By Seema Gupta, MD, MSPH

Clinical Assistant Professor, Department of Family and Community Health, Joan C. Edwards School of Medicine, Marshall University, Huntington, WV

Dr. Gupta reports no financial relationships relevant to this field of study.

SYNOPSIS: In a study of simplified enterotypes as prognostic markers for successful body fat loss on two different diets, participants with a greater ratio of Prevotella to Bacteroides appeared more susceptible to lose body fat on diets high in fiber and whole grains.

SOURCE: Hjorth MF, Roager HM, Larsen TM, et al. Pre-treatment microbial Prevotella-to-Bacteroides ratio, determines body fat loss success during a 6-month randomized controlled diet intervention. Int J Obes (Lond) 2017 Sep 8. doi: 10.1038/ijo.2017.220. [Epub ahead of print].

The human gut contains a complex microbial community of microorganisms known collectively as the “gut microbiota,” which interacts with and influences one’s health status. As a densely populated bacterial collection, with approximately 1,011 organisms per gram of fecal weight, the human gut microbiota is composed of more than 1,000 species, most of which are obligate anaerobes.1 The assessment and characterization of this gut microbiota has become a major research area in human disease, including obesity and type 2 diabetes mellitus (T2DM), illnesses that represent two of the greatest global health challenges of this century associated with significant comorbidities and healthcare costs. Although several factors contribute to the development and progression of obesity and T2DM, in recent years metagenome-wide association studies have revealed potential relationships between intestinal microbiomes and the pathogenesis of T2DM.2,3 The gut microbiota can contribute to human health in multiple ways, including roles in polysaccharide breakdown, nutrient absorption, inflammatory responses, bile acid modification, and gut permeability. Although numerous studies have suggested that disruptions in the relative proportions of gut microbial populations may contribute to weight gain and insulin resistance, most of these studies are conducted with stool or colonic samples and have not compared the relative efficacy of various weight loss diets in relation with the gut microbiota.4 The human gut microbiota has been grouped into three distinct categories of enterotypes based on a relatively high abundance of Bacteroides species (enterotype 1), Prevotella species (enterotype 2), and Ruminococcus (enterotype 3). Research suggests enterotypes 1 and 2 may be associated with long-term diets within individuals. Enterotype 1 is reported to be predominant in individuals consuming Western diet (more protein and animal fat), whereas enterotype 2 appears predominant in those who consume more carbohydrates and fiber.5

As a proxy for enterotypes, Hjorth et al studied the pretreatment Prevotella/Bacteroides ratio (P/B ratio) as a prognostic marker for successful body fat loss on two diets differing greatly in dietary fiber and whole grain content. Researchers randomly assigned 62 participants with increased waist circumference to receive an ad libitum New Nordic Diet (NND, a fiber-rich option that places more emphasis on whole foods such as vegetables and fruits) or an Average Danish Diet (ADD, which includes lean meat, coffee, lettuce, and eggs without grains) for 26 weeks. Participants’ weight and body measurements were taken before and after they started the 26-week diets. They were grouped into two discrete enterotypes by the relative abundance of Prevotella species divided by Bacteroides species (P/B ratio) obtained by quantitative polymerase chain reaction analysis of their stool samples. After the initial 26-week study period, all 62 participants followed the NND for another year.

Researchers found that among individuals with a high P/B ratio, the NND resulted in a 3.15 kg (95% confidence interval [CI], 1.55-4.76; P < 0.001) larger body fat loss compared to ADD, whereas no differences was observed among individuals with low P/B ratio (0.88 kg; 95% CI, 0.61-2.37; P = 0.25). Consequently, a 2.27 kg (95% CI, 0.09-4.45; P = 0.041) difference in response to the two diets was found between the two P/B groups. In essence, study participants who demonstrated a high P/B ratio appeared more likely to lose body fat on diets high in fiber and whole grain when compared to subjects who exhibited a low P/B ratio. Their waistlines also decreased more significantly. Interestingly, during the one-year follow-up period, a 3.99 kg (95% CI, 1.82-6.15; P < 0.001) difference in responsiveness to the NND was found between the two P/B groups.

COMMENTARY

We are what we eat. Everyone has heard it, but most probably don’t quite believe it. A growing body of literature suggests that diet, and not the obese state, may be the major driving force behind gut microbiota changes.6 In fact, the effect of diet on the composition of the gut microbiota begins early in life. As these human intestinal bacteria are linked to the increasing prevalence of overweight and obesity, scientists have started to investigate whether the intestinal bacteria can play a role in the treatment of overweight, obesity, and diabetes. Therefore, while it may be frustrating for our patients attempting to lose weight by trying various weight loss diets, research into the predominant type of human gut microbiota may play an increasing role in helping personalize nutrition, including the recommendation for particular types of diets. We have explored the effectiveness of various weight loss diets based on effects on energy expenditure, body weight, body composition, and metabolic parameters. However, it is becoming clearer that certain bacterial species and imbalances in one’s gut may play a decisive role in weight regulation and loss. Restoring those imbalances in gut bacteria by dietary modifications may be the answer to addressing one of the biggest global public health crises. Clinicians may soon recommend that patients submit a stool sample to determine if they’re able to lose weight on a personalized diet based on the results.

REFERENCES

  1. Qin J, Li R, Raes J, et al. A human gut microbial gene catalogue established by metagenomic sequencing. Nature 2010;464:59-65.
  2. Maccaferri S, Biagi E, Brigidi P. Metagenomics: Key to human gut microbiota. Dig Dis 2011;29:525-530.
  3. Adamski J. Genome-wide association studies with metabolomics. Genome Med 2012;4:34.
  4. Barlow GM, Yu A, Mathur R. Role of the gut microbiome in obesity and diabetes mellitus. Nutr Clin Pract 2015;30:787-797.
  5. Wu GD, Chen J, Hoffmann C, et al. Linking long-term dietary patterns with gut microbial enterotypes. Science 2011;334:105-108.
  6. Bortolin RC, Vargas AR, Gasparotto J, et al. A new animal diet based on human Western diet is a robust diet-induced obesity model: Comparison to high-fat and cafeteria diets in term of metabolic and gut microbiota disruption. Int J Obes (Lond) 2017 Sep 12. doi: 10.1038/ijo.2017.225. [Epub ahead of print].