National Allergy and Asthma Awareness Month: What you need to know about the Impossible Burger


By Dr. Sue Klapholz, M.D., Ph.D., Vice President of Nutrition and Health, Impossible Foods

Note: With the launch of Impossible Burger 2.0, we included some updates to our ingredient and allergen information.

Let’s talk allergies. Here are the basics.

The major food allergens are proteins, most of which are resistant to heat, acid and digestive enzymes. Most foods contain thousands of different proteins, but only a tiny fraction of them have ever triggered allergies. Milk, eggs, peanuts, tree nuts, soy, wheat, fish and crustacean shellfish account for 90% of allergic reactions to food. But many other foods can occasionally elicit an allergic reaction.

In order to develop an allergy, a person must first be exposed to something in the environment that triggers an immune response. In the case of food allergies, the route of exposure is usually ingestion, but may be inhalation, skin contact or injection.

On first exposure, a susceptible individual makes antibodies to the allergen, but they do not show signs of an allergy. On second and subsequent exposures to the same allergen, the allergen is able to bind to antibodies that are present on the surface of cells of the immune system (e.g. mast cells), which then release a number of chemicals, including histamine, into the body.

This is what causes an allergic response.

The reaction may include all or some of the following: itching, hives, sneezing, wheezing, nausea, vomiting and diarrhea. More rarely, the symptoms can be severe and even life threatening, including swelling of the throat, difficulty breathing and a drop in blood pressure, leading to anaphylactic shock. In the United States, as many as 15 million people have food allergies, and the prevalence is increasing. Although the true incidence of anaphylaxis is unknown, it has been estimated that the rate of anaphylaxis to food is about 1 in 250,000 people.

Multiple factors affect the allergenicity of foods and ingredients.

We know that the physical state of an allergen — whether it is raw, partially cooked or fully cooked — and the amount of allergen to which a person is exposed can have a big impact on whether or not an allergic reaction is triggered. For example, some people are allergic to raw but not baked apples, while others may be allergic to cooked but not raw peas. Some people with proven allergy to peanuts can tolerate a small amount of peanuts while others have severe reactions to even the tiniest amount.

Note: Allergies commonly first occur during childhood, but can begin at any age. The frequency of adult-onset allergies is increasing, and for unknown reasons, food allergies that develop in adulthood tend to be more severe. A recent survey found that almost half of American adults with food allergies developed at least one food allergy after age 18. And these allergies are often to foods a person has eaten many times before. In essence, never disregarding allergic symptoms, even in association with familiar foods.

One common type of allergic reaction — one that many people do not recognize as an allergy — is called oral allergy syndrome (or pollen-food syndrome.)

OAS can occur in people who are already allergic to pollen from trees, grasses or weeds. It turns out that pollen (an inhaled allergen) contains proteins that are similar in structure to certain proteins found in many fruits, vegetables, nuts and seeds. Antibodies to pollen may be able to recognize and trigger a response to these allergens too.

In adults, up to 60% of food allergic reactions are due to cross-reactivity between foods and pollen. For example, when someone who is allergic to birch pollen consumes an apple or almonds, that person may experience oral allergy symptoms: itchy or tingling mouth, scratchy throat, or even swelling of the lips, tongue and throat. These symptoms are usually short-lived and mild because the heat of the mouth and/or stomach acid and digestive enzymes inactivate the allergen — and stop the allergic reaction. Many of the foods that cause OAS when raw are not allergenic when cooked.

A small percentage of time, however, the allergens that cause OAS can trigger a more severe reaction — even anaphylaxis. Oral symptoms such as tingling or itching can be the first warning of a pending generalized allergic reaction. It’s therefore very important to pay attention to oral signs and symptoms as indicators of allergy, and to stop eating any food that triggers these symptoms.

Meat Allergy

Serious allergies to “red meat” (i.e., meat from mammals, like beef, pork or lamb) are a growing worldwide problem. The allergies develop when people are sensitized by tick bites to galactose-α-1,3-galactose (“alpha-gal” for short), — a kind of sugar molecule that’s abundant in tissues from every mammal except monkeys, apes and humans. Sensitized individuals typically develop symptoms, ranging in severity from hives to life-threatening anaphylaxis, several hours after consuming red meat. Because the reaction only occurs several hours after red meat consumption, affected individuals may not link their symptoms to meat consumption — delaying diagnosis.

How we’re working to minimize risk of food allergy

While we can’t analyze buns, condiments, seasonings, side dishes or other ingredients that accompany the Impossible Burger everywhere it’s sold, we can provide information about the Impossible Burger itself, so that consumers with allergies can make an informed choice.

The Impossible Burger is made primarily from soy protein, potato protein, coconut oil, sunflower oil, water and heme. The ingredient list can be found on our website.

The Impossible Burger is made from simple ingredients, including soy protein, potato protein, coconut oil and sunflower oil. One special ingredient — heme — contributes to the characteristic taste of meat and catalyzes the creation of all the other delicious flavors when cooked.

The heme in the Impossible Burger is identical to the heme humans have been consuming for hundreds of thousands of years in animal meat. Heme itself is a natural and abundant component in every cell in our own bodies, and therefore cannot trigger an allergic reaction. In nature, heme is always bound to specialized proteins, like hemoglobin in our blood cells or myoglobin in our muscles.

The heme in our product is bound by a protein called soy leghemoglobin, just as heme in animal muscle is carried by myoglobin. Soy leghemoglobin is completely unrelated to any of the proteins responsible for a soy allergy. Scientists at Impossible Foods, and independent experts in food safety and allergenicity, have comprehensively analyzed the ingredient in the Impossible Burger and concluded that it poses an extremely low risk of allergenicity.

We performed extensive allergenicity testing on leghemoglobin; the results of these tests convincingly showed that it has a very low potential to be an allergen and is very safe to eat. The results of our studies have been published in the peer-reviewed journal Molecular Nutrition and Food Research, and the data are also available on the US Food and Drug Administration (FDA) website.

In addition to soy leghemoglobin, the Impossible Burger contains a couple of other ingredients that may cause an allergic reaction in a small percentage of susceptible individuals. The FDA requires explicit labeling of eight common food allergens whenever they might be present in a food: milk, eggs, peanuts, tree nuts, soy, wheat, fish and crustacean shellfish. Our ingredient list and allergen statement, which declare the presence of soy, are located on our product packaging and on our website. It’s also provided to the distributors, chefs and restaurateurs who work with our product.

Soy is a major source of protein in the Impossible Burger. Approximately 0.4% of children are allergic to soy. Soy allergy generally occurs early in childhood and is often outgrown by age 3. The majority of children with a soy allergy will outgrow the allergy by the age of 10. Allergic reactions are typically mild (e.g. rash or hives, itching in the mouth, nausea, vomiting or diarrhea, stuffy or runny nose, wheezing or other asthma symptoms), and rarely can turn severe (e.g. anaphylaxis). While soy allergies acquired in childhood are usually outgrown at a young age, two recent studies ranked soy allergy among the top 5 most common adult-onset allergies. Naturally, people with known or suspected allergy to soy, should not consume the Impossible Burger.

Potato is the second major source of protein in the Impossible burger. Potato allergy is relatively uncommon, and severe allergic reactions to potatoes are rare. (More people are allergic to raw potatoes than to cooked potatoes.) The most common allergic reactions to raw potatoes are respiratory symptoms (e.g., runny nose, wheezing) and/or a skin rash (contact dermatitis) when potatoes are handled (for example, during peeling). Allergic individuals can also experience adverse GI symptoms (nausea, diarrhea) and/or eczema after eating cooked potatoes. Allergy to latex and certain types of pollen including birch, ragweed and plane tree, are also risk factors for potato allergies. Although rare, either raw or cooked potatoes can trigger an anaphylactic reaction. In the case of a food that contains potato protein — depending on how well cooked the food is — the proteins may in a raw or cooked (denatured) state. Therefore, people who are allergic to either raw or cooked potatoes should avoid consuming the Impossible burger.

Yeast extract is derived from Saccharomyces cerevisiae, a yeast commonly used in baking and brewing, and as the source of nutritional yeast. Many different kinds of yeasts are also prevalent in the environment. People with allergies to yeast most often have skin (e.g., eczema) or respiratory (e.g., wheezing) symptoms due to environmental exposure. More serious generalized allergic reactions to ingested yeast are rare, but have been reported. Therefore anyone with known sensitivity to yeast-containing foods should not consume our burger.

The Impossible Burger’s fat comes primarily from two sources: refined coconut oil and refined sunflower oil. While coconut is classified as a tree nut by the FDA, and coconut is a known allergen, refined coconut oil is free of coconut protein and is not allergenic. For this reason, the FDA does not require coconut to be listed as an allergen if it is present only in the form of a refined oil. Seed proteins can also be allergens, and allergic reactions to sunflower seeds have been reported. However, like our coconut oil, the sunflower oil we use is highly refined, and therefore not allergenic.

Our promise to you

We strive to make food that are completely sustainable and at least as nutritious and wholesome as their animal-derived counterparts. Our rigorous safety testing and commitment to transparency comes amidst overwhelming evidence that moving toward a plant-based diet yields both huge benefits for the health of our planet and huge public health benefits.

We’re creating new products in a new category of food, and people naturally have a lot of questions about what we do. We’re committed to answering them, and provide details about our ingredients, processes and science on our website — on our FAQ page and media kit.

Follow this blog to find answers to important questions and issues related to our mission and products. You can also always reach out to [email protected] We’re here to talk.

General resources and articles on food allergies:

  1. Asthma and Allergy Foundation of America

  2. University of Nebraska Food Allergy Research and Resource Program

  3. Allergy UK

  4. The Mayo Clinic

  5. Food Allergy Research and Education (FARE)

  6. Oral Allergy Syndrome: When an Apple a Day Is Not Advised (Medscape: Dec 10, 2015

  7. S. Shahzad Mustafa. Anaphylaxis (Medscape: Feb 22, 1017

  8. Sarah Gibbens: A tick bite could make you allergic to meat — and it’s spreading (National Geographic: June 21, 2017

  9. Patrick Bennett: When Food Allergy Strikes an Adult — January 19, 2016.


Sue Klapholz received her M.D. from The University of Illinois College of Medicine and her Ph.D. in genetics from The University of Chicago. Her postgraduate education included residency training at The University of California, San Francisco and postdoctoral fellowships at The University of Chicago and Stanford University. Prior to joining Impossible Foods in 2013, Dr. Klapholz worked as a scientist, an editor and an educator.

Check out our FAQs for more info. More questions? Contact us at [email protected]