Abstract
Type 2 diabetes mellitus (T2DM) is among the most prevalent diseases in the world, affecting over 420 million people. The disease is marked by a poor metabolic effect of insulin leading to chronic hyperglycaemia, which can result in microvascular complications. It is widely known that postprandial glycaemia is reliant on the total carbohydrate content of a meal. However, the importance of the amount and the source of these carbohydrates remains controversial due to mechanisms other than insulin secretion. Oxidative stress, inflammation, pyruvate production and the quality of the intestinal microbiota, resulting in plasma lipopolysaccharides and short-chain fatty acids production, play an important role in blood sugar control and consequently in type 2 diabetes. Thus, we systematically reviewed the preclinical evidences on the impact of the amount and type of carbohydrate found in different diets and its influence on blood glucose levels in diabetic animals. We used a comprehensive and structured search in biomedical databases Medline (PubMed), Scopus and Web of Science, recovering and analyzing 27 original studies. Results showed that sucrose-rich diets deteriorated diabetic condition in animal models regardless of the total dietary carbohydrate content. On the other hand, fiber, particularly resistant starch, improved blood glucose parameters through direct and indirect mechanisms, such as delayed gastric emptying and improved gut microbiota. All studies used rodents as animal models and male animals were preferred over females. Improvements in T2DM parameters in animal models were more closely related to the type of dietary carbohydrate than to its content on a diet, i. e., resistant starch seems to be the most beneficial source for maintaining normoglycemia. Results show that current literature is at high risk of bias due to neglecting experimental methods.
Highlights
Diabetes mellitus has become one of the most common chronic diseases in the world, with 422 million people affected worldwide
The main question to be answered in this systematic review was: what are the ideal type and amount of dietary carbohydrate in order to improve Type 2 diabetes mellitus (T2DM) parameters in animal models, and what are the main mechanisms involved in it?
Eighteen studies reported a worsening in blood glucose parameters; six of them intervened with a high carbohydrate diet [23,24,25,26,27,28]
Summary
Diabetes mellitus has become one of the most common chronic diseases in the world, with 422 million people affected worldwide. Some foods’ intake induce a marked rise followed by a more or less rapid fall in blood glucose, while others produce a smaller peak along with a more gradual decline in plasma glucose [10] It is recommended for T2DM patients an intake of 26–44% of total daily energy from carbohydrates, preferably from high-quality sources, such as vegetables, whole fruits and legumes [11], which are rich in fiber. This study was designed to systematically review the in vivo preclinical effects of the type and amount of dietary carbohydrates in studies involving T2DM animal models, in order to clarify these aspects for improving T2DM management. This review evaluated the methodological quality of current evidence, pointing out the main sources of bias in the selected studies
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