The gut microbiota is one of the most highly active areas of research in nutrition.
Recently, a team of researchers examined the effects of a weight-loss program on the gut microbiota of obese individuals.
Here we discuss their main results, recently published in PLOS ONE.
The gut microbiota appears to play a role in obesity and metabolic disorders, as discussed in our previous research review.
This is because the bacteria feed on what you eat. What’s more, individual species of bacteria are often highly selective, feeding only on certain food components.
In this way, your diet can influence health through its effects on the gut microbiota.
A team of German scientists examined changes in the gut microbiota during a weight-loss program in obese people.
This observational study examined changes in the gut microbiota during and after a weight-loss program in obese adults.
The researchers also wanted to find out if bacteria in stool samples could predict successful weight loss, or if the microbiota of people with metabolic syndrome or non-alcoholic fatty liver disease differed from that of healthy individuals.
The weight-loss trial lasted for one year. It involved a 3-month, very low-calorie diet (800 kcal/day) using a dietary formula enriched in inulin.
After that, the participants gradually replaced the formula with real food, and started weight maintenance. Additionally, the program involved exercise and behavioral therapy. These results and methods are described elsewhere (6).
In the present observational study, 16 obese individuals who participated in the trial were chosen based on their weight-loss success.
These 16 individuals were followed for two years — for the duration of the weight-loss trial and for another year afterwards.
Based on their weight-loss success, they were divided into two groups:
- Persistent weight-loss success: A total of nine participants were successful in maintaining a 10% weight loss for one year after the weight-loss trial finished.
- No persistent success: Seven of the participants were not successful in maintaining their weight.
The researchers analyzed the participants at the start of the study and after 3, 6, 12, 18 and 24 months. Using DNA sequencing, they measured the types and numbers of bacteria in stool samples.
Bottom Line: This was an observational study examining changes in the gut microbiota during and following a weight-loss trial. It also investigated whether the microbiota profile could predict weight-loss success.
Finding 1: Weight Loss Changed the Gut Microbiota
The study detected around 2,000 different types of bacteria in the participants’ stool samples. There was high individual variability in the microbiota profile, and some species were only found in one or a few of the participants.
The microbiota turned out to be quite stable during the weight-loss trial. Yet, the researchers detected 56 species of bacteria whose numbers changed significantly, mainly during the three months of calorie restriction.
Most notably, the following groups increased in counts: Alistipes, Lachnospiraceae, Ethanoligenens and Holdemania.
Only one group, Roseburia, decreased significantly. This group of bacteria convert fiber into butyrate, a healthy short-chain fatty acid.
However, these changes were only temporary. After the 3-month weight-loss period, the counts of these bacteria gradually returned to initial levels.
When the whole 2-year study period was examined, only Akkermansia increased significantly. Specifically, it increased 11-fold, from 0.26 to 2.9% of total counts.
Bottom Line: The gut microbiota in obese adults changed during the weight-loss program, which involved an inulin-enriched, calorie-reduced diet.
Finding 2: Certain Groups of Bacteria Predicted Successful Weight Loss
Participants who consistently lost weight over the 2-year study had a slightly different microbiota at the start of the study, compared to those who were unsuccessful.
Specifically, they had a microbiota rich in the following groups of bacteria:
The level of weight loss was also linked with increases to the numbers of bacteria of the genus Akkermansia in stool samples.
By looking at food diaries, the researchers couldn’t find any dietary patterns explaining these differences.
Bottom Line: Successful weight loss was linked with higher initial counts of certain bacteria, such as Alistipes. Weight loss was also associated with higher counts of Akkermansia throughout the study.
Finding 3: The Ratio of Firmicutes and Bacteroidetes Was Not Linked With Obesity
In an attempt to explain this, scientists have speculated that Firmicutes may increase calorie absorption. In fact, they convert fiber into short-chain fatty acids, such as butyrate, which are absorbed by the cells lining the colon (18).
These inconsistencies might be explained by genetic differences. One recent study suggests that numbers of Firmicutes may depend on individual genetics, whereas numbers of Bacteroidetes are mainly influenced by diet (22).
Bottom Line: Unlike some studies, this study did not find a significant link between the ratio of Firmicutes and Bacteroidetes and body weight.
Finding 4: Metabolic Syndrome Was Associated With a Different Microbiota Profile
The ratio of Firmicutes and Bacteroidetes was significantly higher (0.64) in those with metabolic syndrome at the start of the study, compared with those who were “healthy” obese (0.27).
Counts of Akkermansia were also lower in those with metabolic syndrome.
Additionally, the researchers compared the bacterial composition of people with non-alcoholic fatty liver disease (NAFLD) to those who didn’t have it.
These analyzes were done at the end of the study, to minimize the influence of the weight-loss trial.
They found several significant differences. Participants with NAFLD had:
- Lower counts of Subdoligranulum, which are also lacking in patients with cirrhosis (23).
- Lower counts of Lactococcus, which produce lactic acid from glucose and are used in the production of fermented dairy products, such as cheese. They may slow the development of colitis in mice (24).
- Higher counts of Paraprevotella.
Bottom Line: Metabolic syndrome and non-alcoholic fatty liver disease were linked with differences in the gut microbiota.
This study had several limitations. First, it was an observational study that couldn’t demonstrate causation.
Second, the study was very small, including only 16 obese adults. This limited its statistical power.
Third, the participants were selected to reduce individual variability. For this reason, the results may not apply to all obese people.
Bottom Line: This observational study has a few limitations, including small size. It also can’t demonstrate causation, and its findings may be limited.
Summary and Real-Life Application
In short, this study indicates that the bacterial composition of stool samples may be used to predict success during a weight-loss program.
Specifically, high levels of Akkermansia were the strongest predictor of weight-loss success. However, these findings have no real-life application for weight loss.
Yet they are important to science, helping us understand what role the gut microbiota plays in obesity, weight loss and health.