Introduction

The debate continues to rage on about the best type of diet to eat for ensuring optimal health. The mass media is fickle and may change its general attitude about such matters depending on the marketing acumen of the particular company spouting off about what is the best strategy for eating healthy.  In my life, I have witnessed several companies suggest that their way of eating is the best, e.g., the Robert Adkins diet, the South Beach diet, the Zone diet, and now the Paleo diet has taken hold of some share of the popularity.  What these philosophies all have in common is an emphasis on lots of protein and to a lesser degree fat, with differences in the type and amount of fat, depending on not completely clear purposes.  Meanwhile, Weight Watchers has been around for a very long time previously emphasizing counting calories, but now shifting to counting elements in the diet.  Nonetheless, all of these philosophies have more so relied on great marketing, rather than emphasizing what the science says, either through clinical trials or epidemiological observations.

Additionally, we as consumers are left with the unfortunate reality that nutritional science is very flawed. Regardless if it is understood by the layperson, we have no way of knowing definitive cause-and-effect answers from testing nutritionally-oriented hypotheses due to the nature of the field itself.  For example, we cannot take humans at birth, put them in a facility, feed them controlled and exact diets, and then document when and how they die.  Talk about ethical problems with that type of research!  Second, it is impossible to design placebo-controlled, blinded clinical trials with food.  Third, the length of time that it would take to design clinical trials meaningful enough to draw conclusions about the relationships between food and health (or disease) would be likely the most expensive studies of all-time and would be fraught with adherence, compliance, and fidelity issues.  Fourth, observational studies have a certain amount of variance (error) in reporting behaviors due to recall bias and inaccuracy, so their results also have to be weighed accordingly.  Fifth, animal studies showing relationships in lower primates and rodents may not necessarily be translatable to humans due to the obvious genetic and organ system differences between our species and theirs.  I could go on and on about the flaws related to nutritional science, but I think you understand my point.  Thus, the best we can do is take the results from (a) pre-clinical studies in cells, tissues, and animals, (b) small short-term clinical trials, and (c) large long-term observational, epidemiological research and try to see what trends, if any, are consistent across the different types of science.

The Science behind a Plant-Based Diet

So, what does some of the science say? Interestingly enough, a rather impressive amount of data (mostly cross-sectional relationships or large epidemiological observations) suggest that eating a predominantly whole-food plant-based (vegetarian or vegan) diet may likely afford you the best opportunity to live a healthier, longer life by avoiding the chronic diseases that typically kill us.  For example, a recent study last year found that among more than 110,000 Americans a high level of animal protein consumption was significantly associated with cardiovascular disease death and a high level of plant protein consumption was inversely related to all-cause and cardiovascular disease death (Song et al., 2016).  The investigators also found that replacing animal protein (particularly from processed red meat) with plant protein was related to lower death.  Another study showed a similar result in over 500,000 participants, as the consumption of red and processed meat was related to moderate risk increases in total death, cancer death, and cardiovascular disease death in both women and men (Sinha et al., 2009).  Besides the lower risk of overall death and death from cardiovascular disease and cancer, plant-based diets have shown:  reversal of severe coronary artery disease (Franklin et al., 1995; Fraser et al., 1995; Gould et al., 1995; Roberts 1995), lower levels of total serum cholesterol and low density lipoprotein cholesterol levels (Melby et al., 1994), lower incidence of hypertension (Beilin, 1994), a lower risk of death due to type 2 diabetes (Dwyer, 1988), and lower rates of lung and colorectal cancers (Key et al., 1996; Mills et al., 1994).

Why do plant-based diets offer such impressive protection from the leading killers of people? The data are pretty clear.  Plant-based diets are typically lower in fat or saturated fat, which has historically been shown to be related to lower death due to cardiovascular disease and cancers (Sinha et al., 2009), although the recent dietary recommendations seem to suggest that other factors may be at play, rather than just fat.  Typically, plant-based diets provide a higher concentration of folate, which reduces serum homocysteine levels, a risk factor for cardiovascular disease (Janelle & Bart, 1995), antioxidants such as vitamins C and E and carotenoids, and other important phytonutrients that are so crucial to health (Jacob & Burri, 1996).  Increased consumption of fiber, vegetables, and fruit are beneficial to the flora and overall environment of the gut (Adlercreutz et al., 1995).  Finally, people eating a plant-based diet have lesser arachidonic, eicosapentaenoic, and docosahexaenoic acid levels and greater linoleate and antioxidant levels in platelet phospholipids, which may be related to decreased atherogenesis and thrombogenesis (Jacques et al., 1995; Sanders et al., 1997; Wolmarans et al., 1991).

Conversely, cooked and/or processed meat provides several carcinogens, including heterocyclic amines and polycyclic aromatic hydrocarbons (Kazerouni et al., 2001; Knize et al., 1994; Sinha et al., 1998a; Sinha et al., 1998b; Skog et al., 1995; Sugimura et al., 1990) and N-nitroso compounds (Cross & Sinha, 2004; Hughes et al., 2001), all related to increased risk of cancer.  Iron in red meat may increase oxidative damage and increase the formation of N-nitroso compounds (Kabat et al., 2007; Kato et al., 1999; Lee et al., 2004; Wurzelmann et al., 1996).  Furthermore, meat is a major source of saturated fat, which has been positively associated with breast (Bingham et al., 2003; Midthune et al., 2008; Thiebaut et al., 2007) and colorectal cancer (The World Cancer Research Fund/American Institute for Cancer Research, 2007).

Conclusion

Although most human cultures have readily consumed animals throughout their history, science has revealed to us in the last 30 years that eating animal foods likely is a significant contributor to early death and chronic disease morbidity from our leading killers.  Food is very personal to most people based on their culture, sociology, psychology, religion, and other important factors, which unfortunately tend to run counter to our physiology and what is healthiest for us.  While many people are likely unwilling to ever completely eliminate eating animal food, it is important for them to at least acknowledge the large body of science in relationship to eating a plant-based diet and what that means for their health.  In this case, “ignorance is NOT bliss,” as people should be aware of the relationships between consuming certain types of foods and the risks of chronic diseases and untimely death.  Just reducing the amount of animal food consumed would have a positive impact, even if eating such foods is never entirely eliminated.  Ultimately, this level of awareness and behavior change should have positive effects on each person’s quality of life and that of our divergent societies and the greater world at large.  Here is to eating a predominantly, whole-food plant-based diet and enjoying greater health for the rest of your life!