A recent study investigates whether blueberries can improve gut health and relieve symptoms of obesity by reversing the effects of a high-fat diet in rats.
The human body undergoes many changes in response to a high-fat diet that, in conjunction with environmental and genetic factors, ultimately leads to obesity. Increases in fat tissue are associated with a chronic inflammatory state. This systemic inflammation originates in the gut. A high-fat diet reduces the expression of gut-protecting proteins, compromising gut barrier integrity. The gut microbiome has an important role in metabolism and is intimately involved in immune function.
When gut permeability is impaired because of a high-fat diet, the gut microbiota are highly susceptible to alterations. Together, impaired gut permeability and an altered gut microbiome lead to a movement of bacterial pro-inflammatory factors into circulation, where they permit an inflammatory response. Some pro-inflammatory factors that are released in response to increased fat tissue decrease the body’s response to insulin, the hormone that senses blood sugar levels and allows sugar absorption into cells.
For example, LPS is a pro-inflammatory factor that causes weight gain, fat tissue inflammation, and insulin resistance when in circulation. Therefore, a high-fat diet contributes to the development of obesity but may also compromise gut barrier integrity and elicit an inflammatory response that perpetuates obesity by causing weight gain and insulin resistance.
Health benefits of blueberries
Blueberries contain anthocyanins, antioxidants, and anti-inflammatory compounds that benefit overall health and contribute to disease prevention. Previous studies revealed that dietary supplementation with whole blueberries reduced the expression of genes involved in the body’s inflammatory response and reduced body weight in male mice fed a high-fat diet. High concentrations of anthocyanins, the compound that give blueberries its characteristic colour, are found in the intestine where they interact with and are metabolized by microorganisms. Through this interaction, blueberries have the ability to alter the composition of the gut microbiome.
Further, blueberries have been demonstrated to improve insulin sensitivity in humans. Based on the anti-inflammatory properties of anthocyanins in blueberries and the potential for blueberries to remodel the gut microbiome, researchers were interested in determining the effect of blueberry supplementation in rats fed a high-fat diet to reduce systemic inflammation and improve insulin sensitivity by modulating the gut microbiome. The results of the study were recently published in The Journal of Nutrition. The researchers fed rats either a low fat, high fat, or high fat with 10% blueberry powder diet. They wanted to know whether dietary blueberry supplementation could restore the health of rats with a high-fat diet.
Effects of blueberries on microbiota
The researchers found that the rats fed a high-fat diet with dietary blueberry supplementation possessed a unique gut microbiota profile, while the rats fed low fat and high-fat diets with no blueberries had similar microbiota profiles. With blueberry supplementation, proteobacteria, a bacterial species associated with metabolic health, was significantly increased in rats fed the blueberry supplementation. This change in gut microbiota resulted in numerous downstream effects that improved the overall health of the rats that consume a high-fat diet.
Effect of blueberries on gut epithelial integrity and inflammation
The microbiota profile of the rats fed a high-fat diet with blueberry supplementation was associated with an increase in intestinal villi height which are important for nutrient absorption, an increase in goblet cell numbers that protect the gut epithelial barrier by releasing mucus, and an increase in the expression of the genes that produce mucus.
Changes in the gut microbiota induced by blueberry supplementation in the rats fed a high fat-diet are associated with improved gut epithelial barrier integrity compared to the rats fed a high fat-diet with no blueberry supplementation. Gut epithelial barrier integrity prevents bacterial inflammatory compounds such as LPS from crossing the epithelial barrier and entering the circulation to elicit a systemic inflammatory response. Therefore, blueberry supplementation with a high-fat diet was able to restore levels of inflammation associated with obesity back to levels that would normally be seen in rats fed a low-fat diet.
Effect of blueberries on insulin sensitivity
A high-fat diet associated with obesity may lead to insulin resistance. Insulin resistance causes inefficient use of energy by cells and can quickly advance into type 2 diabetes, a major health issue in the developed world. Rats fed a high-fat diet and blueberry supplementation had less insulin in the blood and required less insulin to clear glucose than rats fed a high-fat diet alone. The researchers also found that a high-fat diet increased the expression of IRS1, a biomarker for insulin resistance, and blueberry supplementation restored normal levels of IRS1. GLP1, a gene whose expression improves insulin secretion and sensitivity, was downregulated by a high-fat diet, and blueberry supplementation restored GLP1 reduction to normal levels. This data indicates that insulin resistance due to a high-fat diet can be reversed or prevented by blueberry supplementation in rats.
Many of the symptoms that occur in patients with obesity, such as inflammatory responses, actually perpetuate the disease, resulting in a positive feedback loop that worsens the disease and makes it difficult to resolve symptoms. This study demonstrates that many negative health effects associated with obesity, such as impaired epithelial gut barrier, chronic inflammation, and insulin resistance can be improved by modulation of the gut microbiota through dietary blueberry supplementation in rats. Although physiology and gut microbiota differ between rats and humans, there is promising evidence for the use of dietary blueberry supplementation to improve gut health and minimize the effects of obesity associated with a high-fat diet.
Written by Mallory Wiggans
Reference: Lee, S. Keirsey, K.I., Kirkland, R., Grunewald, Z.I., Fischer, J.G. & de La Serre, C.B. (2018). Blueberry Supplementation Influences the Gut Microbiota, Inflammation, and Insulin Resistance in High-Fat-Diet-Fed Rats. J Nutr. 148, 209–219.