I hope that you’re reading this before you decided to throw that new bunch of asparagus directly in the trash can (if not, I’m sorry for your loss). Many of you may have come across several news stories this week detailing the relationship between the amino acid asparagine and breast cancer metastasis (in mice). The research in question – which was done on a few mice on tightly controlled, lab-created diets – has generated media headlines around the world. Some have suggested that we should make swift and severe dietary changes to limit the amino acid in question. But what, if anything, in this study can be applied to humans? Just how far could these results reach into our everyday life? Let’s take a closer look.
What is asparagine? And can you give me the TL;DR version?
First, let’s briefly talk about asparagine. Amino acids are the building blocks of proteins, which are essential for growth, development and maintenance of our bodies. Everything from digesting and absorbing our lunch to healing a broken bone requires proteins, so it’s critical that we have a good store of them to maintain our health and minimize risk for disease. Asparagine is widespread in our food supply – it’s present in some plant-based foods like whole grains, nuts and seeds, soy and some vegetables (yes, including asparagus). It’s also found in high amounts in dairy products, eggs, fish, seafood, beef and poultry. While it’s found in some produce, most other fruits and vegetables are generally low in asparagine.
The study looked at mechanisms of how cancer cells spread through the body – called metastasis – in a mouse model of triple-negative breast cancer, a type of breast cancer that is notoriously difficult to treat in mice and humans. They first learned that the appearance of one enzyme involved in making asparagine in a breast cancer tumor was strongly associated with later metastasis. Piggybacking on this discovery, mice were then fed diets that differed in their content of asparagine, ranging from an asparagine-free diet, to 0.6 percent asparagine in the total diet (the typical amount found in foods), all the way up to 4 percent asparagine in the total diet. When the mice were injected with cancer cells, they found that mice who were on the high-asparagine diet showed higher incidence of metastasis as compared to the asparagine-free group.
So should I avoid foods with asparagine?
Not so fast! There are several reasons why we should take a step back and evaluate what this study teaches us, and why we should avoid the fear-mongering that has sprung out of it. First, have I mentioned that this research was done in mice? Human participants were not involved. Animal studies are important for a lot of reasons. They allow us to understand physiology in ways that wouldn’t be ethically or physically possible in humans. They also generate a lot of new research questions that could be studied in people. But a mouse is not a human. While there may be some similarities, our bodies work quite differently from animal models. We break down food differently, we have different susceptibilities to certain diseases, and our immune systems and microbiomes are far from the same. That’s why it’s next to impossible to directly apply the results of an animal study to people.
Second, this research did not involve specific foods. Asparagus was not part of the mouse diet. Neither was any kind of whole grain, dairy product, or animal- or plant-based protein. Mice were fed what is essentially lab-generated pet food supplemented – or devoid of, in the case of the no-asparagine diet – one specific amino acid. And remember the 4 percent asparagine diet? That’s a lot of asparagine. It’s unlikely that getting this amount in foods from the grocery store or a restaurant would be realistically possible.
And lastly, we cannot forget that this study was conducted in mice who already had cancer – from cells that were injected into them. Therefore, it’s not possible to conclude that limiting asparagine would even be helpful to mice who don’t have cancer, let alone generally healthy humans.
The study’s authors say that they are considering testing whether a low-asparagine diet could be a therapeutic option for people with cancer, and that this research would probably be done in combination with standard treatments like chemotherapy and immunotherapy. It will be several years until we know more about how this dietary approach impacts humans, so please don’t sign up for the Fruitarian Diet just yet. In fact, the National Cancer Institute states that “higher consumption of vegetables in general may protect against some diseases, including some types of cancer”. Registered dietitians, doctors, and other health professionals will continue to encourage everyone to follow a healthful and varied diet rich in fruits, vegetables, whole grains and lean protein.