Chronic low-grade inflammation in humans is drawing a lot of interest because it is linked to so many diseases (diabetes, cancer, etc). Key ways to lower this inflammation appear to be losing weight (if overweight), exercising, not smoking, and eating a healthy diet rich in fruits, vegetables, whole grains, nuts, and seeds (thus lots of fiber). Research also shows that the type of diet a person generally eats has an effect on the composition of gut microbes (you want to feed beneficial microbes!). But which is more important for health and lowering inflammation - whole grains or fruits and vegetables or neither?
A recent study attempted to answer this question. They put 49 overweight or obese individuals, who typically ate low amounts of fruits, vegetables, and whole grains (less than 1 serving per day), into 1 of the following 3 groups for 6 weeks: 1) Whole grains (WG), 2) Fruits and vegetables (FV), and 3) a Control group (who ate refined grains). All persons were given 3 servings per day of "treatment" foods to eat at home, but the rest of their Western style diets stayed the same. The individuals did not all consume the same foods, but rather consumed their choice of foods from their group's food category.
The researchers collected blood and stool samples (both at the beginning of the study and after 6 weeks) to measure inflammation levels, and types of microbes and fatty acids in the gut. Inflammatory markers that they measured were: tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), lipopolysaccharide binding protein (LBP), and high sensitivity C-reactive protein (hs-CRP).
The researchers found an increase in microbial diversity in the FV group (perhaps due to the new variety of fibers in the fruits and vegetables), but otherwise there were no significant changes in gut microbiome composition among the groups. [Note: but each group had only some dietary changes, not drastic changes]
The researchers found that whole grains and fruits and vegetables lowered markers of inflammation - but each treatment (FV or WG) lowered different types of inflammation markers. And note that for the fruit/vegetable group - the 3 servings per day, was still below government recommendations of 5 servings per day for adults. And the rest of their diet was the same Western diet that they normally ate. So the whole grains or fruits and vegetables were not major dietary changes. And yet there were positive changes - lowering of inflammation.
So the final answer is that it is best for your health (and gut microbes) to eat a diet rich in fruits, vegetables, and also whole grains. And they didn't even mention legumes, nuts, and seeds - all high fiber foods with lots of micronutrients, and known to be good for beneficial gut microbes. So yes, eat them also. What was a serving in this study? 1 serving = 1 cup fruits or vegetables, and 1 serving = 1 oz of whole or refined grains.
Excerpts from the study by J.C. Kopf et al in Nutrition Journal:
Role of whole grains versus fruits and vegetables in reducing subclinical inflammation and promoting gastrointestinal health in individuals affected by overweight and obesity: a randomized controlled trial
BACKGROUND: Whole grains (WG) and fruits and vegetables (FV) have been shown to reduce the risk of metabolic disease, possibly via modulation of the gut microbiota. The purpose of this study was to determine the impact of increasing intake of either whole grains or fruits and vegetables on inflammatory markers and gut microbiota composition.
METHODS: A randomized parallel arm feeding trial was completed on forty-nine subjects with overweight or obesity and low intakes of FV and WG. Individuals were randomized into three groups (3 servings/day provided): WG, FV, and a control (refined grains). Stool and blood samples were collected at the beginning of the study and after 6 weeks. Inflammatory markers [tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), lipopolysaccharide binding protein (LBP), and high sensitivity C-reactive protein (hs-CRP)] were measured. Stool sample analysis included short/branched chain fatty acids (S/BCFA) and microbiota composition.
RESULTS: There was a significant decrease in LBP for participants on the WG and FV diets, with no change in those on the control diet. The FV diet induced a significant change in IL-6, but no significant change was observed for the other treatments. The WG diet resulted in a significant decrease in TNF-α, whereas no significant effects were found for those on the other diets. The treatments induced individualized changes in microbiota composition such that treatment group differences were not identified, except for a significant increase in α-diversity in the FV group. The proportions of Clostridiales (Firmicutes phylum) at baseline were correlated with the magnitude of change in LBP during the study.
CONCLUSIONS: These data demonstrate that WG and FV intake can have positive effects on metabolic health; however, different markers of inflammation were reduced on each diet suggesting that the anti-inflammatory effects were facilitated via different mechanisms. The anti-inflammatory effects were not related to changes in gut microbiota composition during the intervention, but were correlated with microbiota composition at baseline.