Gut feedback mechanisms and food intake: a physiological approach to slow carbohydrate bioavailability

Abstract

Glycemic carbohydrates in foods are an important macronutrient providing the biological fuel of glucose for a variety of physiological processes. A classification of glycemic carbohydrates into rapidly digestible carbohydrate (RDC) and slowly digestible carbohydrate (SDC) has been used to specify their nutritional quality related to glucose homeostasis that is essential to normal functioning of the brain and critical to life. Although there have been many studies and reviews on slowly digestible starch (SDS) and SDC, the mechanisms of their slow digestion and absorption were mostly investigated from the material side without considering the physiological processes of their in vivo digestion, absorption, and most importantly interactions with other food components and the gastrointestinal tract. In this article, the physiological processes modulating the bioavailability of carbohydrates, specifically the rate and extent of their digestion and absorption as well as the related locations, in a whole food context, will be discussed by focusing on the activities of the gastrointestinal tract including glycolytic enzymes and glucose release, sugar sensing, gut hormones, and neurohormonal negative feedback mechanisms. It is hoped that a deep understanding of these physiological processes will facilitate the development of innovative dietary approaches to achieve desired carbohydrate or glucose bioavailability for improved health.

Potential Sugar Reduction in Cookies Formulated with Sucrose Alternatives

“…The ileal brake is a term describing a specific status of gastrointestinal activity (such as slow contraction, secretion inhibition) resulting from undigested nutrients reaching the ileum under normal physiological conditions, and it is defined as ‘the primary inhibitory feedback mechanism to control transit of a meal through the gastrointestinal tract in order to optimize nutrient digestion and absorption.’” Maltotriose, maltotetraose, and maltopentaose all display a fairly strong ileal brake effect on the activity of the brush border enzyme, maltase‐glucoamylase (MGAM). This substrate brake effect suggests that the total digestion rate of carbohydrate by MGAM can be regulated, and carbohydrate with certain molecular structures (e.g., Mylose 351 or Glucodry 314) might be used to modulate carbohydrate digestion to achieve the desired rate of glucose release (Zhang et al 2015).…”

“…Nevertheless, based on its unique saccharide composition and distribution, one can infer the following major health benefit for a food ingredient like Mylose 351. As described and reviewed by Zhang et al (2015), "Sugar sensing is the basis for gastrointestinal activity modulation through the neurohormonal feedback mechanisms of the ileal brake and gut-brain axis. Liberated glucose from carbohydrate digestion stimulates the secretion of gut hormones through glucose sensing, and the gut hormones may directly or indirectly regulate gastrointestinal activity including digestion, nutrient absorption, gastric emptying and intestinal motility, leading to certain health effects such as appetite control.…”

“…Maltotriose, maltotetraose, and maltopentaose all display a fairly strong ileal brake effect on the activity of the brush border enzyme, maltase-glucoamylase (MGAM). This substrate brake effect suggests that the total digestion rate of carbohydrate by MGAM can be regulated, and carbohydrate with certain molecular structures (e.g., Mylose 351 or Glucodry 314) might be used to modulate carbohydrate digestion to achieve the desired rate of glucose release (Zhang et al 2015).…”

Dietary Slowly Digestible Starch Triggers the Gut–Brain Axis in Obese Rats with Accompanied Reduced Food Intake

“…In pigs, SDS caused increased glucose transporter in the ileum and in humans, resulted in sustained release of the incretin hormone GLP‐1, which has a role in appetite control and body weight regulation . Considering the existence of the GLP‐1‐mediated ileal brake and its role in the gut–brain axis, and evidence that glucose is a stimulator of GLP‐1 secretion from L‐cells in the rat ileum and suppresses food intake, we postulated that ileal location of starch digestion is important for the activation of this feedback control of appetite . Although not all SDS‐containing foods digest as far as the ileum, some do so and may induce the secretion of the gut hormone GLP‐1 .…”

Starch digestion in the upper gastrointestinal tract of humans

“…There are variable amounts of protein and lipid within the starch granules and tissue of edible plants, which are surrounded by cell walls in the parenchyma, which is itself often surrounded by other macroscopic structures in unprocessed foods like the aleurone layers of a grain caryopsis or the skin of a root vegetable . This complex packaging of starch granules within edible plants tends to limit access to starch molecules by digestive enzymes, although the mechanical processes of the gut counteract this and increase the potential for hydrolysis . Common food preparation methods like boiling, soaking, and mashing also tend to release starch granules into aqueous media where they may form an unbound matrix which can interact with other food components .…”