People on a plant-based diet are consistently slimmer and healthier than meat eaters, with a lower risk of cardiovascular disease, cancer and diabetes, according to research unveiled at the 6th International Congress on Vegetarian Nutrition (ICVN).
The headline-grabbing news from the three-day conference at Loma Linda University in California, was the results of a clinical trial - published today in the New England Journal of Medicine - which found that primarily plant-based diets supplemented with nuts and virgin olive oil can reduce risk of cardiovascular events by 30%. Click here for details.
However, vegetarians - who typically have lower blood pressure and lower LDL cholesterol - also have a lower BMI, lower fasting blood glucose (resulting in a lower incidence of type 2 diabetes) and a lower risk of developing certain cancers (notably stomach cancer), said successive speakers at the event, which attracted more than 750 delegates from all over the world.
Why are the health outcomes of vegetarians better?
Precisely why remains the subject of intense debate, with some speakers suggesting that vegetarians’ lower calorie intake - and lower BMI - is the critical factor from which the other health benefits all stem; but others claiming that higher levels of fiber and health-promoting phytochemicals, coupled with lower levels of saturated fat may be responsible.
Other argued that vegetarians might simply be better educated, more health-conscious, more disciplined or less likely to smoke and drink.
But regardless of the reason, the epidemiological evidence that people on plant-based diets have a reduced risk of chronic disease is pretty compelling, said Gary Fraser, PhD, who presented findings from an analysis of data from the Adventist Health Study-2*, a cohort of 96,000 adults in the US and Canada that have been monitored since 2002.
Results to date show that vegetarians, especially vegans, have much lower BMI than non-vegetarians, he said. "Blood pressures and serum cholesterol is lower in vegetarians, as is the prevalence of hypertension and hyperlipidemia. Prevalence and incidence of diabetes is lower, as are levels of fasting glucose."
"Risk factors for cancer, including blood insulin, and CRP are lower in vegetarians, but IGF-1 and IGFBP-3 are low in vegans and non-vegetarians but higher in lacto-ovo vegetarians. Measures of immune function such as IL-6, IL-10 and TNF-alpha did not vary significantly by dietary pattern."
The challenge when trying to describe vegetarianism as a dietary pattern, is that there are so many different variations on the vegetarian diet
Preliminary total cancer incidence data also indicates lower risk among vegans when compared to non-vegetarians in the cohort, he added. "Regarding total mortality the main observation is that all vegetarian categories combined have significantly lower mortality than non-vegetarians. Cardiovascular, endocrine (mainly diabetes), and renal deaths were significantly lower among vegetarians.
“There’s not a clear consensus as to why vegetarians have better health outcomes, but clearly the lower BMI must play a key role”, he told FoodNavigator-USA.
“The challenge when trying to describe vegetarianism as a dietary pattern, is that there are so many different variations on the vegetarian diet, from vegans (who eat no animal products), lacto vegetarians (who eat eggs and dairy), to pesco vegetarians (who eat fish, but not meat), before you even get to the difference between a vegetarian in the UK or the US versus a vegetarian in India or Africa.”
And then within all of these subgroups, he says, “you have the vegetarians who get their protein from grains and legumes and eat a lot of vegetables, nuts and fruits; and you have the ‘pudding and cake’ vegetarians” (who are more likely to get their protein from a Margarita pizza and Mac & cheese instead of quinoa and lentils, he says.
“However, you do generally see that vegetarians eat more fiber, less saturated fat and fewer calories.”
"The problem is, the absence of one food -eg. meat - cannot adequately define a dietary pattern, which makes it hard to compare vegetarian research results, so it would be helpful to to define and publish a recommended vegetarian diet."
Contrary to popular belief, vegetarians consume about the same levels of many key nutrients of concern as meat-eaters
As for concerns about nutrient deficiencies in the vegetarian diet, analysis of US NHANES (National Health and Nutrition Examination Survey) dietary intake data reveals that with the exception of zinc and vitamin B12; vegetarians’ intakes of ‘nutrients of concern’ including calcium, vitamin D, C, A, E , magnesium and iron, are typically no lower than those of their meat-eating counterparts, delegates were told.
With NHANES data also showing that on average, vegetarians consumed 364 fewer calories per day than non-vegetarians, it is also easy to see why they typically have a lower BMI, said Bonnie farmer, MS, RD, professor of family and consumer sciences at Western Michigan University and a regulatory scientist at Kellogg.
Meanwhile, a meta-analysis of intervention trials of meat-eaters that switch to a vegetarian diet also demonstrated that this is an equally effective - and more sustainable - approach to weight loss than diets focused on calorie restriction, claimed Neal Barnard, MD, president of the Physicians Committee for Responsible Medicine.
“It’s actually easier to follow a vegetarian diet than diets where you have to count calories and restrict yourself all the time.”
Vegetarian diets have more favorable chronic disease outcomes. This is one of the most consistent findings of nutritional epidemiology
In a presentation urging nutrition researchers and educators to focus on food and overall dietary patterns rather than the health benefits of isolated nutrients, David Jacobs, PhD, Mayo professor in epidemiology at the University of Minnesota, said: “In general, plant-centered and vegetarian diets have more favorable chronic disease outcomes.
“This is one of the most consistent findings of nutritional epidemiology.”
Meat is not the enemy
But meat is not the enemy, he said: “It seems that the presence of more phytochemical-rich plant foods rather than the complete absence of animal foods what makes a vegetarian diet so successful.”
And his advice to delegates?
“We may double Michael Pollan’s seven word dictum to 14 words: Eat food. Mostly plants. Not too much. In colorful variety. Maximize nutrients per bite.”
*The Adventist Health Study-2 cohort consists of 96,000 Seventh-day Adventists from the US and Canada. Comprehensive dietary information was gathered at study baseline (2002-2007), and then subjects were followed for mortality and cancer incidence. Sub-studies gathered blood and other bio-specimens from 2,700 subjects.
Many biomarkers of dietary intake have also been analyzed in 900 representative subjects, said Fraser. "At present we have more than 5,000 fatal end-points and will have about 5,000 incident cancer endpoints in about one year after completing matching with state cancer registries."