Let me preface this by saying that I’m not vegan, vegetarian, or even pescatarian. I’m not any of the -arians. But I am a foodie. So when I heard about the Impossible Burger, a plant-based “beef” burger, I had to try it. Unlike other plant-based burgers, where you can see the beans and corn that are squished together to make the patty, the Impossible Burger truly resembles a beef burger.

Now, my best friend is allergic to beef, so I was bursting to tell her about this alternative. But, she was actually pretty sketched out by it. For me, as I am with most tasty things, ignorance is bliss. But she got me curious…what made this Impossible Burger so impossible? What gave it the same color, texture, and consistency of beef that let it bleed when you cut it? And, after lots of effort to get these mystery ingredients approved by the FDA, how can we be sure it’s safe to eat?

Before we understand what the Impossible Burger is made of, let’s first go over what makes up a typical beef burger. Allrecipes provides a “Juiciest Hamburgers Ever” recipe: ground beef, 1 egg, breadcrumbs, milk, Worchestershire sauce, and some spices. Ground beef is known to be a great source of protein. In fact, proteins are the primary component of meat itself. They are molecules that have a wide variety of jobs within both our own bodies, as well as the bodies of cattle. In ground beef, there are proteins whose jobs are structural—i.e. to help the ground beef stay in one piece. This raises two questions about the Impossible Burger: without beef, how does it get its protein value and how does it stay together?

Let’s first understand the protein source. The major protein content comes from soy protein concentrate. These concentrates are made by removing the oil from soybeans so you’re left with something called a “deffated flake.” After that, the company removes broken-up starches called oligosaccharides (the carbohydrates—think what bread is made of), as well as other small components of the flake. At the end of the process, all that’s left is the protein from the soy

Next, we need something to help bind the burger. This something is called methylcellulose. This molecule comes from cellulose, which plants use to help maintain their structure (what gives celery that good crunch when you bite into it). For the burger, it’s extracted from natural products such as wood or cotton. When you cook with Methylcellulose, a gel forms. This gel locks the patty into place so it doesn’t lose its shape. As the burger cools, the gel melts, leaving a perfectly perky burger.

Now, let’s tackle what truly makes or breaks a burger—the juiciness and flavor. In a typical beef burger, the juiciness comes from the fat in the meat. The cow likely wasn’t a body builder, so it probably had some ~fluff~ to it. This fluff, or fat, is what contributes to the burger’s taste. However, plants don’t lounge around eating holiday sweets. So, to replace the fat, the company adds oils, such as those obtained from coconut or sunflower

Now onto the final component: the flavor. 

what's in an impossible burger. Edited wagon wheel to mimic heme molecule. Unedited wagon wheel from AIFEATI/ iStock by Getty Images.
A heme molecule mimics the shape of a wagon wheel. Iron is the inner wheel and it’s connected to porphyrin, the outer wheel.

The all-star of the Impossible Burger flavor is heme. You’re probably saying “what the fudgesicle is heme!?” Structurally, heme consists of an iron molecule surrounded by porphyrin, a ring-shaped molecule. Think of a wagon wheel, with the iron being the inner circle of the wheel and the porphyrin being the outside circle. The two circles are connected by the spokes.

Heme is absolutely everywhere. It’s inside your body right now, even if you haven’t eaten an Impossible Burger. For example, heme is one of the molecules that make up hemoglobin, the protein that gives our blood its red color and carries oxygen around our bodies. Heme is also found in the tissue of animals, the stuff that makes up their organs. According to Impossible Foods, heme gives meat its meat taste. Since this is a plant-based burger, though, Impossible Foods can’t get their heme from animal tissue. Rather, they need a plant-based source of heme. This ended up being soy leghemoglobin.

Soy leghemoglobin is a protein found in soybeans. It’s classified as a globular protein, meaning it’s shaped like a globe. In legumes (a category of plants) leghemoglobin carries oxygen throughout the plant. But in an Impossible Burger, it’s used a little differently. When an Impossible Burger is cooked, the soy leghemoglobin breaks down and releases the molecule heme (which, as we saw earlier, gives meat its meatiness).

After discovering this plant-based heme, Impossible Foods went to get it approved by the FDA, even though they didn’t have to since heme falls under Generally Recognized As Safe regulations. Yet, to be as transparent as possible with consumers, they sought FDA approval anyway. The road wasn’t easy—this is where much of the health concern about Impossible burger became apparent. The FDA was worried about soy leghemoglobin.

While humans eat soybeans, soy leghemoglobin is found in the root nodule of plant, which we don’t normally eat. Remember from earlier that heme is in our bodies right now, and in the meat that we do (or don’t) eat. So if we’ve eaten heme from animals for millenia…why would eating it from plants be any different?

what's in an impossible burger
The portion of the soybean plant we normally consume is the soybeans, which are located inside the pods. The root nodules sit on the roots, where are in the soil. We don’t normally eat the nodules, but they contain the majority of the soy leghemoglobin found in the plant. Image derived from GetDrawings.com.

When heme enters the body, it’s broken down in either the small intestine or the liver. Your body removes the iron molecule from the heme so that only porphyrins (the outer circle of the wagon wheel) are left.

Impossible Foods claims that plant heme is the same exact molecule as the heme that humans are used to eating. Therefore, the soy leghemoglobin should break down the same way in the body. 

During the FDA approval process, the FDA reviews all the studies provided by the company that demonstrate the safety of the food additive, or something added to food to improve its flavor, texture, etc. In one study from 2018, Impossible Burger showed no toxic effects of soy leghemoglobin in rats fed over 100 times greater than the estimated daily intake of the molecule. While no studies examined the effects of soy leghemoglobin on humans, the FDA made the decision to approve soy leghemoglobin in the summer of 2018.

Ultimately, it’s your decision whether or not to eat the Impossible Burger (although, my vote is you venture out and try it!) But, when making decisions about anything you’re going to consume, you should always be aware of the ingredients (such as salt, fat, and sugar) and their possible effects on your long-term health. 

Check out the Impossible foods ingredient list and nutrition label for yourself by clicking here!

Diclaimer: Neither the author nor the Illinois Science Council has received any form of compensation form Impossible Foods in relation to this article.

Alyson’s article is part of a collaboration between the Illinois Science Council and the University of Chicago.


  • Alyson Thorne

    Alyson is a 3rd-year student at the University of Chicago majoring in Biology. She loves baking, playing sports, bursting out into song and dance, and learning (even if it makes her a stress snacker). Find out more about her on LinkedIn.

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