Can Dogs Eat Soy?

can dogs eat soy
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Soy is a controversial food. For many people it’s a health food and a popular plant-based source of protein that improves heart health and more. Others say it’s a hormone disruptor that increases the risk of certain cancers.

But what about soy for your dog? Can dogs eat soy? It’s in many commercial pet foods, so here’s what you need to know.

What Is Soy?

Soy comes from soybeans, a legume. The bean itself is edible, and soy is used in many other products. Soy products include tofu, tempeh, soy milk and soy sauce, vegan meat and cheese substitutes. Soy extracts like soy lecithin and emulsifiers are added to processed foods.

Why Is Soy In Dog Food?

Soybean meal in dog food is popular with pet food manufacturers as a cheap protein source that allows them to save costs on meat ingredients. It’s also used in allergy diets. And the manufacturers boast about the health benefits of nutrients like amino acids, fatty acids and antioxidants in soy … as well as its digestibility and fiber content.

But despite these potential benefits (and the fact that soy in dog food probably makes it less expensive) … there are plenty of reasons to avoid soy dog food.

Is Soy Bad For Dogs?

Here are just a few of the health concerns about soy for dogs …

Glyphosate In GMO Soybeans
The first reason to avoid soy is that most US-grown soybeans are genetically modified (GMO). The FDA says that in 2018, 94% of US soybean crops were GMO. And GMO foods come with high levels of glyphosate (Roundup), which the WHO has designated as a “probable carcinogen.” A 2014 Norwegian study found that GMO soy contained “high residues of glyposate” at a rate of 3.3mg/kg (1). In addition to the toxicity of glyphosate itself, the same study found that nutrition in GMO soybean crops was different from organic or conventional soybeans, and were significantly lower in protein and higher in omega-6 fatty acids. And glyphosate destroys the good bacteria in your dog’s gut, weakening your dog’s immune system.

Antibiotic resistant genes in GMO crops are also implicated in the growing world threat of antibiotic resistant bacteria (2).

RELATED: Is Roundup safe for dogs?

Antinutrients And Leaky Gut
Like other legumes, soy contains proteins called lectins, which have an “antinutrient” effect. Lectins are sticky proteins that bind to carbyhydrates and interfere with digestive enzymes. So they block your dog’s absorption of vitamins and minerals. Antinutrients in soy can cause digestive issues like gas, diarrhea and bloating.

The damage lectins do in the gut may lead to leaky gut syndrome. A 2018 international study found that soybean agglutinin (the main antinutrient in soy) ” … negatively affects intestinal structure, intestinal permeability, mucosal immune system, and intestinal flora” (3). Leaky gut in dogs causes many chronic health issues … including allergies, arthritis and autoimmune disease.

Thyroid Risks
Some studies show that soy may lower thyroid function and could lead to hypothyroidism in dogs. Veterinarian Dr Jean Dodds says …

Soy interferes with the thyroid gland’s ability to make T4 (thyroxine) and (T3) tri-iodothyronine, hormones necessary for normal thyroid function. In dogs, the result is hypothyroidism.”

Soy may have goitrogenic effects, meaning it can suppress thyroid function by interfering with iodine uptake. In fact, if you have a hypothyroid dog on medication, Dr Dodds recommends giving the meds away from foods that contains soy.

Allergies
This is ironic, because soy is a common ingredient in prescription allergy diets for dogs … but there’s growing concern that GMO foods, including soy, may be triggering a steep increase in food allergies. The Institute for Responsible Technology reported in May 2007 that GMO foods may be causing rising food allergies (5). that As long ago as 1999, researchers the UK’s York Laboratory found that allergic reactions to soy had shot up by 50% over the previous year. This was thought to be due to the fact that GMO soy had recently entered the UK and the soy used in the study was largely GM. If this is happening in people, it’s likely to be the same for your dog. If your dog has allergies or food sensitivities, consider whether an ingredient like soybean meal in dog food could be the culprit (6).

Phytoestrogens In Soy
Phytoestrogens are estrogens in plants that are potentially harmful. Soy is high in phytoestrogens with hormonal effects that are thought to be mostly harmful. In people they can lead to infertility, polycystic ovarian syndrome and perhaps breast cancer. So it’s worrying that a 2004 study of commercial dog foods by University of Pennsylvania found that 11 out of 12 foods that contained soybean ingredients contained phytoestrogens (isoflavones, coumestans, and lignans). The researchers concluded that “…certain commercial dog foods contain phytoestrogens in amounts that could have biological effects when ingested long-term.” Phytoestrogens may also increase dementia risk.

Possible Cancer Risk
There’s more controversy when it comes to whether soy increases or lowers cancer risk, and there are many conflicting studies. For example, some believe that the estrogen-mimicking effects of soy isoflavones may increase the risks of breast cancer … but other studies have found no negative effects, or even that soy may protect against certain cancers (7).

Other Problems With Soy Dog Food
Here are some other potential harmful effects of soy for dogs …

  • Soy is antigenic (meaning it can stimulate the production of antibodies)
  • Soy denatures during high temperature processing causing formation of toxic lysinoalanine and highly carcinogenic nitrosamines
  • Soy contains trypsin inhibitors (which have caused stunted growth in test animals)
  • Soy is high in phytic acid, which reduces the digestion of key nutrients
  • Eating soybean products is linked to seizures in dogs

How To Spot Soy In Pet Foods

You can find soy products in most kibble, canned and veterinarian-based diets today. But it’s not always to spot it on the ingredient label.

Soy can be buried in ingredient lists under many different names: lecithin, hydrolyzed protein (usually in allergy diets), monosodium glutamate, vitamin E, tocopherols. Many products with vegetable, plant or bean in the name (plus tofu, tempeh and textured vegetable protein) are all soy based … textured vegetable protein, textured soy flour (TSF), vegetable broth, guar gum, and even the all-encompassing “natural flavoring.”

Why is soy bad for dogs?

There are many reasons soy is bad for your dog. Most soy is genetically modified and contains toxic glyphosate that may cause cancer and leaky gut. Soy may also lead to problems like hypothyroidism, allergies or seizures.

Can soy make dogs sick?

Soy can make dogs sick, most likely with chronic issues as a result of long term feeding of soy ingredients, as described earlier. But you could see more immediate problems like an allergic reaction or seizures.

Can dogs eat tofu?

Tofu isn’t toxic to dogs, but it shouldn’t be part of a canine diet. It’s not a complete protein for dogs so regular feeding of tofu could lead to nutritional deficiencies. If you eat tofu and want to share a taste with your dog, a small amount shouldn’t be harmful as a treat.

So, if you see soy ingredients on your dog food label, leave it on the shelf. Raw whole food diets are best, but if you feed kibble or canned foods, be on the lookout for soybean meal in dog food, or other soy products that can harm your dog.

References
  1. Bøhn T, Cuhra M, Traavik T, Sanden M, Fagan J, Primicerio R. Compositional differences in soybeans on the market: glyphosate accumulates in Roundup Ready GM soybeans. Food Chem. 2014 Jun 15;153:207-15. 
  2. Midtvedt T. Antibiotic resistance and genetically modified plants. Microb Ecol Health Dis. 2014;25:10.3402/mehd.v25.25918. Published 2014 Sep 25.
  3. Bøhn T, Cuhra M, Traavik T, Sanden M, Fagan J, Primicerio R. Compositional differences in soybeans on the market: glyphosate accumulates in Roundup Ready GM soybeans. Food Chem. 2014 Jun 15;153:207-15. 
  4. Institute For Responsible Technology. Genetically Engineered Foods May Cause Rising Food Allergies. IRT Media, May 7 2007. 
  5. Frick OL. Food allergy in atopic dogs. Adv Exp Med Biol. 1996;409:1-7. 
  6. Cerundolo R, Court MH, Hao Q, Michel KE. Identification and concentration of soy phytoestrogens in commercial dog foods. Am J Vet Res. 2004 May;65(5):592-6.
  7. Messina M. Impact of Soy Foods on the Development of Breast Cancer and the Prognosis of Breast Cancer Patients. Forsch Komplementmed. 2016;23(2):75-80. 

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