Submitted by A.B. Youngman on Fri, 10/02/2023 - 15:03
Dr Daniel Borch Ibsen, Research Associate, MRC Epidemiology Unit, University of Cambridge, writes in response to recent findings.
Plant-based meat alternatives are marketed as a direct replacement of meats, but a new study from Chalmers University, Sweden, puts this into question.
The study examined the nutritional composition of many plant-based meat alternatives and found that most of these foods are far from their meat counterparts in important nutrients from meat, particularly red meat, such as iron and zinc (1). Even among the products with a higher content of iron and zinc, the minerals may not be absorbed by the gut because these foods also contain high amount of phytate, a so-called “antinutrient,” that chelates with iron and zinc and inhibits absorption. This leaves us with the question of whether plant-based meat alternatives are real alternatives?
There are and they aren’t. Here’s why:
Iron, zinc and phytate
Despite being associated with a higher risk of developing colorectal cancer (2), cardiovascular disease (3) and type 2 diabetes (4) and having a large carbon footprint (5), red meat is a good food source of the minerals iron and zinc that was investigated in the study.
Iron is essential for oxygen transport around the body and iron deficiency is considered the most common cause of anaemia – a condition where the number of red blood cells or the haemoglobin concentration within them is lower than normal (6). Anaemia can cause fatigue and weakness and can affect cognitive development in children and reduce productivity in adults. Zinc is essential in many functions such as reproduction, immune function and wound repair (7). Meat is one of the main contributors to iron and zinc in the UK diet (8) whereas cereals and legumes are main contributors in many low- and middle-income countries (9).
One of the findings of the new study was that almost all the 44 meat substitute products analysed had a low content of iron and zinc (1). It was also found that the phytate content of many of the products was high. Phytate is an antinutrient and inhibits the absorption of iron, zinc and calcium in the gut (10). Cereals and legumes can be high in phytate, but the food processing method play a key role in this. For instance, other studies have shown that products based on protein extracts, like many plant-based meat alternatives, have higher contents of phytate (11). This is likely due to the accumulation of phytate during the protein extraction and extrusion process (11).
To quantify the bioavailability of the iron and zinc in the products evaluated, the researchers used the phytate to mineral ratio. The higher the ratio, the poorer the absorption. All products with an iron content greater than 2.1 mg/100g (which is a threshold suggested for a food to be a reasonable source of iron) had a phytate:iron ratio above 0.4, which suggest inhibited absorption. Most products had a ratio above 6, which is the suggested limit for when absorption enhancers such as vitamin C can still counteract the inhibition (10).
Implications of the findings
In short, the study suggests that most of the analysed foods are poor food sources of iron and zinc. But does that mean that plant-based meat alternatives are a poor substitute for meat? Yes and no.
In high-income countries with good access to food, particularly meat products, and a varied diet, iron and zinc deficiency is not common. In a modelling study, it was estimated that reducing red meat intake among UK adults with the highest intake would have little effect on the number of adults that would have iron deficiency (8). Because of the disease and climate concerns connected to a high intake of red meat, replacing red meat with plant-based meat alternatives, likely offer a benefit, despite the lower levels of iron and zinc.
There are, however, some vulnerable groups such as children aged 1.5-3.5 years, girls aged 11-18 and women aged 19-49 that, if they do not consume high amounts of meat, or take supplements, may become at risk of anaemia when replacing red meat with plant-based meat alternatives (8). Similarly, in low- and middle-income countries where intake of meat is generally lower, it may not be advisable to further reduce intake of meat with plant-based meat alternatives (9,12).
Limitations of the study
The study itself highlights some nutritional limitations of plant-based meat alternatives. Its main limitation is that it did not directly test whether replacing meat with any of the plant-based meat alternatives changed iron or zinc status in a group of individuals. This will be important to investigate in future studies for two main reasons.
Firstly, the studied population is important for whether replacing red meat with plant-based meat alternatives offers health benefits. The main factor impacting absorption of iron in the diet is not from the diet itself, but the iron status of the individual (6,8). The body regulates absorption; low iron status leads to enhanced absorption. The usual intake of red meat also impacts this. If the intake of red meat is low and the iron status is low in the population, the replacement of red meat with a plant-based alternative may negatively impact iron status, whereas it may not matter in a population with a high intake of red meat and good iron status.
Secondly, the rest of the diet matters. The study analysed the foods in isolation. However, foods are consumed as part of a whole dietary pattern and other food components, such as vitamin C, may enhance the iron and zinc absorption or intake of iron and zinc may come in adequate amounts from other food sources (10).
Future perspectives of plant-based meat alternatives
The study of nutritional composition gives us insights into some nutritional aspects of the products that can be improved. In the context of plant-based meat alternatives, the processing methods may need to be altered to reduce the amount of phytate and increase the amount of iron and zinc. The study also investigated different fatty acids and proteins but did not measure other nutrients such as B-vitamins, including B12, which red meat also is a substantial contributor to in UK diets. All in all, it highlights that there is still much to be learned about the role of food processing on human health, particularly in the long-term.
From a nutritional point of view, many plant-based meat alternatives are not a 1-to-1 alternative to meat. However, in populations with a high intake of meat and adequate iron status, they may not need to be – provided that the nutrients such as iron and zinc are provided from other foods in the diet. This caveat sheds light on the bigger issue pervasive in many Western food environments: they are not built to improve population and planetary health. Thus, plant-based meat alternatives can be a step in the right direction, replacing some meat products with plant-based products. However, for a bigger transformation in the long-term we still need to move beyond the single food focus and change whole dietary habits and our food culture (13).
References
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6. World Health Organization. Anaemia [Internet]. [cited 2023 Jan 2]. Available from: https://www.who.int/health-topics/anaemia
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8. Scientific Advisory Committee on Nutrition. Iron and Health [Internet]. Department of Health; 2010. Available from: https://www.gov.uk/government/publications/sacn-iron-and-health-report
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12. Al Hasan SM, Hassan M, Saha S, Islam M, Billah M, Islam S. Dietary phytate intake inhibits the bioavailability of iron and calcium in the diets of pregnant women in rural Bangladesh: a cross-sectional study. BMC Nutrition 2016;2:24.
13. Ibsen DB, Mogensen L, Corredig M, Dahm CC. Legumes in a sustainable healthy diet: (How) to be or not to be, that is the question. International Journal of Food Design 2022;7:171–85.