Obesity and the gut microbiome – What you should know as a health practitioner

Obesity awareness week is held during January. The campaign aims to create a national New Year’s resolution to improve the nation’s health, which could include cooking healthier food, avoiding snacks and being more active. Although obesity is largely preventable, the epidemiology is complex. We need to improve our understanding to address the global challenge as individuals and at public health level (1).

Lifestyle factors improve health for people who are overweight or obese, but the goal of reducing energy intake alone could be too simple for solving the obesity epidemic. Evidence in animal and human studies suggests that the gut microbiome is linked to obesity (2). Could the gut microbiome be one of the missing links as to why some people gain, or lose weight easier than others?

Impact of the gut microbiome on obesity

People classified as obese often have a gut microbiome lacking in bacterial diversity (dysbiosis) with a dominance in a type of bacteria, firmicutes (which yields more energy from food) and less of the other dominant type, bacteroidetes. The reverse is associated with lean people. Simply put this means that their dominant bacteria create more calories than those in a non-obese person, even after eating the same food. However, the research isn’t clear yet on whether being obese causes the shift in bacteria in the gut microbiome or whether the bacterial changes cause obesity. Interestingly animal models have demonstrated a causal link between gut microbiome diversity and obesity, yet further research is needed in humans (3). The gut microbiome is thought to be associated with obesity due to its impact on metabolic function and this is not surprising since obesity is a component of metabolic syndrome (4). Obesity is no longer seen as a single condition but has a cluster of features associated with metabolic diseases, such as type 2 diabetes. By better understanding the mechanisms behind the modulatory affect of the gut microbiome on obesity, this could provide therapeutic strategies for treating people with obesity and metabolic disease (5).

Diet, exercise and medications can all change the bacterial balance of the gut microbiome.

Impact of diet on gut health

A western-style diet, low in dietary fibre and high in fat, is associated with obesity and also dysbiosis of the gut microbiome. A diet high in simple carbohydrates and saturated fat, typical in the western diet, has negative effects on the gut microbiome (6). Populations with varied diets with a greater proportion of plant-based foods have a greater proportion of bacteroidetes and prevotella. This particular strain appears to be beneficial as it has a protective role against inflammation in the gut (7). A greater variation of plants in the diet could be a goal to improve the gut microbiome in those who are obese, aiming for a dietary pattern that reflects those with healthier metabolic profiles. An intervention study has shown that a whole-grain diet also rich in fruit and vegetables can reduce inflammatory markers in participants who are obese (8). Additionally, a multi-functional diet was shown to reduce cardiometabolic risk factors in overweight and obese people, while increasing prevotella abundance. The multi-functional diet included specific components: antioxidant rich foods, prebiotic rich foods, omega 3s, low glycaemic index foods and foods with blood cholesterol normalising properties (9). These foods also have positive effects on the gut microbiome and aaa lack of these in the diet has been associated with dysbiosis.

In summary, obesity is associated with gut dysbiosis and a western diet is strongly correlated to this imbalance. A high fat and high sugar diet can lead to gut dysbiosis and gut inflammation which in turn could be a cause of metabolic syndrome. More research is required to determine the exact mechanism and causality, but the current research does suggest the use of a more personalised approach to treating obesity using diet and the gut microbiome.

References

1. Hruby, A. and Hu, F.B., 2015. The epidemiology of obesity: a big picture. Pharmacoeconomics, 33(7), pp.673-689.
2. John, G.K. and Mullin, G.E., 2016. The gut microbiome and obesity. Current oncology reports, 18(7), p.45.
3. Tseng, C.H. and Wu, C.Y., 2019. The gut microbiome in obesity. Journal of the Formosan Medical Association, 118, pp.S3-S9.
4. Apovian, C.M., 2016. Obesity: definition, comorbidities, causes, and burden. Am J Manag Care, 22(7 Suppl), pp.s176-85.
5. Marchesi, J.R., Adams, D.H., Fava, F., Hermes, G.D., Hirschfield, G.M., Hold, G., Quraishi, M.N., Kinross, J., Smidt, H., Tuohy, K.M. and Thomas, L.V., 2016. The gut microbiota and host health: a new clinical frontier. Gut, 65(2), pp.330-339.
6. Sonnenburg, J.L. and Bäckhed, F., 2016. Diet–microbiota interactions as moderators of human metabolism. Nature, 535(7610), p.56.
7. De Filippo, C., Cavalieri, D., Di Paola, M., Ramazzotti, M., Poullet, J.B., Massart, S., Collini, S., Pieraccini, G. and Lionetti, P., 2010. Impact of diet in shaping gut microbiota revealed by a comparative study in children from Europe and rural Africa. Proceedings of the National Academy of Sciences, 107(33), pp.14691-14696.
8. Kopf, J.C., Suhr, M.J., Clarke, J., Eyun, S.I., Riethoven, J.J.M., Ramer-Tait, A.E. and Rose, D.J., 2018. Role of whole grains versus fruits and vegetables in reducing subclinical inflammation and promoting gastrointestinal health in individuals affected by overweight and obesity: a randomized controlled trial. Nutrition journal, 17(1), p.72.
9. Marungruang, N., Tovar, J., Björck, I. and Hållenius, F.F., 2018. Improvement in cardiometabolic risk markers following a multifunctional diet is associated with gut microbial taxa in healthy overweight and obese subjects. European journal of nutrition, 57(8), pp.2927-2936.