- Researchers have previously identified a link between fiber intake and positive health outcomes.
- Fiber promotes a healthy gut microbiome once bacteria metabolize it.
- A recent study found that a 2-week increase in fiber intake significantly altered the gut microbiome.
Researchers have found that a 2-week increase in fiber intake can significantly alter a person’s gut microbiome, including increasing species of bacteria that break down fiber.
However, the quantity of short-chain fatty acids (SCFAs) did not increase. SCFAs are the result of bacteria breaking down fiber, and they have diverse roles within the body.
For instance, SCFAs are used as a source of energy for the cells of the colon and are involved in cell signaling. Some SCFAs also have anti-inflammatory properties and might influence insulin sensitivity and body weight.
The research, which appears in the journal mSystems, lays the groundwork for future studies to explore in more detail the relationship between fiber intake, gut bacteria, and SCFAs.
Fiber plays an important role in human health. For example, a recent review of various meta-analyses found that people who eat the most fiber significantly reduce their chances of dying due to a cardiovascular event.
However, only 1 in 20 people in the United States consume the recommended amount of fiber.
According to Dr. Katrine Whiteson, associate professor of molecular biology and biochemistry, co-director of the University of California, Irvine (UCI) Microbiome Initiative, and co-author of the present study:
“The lack of fiber intake in the industrialized world is starving our gut microbes, with important health consequences that may be associated with increases in colorectal cancer, autoimmune diseases, and even decreased vaccine efficacy and response to cancer immunotherapy.”
The small intestine cannot digest fiber. Instead, according to the authors of the present study, it passes into the colon, where microbes are able to break the fiber down.
The authors of the present study wanted to study the relationship between a short-term increase in dietary fiber, the makeup of the gut microbiome, and the presence of SCFAs.
To investigate, the researchers conducted a study involving 26 undergraduate students enrolled on a biology course at UCI, as well as their instructors.
In week 1, participants ate their normal diet and provided three stool samples for analysis.
In week 2, the participants started a high fiber diet. They tracked their nutritional intake using a fitness app, aiming for 40 grams (g) of fiber each day. To assist, the researchers provided them with 10 meals each week that were high in fiber from a range of different plants.
In the third week, the participants were encouraged to increase their fiber intake to 50 g per day. During this week, participants provided another three stool samples.
According to graduate student Andrew Oliver, a teaching assistant for the course, “students raised their fiber intake by an average of 25 g per day, but the variability of pre-intervention fiber intake was substantial.”
“A few students had to go from nearly zero to 50 g daily by the end of the study. We all became a little obsessed with how much fiber was in the food we were eating.”
The researchers then analyzed the samples using DNA sequencing to identify the makeup of the bacteria. They used gas chromatography to measure SCFAs.
The researchers found that the composition of the participants’ gut microbiomes changed by around 8% following the dietary intervention.
This was largely due to increases in bacteria known for breaking down fiber, including Bifidobacterium, Bacteroides, and Prevotella.
However, the researchers saw no statistically significant increase in SCFAs. They speculate that this may be because stool samples do not accurately represent levels of SCFAs in the gut, which are primarily found in the cell walls of the intestines.
The researchers also suggest that the 2-week intervention may not have been long enough to see any difference in SCFAs.
According to Dr. Whiteson, “we hope to carry out longer dietary fiber interventions and study how fiber can support the gut microbiome and promote health.”
“At this time during a pandemic, when we need our immune health and healthy vaccine responses, we encourage everyone to think about the plant diversity of their diets and add some beans, berries, and avocados where they can.”