The digestive tract is home to trillions of microorganisms. Collectively known as the microbiome, these “bugs” that live in everyone’s gut influence a surprising number of daily operations in the human body.
Research is still in its infancy, but animal and human studies point to the microbiome as being a mini ecosystem that interacts with cells, organs, and systems throughout the body. In doing so, it modulates the risk of a wide range of diseases. It’s not surprising that gastrointestinal diseases are influenced by the microbiome, but researchers are also looking at its role in autism spectrum disorder, mood disorders, and metabolic diseases including obesity and diabetes. (1,2)
The microbiome, obesity, and metabolic disease
It seems there are differences in the microbiota among people with diabetes compared to healthy individuals, and also, in lean versus obese individuals. It’s thought that changes in a person’s microbiome might affect their weight, how they extract energy from their diet, their insulin sensitivity, and in turn, their risk of developing diabetes. (1,2)
Among the trillions of microbes in the gut, two types, Firmicutes and Bacteroidetes make up a majority of “healthy bacteria”. While both are beneficial, Bacteroidetes appear to influence a healthier weight, while Firmicutes encourage more fat storage and are associated with weight gain. Studies show having a higher ratio of Firmicutes to Bacteroidetes is associated with increased BMI. In addition, research on adults suggests that that F/B ratio increases as BMI increases. (3,4)
These changes in the microbiome might actually make it harder to lose weight. Both animal and human research suggests that the obese microbiota is able to extract more energy from the diet and indirectly control energy expenditure and fat storage. (3)
Researchers have also noted people with insulin resistance and diabetes have less butyrate-producing bacteria. Butyrate is a short chain fatty acid that’s thought to influence insulin sensitivity and energy expenditure. Interestingly, human studies have shown that fecal transplant from lean to obese donors can reduce insulin resistance, at least for a short-term of 6 weeks. (5)
Causes of gut dysbiosis
While we all have the same basic gut microbiota, the variations associated with metabolic disease are influenced by several factors including:
Long term medication use – In addition to antibiotics, proton pump inhibitors, antipsychotic medications, opioids, metformin, and NSAIDS have all been shown to alter the gut microbiota. (6)
Illness or infection, especially those which affect the GI tract, can disrupt the microbiota.
Stress or anxiety – Both short and long-term stress can have an affect gut motility, diet choices, and sleep quality, and collectively these may impact the microbiota.
Diet quality and quantity – Much of the research on dysbiosis has focused on the effect of various diets. Researchers have identified the following as being associated with dysbiosis:
Higher fat (40% of calories) diets are associated with unfavorable changes in the gut microbiota compared to lower fat (20-30% of calories) diets. (7)
Lower fiber diets are associated with less bacterial diversity, whereas diets that are higher in fiber and resistant starch promote a richer and more diverse microbiome. (8)
Artificial sweeteners may disrupt the microbiome, and it’s thought that they might even contribute to glucose intolerance. (9)
Consuming more calories than are needed for weight maintenance has been shown to alter the gut microbiome, regardless of the quality of the diet.
Dietary strategies to support a healthier microbiome
A person’s microbiome evolves over time, and diet is one of the biggest controllable factors that determines whether the changes are harmful or beneficial. Even small diet changes can result in temporary improvements in the microbiome. Many studies suggest the improvements happen quickly – in as little as 24 hours to a few days. This can be motivating to patients.
The best strategy for everyone, and especially those with diabetes, is to increase consumption of plant foods such as fruits, vegetables, whole grains, legumes, nuts and seeds. Not only are these lower in calories and high in nutrients, but also, their lower glycemic index makes them diabetes-friendly compared to more processed foods.
More importantly, plant foods provide dietary fiber as well as resistant starches which can’t be broken down in the digestive tract. These promote a healthier, more diverse microbiome, and increase production of short chain fatty acids, including butyrate.
While all sources of fiber are beneficial, researchers have noted that including sources of prebiotic fiber is especially helpful in reversing dysbiosis. Prebiotic fiber functions as food or “fertilizer” for beneficial bacteria. Prebiotic supplements are available, but simply incorporating foods like under-ripe bananas, garlic, onions, leeks, and asparagus several times a week can easily do the job.
Eating more bacteria-rich fermented foods also has a positive impact on a patient’s gut health. Increases in beneficial bacteria are often seen after eating fermented dairy foods, especially kefir, as well as fermented vegetables like sauerkraut or kimchi.
Finally, RDs should help patients identify areas in their diet that might be contributing excess calories. Remind them that reducing calories will not only promote weight loss, but also, it will help to encourage a healthier, more balanced, and “obesity-fighting” microbiome. Incorporating more high-fiber plant foods is a great strategy to help reduce overall calories, while also working to improve the microbiome.
The Bottom Line
Even though human studies are limited, it seems clear that dysbiosis plays a role in the risk and development of diabetes and other metabolic diseases. Patients should be educated about the impact of stress, long-term medication use, and diet on their gut health. Diet interventions that promote a healthier microbiome should be one of the strategies patients use to reduce their risk of diabetes, and better manage their disease.
References:
- Brunkwall L, Orho-Melander M. The gut microbiome as a target for prevention and treatment of hyperglycemia in type 2 diabetes: from current human evidence to future possibilities. Diabetologia. 2017 Jun 1;60(6):943-51.
- Kho ZY, Lal SK. The human gut microbiome–a potential controller of wellness and disease. Frontiers in microbiology. 2018;9.
- Jumpertz R, Le DS, Turnbaugh PJ, Trinidad C, Bogardus C, Gordon JI, Krakoff J. Energy-balance studies reveal associations between gut microbes, caloric load, and nutrient absorption in humans. The American journal of clinical nutrition. 2011 May 4;94(1):58-65.
- Koliada A, Syzenko G, Moseiko V, Budovska L, Puchkov K, Perederiy V, Gavalko Y, Dorofeyev A, Romanenko M, Tkach S, Sineok L. Association between body mass index and Firmicutes/Bacteroidetes ratio in an adult Ukrainian population. BMC microbiology. 2017 Dec;17(1):120.
- Kootte RS, Levin E, Salojärvi J, Smits LP, Hartstra AV, Udayappan SD, Hermes G, Bouter KE, Koopen AM, Holst JJ, Knop FK. Improvement of insulin sensitivity after lean donor feces in metabolic syndrome is driven by baseline intestinal microbiota composition. Cell metabolism. 2017 Oct 3;26(4):611-9.
- Le Bastard Q, Al-Ghalith GA, Grégoire M, Chapelet G, Javaudin F, Dailly E, Batard E, Knights D, Montassier E. Systematic review: human gut dysbiosis induced by non-antibiotic prescription medications. Alimentary pharmacology & therapeutics. 2018 Feb;47(3):332.
- Wan Y, Wang F, Yuan J, Li J, Jiang D, Zhang J, Li H, Wang R, Tang J, Huang T, Zheng J. Effects of dietary fat on gut microbiota and fecal metabolites, and their relationship with cardiometabolic risk factors: a 6-month randomized controlled-feeding trial. Gut. 2019 Jan 18:gutjnl-2018.
- Holscher HD. Dietary fiber and prebiotics and the gastrointestinal microbiota. Gut Microbes. 2017;8(2):172–184.
- Singh RK, Chang HW, Yan D, et al. Influence of diet on the gut microbiome and implications for human health. J Transl Med. 2017;15(1):73.
