Can Common Foods Stop Cancer?

Hippocrates said it first, “Let food be thy medicine”. People have been trying to heal disease with food for thousands of years. Several prominent doctors have claimed that food can even heal cancer. Today I am going to explore one of these claims.

Internal medicine doctor, William Li, gave a viral TED Talk in 2012 describing how he believes food can prevent and even help cure many kinds of cancer. A reader provided me with the link to the talk below and asked for my thoughts.

In order to understand his hypothesis, a little bit of background info on a process called angiogenesis is needed. Here is the description from the National Cancer Institute:

“What is angiogenesis?

Angiogenesis is the formation of new blood vessels. This process involves the migration, growth, and differentiation of endothelial cells, which line the inside wall of blood vessels.

The process of angiogenesis is controlled by chemical signals in the body. These signals can stimulate both the repair of damaged blood vessels and the formation of new blood vessels. Other chemical signals, called angiogenesis inhibitors, interfere with blood vessel formation. Normally, the stimulating and inhibiting effects of these chemical signals are balanced so that blood vessels form only when and where they are needed.

Why is angiogenesis important in cancer?

Angiogenesis plays a critical role in the growth and spread of cancer. A blood supply is necessary for tumors to grow beyond a few millimeters in size. Tumors can cause this blood supply to form by giving off chemical signals that stimulate angiogenesis. Tumors can also stimulate nearby normal cells to produce angiogenesis signaling molecules. The resulting new blood vessels “feed” growing tumors with oxygen and nutrients, allowing the cancer cells to invade nearby tissue, to move throughout the body, and to form new colonies of cancer cells, called metastases.

Because tumors cannot grow beyond a certain size or spread without a blood supply, scientists are trying to find ways to block tumor angiogenesis. They are studying natural and synthetic angiogenesis inhibitors, also called antiangiogenic agents, with the idea that these molecules will prevent or slow the growth of cancer.”

There are many FDA approved drugs that treat cancer by preventing or slowing angiogenesis. Dr. Li promotes these drugs. However, he also makes the claim that many foods work just as well or even better than these drugs at inhibiting angiogenesis.

The Claim

Certain foods can inhibit angiogenesis just as well as or better than drugs to treat cancer patients.

Initial Search

After spending several hours googling things like “cancer diet” and “angiogenesis food”, I kept coming up with results leading me back to Dr. Li’s TED Talk. I also came across several websites and foundations represented by Dr. Li including: Eat to Beat, The Angiogenesis Foundation, Alternative Daily, Forks Over Knives, Food Revolution, Collective Evolution, and everyone’s favorite doctor, Dr. Oz.

Interestingly, not one mainstream reputable source mentioned his hypothesis and I was unable to find other doctors in his line of work. Could it be a conspiracy? Big Pharma? Or…….MONSANTO??? Kidding. But really, he seems to be the only one out there peddling this stuff.

Some of his associations provide links to articles by other professionals. However, you have to register to get access to them and many of the authors don’t have doctorates or even any credentials at all.

Several more reputable sources including: MD Anderson, the American Institute of Cancer Research, the World Cancer Research Fund, and WebMD do list foods that can help lower your risk of cancer. However, they do not discuss angiogenesis. I can’t tell whether it’s because the topic is too scientific or because they help prevent cancer through another mechanism or because they just don’t know how the foods help. None of these sources claim that foods can cure cancer or that foods work as well as or better than drugs for prevention and/or treatment. It’s worth noting that many of the foods are similar to those Dr. Li recommends. All of the food lists are heavy on fruits, veggies, legumes and spices. Some include coffees, teas, nuts and even yogurt and sea foods.

Follow-up Questions

What is the quality of the research to support this claim? Are we going to find a bunch of retrospective observational studies that rely on people to remember what they ate over long periods of time?

Do any animal foods also have anti-angiogenic properties?

Do any studies compare outcomes of cancer patients who treated with diet to those who treated with anti-angiogenic drugs?

Reader Comments (see link above to Dr. Li’s TED Talk via Forks Over Knives)

Peer Reviewed Research

1.Tumor Angiogenesis as a Target for Dietary Cancer Prevention (2012)

This is the only peer reviewed article I found directly linking diet to angiogenesis and cancer treatment. Dr. Li from the TED Talk is the first author. It is not a clinical trial, but a review of how specific micronutrients in specific plant foods promote anti-angiogenesis or otherwise inhibit cancer.

First he presents a list of “angiogenic factors” that have been discovered. He then lists “endogenous inhibitors of angiogenesis” that suppress cancer growth. He then describes how genes work to control when new blood vessels are formed. He states that small cancers are common once people reach about 40-50 years of age and that the inhibitors of angiogenesis prevent these cancers from growing too much and becoming dangerous.

Li goes on to describe how some cancers progress to hyperplasia, dysplasia, and then invasive carcinoma by recruiting surrounding blood vessels and enabling new vessels to form. New blood vessels are able to form “by the production and release of one or more angiogenic growth factors…”. He describes how cancers grow and metastasize from there.

Dr. Li discusses current angiogenic therapies that have been proposed and that are in use today. He stresses early treatment before new blood vessels are able to start forming.

Finally, he lists antiangiogenic factors in common foods. For each food, he cites research that supports how they might be preventing cancer in mice, in vitro (test tube), or in human observational epidemiologic or prospective cohort studies. He provides links to all of the studies cited. The factors he describes include:

Green tea catechins, genistein (found in soy beans), resveratrol (found in mulberries, peanuts, grapes, and grape products), lycopene (found in tomatoes, watermelon, and papaya), omega-3 polyunsaturated fatty acids (found in salmon, herring, mackerel, anchovies, sardines and trout), glucosinolates, isothiocynates and indole-3-carbinol (found in cruciferous vegetables such as cabbage, broccoli, cauliflower, collard greens, mustard greens, radishes, brussel sprouts, bok choy, and kale), flavonoids and quercetin (found in many fruits and vegetables), anthocyanins (pigments in berries and grapes), proanthocyanidins (found in cacao and some fruits and vegetables), ellagitannins (found in fruits, vegetables and nuts), manaquinone (vitamin K2 found in dark leafy vegetables and cheese), curcumin (turmeric), beta-cryptoxanthin (found in brightly colored foods).

In the discussion section, Dr. Li does state some of the flaws in the types of studies he reviewed. No human controlled experimental trials have been done. However, he still trusts overall that foods with antiangiogenic factors will help prevent cancer. Interestingly, his paper does not make the claim that these foods work as good as or better than cancer treatments that are already on the market. Instead, he suggests that these foods should be used to help prevent cancer rather than to treat. The paper also never makes bold claims that eating these foods will prevent cancer; only that they may lower one’s chances. Most of the studies he cited showed modest reductions in specific forms of cancer paired with study designs that are known to have high rates of error.

Many other studies address how certain diets can impact cancer. However, I did not find anything other than Dr. Li’s article that claims that the diets are working by inhibiting the growth of new blood vessels. Here are a few reviews, meta-analyses, and one randomized trial I found related to the general question of how diets may cause or help prevent cancer.

2. Influence of a diet very high in vegetables, fruit, and fiber and low in fat on prognosis following treatment for breast cancer: the Women’s Healthy Eating and Living (WHEL) randomized trial. (2007)

CONCLUSION: Among survivors of early stage breast cancer, adoption of a diet that was very high in vegetables, fruit, and fiber and low in fat did not reduce additional breast cancer events or mortality during a 7.3-year follow-up period.

3. Roles of caloric restriction, ketogenic diet and intermittent fasting during initiation, progression and metastasis of cancer in animal models: a systematic review and meta-analysis. (2014)

CONCLUSIONS: Caloric restriction and ketogenic diet are effective against cancer in animal experiments while the role of intermittent fasting is doubtful and still needs exploration. More clinical experiments are needed and more suitable patterns for humans should be investigated.

4. Vegetarian diets, low-meat diets and health: a review. (2012)

RESULTS: Both vegetarian diets and prudent diets allowing small amounts of red meat are associated with reduced risk of diseases, particularly CHD and type 2 diabetes. There is limited evidence of an association between vegetarian diets and cancer prevention. Evidence linking red meat intake, particularly processed meat, and increased risk of CHD, cancer and type 2 diabetes is convincing and provides indirect support for consumption of a plant-based diet.

5. Diet and cancer: risk factors and epidemiological evidence. (2014)

CONCLUSIONS: There is a direct relationship between unhealthy diet and lifestyle with the increase of tumor development and cancer risk. For this reason, a good nutritional status based on a balanced diet constitutes one of the main preventive factors from tumors. However the mixed results from epidemiologic studies hinder to get unequivocal and consistent evidence about the interaction between diet and cancer risk. More epidemiological studies will be needed in the future to clarify this issue.

6. Diet and Colorectal Cancer Risk in Asia–a Systematic Review.

ABSTRACT SELECTION: We found that red meats, processed meats, preserved foods, saturated/animal fats, cholesterol, high sugar foods, spicy foods, tubers or refined carbohydrates have been found by most studies to have a positive association with colorectal cancer risk. Inversely, calcium/dairy foods, vitamin D, general vegetable/fruit/fiber consumption, cruciferous vegetables, soy bean/soy products, selenium, vitamins C,E and B12, lycophene, alpha-carotene, beta-carotene, folic acid and many other vitamins and minerals play a protective role against colorectal cancer risk. Associations of fish and seafood consumption with colorectal cancer risk are still inconclusive due to many varying findings, and require further more detailed studies to pinpoint the actual correlation. There is either a positive or no association for total meat consumption or white meats, however their influence is not as strong as with red and processed meats.

7. Nutrition and cancer. (2015) translated from Spanish

RESULTS: Fruits and vegetables are the foods that can prevent from cancer disease, soya and fishes also have demonstrated as preventive from some types of malignancies. Clear factors causing cancer are red meat and processed meat, dairy products and alcohol. The protective roles of vitamins, antioxidants and micronutrients still have to be deeply investigated. Obesity is a clear risk factor for cancer, calorie reduction has been proposed as a factor that has protective properties in laboratory studies, but this has to be demonstrated in a clinical scenario.

8. Meat, dairy, and cancer. (2014)

ABSTRACT: In 2007 the World Cancer Research Fund and American Institute for Cancer Research (WCRF/AICR) report judged that the evidence for an association between red and processed meat consumption and colorectal cancer was convincing. In addition, the effect of other animal products on cancer risk has been studied, and the WCRF/AICR report concluded that milk probably decreases the risk of colorectal cancer but diets high in calcium probably increase the risk of prostate cancer, whereas there was limited evidence for an association between milk and bladder cancer and insufficient evidence for other cancers. There are several potential mechanisms relating meat to cancer, including heterocyclic amines, polycyclic aromatic hydrocarbons, N-nitroso compounds, and heme iron. Although the evidence in favor of a link between red and processed meat and colorectal cancer is convincing, the relations with other cancers are unclear. In this review, we summarize cohort studies conducted by the National Cancer Institute on meat and dairy intake in relation to cancer since the 2007 WCRF/AICR report. We also report the findings of meta-analyses published since 2007.

9. Dairy products and cancer. (2011)

ABSTRACT SELECTION: Based on a systematic review of the epidemiologic literature, the World Cancer Research Fund and American Institute for Cancer Research report concluded there was a probable association between milk intake and lower risk of colorectal cancer, a probable association between diets high in calcium and increased risk of prostate cancer, and limited evidence of an association between milk intake and lower risk of bladder cancer. For other cancers, the evidence was mixed or lacking.

10. Adherence to Mediterranean diet and risk of cancer: an updated systematic review and meta-analysis of observational studies. (2015)

ABSTRACT SELECTION: The aim of the present systematic review and meta-analysis of observational studies was to gain further insight into the effects of adherence to Mediterranean Diet (MD) on overall cancer mortality, incidence of different types of cancer, and cancer mortality risk in cancer survivors. An overall population of 1,784,404 subjects was included in the present update. The highest adherence score to an MD was significantly associated with a lower risk of all-cause cancer mortality, colorectal cancer, breast cancer, gastric cancer, prostate cancer, liver cancer, head and neck cancer, pancreatic cancer, and respiratory cancer. No significant association could be observed for esophageal/ovarian/endometrial/and bladder cancer, respectively. Among cancer survivors, the association between the adherence to the highest MD category and risk of cancer mortality, and cancer recurrence was not statistically significant. The updated meta-analyses confirm a prominent and consistent inverse association provided by adherence to an MD in relation to cancer mortality and risk of several cancer types.

11. Mediterranean diet and cancer: epidemiological evidence and mechanism of selected aspects. (2013)

DISCUSSION: The most recent pooled analyses of epidemiological studies supported strongly the hypothesis that the Mediterranean diet may play a role in preventing several types of cancers, especially those of digestive tract, whereas contrasting results were reported for hormone-dependent cancers. Specific aspects of the Mediterranean diet such as high fruit and vegetables and low red processed meat intake may explain such protective effects. Moreover, evidence regarding olive oil and whole grains increase the beneficial effects of such dietary pattern against cancer.

12. Nutrition and prostate cancer: an overview. (2014)

ABSTRACT SELECTION: Obesity and metabolic syndrome are important risk factors for prostate cancer and their management is key. The amount and type of fats consumed are also clearly related to prostate cancer risk. Saturated fats and trans fats are identified as having a negative impact. Nutraceuticals and supplements, particularly antioxidants, polyphenols and soy have evidence for benefit for prevention of prostate cancer and progression of the disease.

13. Ketogenic Diet and Cancer-a Perspective. (2016)

ABSTRACT SELECTION: Exercise or severe restriction of caloric intake is not always advisable for patients, in particular those suffering from cancer. The ketogenic diet (KD), characterized by high fat, moderate protein and very low carbohydrate composition can evoke a physiological state similar to that triggered by exercise or fasting. These attributes of KD prompted its possible use in treatment of a number of metabolic diseases, including several types of malignancies. Although results from clinical studies employing KD in the treatment of cancer are still limited, the results obtained from animal models are encouraging and show that KD presents a viable option as an adjunct therapy for cancer.

14. The role of dietary factors in prevention and progression of breast cancer. (2014)

RESULTS: Consumption of well-done red meat appears to be associated with increased risk of BC, whereas fish may be protective. Total cholesterol, triglyceride levels and glycaemic load should be monitored and controlled in at risk populations because they may be associated with increased risk of BC, although the exact mechanisms involved are not clear. Alcohol intake should be minimized since it is a risk factor for BC. High intake of polyphenol/phyto-oestrogen -rich food (i.e. flavonoids, soya products), as well as fibres, fruits and vegetables, may have potential protective effects against BC occurrence but the results might vary according to hormonal status. Vitamin D supplements appear protective against BC development and similarly other vitamins and oligo-elements might decrease BC risk, although further large prospective studies are required.

15. Dietary intake and ovarian cancer risk: a systematic review. (2014)

ABSTRACT SELECTION: Higher risk for ovarian cancer was shown for total, animal, and dairy fat (five of nine studies), as well as total nitrate and possibly total vitamin C. No associations were demonstrated for red meat, fiber, vitamin A, vitamin E, β-carotene, or folate. Vegetables were associated with lower risk in one of three studies; fruit showed no association, although risk estimates were all greater than 1.0. Isoflavones and flavonoids were associated with modestly lower risk in two studies and tea intake was associated with lower risk in one of two studies. This review suggests that no specific dietary factors are consistently associated with ovarian cancer risk.

What we know and don’t know:

After the research, we can see that angiogenesis is a necessary process for cancers to grow and become dangerous. We know there are FDA approved drugs to help slow this process. We also know that people who eat a lot of fruits, vegetables, fish, soy, and tea tend to have lower chances of developing most types of cancer than people who drink a lot of alcohol, eat a lot of red and processed meat, eat a lot of trans and saturated fat, and eat foods cooked at high temperatures. There is quite a bit of data to support these general ideas, but few randomized control trials. That means it may be hard to assign cause and effect and the studies may have other various flaws making them less reliable.

Research does not directly support that eating certain properties of plant foods can prevent cancer from establishing a blood supply. However, the research does not directly deny that this is happening. I wasn’t able to find any studies to directly test this hypothesis. No studies were found that compare treating patients with medication to treating patients with diet.

Even if plants are helping to protect people from cancer by way of antiangiogenic properties, it is highly unlikely that plant foods could replace medications. Dr. Li himself doesn’t even suggest this in his own paper. Additionally, Dr. Li’s research supports consumption of certain animal products such as fish, which is conveniently overlooked when presented by vegan groups.

Another common theme throughout the research in the relationship between cancer and diet is simply that eating less can help. Several studies show that reducing calories lowers the chance of developing cancer and that being overweight is a huge cancer risk factor. Some studies also show that a ketogenic diet can prevent and even help treat cancer. In fact, I was able to find more support for ketogenic diets as a cancer treatment than for vegan or nearly vegan diets.

Conclusions and applications:

What should we do with this information? Here’s my list of ideas based on my research:


  • Eat lots of fruits and vegetables every day
  • Eat fish several times a week
  • Soy products are probably good for you, although this is another hot topic
  • Avoid processed meat
  • Eat less red meat and opt for cuts that don’t need to be well done
  • Avoid processed foods, trans fats and sugar
  • Avoid alcohol
  • Maintain a healthy weight
  • If you already have cancer, traditional treatments work better than a plant-based diet, although a ketogenic diet may be helpful.

Should I go Vegan?

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.

The Claim:

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.

Follow-up questions

  • 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!)

Peer-reviewed research

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. (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. (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)

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)

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)

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)

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)

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)

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)

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. (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.

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!