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Another study has shown health benefits from eating a diet rich in whole grains, as compared to one with lots of refined grains (think bagels, muffins, white bread). Fifty overweight Danish adults were randomly assigned to either a group where all grains eaten were whole grains or a group where all grain products were of refined grains. They did this for 8 weeks, then ate their usual diet for a few weeks (the "washout period"), and then were assigned to the other dietary group for 8 weeks.

They found that eating the diet rich in whole grains resulted in: consuming fewer calories (the whole grains made them feel fuller), losing weight, and a decrease in chronic low-grade inflammation (by measuring blood inflammation markers). The whole grain rye seemed to be especially beneficial. But interestingly, the researchers found that the whole grain diet did not significantly change the gut microbe composition. But they did find that 4 strains of Faecalibacterium prausntzii and one of Prevotella copri increased in abundance after whole grain and decreased after refined grain consumption. F.prausnitzii is a desirable and beneficial keystone species in the gut (here and here).

Other studies show that eating a diet rich in whole grains (rather than refined grains) is associated with a decreased risk of several diseases, including type 2 diabetes and cardiovascular diseases. Bottom line: choose whole grains whenever possible. From Science Daily:

Several reasons why whole grains are healthy

When overweight adults exchange refined grain products -- such as white bread and pasta -- with whole grain varieties, they eat less, they lose weight and the amount of inflammation in their bodies decreases. These are some of the findings of a large Danish study headed by the National Food Institute, Technical University of Denmark. 

The study included 50 adults at risk of developing cardiovascular disease or type 2 diabetes. Blood tests showed that the participants had less inflammation in their bodies when eating whole grains. In particular, it appeared that rye had a beneficial effect on the blood's content of inflammatory markers. Inflammation is the natural response of the body to an infection, but some people have slightly elevated levels of inflammation (so-called low-grade inflammation) even though there is no infection. This is particularly the case in overweight people. In overweight people, an increased level of 'unnecessary' (subclinical) inflammation may lead to increased risk of developing type 2 diabetes.

The study also shows that participants eat less when whole grain products are on the menu -- presumably because whole grain consumption causes satiety. While eating the whole grain diet, participants have generally lost weight. The researchers used DNA sequencing to analyze stool samples from the participants in order to examine whether the different diet types affected the participants' gut bacteria composition. Overall, the analysis did not shown major effects of the dietary grain products on the composition of the gut bacteria. [Original study.]

 A second study was just published about the benefits of eating whole grains daily - again a significantly lower risk of premature death, and again the effects were dose-related. That is, the more whole grains eaten daily, the lower the risk of early death. Like the first study, this also was a review study. This study (published in BMJ) found that whole grain consumption was associated with a reduction in the risk for death from cancer, coronary heart disease (heart attack and stroke), respiratory disease, infectious disease, and diabetes.

A slice of 100 percent whole grain bread contains about 16 grams of whole grains, and current U.S. dietary guidelines recommend 48 grams or more of whole grains daily, but this study suggests that eating even more whole grains daily is best (eating 90 grams of whole grains a day reduced the risk for mortality from all causes by 17 percent).

Grains are divided into two subgroups: whole grains and refined grains. Whole grains or foods made from them contain all the essential parts and naturally-occurring nutrients of the entire grain seed in their original proportions. This definition means that 100% of the original kernel – all of the bran, germ, and endosperm – must be present to qualify as a whole grain. Some whole grains are: whole wheat. barley. buckwheat, corn (including whole cornmeal and popcorn), millet, oats (including oatmeal), quinoa, brown rice, rye, sorghum, spelt, bulgur, and wild rice. From Eurekalert:

Seven servings of whole grains a day keep the doctor away

Eating three more portions of dietary fiber a day--say, two pieces of whole grain bread and a bowl of whole grain breakfast cereal--is associated with a lower risk for all cardiovascular diseases and for dying of cancer, diabetes, and respiratory and infectious diseases, a study just published in the BMJ has shown. The study is strong proof that consuming lots of whole grains is good for our health, says first author Dagfinn Aune, a PhD candidate at the Norwegian University of Science and Technology who is currently working at Imperial College, London.

....In general, the study showed that the higher the consumption, the better protected you are. "We saw the lowest risk among people who ate between seven and seven and a half servings of whole grain products a day, which was the highest intake across all the studies. This corresponds to 210-225 grams of whole grain products in fresh weight and about 70-75 grams of whole grains in dry weight, and is about the same as the health authorities in Norway and other Nordic countries recommend as the minimum daily allowance," says Aune.

The researchers' analyses showed fewer risk factors for people who consumed more bread and cereal with whole grains, as well as foods with added bran. On the other hand, people who ate a lot of white bread, rice or cereals with refined grains did not show reduced risk.

Nine studies with a total of more than 700,000 participants examined the risk for all types of cardiovascular disease and correlated cardiovascular deaths....The risk of dying prematurely from all causes was 18% lower for individuals who consumed a lot of whole grains compared to those who consumed lesser amounts, while three additional servings each day were associated with a 17% reduction in mortality. The risk for deaths associated with cancer (15%), respiratory diseases (22%), diabetes (51%) and infectious diseases (26%) was also lower the more whole grains individuals consumed.