A mother’s diet can have health impacts not only on her immediate offspring, but also on the next generation, a mouse study suggests. Compared with controls, the offspring of mice fed a high-fat diet suffered both an altered gut microbiome and deficits in social interactions. In turn, their offspring too showed social dysfunction, as well as slight abnormalities in microbiome composition. The findings were published in Cell Reports on October 11.

“The current study lends to the growing body of evidence that . . . a maternal high fat or Western style feeding during pregnancy and lactation modifies their offspring’s microbiome in both early life and later in childhood,” Kjersti Aagaard, an expert in maternal-fetal medicine at Baylor College of Medicine who was not involved in this study, writes in an email to The Scientist.

Notably, she adds, “this altered microbiome and associated abnormal neurobehavior is not only evident in the first generation of offspring, but in the second generation as well—even when it was only the ‘grandmother’ that was fed a high fat diet.”

High-fat diets have previously been shown to alter the gut microbiome of mice, and of their immediate offspring. In a 2016 study, some of the authors of the current paper showed that male pups born to mothers fed a high-fat diet suffered disruptions, or dysbiosis, in their gut microbiota, with roughly a third fewer bacterial species compared with controls. The male pups also showed reduced sociability and a lack of preference for social novelty—traits similar to one of the core phenotypes of autism, says Shelly Buffington, a neuroscientist at the University of Texas Medical Branch and a coauthor of both the current study and the 2016 study. 

“I got thinking that we had missed a little bit of an opportunity, because we never followed up on the females,” says Buffington. “In mammals, there’s this vertical transmission of gut microbiota from mom to baby, so if [the enduring dysbiosis] was in the males, surely we would see it in the females too.” 

Indeed, when the researchers behind the current study analyzed the gut microbiome of female pups born to mice that had been fed a high-fat diet for six weeks prior to conception, during gestation, and during lactation, they found a similar effect to the one they had found in male pups: About a third of bacterial species had been lost from the gut microbiomes of the first, or F1, generation of offspring. 

Some caution should be exercised in interpreting the results as demonstrating that the maternal microbiota is necessary and sufficient for driving these adult phenotypes.

Eldin Jašarević, Magee-Womens Research Institute and University of Pittsburgh  

“Even if those F1 females are now on a regular diet, if they have this dysbiotic gut microbiome, could this have an impact on the F2 generation?” Buffington recalls asking. To find the answer, the team fed the F1 mice a normal diet and measured whether any social deficits arose in their offspring.

Like the F1 pups, the F2 offspring never received a high-fat diet themselves. Nevertheless, both male and female F2 pups showed deficits in social behavior compared to pups whose grandmothers had eaten normal diets. The female F2 mice only showed a statistically significant difference from control mice on one of three behavioral tests designed to assess different aspects of social function. In contrast, the F1 and F2 males showed strong deficits in all three tests. 

The researchers then tried feeding the F2 mice a bacterium called Limosilactobacillus reuteri, which they had previously shown protected against social deficits in the offspring of mothers fed a high-fat diet. Feeding L. reuteri after weaning rectified social behavior in both sexes. In the males, social behaviors were rescued to the levels observed in mice whose grandmothers ate regular diets. 

The F2 females no longer showed a deficit in the one behavioral test they’d scored poorly on.  “In the other two tests, it caused the females to perform even better, have a stronger inclination towards social behavior than the regular diet counterparts,” says Buffington, who is named as an inventor on a patent related to the use of L. reuteri for treating disorders characterized by social dysfunction.

The findings highlight the importance of studying both sexes, she adds. “We didn’t expect [the effect in females] because a lot of autism work has been done almost exclusively in male mice. . . . I think we’re missing many possible exciting discoveries by only focusing on males.” Buffington says that her lab is currently developing new approaches to analyze female social behavior in mice.

An uncertain mechanism behind multigenerational effects of diet

Although the F2 pups had social deficits, their microbiomes were only slightly disturbed, the researchers found: While the same number of bacterial taxa was found in their guts as in the guts of mice whose grandmothers ate normal diets, the species composition differed somewhat. 

Buffington speculates that the F1 generation’s altered gut microbiome, rather than the F2 generation’s, may be the culprit behind the “adverse social behaviors” in the younger animals, adding that the F1 microbiome may have impacted their fetal neurodevelopment. F3 mice born to these F2 mothers did not display any social deficits, the study showed.

See “The Role of Mom’s Microbes During Pregnancy

The results are “consistent with a vertical transmission of microbes down the maternal lineage, resulting in social dysfunction behavior being seen from one generation to the next and the next,” writes Aagaard.  

However, Eldin Jašarević, an expert in maternal microbiota at the Magee-Womens Research Institute and the University of Pittsburgh who was not involved in the work, writes in an email that “[s]ome caution should be exercised in interpreting the results as demonstrating that the maternal microbiota is necessary and sufficient for driving these adult phenotypes. One challenge in establishing causality between maternal diet, microbiota, and offspring phenotype is that these environmental perturbations exert disruptive effects on both mother and developing fetus.” 

Jašarević adds that the prenatal environment is shaped by lifetime exposures to environmental conditions, as is the colonization of neonates at birth. “As such, teasing apart the contribution of high-fat diet on prenatal development, the effect of [vertical] transmission of microbial communities shaped by high-fat diet, and their interaction is quite complex and technically difficult.” 

Such a question could be disentangled, Aagaard says, by stopping the high-fat diet around the timing of pregnancy implantation or conception with or without an intervention to alter the microbiome, such as a probiotic, and seeing if this eliminates the multigenerational effects observed in this study. 

In next steps, Buffington says, the team is investigating whether giving probiotics to the F1 generation females would protect the F2 pups from developing social deficits. As for how translatable these findings are to humans, Buffington points out that “we are only just beginning to understand how this relatively recent change in [humans’] dietary patterns [towards high-fat, high-sugar and processed foods] affects health and disease risk, let alone its impact across generations.” As the new study reveals a potential generational reach of unbalanced maternal diets, Buffington says, she is “excited to extend this line of investigation.”