Ever wonder whether classic healthy-eating advice–“load your plate with produce and whole grains”—really improves your blood sugar and health? In a recent review of nine well-designed studies involving 664 people with diabetes, an international team of researchers has found that plant-based eating improved long-term glucose control significantly and also nudged levels of heart-threatening LDL cholesterol downward.
Published in the June issue of the journal Clinical Nutrition, the review compared a wide range of vegetarian diets—low-fat, high-protein, low glycemic index, vegan (no dairy products or other animal products such as honey), lacto-ovo (plant foods plus dairy and eggs)—to conventional diabetes-friendly meal plans that included more meat and animal products.
In eight of the studies, most in people with Type 2 diabetes, vegetarian diets lowered HBA1c levels (a measure of blood-sugar control over several months) by an average of 0.3%. Plant-based eating also lowered their LDLs by about 5%.
That’s significant, says study author Hana Kahleova, MD, PhD, MBA, Director of Clinical Research for the Washington, DC-based Physicians Committee for Responsible Medicine. “This research is groundbreaking and has the ability to change the way we think about and treat type 2 diabetes,” she says. “In the past, doctors thought of type 2 diabetes as a one-way street. Once you had it, you would always have it. But research is now showing that diet, unlike drugs, can treat and sometimes even reverse the problems that caused the disease in the first place.”
The 0.3% drop in HBA1c levels is on par with the glucose-lowering effect that the US Food and Drug Administration looks for in potential new diabetes medications still in development, the researchers note. And the 5% LDL drop could reduce risk for heart attack, stroke and other major cardiovascular problems by 5%.
That’s important, Dr. Kahleova says, because heart disease and type 2 diabetes are closely linked. “Many people don’t realize that the leading cause of death for those with diabetes is actually heart disease. People with diabetes are two to four times more likely to die from cardiovascular disease than people who don’t have diabetes. In fact, up to 70% of people who have type 2 diabetes ultimately die of heart disease.”
How does vegetarian eating help? “A plant-based diet addresses the root cause of type 2 diabetes by reducing fat buildup inside muscle and liver cells, which improve insulin sensitivity and lower blood sugar,” Dr. Kahleova explained to On Track Diabetes. Vegetables, fruit and whole grains help with blood sugar control in yet another way, according to a recent Rutgers University study conducted in China.
Researchers found that high-fiber plant foods “feed” beneficial bacteria in the large intestine. This starts a healthy chain reaction. The “good bugs” burp out health-promoting compounds called short-chain fatty acids (SCFAs). The SCFAs in turn trigger chemical changes that stimulate the release of insulin into the bloodstream. Compounds produced by good gut bacteria called acetic and butyric acids also make the environment within the large intestine more acidic and as a result “potentially detrimental bacteria which are intolerant to low pH will decline,” says lead researcher Liping Zhao , PhD, the Eveleigh-Fenton Chair of Applied Microbiology in the School of Environmental and Biological Sciences at Rutgers University in New Brunswick, New Jersey.
Knocking back bad bacteria is good, Dr. Zhao told On Track Diabetes. Among the bad actors reduced by the healthy diet were types that churn out indoles and hydrogen sulfide, which interfere with production of a beneficial peptide called glucagon-like peptide-1 that promotes insulin release. The high-fiber diet also lowered populations of bacteria that produce endotoxins which increase inflammation and reduce insulin sensitivity, Dr. Zhao says. The 15 beneficial bacteria that thrived on fibers in the study work together to create an environment where other healthy bacteria can flourish while detrimental types are kept in line, he notes.
For the study, 49 people with type 2 diabetes followed a conventional, healthy diet with about 16 grams of fiber or an experimental diet containing 37 grams of fiber—mostly from specially-formulated supplemental foods based on Traditional Chinese Medicine.
Both diets had the same number of calories and the same levels of fat, protein, and carbohydrates. Both groups had high blood sugar at the start, with an average HBA1c of 8.3%. After seven months on the study diets, the high-fiber group saw their A1c drop to a healthy 6.3% while the control group's fell to 7%.
The high-fiber foods tested in the study are not commercially available. But they contain types of fiber you can find on American supermarket shelves. These include soluble fiber found in oats, barley, pears and psyllium fiber supplements. Specific fiber varieties in the experimental foods included beta-glucan (found in oats, barley and in reishi, shiitake and maitake mushrooms); resistant starches (found in whole grains, seeds, chickpeas, lentils and kidney beans); and inulin (found in chicory root, dandelion greens, Jerusalem artichoke, garlic, onions, asparagus and under-ripe bananas).
“Eating more fibers with diverse structures should help you,” Dr. Zhao adds. His future research at Rutgers will look more closely at how different fiber types affect the gut microbiome in different people. “Each individual has their own combination of foundation bacteria which have different fiber-fermenting capacity. One fiber subtype which works for you may not work for my foundation bacteria,” he says. “This is where personalized nutrition needs to kick in. We are working on this.