Abstract
Numerous studies, including our previous work with lemon juice, have reported that low-pH meals reduce the glycemic response to starchy foods. However, the underlying mechanism is not yet understood. Tea, for its polyphenol content, has also been investigated. The main objective of this research was to concurrently study gastric emptying, appetite perceptions and glycemic responses to bread consumed with water, tea, or lemon juice. In this randomized, crossover intervention, ten participants consumed equal portions of bread (100g) with 250mL of water, water-diluted lemon juice, or black tea at breakfast. Gastric volumes, blood glucose concentrations and appetite perceptions were alternately assessed over 180min using magnetic resonance imaging, the finger-prick method and visual analogue scales, respectively. Compared to water, lemon juice led to a 1.5 fold increase of the volume of gastric contents, 30min after the meal (454.0 ± 18.6 vs. 298.4 ± 19.5mL, [Formula: see text] ± SEM P < 0.00001). Gastric emptying was also 1.5 times faster (P < 0.01). Conversely, lemon juice elicited a lower glycemic response than water (blood glucose concentrations at t = 55min were 35% lower, P = 0.039). Tea had no effect. Changes in appetite perceptions and gastric volumes correlated well, but with no significant differences between the meals. Lemon juice lowered the glycemic response and increased both gastric secretions and emptying rate. The results are compatible with the hypothesis that the reduction of the glycemic response is mainly due to the interruption of starch hydrolysis via the acid-inhibition of salivary α-amylase. NCT03265392, August 29, 2017.
Highlights
Postprandial glycemic profiles are the net balance between the rates of appearance of exogenous and endogenous glucose and the rate of disappearance of glucose due to tissue uptake [1]
We have studied the gastric phase of digestion, blood glucose response and appetite perceptions following the consumption of equal portions of bread with water, tea or lemon juice at breakfast
We had previously observed that black tea had no effect on the glycemic response to bread, but that lemon juice can attenuate it significantly
Summary
Postprandial glycemic profiles are the net balance between the rates of appearance of exogenous (from food) and endogenous glucose and the rate of disappearance of glucose due to tissue uptake [1]. Members of our team have reproduced such digestive conditions in vitro observing that up to 20% and 50% of the starch respectively in pasta and bread was hydrolyzed during the gastric phase [5, 12] This is in agreement with in vivo studies of human [13] and porcine digestion [14]. Using magnetic resonance imaging (MRI), the main objective of the present work was to study gastric emptying and blood glucose responses concurrently, to better understand the physiologic impact of combining starch-rich foods with beverages characterized by a rich polyphenol content or a low pH
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