The availability of plant-based protein foods to replace meat has increased dramatically as more and more people choose a plant-based diet. At the same time, there are many challenges regarding the nutritional value of these products. A study from Chalmers University of Technology in Sweden now shows that many meat substitutes sold in Sweden claim a high iron content, but in a form that cannot be absorbed by the body.
A diet consisting largely of plant foods such as root vegetables, legumes, fruits and vegetables generally has a low climate impact and is also associated with health benefits such as: a reduced risk of age-related diabetes and cardiovascular disease, as shown in several large studies. But there have been far fewer studies of how people’s health is affected by consuming products made from so-called textured vegetable proteins*.
In the new Chalmers study, a research team from the Food and Nutrition Sciences Division analyzed 44 different meat substitutes sold in Sweden. The products are primarily made from soy and pea protein, but also include tempeh, a fermented soy product, and mycoproteins, i.e. mushroom proteins.
“Among these products, we’ve seen a wide variation in nutritional content and how sustainable they can be from a health perspective.” In general, the estimated absorption of iron and zinc from the products was extremely low. Indeed, these meat substitutes contained high levels of phytates, antinutrients that inhibit the absorption of minerals in the body,” explains Cecilia Mayer Labba, the lead author of the study, who recently defended her thesis on the nutritional limits of the transition from animal proteins to vegetable proteins. protein-based.
The body lacks necessary minerals
Phytates are found naturally in beans and grains – they accumulate when proteins are extracted for use in meat substitutes. In the gastrointestinal tract, where mineral absorption takes place, phytates form insoluble compounds with essential dietary minerals, especially non-heme iron (iron found in plant foods) and zinc, which means that they cannot be absorbed in the intestine.
“Iron and zinc also accumulate during protein extraction. This is why high levels are listed among the ingredients of the product, but the minerals are bound to phytates and cannot be absorbed and used by the body”, explains Cecilia Mayer Labba.
Iron deficiency in women is a widespread and global problem. In Europe, 10 to 32% of women of childbearing age are affected** and nearly one in three teenagers in secondary school in Sweden***. Women are also the group in society most likely to have switched to a plant-based diet and to eat the least amount of red meat, which is the main source of iron that can be easily absorbed in the digestive tract.
“Clearly when it comes to minerals in meat alternatives, the amount available for absorption by the body is a very important consideration. You can’t just look at the ingredient list. Some of the products we studied are fortified with iron but it is still inhibited by phytates. We believe that making nutrition claims only about nutrients that can be absorbed by the body could incentivize industry to improve these products,” says Ann-Sofie Sandberg, professor of food science and nutrition at Chalmers and co. – author of the study. .
The food industry needs new methods
Tempeh, made from fermented soybeans, differed from other meat alternatives in the amount of iron available for absorption by the body. This was expected, as tempeh fermentation uses microorganisms that break down phytates. Mycoproteins are distinguished by their high zinc content, without containing known absorption inhibitors. However, according to the researchers, it is still unclear to what extent our intestines can break down mycoprotein cell walls and how this in turn affects nutrient absorption.
“Plant-based foods are important for the transition to sustainable food production, and there is huge development potential for plant-based meat substitutes. The industry needs to think about the nutritional value of these products and use and optimize known processing techniques such as fermentation, but also develop new methods to increase the absorption of various important nutrients,” says Cecilia Mayer Labba.
Plant protein production
- Most plant-based protein products on the market are based on protein extracted from a crop plant, such as soy, and separated from other plant components.
- The protein is then subjected to high pressure and temperature, which restructures the proteins, called *texturing, so that a product can be obtained that is meatier and chewier in combination with other ingredients.
- The Chalmers study shows that the nutritional value of meat substitutes available today is often deficient depending on the choice of raw material (often imported soy) and processing conditions (anti-nutrient content), and additives (fat and salt quality).
- A meal containing 150 grams of meat alternatives contributes up to 60% of the maximum recommended daily intake of salt, which according to the Nordic nutritional recommendations is 6 grams.
* The protein is restructured by high pressure and temperature.
** Milman, Taylor, Merkel and Brannon: Iron status of pregnant women and women of childbearing age in Europe. Am J Clin Nutr 2017; 106 (additional): 1655S-62S.
*** Riksmaten Adolescents Survey 2016-2017, Swedish National Food Agency (Livsmedelsverket) report series no. 23, 2018. Swedish National Food Agency (Livsmedelsverket) 2018.