Antinutrients – a pitfall in the protein shift?

To clarify some of the questions about antinutrients, I, Susanne Bryngelsson, was recently interviewed by my colleague Maria Biörklund Helgesson for the Måltid Sverige Research Podcast. Both Maria and I work as project managers at RISE, where Maria's focus is primarily on sustainable meals while I work more broadly with nutrition, including the area of sustainable nutrition. This blog is based on the conversations Maria and I had before and during the podcast recording.

Let's start from the beginning. Can you start by explaining what antinutrients are?

– Antinutrients are substances that interfere with or completely inhibit the absorption and metabolism of nutrients. This can involve substances that make it more difficult for the body to absorb and utilize minerals such as iron, calcium, and zinc, or that hinder the breakdown and absorption of proteins from the diet. Some antinutrients also have more direct negative effects, such as stomach pain, or even toxic effects.

Okay, that sounds like something one would want to keep an eye on. Can you tell me more about which foods contain antinutrients and perhaps more about what kinds of substances they are?

– Antinutrients encompass many different types of substances, with highly varied chemical structures and properties - some are proteins, others are glycosides or phenolic compounds.

– Substances that can act as antinutrients occur naturally in most plant-based raw materials, such as whole grains and legumes, like peas and beans, but also in, for example, the skins of grapes, tea leaves, rhubarb, and certain types of cabbage. In the plant, antinutrients serve many functions; they can, for instance, act as part of the plant's defense or be used for nutrient storage.

When you say that antinutrients can be proteins or phenolic compounds, I get a bit curious. Protein is a nutrient, and phenolic compounds are often mentioned as a possible explanation behind the positive health effects of, for example, fruits and berries. Can you elaborate on this a bit?

– Absolutely. The term antinutrient implies that the substance has a negative effect by counteracting the positive effect of nutrients. However, many of the substances that can act as antinutrients also have other functions in the body that can be positive. For example, some antinutrients can also function as antioxidants.

– Antinutrients can also contribute to desirable properties in foods, such as providing color and flavor. In other words, it is not always necessary or realistic to completely eliminate all antinutrients from foods.

Which antinutrients are most relevant to know and consider?

– Generally speaking, it is most important to be aware of the antinutrients that have the most severe effects, that is, antinutrients that cause acute or toxic effects. For example, if you work with fava beans, you should know that they contain antinutrients that can cause so-called "favism" in certain individuals. And all fresh and dried legumes contain varying levels of lectins, which can cause acute symptoms such as nausea, vomiting, diarrhea, and stomach pain.

– When it comes to prioritizing antinutrients that do not cause acute effects but "only" inhibit the absorption or metabolism of nutrients, one can start by considering which nutrients we most need to obtain from food. For example, antinutrients that inhibit the absorption of iron can be considered generally problematic, as iron deficiency is the most common nutritional deficiency globally. Therefore, the antinutrient phytic acid has received a lot of attention. Phytic acid is present to varying degrees in all grains and legumes and has a very strong ability to bind to iron, which then cannot be absorbed by the body. Phytic acid can be especially problematic for young women and the elderly, who are vulnerable groups when it comes to the risk of iron deficiency.

You mentioned that one can combine foods consciously, can you elaborate on that?

– When it comes to iron, there are a few tricks that can be used to counteract the negative effect of phytic acid. For example, it is well known that vitamin C improves the absorption of iron, so it is a good idea to include vitamin C-rich fruits and vegetables in the meal.

– Another trick can be to include a small amount of poultry, meat, or fish in the meal. Besides the fact that meat itself contains a different form of iron than plants, called heme iron, which is well absorbed by the body and not affected by phytic acid, meat also contains a so-called "meat factor" that stimulates the absorption of the iron from the rest of the food.

You also mentioned that cooking and processing can reduce the content of antinutrients in food? Can you tell me more about that?

– Yes, the positive thing is that the levels of many antinutrients, including lectins in beans, are effectively reduced through relatively simple techniques, where soaking and boiling beans are old and wise "household knowledge" that can sometimes risk being forgotten in a time when trends about eating as "natural" and "minimally" processed foods as possible are flourishing. It is important to remember to discard the water in which the beans have been soaked or boiled and not use it for cooking.

– Many antinutrients are also sensitive to heat. It is worth noting, however, that for lectins, it is not enough to cook the beans in a microwave; they need to be rinsed away with boiling.

– For phytic acid, which is a heat-stable antinutrient, you can, for example, reduce the levels in bread through sourdough baking. Generally, there is great interest in the potential of so-called "bioprocesses" such as sprouting, fermenting, and fermentation. But there are also other, more advanced processing techniques that may be of interest to the food industry, such as extrusion, ultrasound, high-pressure processing, and so-called "Electric Field Pulse."

Interesting. When thinking about plant-based so-called meat analogs, can one assume that they have low levels of antinutrients since they have undergone several processing steps to create a product that mimics meat?

– One might think so, but unfortunately, that's not quite the case. Phytic acid, on the contrary, has proven to be a challenge in plant-based meat analogs and even in plant-based dairy analogs. When purifying the protein used as the base for meat analogs, phytic acid often follows along. During extrusion, some phytic acid can be broken down, but the content is usually still high enough in the final product to negatively impact iron absorption.

– However, this is an issue that researchers, food companies, and RISE are actively working on, so hopefully, the problem with phytic acid and other antinutrients will be less in future plant-based meat and dairy analogs.

Indeed, an exciting development to follow. If a company or public entity becomes curious about learning more about antinutrients, can they turn to RISE?

– Yes, absolutely. At RISE, my nutrition colleagues and I work together with experts in product design, process technology, environment/climate, sensory analysis, consumer behavior, and food safety, aiming for the competitive and healthy foods of the future. We are happy to assist with everything from training to practical development projects, focusing on products or meals.