A new meta-analysis has found that in many cases, switching from an animal product to a plant-based alternative is associated with less cardiovascular, diabetes, and all-cause mortality risk [1].
Supplant with plant?
Whether a completely or mostly plant-based diet is good for you has been the subject of a raging debate. On one hand, studies have consistently placed plant-based diets among the healthiest dietary options available [2]. On the other hand, complete exclusion of animal-based foods might not be ideal, especially for younger and older people [3]. Going vegan can make maintaining a balanced diet harder since some nutrients are scarce or even nonexistent in plants.
Apparently, a more nuanced analysis is needed into what happens when people substitute specific animal products with plant-based alternatives. This is the topic of a new review published in BMC. After sifting through hundreds of papers, the authors included 37 of them in their analysis. They then investigated associations between abandoning animal products in favor of plant-based alternatives and cardiovascular health, occurrence of type 2 diabetes, and all-cause mortality.
All of this review’s featured studies were prospective cohort studies, and no randomized, controlled trials were included. This is understandable, since detecting the occurrence of cardiovascular disease or diabetes, not to mention death, requires a long follow-up period: in this review, the mean follow-up duration was 19 years.
Switching to plants lowers risk
The researchers calculated shared hazard ratios (SHR): the difference in the prevalence of an outcome between two groups. For instance, substituting 50 grams of processed meat a day for 28-50 grams of nuts resulted in an SHR of 0.73 – that is, it lowered chances of getting any type of cardiovascular disease (CVD) by a hefty 27%. Substituting with 50 grams of legumes gave an SHR of 0.77. Whole grains scored the best, with an SHR of 0.64: a full 36% decrease in CVD incidence. This is consistent with previous research that has marked processed meat as highly unhealthy. The World Health Organization considers processed meat to be a carcinogen, but its detrimental effects are probably much broader.
Substituting one egg a day with nuts resulted in a 17% decrease in CVD incidence. Interestingly, substituting butter with olive oil only led to a slight 4% decrease in risk. The researchers also found that replacing red meat with nuts, unprocessed red meat with nuts or legumes, poultry with nuts, and eggs with legumes was associated with a lower risk of CVD, but for these associations, the certainty of evidence was low.
Butter, however, did not fare well in the analysis of type 2 diabetes incidence. The researchers calculated that replacing butter with olive oil was associated with a slight decline in risk. Interestingly, red meat also seemed to be more strongly associated with diabetes than with CVD: substituting red meat for nuts was associated with an 8% decrease in risk. The same parameter for replacing processed meat with nuts was 22%, replacing poultry with whole grains was 13%, and replacing eggs with nuts or whole grains was 8%.
Finally, replacing processed meat with nuts or whole grains was associated with a 21% decrease in all-cause mortality risk with a moderate certainty of evidence. Replacing eggs with nuts or legumes was a 15% decrease, replacing red meat with nuts or whole grains was a 7% decrease, and replacing butter with olive oil was a 6% decrease.
Importantly, switching to a plant-based alternative was never associated with an increase in risk, except for the slight uptick in CVD risk when replacing butter with margarine. However, the certainty of evidence for that particular association was very low.
Plant eaters tend to lead healthier lives in general
Populational studies can only indicate association, but not causation, so their results should be taken with a grain of salt. While meta-analyses generally improve the quality of evidence, they are still prone to the same problems as the individual studies they consist of.
According to the authors, the included studies were all adjusted for major lifestyle confounders, such as total energy intake, physical activity, alcohol intake, and smoking. However, completely eliminating confounding is impossible. One of the alternative explanations for the observed associations the authors provide is that people on plant-based diets tend to follow healthier lifestyles in general.
Our findings suggest that a shift in diet from a high consumption of animal-based foods, especially red and processed meat, to plant-based foods (e.g., nuts, legumes, and whole grains) is associated with a lower risk of all-cause mortality, CVD, and T2D. Thus, a change in dietary habits towards an increment of plant-based products appears to be important for cardiometabolic health. However, more research is needed in order to strengthen the existing evidence and to investigate new associations, especially with a focus on meat and dairy replacement products.
Literature
[1] Neuenschwander, M., Stadelmaier, J., Eble, J. et al. (2023). Substitution of animal-based with plant-based foods on cardiometabolic health and all-cause mortality: a systematic review and meta-analysis of prospective studies. BMC Med 21, 404.
[2] Hodge, A. M., O’Dea, K., English, D. R., Giles, G. G., & Flicker, L. (2014). Dietary patterns as predictors of successful ageing. The journal of nutrition, health & aging, 18(3), 221–227.
[3] Domic, J., Grootswagers, P., van Loon, L. J., & de Groot, L. C. (2022). Perspective: vegan diets for older adults? A perspective on the potential impact on muscle mass and strength. Advances in nutrition, 13(3), 712-725.
