2012 Jan 5.

6. Teixeira JS, McNeill V, Gänzle MG. Levansucrase and sucrose phosphorylase contribute to raffinose, stachyose, and verbascose metabolism by lactobacilli. Food Microbiol. 2012;31(2):278-284. doi: 10.1016/j.fm.2012.03.003.