by Christina Sanzari and Afrouz Abbaspour
Christina is a rising 2nd year clinical psychology graduate student at SUNY Albany and Afrouz is a senior post-doctoral fellow at CEDI at Karolinska Institutet in Sweden
A quick google search of “how to improve my gut health” yields millions of websites with information on probiotics, prebiotics, “The Microbiome Diet,” and natural remedies for healing your gut. These search results reflect the growing popular media attention to the health implications of the human microbiota.
But what really is the microbiota and how does it relate to our health?
The human microbiota consists of different microbes (bacteria, archaea, unicellular and multicellular eukaryotes, and viruses) in and on our bodies. An imbalance in the human microbiota (sometimes called a dysbiosis) has been associated with multiple medical conditions such as cardiovascular disease, obesity, diabetes (type 1 and type 2), and irritable bowel syndrome.1-4 The intestinal microbiota also plays a role in energy extraction from the diet. In other words, a pea is not always just a pea. Depending on your microbiota, you may extract more or less energy from the same type of food and amount of food eaten as another person. These associations motivated eating disorders researchers at UNC to examine the link between the intestinal microbiota and anorexia nervosa (AN). AN is a serious, sometimes life-threatening illness that affects millions of people in the United States.5 Unfortunately, treatments for AN are limited and only about 30% of individuals with AN make a full recovery.6
The first step in AN treatment is nutritional rehabilitation, or the process of reintroducing food after starvation to restore a healthy weight. Renourishment can be a very uncomfortable experience for patients, as it often requires large amounts of food that can lead to bloating and discomfort. Growing attention to the human microbiota in the scientific community is pointing toward new interventions that might make renourishment more tolerable for individuals with AN. New research has found that that the gut microbiota is dysregulated in AN and actually contains certain taxa (groups of organisms classified based on shared characteristics) that thrive in a malnourished environment. This means that some of the microbes in the gut of individuals with AN that survived and thrived during prolonged starvation, may make it harder for individuals with AN to gain weight.7
We are not able to say whether imbalances in the gut microbiota make someone more likely to develop AN or if the malnourishment characteristic of AN changes the microbes in the gut (or both!). Nonetheless, these study findings still have important implications for future treatment of this disorder. Even if the changes in the gut microbiota are consequences of malnourishment, microbial changes might still play a role in maintaining AN. This research provides the foundation for exploration into novel approaches to target the microbiota in AN treatment.
If we can identify specific taxa in the gut whose promotion or elimination would improve the renourishment process, then probiotic (a microorganism introduced into the body for its beneficial qualities), prebiotic (compounds in food that induce the growth or activity of beneficial microorganisms), or synbiotic (combining probiotics with prebiotics to improve the survival of probiotic bacteria) therapeutic approaches may be developed to make this aspect of treatment more tolerable for AN patients.8
One of the biggest challenges in treating AN is maintaining therapeutically restored weight. A revolving door cycle can emerge of inpatient renourishment followed by rapid weight loss post discharge. Augmenting the diet with tailored pro-, pre-, or synbiotics may have the potential to reduce this dangerous weight cycling by making refeeding more comfortable for AN patients and introducing specific microbes to the intestinal environment that thrive in a well-nourished environment. Although this treatment is speculative at this time, research is ongoing in various centers around the world to inform these types of precision interventions for AN. It is conceivable that similar approaches may be valuable for other eating disorders as well, although research on other eating disorders lags behind that of AN.
Too often, the inability of patients with AN to regain weight is attributed to psychological factors. To be sure, AN is characterized by an overevaluation of weight and shape and a drive for thinness; however, research on the intestinal microbiota of these individuals bends the narrative and suggests that other factors may also contribute to the inability to gain and maintain weight. Although this research is still in its infancy, we anticipate that it will contribute to the development of novel interventions that are both effective and acceptable to individuals with AN.
- Igudesman D, Sweeney M, Carroll IM, Mayer-Davis EJ, Bulik CM. Gut- Brain interactions: Implications for a role of the gut microbiota in the treatment and prognosis of anorexia nervosa and comparison to type 1 diabetes. Gastroenterol Clin N Am. 2019 Sep;48(3):343-356. doi: 10.1016/j.gtc.2019.04.003.
- Lau K, Srivatsav V, Rizwan A, Nashed A, Liu R, Shen R, et al. Bridging the Gap between Gut Microbial Dysbiosis and Cardiovascular Diseases. Nutrients. 2017;9(8):859. doi:10.3390/nu9080859.
- Moser G, Fournier C, Peter J. Intestinal microbiome-gut-brain axis and irritable bowel syndrome. Wien Med Wochenschr. 2018;168(3-4):62-66. doi:10.1007/s10354-017-0592-0
- Sikalidis AK, Maykish A. The Gut Microbiome and Type 2 Diabetes Mellitus: Discussing A Complex Relationship. Biomedicines. 2020; 8(1):8. https://doi.org/10.3390/biomedicines8010008
- Hudson JI, Hiripi E, Pope HG Jr, Kessler RC. The prevalence and correlates of eating disorders in the National Comorbidity Survey Replication [published correction appears in Biol Psychiatry. 2012 Jul 15;72(2):164]. Biol Psychiatry. 2007;61(3):348-358. doi:10.1016/j.biopsych.2006.03.040
- Fichter MM, Quadflieg N, Crosby RD, Koch S. Long-term outcome of anorexia nervosa: Results from a large clinical longitudinal study. Int J Eat Disord. 2017 Sep;50(9):1018-1030. doi: 10.1002/eat.22736.
- Carr J, Kleiman SC, Bulik CM, Bulik-Sullivan EC, Carroll IM. Can attention to the intestinal microbiota improve understanding and treatment of anorexia nervosa?. Expert Rev Gastroenterol Hepatol. 2016;10(5):565-569. doi:10.1586/17474124.2016.1166953
- Kleiman SC, Watson HJ, Bulik-Sullivan EC, Huh, EY, Tarantino LM, Bulik CM, Carroll IM. The intestinal microbiota in acute anorexia nervosa and during renourishment, Psychosom Med. Nov-Dec 2015;77(9):969-81. doi: 10.1097/PSY.0000000000000247