July 06, 2018
Vegan and vegetarian diets help lower HbA1c and cholesterol levels and improve other cardiometabolic risk factors in middle-aged, overweight people controlling their type 2 diabetes with medications, say authors of a literature review published online in Clinical Nutrition.
Effie Viguiliouka, MSc, with the Clinical Nutrition and Risk Factor Modification Center at St. Michael's Hospital in Toronto, Ontario, and colleagues, analyzed findings from nine randomized controlled trials involving 664 participants who were taking oral glucose-lowering drugs, insulin, lipid-lowering agents, and/or anti-hypertensive agents.
They found that vegetarian diets compared with nonvegetarian diets improved the primary outcome of HbA1c by 0.29%.
While the HbA1c reduction may seem moderate, Cara Schrager, MPH, RD, CDE, of the Joslin Diabetes Center in Boston, Massachusetts, pointed out that the improvement is the same as the therapeutic threshold the US Food and Drug Administration uses when considering new medications for diabetes.
Schrager told Medscape Medical News that this level of reduction suggests that patients could consider moving toward a plant-based diet with primarily vegetables, fruits, whole grains, and legumes, perhaps even before they move to diabetes medications.
Vegetarian Diet Also Helped Reduce BMI
Other results included reductions in fasting glucose of 0.56 mmol/L; LDL-cholesterol (0.12 mmol/L); non-HDL-cholesterol (0.13 mmol/L); body weight (2.15 kg or 4 lbs, 12 oz); body mass index (BMI) (0.74 kg/m2), and waist circumference (2.86 cm) with the vegetarian compared with nonvegetarian diets.
Only diets that excluded meat and fish (from vegan [no animal products] to vegetarian diets that included eggs and dairy products) were considered vegetarian in the meta-analysis.
"Sixty to seventy percent of people who have type 2 diabetes die of heart disease," study coauthor Hana Kahleova, MD, PhD, director of clinical research at the Physicians Committee for Responsible Medicine said in a press release.
"This study shows that the same simple prescription — eating a plant-based diet — can reduce our risk for heart problems and improve type 2 diabetes at the same time."
The researchers acknowledge, however, that the findings had a low-to-moderate confidence level and they encourage further study.
Findings Build on Body of Evidence: No Downside to a Plant-Based Diet
Katherine Zeratsky, a registered dietitian nutritionist (RDN) at the Mayo Clinic in Rochester, Minnesota, told Medscape Medical News that this new review adds to a body of evidence that indicates eating less red meat and more vegetables can benefit people with type 2 diabetes.
Many of the noted reductions in this study fit with what others have shown, she said.
"We know that weight in and of itself is a strong risk factor for diabetes — so it makes sense that a plant-based diet will have a large impact on health overall," she said, while countering that she wished the evidence "was stronger."
But as with all nutrition research, she said, "It's very difficult to say with absolute certainty that if you do this, this will happen."
However for most patients, she added, there isn't a downside to trying a plant-based diet.
It Doesn't Have to Be All or Nothing: How to Move Away From Meat
Still, fewer than 10% of people in North America and Europe have adopted vegetarian diets, according to national survey data cited by the authors.
Zeratsky emphasized that moving away from meats and toward vegetables, fruits, and whole grains doesn't have to be an all-or-nothing effort.
A good start is cutting meat consumption at a meal from 8 oz to 6 oz and filling the plate with more fruits and vegetables to curb hunger, she said.
Schrager suggested adding "meatless Mondays" or trying the diet one day a week at first.
"It is a shock to the system if you suddenly stop eating a certain group of foods," she said.
Some foods, such as lasagna or chili, have comparable meatless versions, she noted, and beans can add bulk. Adding protein sources such as tofu and tempeh can also give dishes a meaty texture.
More Studies Will Help Answer Questions
Viguiliouka and co-authors say more randomized controlled trials will help answer questions this one couldn't, including what kind of plant-based diets have the most beneficial effects and how a vegetarian diet might affect people with type 1 diabetes.
Schrager says she also suspects, though this study didn't address it, that the microbiome has an important role in the mechanism that links vegetarian diets and improved diabetes outcomes.
The mechanism may be related to more than the low-calorie and low-fat aspects and may be rooted in the better balance of gut bacteria produced by the amount of fiber in the vegetarian diet, she hypothesized, adding that she would like to see if further research sheds light on this.
The review was funded by the Diabetes and Nutrition Study Group of the European Association for the Study of Diabetes. A complete list of disclosures is available on the journal website.