As of yesterday afternoon, I finished my master’s degree project!!!
I still have one more class to finish this fall before I will get my master in public health nutrition, but this was definitely the biggest part of my degree and took me nearly eight months from planning to completion.
Last fall when I started doing the planning, I reached out to several organizations to see about opportunities for collaborating. It turns out that Dr. Neal Barnard of the Physicians Committee for Responsible Medicine (PCRM) was planning an update to a paper and needed some background research done.
Dr. Barnard is one of my heroes and I didn’t have to think twice before realizing that this was a fantastic chance for me to use my project as a way to help. I also had the opportunity to work with another icon in the world of vegetarian nutrition, Dr. Reed Mangels, who acted as my advisor.
By the way, for anyone who does research-based or scientific work for a living, you have my sincere regard. I really had no idea of what I was getting myself into until I got in far enough that there was no turning back. 🙂
However, I survived and lived to tell about it (yay!).
This is an untraditional blog post for me, but I’m presenting you with the abstract from my paper and then some of the highlights. I’m not including the full references, but if you are curious about a certain study or want to read my paper in its entirety, please feel free to email me at carrieonvegan@gmail DOT com.
I’m also including some of the slides that were part of my project presentation.
“The Difference in Selected Disease Occurrence Between Vegetarians and Non-Vegetarians”
Introduction: With rising healthcare costs in the United States (US), it is important to identify modifiable risk factors for diet-related diseases and conditions. One such modifiable choice is diet.
Objective: The objective of this review is to identify and review the scientific literature in the English language published between 1995-2013 on the difference in selected disease occurrence between vegetarians and non-vegetarians. The diseases being studied are type 2 diabetes, hypertension, ischemic heart disease (IHD), cancer, gallbladder disease, obesity-related musculoskeletal disorders, and foodborne illness.
Methods: Searches for each disease or condition were performed for relevant articles published between January 1995 and March 2013 primarily using the PubMed database. The search included all articles in the English language, including international articles, for all age groups, ethnicities and ages.
Results: The literature supports the assertion that vegetarian dietary patterns have associations with reduced risk of type 2 diabetes, hypertension, and IHD, with less consistent protective associations with cancer. There is no evidence showing a lower prevalence of gallbladder disease and obesity-related musculoskeletal disorders between vegetarians and non-vegetarians, and no research available comparing the differences in foodborne illness between these dietary groups.
Overview of Differences in Disease Between Vegetarians vs. Non-Vegetarians:
- 6 of 7 studies found showed reduced occurrence of diabetes in veg vs. non-veg.
- 2008 article part of AHS-1 looked at over 8,400 subjects and found an odds ratio for subjects consuming any amount of meat at least once weekly and incidence of diabetes was 1.29 compared to no meat consumption.
- Fraser article from 1999 also part of AHS-1 found that the statistically significant odds ratio for nonvegetarians and diabetes was 1.97 for men and 1.93 for women (not adjusted for BMI).
- 2009 article from Adventist Health Study-2 with 60,000 subjects. Odds ratio for type 2 diabetes when adjusted for BMI was 0.51 for vegans (95% CI 0.40-0.66), 0.54 for lacto-ovo (95% CI 0.49-0.60), 0.70 pesco-ovo (95% CI 0.61-0.80), and 0.76 for semi-vegetarians (95% CI 0.65-0.90), compared with non-vegetarians. When not adjusted for BMI, the statistically significant odds ratio for type 2 diabetes was more pronounced.
- Lower rates of diabetes found among vegetarians is likely due to their lower rates of obesity, but seem to extend beyond body mass. Three of the seven studies in this review adjusted for BMI and still found statistically significant differences in disease occurrence. Could be due to adverse consequences of metabolizing meat, protective effects of dietary components vegetarian diets such as fruits, vegetables, whole grains and legumes, or a combination of the two.
- Research seems to show that vegetarian diets may be protective against diabetes.
- 5 of 7 studies showed reduced occurrence of hypertension in veg vs. non-veg.
- Appleby study compared both blood pressure and hypertension between four dietary groups: meat eaters, fish eaters, vegetarians, and vegans using data from 11,000 subjects as part of EPIC-Oxford. The prevalence of hypertension in men was 15.0% for meat eaters, 9.8% for fish eaters, 9.8% for vegetarians, and 5.8% for vegans with similar results for women.
- Fraser examined incidence data from over 34,000 subjects as part of the Adventist Health Study-1. The odds ratio for nonvegetarians and hypertension was 2.23 for men and 2.24 for women, compared respectively to men and women vegetarians in the cohort.
- Five of the seven studies from this review found statistically significant associations between vegetarian diets and a lower prevalence of hypertension. Two of the studies adjusted for BMI which then resulted in a lack of significance between diet and hypertension. Therefore, it appears as if the effect of vegetarian diets on hypertension is related to the lower body mass of those subjects. While the Pettersen et al. (2012) study noted the higher fiber and potassium intakes in vegetarians, more research is required to determine the specific mechanisms by which vegetarian diets influence a lower prevalence of hypertension, outside of a lowered body mass.
- However, research does seem to support a reduced occurrence of hypertension and vegetarian diets.
Ischemic Heart Disease:
- 5 of 7 studies showed reduced occurrence of IHD in veg vs. non-veg.
- One of the most important studies of IHD and diet came from the EPIC-Oxford cohort that included over 40,000 subjects and showed a statistically significant hazard ratio for the risk of IHD of 0.68 for vegetarians versus non-vegetarian.
- Even more so than identifying risk of developing cardiovascular disease, a meta-analysis from Huang in 2012 identified the relative risk of 0.71 for death from IHD for vegetarians compared with nonvegetarians.
- A 2013 article from Crowe hypothesized that the lower risk ratios are a result of reduced risk factors for IHD among vegetarians, including better lipid profiles and lower BMI. Research suggests that a vegetarian diet may be protective against both the risk of and mortality from IHD.
- The literature review for studies examining the differences in the occurrence or risk of cancer between vegetarians and non-vegetarians resulted in ten relevant articles, including one meta-analysis.
- The studies were varied in their approaches; two evaluated overall mortality rates from cancer in vegetarians and non-vegetarians, four looked at the differences in incidence of specific types of cancer between dietary groups, and four reviewed both specific and overall cancer incidence.
- In all but one of the six studies that examined an association between overall incidence of or mortality due to malignant neoplasms, there was a statistically significant reduced risk for vegetarian dietary groups.
- A meta-analysis by Huang included data from over 124,000 subjects. Results from this meta-analysis showed a statistically significant relative risk of 0.82 for incidence of overall cancer for vegetarians versus non-vegetarians.
- A 2013 article evaluated associations between dietary patterns and cancer incidence using data from the Adventist Health Study-2 and nearly 70,000 subjects. The hazard ratio for risk of cancer of any type was statistically significant 0.92. HR for cancer of the GI tract was also statistically significant at 0.76. Vegan diets had a statistically significant HR of 0.84 for all cancers. While overall the trend showed lower associations between cancers and variations of the vegetarian diet, no statistically significant associations were made between a vegetarian diet and cancers of the respiratory tract, urinary tract, male cancers, and female cancers. There was a statistically significant hazard ratio of 0.71 for female cancers and a vegan diet.
- More research is needed to determine the association between vegetarian diets and both overall and specific cancer rates and whether any protection comes from the lack of meat consumption or as a result of increased fruits and vegetables, a combination of both, or because of other factors such as BMI. It could be hypothesized that cancers of the GI tract may be more affected by a diet rich in dietary fiber, fruits and vegetables, due to decreased transit time or increased intake of antioxidants. If meat consumption has an effect on hormone levels, then cancers of the reproductive system may be affected more by dietary patterns. Lastly, the difficulty in examining the question of diet and the causes of cancer should be noted due to the fact that many cancers take years to develop and that various aspects of the diet may affect the risk for various types of cancer differently. Additionally, special attention should be paid to the differences in vegetarian and vegan diets and whether or not those variation have an effect on the development of specific or overall types of cancer.
- Three relevant studies found, but none showed association between gallbladder disease and a vegetarian diet.
Obesity-Related Musculoskeletal Disorders:
- The focus of this section was on musculoskeletal disorders because many of the other conditions associated with obesity were captured in other sections. Conditions examined included osteoarthritis and increased risk of fracture or injury related to overweight or obesity.
- There was one article relevant to this study of the differences between obesity-related musculoskeletal disorders between vegetarians and non-vegetarians from Hailu, et al. (2006). Data came from the Adventist Health Study. The statistically significant odds ratio for the prevalence of degenerative arthritis and soft-tissue disorders for women who consumed greater than or equal to one serving of meat a week compared to women who never consumed meat was 1.49 and was 1.43 for men.
- The authors hypothesized that this increased risk for these conditions may be due to the increase in overall inflammation in the body resulting from the consumption of meat or an associated higher BMI seen in meat-eaters.
- No relevant articles were found that examined the differences in the prevalence of foodborne illness between vegetarians and non-vegetarians.
Special Note on Vegan Diets:
When the studies included in this review examined various dietary patterns, the results showed that subjects identified as consuming vegan diets as categorized by not including any animal products or by eating meat, fish, and dairy less than once a month (Petterson, et al., 2012), had the lowest risk ratios for diabetes (Tonstad, 2009), hypertension (Appleby, 2002; Pettersen, 2012), and cancer (Tantamango-Bartley, 2013). These findings suggest that the protection against disease by vegan dietary patterns is a subject worth further investigation.
My literature review found statistically significant research supporting differences in the occurrence of diabetes (type 2 was primarily addressed in the literature), hypertension, IHD, and certain types of cancer as well as the overall risk of malignant neoplasms, between vegetarians and non-vegetarians. There was no evidence supporting the differences in the prevalence of gallbladder disease and arthritis between these dietary groups and no research found that studied the difference in foodborne illness between vegetarians and non-vegetarians.
So how did I celebrate finishing my master’s degree final project? I know it’s a bad idea to use food as a reward, but a Peanut Butter Pie made from silken tofu, PB, dates, and vanilla bean served in a raw crust seemed in order:
What’s next for me? It’s onto bigger and better things, I hope. As mentioned, I have one more class for my degree that will keep me busy through the end of the year. I’m still formulating my plans for what I will do after that. I seriously considered applying to a doctorate program in public health, but my heart is telling me to focus on more creative and practical pursuits for at least a little while. For now, that means more blogging and recipe creating…exactly what I love doing the most!
Thank you to everyone who supported me during the past several months and to you for being patient when I took time away from my blog to focus on my research.
Like the end of my pie, it’s the end of an era, but I can’t wait to see what’s next!