It’s well established that bacterial diversity rules in the gut: study after study of intestinal microbiota composition shows that groups of people with a disease have a less diverse gut microbial community than groups without the disease. In some cases, the lack of diversity is referred to as a ‘dysbiosis’. The tricky part is figuring out how the principle of gut microbiota diversity can be used to improve human health.

Turning to weight loss: gut microbial diversity seems related to body weight, but the scientific results to date have been confusing. Some studies, but not others, have found a decreased gut microbiota diversity in those with obesity.

One of the main problems with studying the gut microbiota-obesity connection is that a high body mass index (BMI) often co-occurs with a ‘Westernized’ dietary pattern—frequent consumption of processed foods (many high in fat) and lower consumption of fresh foods. So it’s difficult to sort out whether it’s BMI or dietary pattern that’s driving the observed gut microbiota composition.

A new investigation by researchers in Alabama and Ohio (USA) attempted to shed light on this issue. In the study, individuals of different weights (from normal-underweight to overweight-obese) donated samples of stool and filled out questionnaires about dietary patterns and health status.

In most studies of this kind, researchers try to answer a discrete question like: “Do individuals with obesity have more bacteria from the Firmicutes phylum as opposed to the Bacteroidetes phylum?” or simply “Do people with a higher BMI have lower gut microbiota diversity?” But in this case, they took a broader approach and looked at the overall statistical pattern. They focused on identifying the factor that mathematically accounted for increased gut microbiota diversity in the subjects.

The researchers found when it came to gut microbiota diversity, the ‘Westernized’ diet type had an effect size greater than BMI. This indicates, they say, that diet may be a critical factor in gut microbiota dysbiosis, regardless of a person’s body weight.

This study backs heavy-hitting previous studies on different populations around the world. In groups like rainforest hunter-gatherers and agriculturalists in the Central African Republic, for example, who have diets and lifestyles very different from those in Westernized countries, scientists observe significantly higher gut microbiota diversity. Since the genes in the gut microbiota of these groups appear adapted to what they eat, diet is thought to be the primary contributor to their higher gut microbial diversity.

While scientists are still unravelling how to make the gut microbiota become more diverse, this study provides a hint that diversity could be modifiable through dietary interventions.

More studies that manipulate people’s diets are warranted. But so far we know this: whether you’re talking about trees, insects or gut microorganisms, an ecosystem is at its best as a tangled web of interdependent relationships. And if diversity is the name of the game, pay attention to your diet.



Davis SC, Yadav JS, Barrow SD, & Robertson BK. Gut microbiome diversity influenced more by the Westernized dietary regime than the body mass index as assessed using effect size statistic. MicrobiologyOpen. 2017. doi: 10.1002/mbo3.476.