TL;DR:
The gut microbiome — the trillions of bacteria in your digestive tract — plays a major role in weight, metabolism, and inflammation. Polyphenols from fruits and vegetables can nourish beneficial bacteria, reduce inflammation, and improve insulin sensitivity. Supporting the microbiome with polyphenols, probiotics, and fiber may help manage weight and metabolic balance.
What Is the Microbiome?
You have several pounds of bacteria in your bowel. The makeup of that flora, or the microbiome, has a great deal to do with the quality of your health. There are more bacterial cells in your colon than there are in your entire body. Intestinal flora produces vitamins like folic acid and B12, as well as nourishing the intestinal lining. Bowel flora can also inhibit harmful bacteria and break down toxins. In natural health care, we have been dealing with bowel ecology for decades. Now, it seems that the research is beginning to catch up. We are beginning to learn about the role of specific species of bacteria as well as strategies to control what grows in our intestines. For a broader introduction to gut bacteria and digestive health, see our overview of Gut Microbiome Health.
The Microbiome in Health and Weight Loss
For the last 15 years, there has been increasing attention paid to bowel ecology, or the microbiome. Scientists are looking at the connection between the microbiome and many health issues, including neuropsychiatric disorders, autoimmune disease, and inflammation [1,2,3].Inflammation biomarkers and how they relate to obesity is of particular interest. Obesity and concomitant issues like inflammation, metabolic syndrome, diabetes and heart disease may be linked to the microbiome. Furthermore, we may be able to affect the microbiome with consumption of polyphenols. A detailed research review of these connections can be found in our article on the microbiome and chronic disease.
A recent article [4] gave an overview of the role of the microbiome in weight control. The authors concluded, “While diet and behavioral modification programs aiming to reduce weight gain and promote weight loss are effective in the short term, they remain insufficient over the long haul as compliance is often low and weight regain is very common. As a result, novel dietary strategies targeting the gut microbiota have been successful in decreasing obesity and metabolic disorders via different molecular mechanisms.”
For the last 15 years, there has been a lot of interest in the microbiome and its role in weight-loss. Research supports this idea. The authors of an earlier article state, “Manipulation of gut microbiota through the administration of prebiotics or probiotics could reduce intestinal low grade inflammation and improve gut barrier integrity, thus, ameliorating metabolic balance and promoting weight loss [5].” Addressing bowel ecology may be a good way to address metabolic syndrome and obesity.
Polyphenols and the Microbiome
Scientists are becoming increasingly interested in polyphenols and how they affect the microbiome [6]. An earlier paper discussed consequences of increasing the consumption of whole plant foods on the gut microbiota and subsequent implications for human health. In humans, whole grain cereals can modify fecal bacterial profiles, increasing relative numbers of bifidobacteria and lactobacilli. Polyphenol-rich chocolate and certain fruits (especially berries) have also been shown to increase fecal bifidobacteria [7].
In fact, one study looked at obesity-associated gut microbial species. It identified species that may be associated with keeping the weight off. Bacteroides thetaiotaomicron, a glutamate-fermenting commensal, was markedly decreased in obese individuals and was inversely correlated with serum glutamate concentration. This is consistent with findings in animal studies [5]. The researchers concluded, “Our findings identify previously unknown links between intestinal microbiota alterations, circulating amino acids and obesity, suggesting that it may be possible to intervene in obesity by targeting the gut microbiota [4].”
There is a strong connection between polyphenols and gut microbiota. It is beginning to look like polyphenols can help balance bowel flora, resulting in improvement in blood glucose levels and even weight-loss. Several animal studies support this idea. An animal study [8] found that supplementing with green tea polyphenols lowered blood sugar and reduced mesenteric fat in female db/db mice (mice bred to develop diabetic dyslipidemia). Research performed in 2012 also found that the consumption of polyphenols and fiber can affect the microbiome [7,13,14]. Polyphenolic supplementation helped with obesity and fatty liver in another animal study [9].
Authors of a recent meta-analysis concluded, “Overall, when the utilization of gut microbiome-modulating dietary agents (prebiotic/probiotic/synbiotic) was compared to placebo, there were significant decreases in BMI, weight and fat mass. In summary, dietary agents for the modulation of the gut microbiome are essential tools in the treatment of obesity and can lead to significant decreases in BMI, weight and fat mass [10].” Other authors found several studies that support the idea of improving the microbiome with polyphenols to reduce obesity. The authors fall short of recommending supplementing with polyphenols, stating that more research is needed [11].
One study ironically found that artificial sweeteners may affect the microbiome. The animal study found a gender-specific effect that Acesulfame-potassium had on the microbiome of male rats, favoring weight gain [12].
Overall, it looks like future success in addressing obesity, insulin insensitivity, and fatty liver will likely involve the microbiome. Furthermore, it looks like polyphenols may help in this capacity. Eating vegetables has always been an important part of any weight-loss program. Vegetables are low in calories and high in fiber, but their effect on weight and insulin insensitivity may go beyond that. Vegetables are high in polyphenols, which are micronutrients that are obtained from plants. They are rich in antioxidants and are produced by the plant to protect itself from ultraviolet radiation, the oxidative stress of photosynthesis and from pathogens. Polyphenols found in fresh produce may affect the microbiome, which in turn can help with weight-loss.
