Obesity and Gut Health

By: Alexis Villaret, LWDI Intern

Ahhh… the holidays festivities have finally ceased. Family gatherings may have not inspired the finest eating moments. Usually, temptations are reserved for an occasional birthday or anniversary but with the consecutive holidays indulgences of eggnog, cookies, cakes, holiday roasts and alcohol are hardly avoidable. We are all aware by now of the guilt felt eating one too many of grandma’s cookies and of course the impact on the waistline. It makes sense right…too many cookies equals extra calories and extra fluff in the midsection. That is no secret. Now that January is here the daunting task of shedding that “winter coat” ensues. The Peloton bike that has served as a clothes rack gets dusted off, the gym membership is renewed and we begin the arduous task of losing the same ole L-B’s we gain every year. However it never has occurred to us that our gut bacteria may be playing a less obvious role. We are all probably familiar with gut bacteria and its significant role in our immune system. However an emerging body of research is exploding that suggests a correlation between obesity and gut microbes exists. 


Understanding the roles in the community of bacteria lining our gastrointestinal tract also known as the microbiota may aid in understanding the mechanisms responsible in weight gain. The microbiota is the ecosystem of bacteria that pertains to the gastrointestinal tract. 

Specifically, the five species of bugs that occupy the gut are called Bacte-roidetes, Firmicutes, Actinobacteria, Proteobacteria, and Verru-comicrobiai. Bacteroidetes and Firmicutes are the most dominate and contribute to the majority of microbiota. Collectively only 10% of the remaining microbes contributes to the overall microbiota population(7). 

These bacteria are vital for good health as they produce B vitamins and vitamin K(3) while assisting in nutrient absorption and storage(4). These microbes also aid in degrading fiber for energy, which simultaneously fuels growth of beneficial bacteria to prevent overgrowth of pathogeneic bacteria. The most well known role of bacteria in the gut is support of a healthy immune system (3).


The connection between gut bacteria and obesity is not completely understood. However several animal studies are providing clues. The gut bacteria profiles actually vary in lean and obese animal models and potentially human. Therefore the type of bacteria matters! Specifically within the microbiota, Bacteroidetes and Firmicutes are responsible for breaking down dietary carbohydrates and utilizing them for energy(10).Therefore when there is a disruption in this delicate balance of gut bugs, a condition called dysbiosis, energy production is inhibited leading to weight gain. Other animal studies have revealed depleted Bacteroidetes populations combined with increases of Firmicutes populations were present in obese mice compared to mice of a healthy weight(4). So what does a spiked eggnog over the holidays have to do with all of this? Those indulgences may have also contributed to dysbiosis or a change in your bacteria profile. Animal studies suggest high fat animal based foods coupled with sugar actually increases Firmicutes species while beneficial bacteroidetes are depleted reducing energy production from food (2). 

An additional study of obese mice demonstrated how two different diet patterns (High Fat and High Carbohydrate) common during the holiday season impact gut bacteria. A HFD (High Fat Diet) decreased gut diversity, which lead to dysbiosis. A high fat diet will 

naturally lack adequate fiber (also known as prebiotics) a fuel source for beneficial bacteria including Bacteroidetes. Bacteroidetes have a positive association with adiposity(5). This infers a reduction in good bacteria translates to decreased utilization of food for energy production and subsequently an increased likelihood of energy stored as fat. 

The HCD (High Carbohydrate-Sucrose Diet) was more problematic than the HFD since it promoted the growth of obesogenic related bacteria Acinetobacter,Blautia, and Dorea(7). 

These are all animal studies and this data may not be extrapolated to humans. However a compelling human trial also linked lack of gut diversity and chronic weight gain which was sustained over 10 years (10). 

What we can extract from this emerging data is a prebiotic rich diet is necessary to support growth of beneficial Bacteroides that are associated with lower body fat percentage. Also when Bacteroides are flourishing it does not allow for fat promoting bacteria to survive through displacement. Furthermore prebiotics or resistant starches provide an acidic environment in the gut created through fermentation. Beneficial gut bacteria actually feeds on prebiotics and this may inhibit the growth of pathogenic bacteria and dysbiosis (9).






brussel sprouts 
















dried fruit


In conjunction with prebiotics, a well balanced diet represented by a model such as MyPlate is essential in promoting gut diversity (11). 


It may not be a coincidence that high fat, high sugar holiday food that is representative of the Standard American diet is contributing to weight gain, especially post holiday weight gain. It potentially may be an insight into one of the several mechanisms contributing to the nations and worlds for that matter obesity rates. While this research is still in its infancy it serves as one more reason Americans need to ditch SAD (Standard American Diet) and adopt GLAD (Gut Loving American Diet) to potentially thwart weight gain. So yes, dry January is in full effect and do not let that gym membership expire just yet. However, please do focus on including more fiber rich plant sources and do not settle for SAD, get a GLAD. 


1.Aoun A, Darwish F, Hamod N. The influence of the gut microbiome on obesity in adults and the role of probiotics, prebiotics, and synbiotics for weight loss. Prev Nutr Food Sci. 2020;25(2):113-123 

2. Carmody RN, Gerber GK, Luevano JM Jr, et al Diet dominates host genotype in shaping the murine gut microbiota. Cell Host Microbe. 2015;17(1):72-84.   

3.Davis CD. The gut microbiome and its role in obesity. Nutr Today. 2016;51(4):167-174. 

4. Gentile CL, Weir TL. The gut microbiota at the intersection of diet and human health. Science. 2018;362(6416):776-780. 

5. Gomes AC, Hoffmann C, Mota JF. The human gut microbiota: Metabolism and perspective in obesity. Gut Microbes. Published online 2018:1-18.   

6. John GK, Mullin GE. The gut microbiome and obesity. Curr Oncol Rep. 2016;18(7):45. 

7.Kong C, Gao R, Yan X, Huang L, Qin H. Probiotics improve gut microbiota dysbiosis in obese mice fed a high-fat or high-sucrose diet. Nutrition. 2019;60:175-184. 

8. Lv Y, Qin X, Jia H, Chen S, Sun W, Wang X. The association between gut microbiota composition and BMI in Chinese male college students, as analysed by next-generation sequencing. Br J Nutr. 2019;122(9):986-995.   

9.Mahan LK, Raymond JL. Krause’s Food & the Nutrition Care Process. 14th ed. Saunders; 2016. 

10.Menni C, Jackson MA, Pallister T, Steves CJ, Spector TD, Valdes AM. Gut microbiom diversity and high-fibre intake are related to lower long-term weight gain. Int J Obes (Lond). 2017;41(7):1099-1105. 

11.MyPlate. Myplate.gov. Accessed January 22, 2021.https://www.myplate.gov/   

12.Zhang Y-J, Li S, Gan R-Y, Zhou T, Xu D-P, Li H-B. Impacts of gut bacteria on human health and diseases. Int J Mol Sci. 2015;16(4):7493-7519.t

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