Diabetes and microbiota
Current nutritional recommendations for diabetes treatment and prevention focus primarily on lifestyle modifications with dietary interventions. Several diets such as the Mediterranean, low glycemic index or low and very low carbohydrate diets appear to improve glucose control. Different forms of sugar can also affect the postprandial glycemic response. Some dietary products can also interact or alter the composition of the microbiota and increase the risk of certain metabolic diseases such as type 2 diabetes. The microbiota has several important metabolic functions, including lipid and glucose homeostasis, energy production and vitamins, as well as the protection of gut health. Daily nutrition constantly affects the intestinal microbiota; and in many studies, differences have been reported between T2D patients and healthy individuals.
Patients with this condition typically have lower levels of the beneficial short-chain fatty acids (SCFAs) produced by Bifidobacterium, Akkermansia, and Blautia. These patients also have a greater abundance of potentially pathogenic bacteria such as Shigella and Escherichia. This dysbiosis is one of the key characteristics of T2D that can be identified already in the prediabetic phase. SCFAs are considered to be one of the main mediators of different microbiota models that have beneficial or detrimental effects on health. The three most common SCFAs, including acetate, propionate and butyrate, are produced by the gut microbiota through the fermentation of dietary fiber. SCFAs can also induce immune responses through the induction of T-regulatory cells (Tregs) and the enhancement of epithelial barrier function.
FODMAP diet and impact on gut microbiota
The term FODMAP refers to fermentable short-chain carbohydrates, including fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. Some common FODMAPs include lactose, fructans, sorbitol and mannitol. It has been observed that short-term consumption of a low FODMAP diet relieves gut symptoms and induces changes in the gut microbiota. Conversely, a diet rich in FODMAPs can improve glycemic responses and insulin sensitivity. Although there is considerable evidence to support the role of FODMAPs in the pathogenesis of T2D, the relationship between glycemia and FODMAPs must be explored. In a new latest review in the journal Clinical Nutrition, the researchers summarized the available scientific knowledge about FODMAPs.
Overall data suggest that short-chain fermentable carbohydrates may play a role in the prevention and treatment of diabetes. FODMAPs are poorly absorbed in the small intestine, tend to cause osmotic effects, and are fermented in the colon. A diet rich in FODMAPs has the potential to increase beneficial intestinal microorganisms to support better lipid and glucose metabolism, as well as immune defenses. In comparison, a low-FODMAP diet can reduce the prevalence of important bacteria that contribute to these processes, thus leading to adverse health effects. Therefore, food products high in FODMAPs can produce a better postprandial glycemic response than supplements.
Fructans and poliol sugars
Fructans are glucose polymers that can promote the growth of beneficial bacteria in the gut. Previous studies on inulin, which is a common fructane, have reported a reduction in HbA1c and plasma glucose levels in patients with DT2. Foods with a higher fructan content have also been found to reduce glycemic variability in patients with DT2. Inulin has also been reported to reduce blood lipid and fasting blood glucose levels, as well as increase Bacteroides. Other studies have shown an increase in Akkermansia muciniphila and Faecalibacterium prausnitzii, along with a decrease in glycated hemoglobin, glucose, C-reactive protein (CRP) and lipopolysaccharides (LPS) after inulin treatment. Polyols are sugary alcohols found in natural and synthetic foods. Xylitol, which is a synthetic polyol, has been shown to improve glucose profiles and reduce visceral fat accumulation after an eight-week treatment. Polyols have also been observed to increase the abundance of bifidobacteria in healthy individuals; however, no such observation has so far been made in patients with diabetes.
What are galacto-oligosaccharides (GOS)?
GOS are prebiotics capable of stimulating the growth of health-promoting bacteria such as lactobacilli and bifidobacteria. GOS are generally found in legumes, popular ingredients in the Mediterranean diet associated with a low glycemic index. As a result, many national diabetes practice guidelines recommend the intake of soy nuts and legumes. Several studies have reported that the consumption of legumes and bean-based diets can help reduce postprandial plasma glucose levels, as well as improve insulin secretion. For example, a three-month randomized study found that a high-FODMAP almond diet was more effective in lowering postprandial blood glucose and HbA1c than a low-FODMAP peanut-based diet.
Impact of low-carbohydrate diets on microbiota diversity
Dietary interventions are useful for preventing the progression of diabetes in pre-diabetic individuals, as well as for improving metabolic control in diabetic individuals. In fact, weight loss can reduce blood glucose levels in overweight pre-diabetic patients by improving insulin sensitivity and reducing insulin resistance. Several diets, such as high-carb, low-protein, ultra-low-carb, high-protein, low-carb, high-unsaturated-fat, and low-saturated-fat diets are capable of improving stability of blood glucose and lipid profiles, as well as reducing the need for diabetes medications. Researchers from the Diabetes Prevention Program have indicated that a diet rich in carbohydrates and fiber, accompanied by a reduced consumption of total and saturated fat, can provide the highest long-term weight reduction. However, more research is needed to clarify the impact of low-carb and high-protein / high-fat diets on the gut microbiota.
A low-calorie, high-FODMAP diet for prediabetes and diabetes
High FODMAPs can elicit beneficial effects on the gut microbiome and metabolism. The microbiota changes induced by following a certain FODMAP diet occur in a dose-dependent manner. Although a diet rich in FODMAPs can support an increase in health-promoting bacteria, it can also lead to abdominal pain, bloating, constipation, and / or diarrhea. Daily consumption of FODMAP foods varies according to geographic regions and cultures. Based on physical activity, body mass index and health status of people with diabetes, women are advised to consume between 1,200 and 1,500 kcal, while men should consume between 1,500 and 1,800 kcal per day. Approximately 3-5% weight loss is recommended for clinical benefit. However, a diet rich in FODMAPs has yet to be designed to limit the consumption of excess fat and calories, while ensuring a balanced intake of micro and macronutrients.
- Edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
Scientific references
Clinical Nutr. 2021; 40(5):3409-3420.
Neurogastroenterol Motil. 2019; 31(10):e13675.
Aliment Pharmacol Ther. 2019; 50(5):517-529.
J Gastroenterol Hepatol. 2017; 32(S1):16-19.
Dott. Gianfrancesco Cormaci
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