Increasing plant-based protein intake reduces the risk of cardiovascular disease

The Canadian Cardiovascular Society’s clinical practice guidelines recommend replacing some animal proteins with plant proteins in the diet to reduce the risk of cardiovascular disease. This recommendation is based on the results of several studies showing that reducing the intake of animal-based foods in favour of plants is associated with improved cardiometabolic health and reduced premature mortality.

However, the majority of protein consumed by the population still comes from animal sources, particularly red and processed meats, poultry, and dairy products: in Canada and the United States, for example, the average ratio of plant to animal proteins in the diet is approximately 1:3 (i.e. a ratio of 0.33).

As we recently mentioned, this over-representation of animal proteins could create inflammatory conditions in the vessel wall and promote the progression of atherosclerotic plaques responsible for myocardial infarctions. The mechanisms involved remain poorly understood, but it seems that certain amino acids present in greater quantities in animal proteins (those with branched side chains such as leucine, in particular) overactivate the cells responsible for inflammation and accelerate the deposition of cholesterol in the artery wall.

It is also well-established that animal proteins have a much greater negative impact on the environment than plant proteins, particularly in terms of greenhouse gas production (see our article on this subject), and that current levels of consumption of animal proteins are unsustainable if we hope to mitigate the devastating impacts of global warming in the coming years.

For all these reasons, there is a general consensus on the importance (and even the urgency) of changing modern eating habits to include more plant proteins and less animal proteins. This does not necessarily mean becoming a strict vegetarian: the Mediterranean diet, for example, contains a lot of plants, but also some foods of animal origin (fish and fermented dairy products, in particular) and is clearly established as one of the best ways to significantly reduce the risk of cardiovascular disease, both in the general population and in coronary patients.

For omnivores, who still represent nearly 90% of the Canadian population, the most important aspect to improve is therefore increasing the current proportion of proteins consumed from plants, which is currently only 1:3 (ratio of 0.33), without having to completely eliminate those of animal origin.

Rising ratio, falling cardiovascular disease
A recent study provides valuable information on the amount of plant protein required to significantly reduce the risk of cardiovascular disease. By examining the eating habits of 202,863 participants in three large cohorts at Harvard University over a period of thirty years, the researchers assessed the ratio of protein consumed according to the source (plant vs. animal) by dividing the percentage of total calories from plant protein by the percentage of total calories from animal protein. A ratio of less than 1 therefore means that the intake of plant protein is lower than that of animal protein, while conversely, a ratio greater than 1 implies a higher intake of plant protein than that of animal protein.

When the incidence of coronary heart disease is examined in terms of this ratio, we see that an increase in plant protein intake (increase in the plant-to-animal ratio) is associated with a rapid decrease of about 25% in the risk of cardiovascular disease, even when the amount of plant protein remains lower than that of animal protein (ratio < 1) (Figure 1). This decrease in risk is particularly striking when examining the incidence of coronary heart disease more specifically, with protection reaching 35% at ratios < 1 and even 40% and more when the amount of plant protein consumed exceeds that of animal protein (ratio > 1). This difference between the protective effect of plant protein on total cardiovascular disease (heart attack and stroke) and coronary heart disease (heart attack) is explained by the absence of a plant protein effect on the incidence of stroke.

Figure 1. Association between cardiovascular disease risk and type of protein consumed. An increase in plant protein intake, which translates into an increase in the plant-to-animal protein ratio, is associated with an optimal reduction in cardiovascular disease risk as soon as the plant protein intake reaches half of animal protein intake (ratio of 0.5). The risk reduction is, however, even more pronounced for coronary heart disease (myocardial infarction) when the plant protein intake exceeds animal protein intake (ratio > 1). Adapted from Glenn et al. (2024).

The protective effect associated with increased plant-based protein intake is particularly evident in a context where protein represents a high proportion of total calories consumed (Figure 2). For example, for plant protein/animal protein ratios high enough to reduce the risk of cardiovascular disease (ratio > 0.5), we observe that this reduction in risk is most pronounced for a protein density (the percentage of calories in the form of protein) of the order of 20%, which corresponds to approximately 100 g of protein out of a total intake of 2000 kcal/day. This is approximately the average amount of protein consumed by the North American population, but mainly from animal sources (red meat, poultry and eggs, and dairy products). To reach this total amount of protein (100 g), while increasing the intake of plants to reach a plant/animal ratio of 1.0 (optimal for the prevention of coronary heart disease), it is therefore simply a matter of consuming 50 g of protein from plant sources and 50 g of protein from animal sources. Given that plants generally contain less protein, particular attention should therefore be paid to preferentially consuming those that are richer in protein, for example legumes and nuts, to achieve this objective.

Figure 2. The reduction in cardiovascular disease risk associated with higher plant-based protein intake is influenced by the total amount of protein consumed. The cardiovascular disease risk observed for each plant-to-animal protein ratio (low, intermediate, and high) is lower among participants whose diets contained a higher protein density, i.e. a higher proportion of total calories coming from protein. Note that the lowest risk is observed for a plant-to-animal ratio > 0.5 combined with a protein intake equal to 20% of total calories. Adapted from Glenn et al. (2024).

Replacing red meats
Further analysis revealed that replacing red meats with plant-based foods provides the greatest benefits in terms of preventing cardiovascular disease, particularly coronary heart disease (Figure 3). In the latter case, it was observed that replacing just 1 daily serving of red meat and/or processed meats with 4 sources of plant-based protein (refined flours, whole grains, nuts, and legumes) was associated with a lower risk. Replacing poultry with whole grains and nuts, as well as replacing dairy products with nuts, were also associated with a reduced risk.

Figure 3. Effect of substituting animal protein with plant-based protein on cardiovascular disease risk. Risk ratios indicated by green circles correspond to substituting 3% of energy intake from animal protein with the equivalent in plant protein. The effect of substituting one daily serving of the main sources of animal protein (red meat, poultry, and dairy) with the equivalent of different types of plant-based foods (refined flours, whole grains, nuts, and legumes) is illustrated by the coloured circles. Note the greater reduction in cardiovascular disease and coronary heart disease risk when replacing red meat with different plants. Adapted from Glenn et al. (2024).

In summary, this study shows that simply changing your diet slightly to include a little more plant-based food and less red meat and processed meats can have very positive effects on cardiovascular health. Several factors may explain this positive impact of plant-based foods: 1) plant-based protein sources are lower in saturated fats and higher in unsaturated fats and complex carbohydrates (such as fibre), a nutritional profile that has repeatedly been associated with a lower risk of cardiovascular disease in epidemiological studies; 2) the amino acid profiles of plant proteins are different from animal proteins, including lower content of branched-chain amino acids (BCAAs), which have been associated with a higher risk of cardiovascular disease, as well as higher amounts of arginine, an amino acid that is beneficial for controlling blood pressure; 3) replacing animal protein sources with plants can reduce the intake of heme iron and and precursors of trimethylamine N-oxide (TMAO), two risk factors for cardiovascular disease. But whatever the mechanisms involved, there is no doubt that even a slight increase in the proportion of plants in our diet can only be beneficial, both for cardiovascular health and that of the planet.