Every few years, Netflix stirs the pot with another vegan “documentary”. First it was Food Inc. and Forks Over Knives, then Cowspiracy, and, most recently, What the Health. I’m sure there have been others. These films can be pretty convincing and surely do tempt some people to try veganism for themselves. They do a great job of presenting peer reviewed studies to support their claims. They also show remarkable recoveries from chronic disease.
However, as I’m sure you suspect, they use some pretty sneaky tactics to overstate their claims. They usually cherry pick their studies while ignoring everything that might conflict with their agenda. They report relative rather than absolute risks. They interview doctors who have personal biases. They malign research and medical agencies that refuse to change their policies based on cherry-picked evidence. They try to convince people that correlation is causation. And sometimes, they even lie outright.
Many bloggers and YouTubers have already “debunked” a lot of the points in these films. My purpose in this blog, therefore, is not to repeat what many have already said. My purpose is to determine what the research really says about vegan diets.
If you eat a whole-foods, plant-based vegan diet, you will not get heart disease, diabetes, or other symptoms of metabolic syndrome. If you already have these diseases, a vegan diet will cure them.
Results from initial search:
There are many reasons why people might choose a vegan diet. Some believe it’s healthier than eating meat while others are more concerned about the environment and animal welfare. It’s widely accepted a vegan diet can be a very healthy option as long as you are sure to get a variety of proteins from different grain and legume combinations, supplement with vitamin B12, and possibly add other supplements to get essential fatty acids.
Most experts also agree that farmed animals are causing plenty of environmental harm, not to mention harm caused to the animals themselves. These concerns are certainly valid. Some people argue that if you purchase animal products from local farmers markets, you can avoid supporting factory farming and have less impact on the environment. Others disagree, stating that all animals fear death and should not be slaughtered for food.
The environmental and animal welfare aspects of a vegan diet, while important, are not within the scope of this blog. I will say that personally, I believe it’s important to support local farms and farms that allow animals to live as naturally as possible. The “Certified Humane” stamp on some animal products is the best indicator of humane animal treatment that can be found at typical grocery stores. Other markers such as “pasture-raised” or “free range” are misleading and practically meaningless when issued by the USDA.
When it comes to the health benefits of a vegan diet, there is quite a bit more controversy. Some pro-vegan arguments include:
- Vegan diets help mitigate some of the world’s biggest health issues such as obesity, diabetes, heart disease and cancer because plants are high in fiber, vitamins, minerals, and antioxidants while being low in saturated fat.
- Processed meat causes cancer.
- Animal products contain saturated fat which caused heart disease.
- You can get more than enough protein by eating and combining high protein grains and legumes.
- Groups of people who live the longest usually eat vegetarian or vegan diets.
- Vegan diets are better for you gut health.
Some pro-omnivore arguments include:
- Iron, zinc, calcium, vitamin B12, DHA and EPA are lacking in vegan diets. Over time, these cause bone loss, heart disease, and other health problems.
- People have been eating meat and animal products for thousands of years. Refined grains and sugar are really what’s causing increased rates of metabolic syndrome and cancer.
- It can be difficult to get enough complete protein through plant sources alone.
- If you supplement and make sure you’re eating foods high in protein, is it really that hard to get all your nutrition from a vegan diet?
- It seems the jury is still out on saturated fat. Could it affect different people differently?
- Have studies compared vegan diets to other whole food diets that include meat or just to the standard American diet?
- If vegans really do have better metabolic profiles, how much better are they?
- Many studies may claim to demonstrate health benefits of vegan diets. Are there other studies that claim equivalent or even better health benefits of other diets?
Reader comments and questions (send me some!)
Inclusion criteria: search terms “vegan diet” on PubMed. Published in last 10 years. Reviewed first 5 pages of results. Vegan diet compared to another diet considered to be healthy. Outcomes related to disease markers for diabetes and heart disease in humans. Italics are my interpretation.
1.Veganism Is a Viable Alternative to Conventional Diet Therapy for Improving Blood Lipids and Glycemic Control. https://www.ncbi.nlm.nih.gov/pubmed/24922183 (2015)
No access to full text. Conclusion suggests vegan diets are somewhat better than healthy omnivorous diets to help people with type 2 diabetes and/or high cholesterol. The authors seem to have reviewed several studies to come to this conclusion. We can’t tell how much better vegan diets are or whether or not the results were clinically significant.
2. Beyond meatless, the health effects of vegan diets: findings from the Adventist cohorts. https://www.ncbi.nlm.nih.gov/pubmed/24871675 (2014)
Full text available. This study compares large groups of vegan/vegetarian, and omnivorous Adventists from several different studies. Vegetarians had a 55% lower chance of developing hypertension and a 25-49% lower chance of developing type-2 diabetes than omnivores. Vegetarians had a 23% lower chance of developing GI cancers, a 50% lower chance of developing colon cancer, and a 35% lower chance of developing prostate cancer. When vegans and vegetarians were separated out, the vegans had even lower chances of developing these diseases. This study only reported relative percentages, not absolute percentages. This study makes a good argument that a vegetarian diet is at least slightly healthier than a diet that includes meat in terms of chronic disease.
3. Vegan diet and blood lipid profiles: a cross-sectional study of pre and postmenopausal women. (2014) https://www.ncbi.nlm.nih.gov/pubmed/24712525
Full text available. This study measured different types of cholesterol in vegetarians, vegans, and omnivores. We now know that HDL cholesterol is good and LDL cholesterol is bad. Many doctors look at the ratio of LDL to HDL and consider it to be a much better measure of health than looking at total cholesterol or LDL or HDL alone. This study says that in premenopausal women, a vegan diet decreases HDL, but does not decrease LDL. The vegetarian diet decreases HDL, but decreases LDL even more. Therefore, the vegetarians would have a better ratio than the vegans. The omnivore ratio was comparable to the vegetarians. The findings only applied to the premenopausal group.
4. Effect of a 6-month vegan low-carbohydrate (‘Eco-Atkins’) diet on cardiovascular risk factors and body weight in hyperlipidaemic adults: a randomised controlled trial. (2014) https://www.ncbi.nlm.nih.gov/pubmed/24500611
Full text available. 50 people were divided into 2 groups of 25 (one group ate a low carb vegan diet while the other group ate a high carb vegan diet). After 6 months, only 13 people were left in the high carb group and 10 in the low carb group. It seems that the main finding in this study is that the diets aren’t easy to stick to. In the end, most people in the low carb group had better cholesterol than those in the high carb group. However, people in both groups made significant progress in terms of weight loss and cholesterol.
5. Effect of a Brown Rice Based Vegan Diet and Conventional Diabetic Diet on Glycemic Control of Patients with Type 2 Diabetes: A 12-Week Randomized Clinical Trial. (2016) https://www.ncbi.nlm.nih.gov/pubmed/27253526
Full text available. A strict vegan diet controls blood sugar better than a healthy omnivorous diet, but for most people, it’s very hard to stick to. The difference between how much each diet decreased blood sugar was relatively small. However, the sample size was small and compliance with the diets varied.
6. Comparison of a Restricted and Unrestricted Vegan Diet Plan with a Restricted Omnivorous Diet Plan on Health-Specific Measures. (2015) https://www.ncbi.nlm.nih.gov/pubmed/27417779
Full text available. 12 people ate a plant based vegan diet with no refined grains, sugar, or sweeteners. 12 people ate a similar diet, but were allowed lean protein and skim milk. 11 people ate a vegan diet, but were allowed refined grains, sugar, and sweeteners. Participants ate these diets for 21 days. All 3 diets showed improvements in health. Cholesterol was improved in the vegan and non-vegan groups who avoided refined grains and sugar. Cholesterol did not improve in the vegan group that continued eating refined grains and sugar. Blood pressure was reduced in all groups, but most in the vegan group that avoided refined grains and sugar.
7. Effect of diet on type 2 diabetes mellitus: a review. (2014) https://www.ncbi.nlm.nih.gov/pubmed/24352832
No access to full text. Vegan, vegetarian, low carb, and Mediterranean diets have all helped people with type 2 diabetes to control their blood sugar. Different people respond differently.
8. A low-fat vegan diet and a conventional diabetes diet in the treatment of type 2 diabetes: a randomized, controlled, 74-wk clinical trial. (2009) https://www.ncbi.nlm.nih.gov/pubmed/19339401
Full text available. 49 people were assigned to the low-glycemic vegan group and 50 to the conventional healthy diet group. The study lasted 74 weeks. Both groups improved in terms of weight, blood sugar, and cholesterol. Blood sugar and cholesterol improved significantly more in the vegan group than the conventional group.
9. Vegetarian diets and incidence of diabetes in the Adventist Health Study-2. (2013) https://www.ncbi.nlm.nih.gov/pubmed/21983060
More than 40,000 healthy people were studied. They were categorized as either: vegan, lacto ovo vegetarian, pesco vegetarian, semi-vegetarian or non-vegetarian (reference group). The researchers wanted to see how many developed diabetes over the next 2 years. Diabetes developed in 0.54% of vegans, 1.08% of lacto ovo vegetarians, 1.29% of pesco vegetarians, 0.92% of semi-vegetarians and 2.12% of non-vegetarians. After other lifestyle factors were controlled for, vegan and vegetarian diets (but not ones including fish) still offered protection against diabetes. Black people were more likely to develop diabetes than white people, but all people benefited from a vegetarian diet.
10. A two-year randomized weight loss trial comparing a vegan diet to a more moderate low-fat diet. https://www.ncbi.nlm.nih.gov/pubmed/17890496 (2007)
This is a randomized trial which can provide more reliable evidence than retrospective or observational studies. The researchers compared a low fat mostly vegan diet to a more traditional low fat/low cholesterol diet. However, the vegan diet did allow for a very small amount of meat and dairy. They also studied whether group support meetings were helpful. All participants were postmenopausal women. After 2 years, the vegan group had kept off about 3 kilograms whereas the control group had kept off about 1. This study only measured weight loss, but we know that being overweight is strongly associated with metabolic syndrome.
11. Comparative effectiveness of plant-based diets for weight loss: a randomized controlled trial of five different diets. https://www.ncbi.nlm.nih.gov/pubmed/25592014(2015)
Full text not available. This study assigned 63 overweight people to vegan, vegetarian, pesco-vegetarian, semi-vegetarian or omnivorous diets. The vegan group lost an average of 7.5% of their body weight after 6 months. The other groups lost about 3%. Calories were not purposefully restricted.
What we know and don’t know
Looking at these studies, we can see that a vegan diet may be a good idea for some people. But, as expected, the results were not as incredible as our favorite Netflix documentaries would suggest.
All of the research I found supports a vegan diet in people who are at risk for metabolic syndrome. However, the effects of the diet were modest and some studies show the diet can be hard to stick to. When people are allowed to eat freely without counting calories, they tend to lose only 5-10% of their body weight by switching to a vegan diet. This moderate amount of weight loss does seem to help reduce other markers of disease, so a vegan diet is likely to help people at risk. However, it is an overstatement to say that a vegan diet cures metabolic diseases.
The studies here did present a few flaws/risks that should be mentioned. First, vegan diets tend to lower good cholesterol (HDL) more than bad cholesterol (LDL) in some people. This may actually give some people a worse overall cholesterol profile. Additionally, most of these studies didn’t parse out different populations of people. For example, we know the diet can help middle aged people who are overweight, but is it also good for children, athletes, or expectant mothers? There are studies available to address these questions, but they were not reviewed here. It does seem that for the populations studied, it is reasonable to get all your nutrition from a vegan diet plus a vitamin B12 supplement.
Several of these studies found that reducing or eliminating refined grains and sugars had equal or even better results than avoiding animal products on health outcomes. Many did not allow the vegan group or the control group to eat refined carbohydrates because they purpose was to compare a vegan diet with another “healthy” diet. This suggests that a diet low in processed foods is healthier than a diet low in animal products, but, that a diet low in both categories of foods may be best.
In these studies, saturated fat was assumed to be “unhealthy” from the beginning. Therefore, it is difficult to determine what effects would be seen if saturated fat levels were increased. Other studies do address this question, but not within the context of a vegan diet.
It is important to remember that in all studies that are not double-blind, randomized, controlled, and include placebo, there is some room for bias. These studies generally found somewhat better health outcomes for vegans than for other groups. There are other studies that show better outcomes for other diets such as Mediterranean or paleo. These diets could each deserve their own blogs.
Conclusions and Applications
This research confirms one of my favorite quotes by author Michael Pollan.
Eat food, mostly plants, not too much.
Over and over we see that these are words of wisdom to live by if you want to be as healthy as possible. I might add slightly alter the quote to include the words “ethically sourced” if it were me.
Please share your comments and thoughts!