With new diet and health claims coming at you everyday, it's sometimes hard to know what to believe. Well, here's a bright spot: A pair of studies confirm that whole grains are healthy for you, and for the diversity of microbes living in your gut.
Grains, and the breads made from them, have fed humans for millennia. All grains start out whole, and corn, barley, farro, oats, rye, and wheat are just a few of them. Each grain has three main parts—germ, endosperm, and bran.
Through the milling process, the outer layer, called the bran, and the inner embryo, or germ, are removed. Refined white bread and grain products are made primarily from the endosperm, the part of the grain that is intended to feed the growing germ as it sprouts.
While baked goods made of white bread were once considered premium products, whole grains and brown breads have made a comeback in restaurants and grocery shelves in the last decade. Research indicates that whole grains help reduce the risk of heart disease, diabetes, and cancer, and assist with weight regulation, as well as provide important micro and macronutrients.
As whole grains have moved into the American diet, awareness of celiac disease has added to conversation about the health benefits of whole grains. For people with celiac disease, the gluten in wheat products triggers an uncomfortable and damaging immune response to the small intestine. Fortunately, there are some whole grains that are naturally gluten-free, including millet, teff, buckwheat, and amaranth.
In your daily diet, the United States Department of Agriculture recommends between one and four ounces of whole grains per day. Nutritionally, whole grains offer a diverse menu of minerals, antioxidants, fiber, vitamins, lignans, inulin, and other phytochemicals. While refined flours are enriched with vitamins to replace those lost during the milling process, the fiber is removed.
Whole grains help feed bacteria present in the gut. These bacteria play an important role in digestion, including synthesis of vitamins, decomposition of foods, elimination of toxins, and breakdown of sugars for utilization in the body.
But there's more. Two studies published in the American Journal of Clinical Nutrition (we'll refer to them as Study 1 and Study 2), performed by the same research team, suggest that eating whole grains makes good sense for your gut, and your immune system, too.
In a clinical trial at Tufts University, researchers studied the effects of whole grain nutrition on a group of adult volunteers between the age of 40 and 65. For the study, 49 healthy men and 32 postmenopausal women ate a typical western diet for two weeks, followed by an identical, balanced diet with the exception that half the group received refined grain products, while the others received whole grains.
During the investigation, food was prepared and provided to participants. Food was measured to maintain the current weight of each participant, to avoid confusing the impact of either diet with physiological changes caused by weight loss.
To our knowledge, this study is the first to examine the effects of whole grains compared with refined grains on energy metabolism during weight stability.
Throughout the study, fecal, blood, and saliva samples were collected, frozen, and analyzed. Participants were screened for medications that could influence gut microbota, including antibiotics, nonsteroidal anti-inflammatory medications, and antihistamines.
Data extraction, lab work, flow cytometry, and statistical analysis were used to evaluate study data and evidence. From an initial screening of 1,714 potential participants, 103 were selected, and 81 people completed the study.
Keeping in mind the study participants were eating the same food, except for whole grains and refined grains during the second half, the findings of the study include:
- The cholesterol levels of those eating refined grains rose.
- Participants eating whole grains had an increase in dietary fiber.
- Insoluble fiber intake doubled for participants eating whole grains. Both kinds of fiber, soluble, and insoluble, are important. Insoluble fiber moves food more quickly through the digestive system, and helps control acidity in the intestines.
- The frequency and weight of bowel movements increased for those eating a whole grain diet.
- Genetic sequencing allowed researchers to compare diversity of microbiota between individuals eating each diet. For the group eating whole grains, there was a decrease in bacteria from the Enterobacteriaceae family. While there are harmless members of this bacterial family, they are associated with inflammation. Some of the better known virulent pathogens also belong to this group, including Salmonella, Klebsiella, and Escherichia coli.
- For the whole grain group, scientists also saw an increase in Lachnospira, a helpful gut bacteria involved with short-chain fatty acids, which aid the immune system.
- Study 2 tested the advice of replacing refined grains with whole grains. The work agreed with those recommendations, noting they "showed that the dietary substitution of whole grains for refined grains conferred favorable energetic benefits" (as measured by differences in stool weight and content—the heavier the poop, the greater the energy loss).
- Participants eating whole grain foods experienced a higher level of memory T cells, which are are an essential aspect of adaptive immunity.
Senior author of Study 1, Simin Nikbin Meydani, the director of the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts, as well as professor of nutrition and immunology at Tufts' Friedman School of Nutrition Science and Policy, said in a press release:
[W]e found modest effects of whole grain on gut microbiota and measures of immune function in the context of a controlled energy and macronutrient diet where all food was provided to participants, allowing them to maintain their body weight constant.
It is not hard to put whole grains in your diet. You can change up whole wheat for white bread, brown rice instead of white, or consider the slightly sweet nutty flavor of whole wheat pasta. If your children or your partner give you grief about brown bread or pasta, use products made of white whole wheat. Lacking only its color genes, white whole wheat has the same natural nutritional profile as red wheat.
These studies suggest there are good reasons, and strong science, to support whole grains as part of a healthy diet.