Proceedings of The Physiological Society
Kings College London (2005) J Physiol 565P, PC5
Long lasting effects of caffeine from cereal bars
Milon, Hubert ;
1. Nestle Research Centre, Nestec Ltd., Lausanne 26, Switzerland.
Fig. 1. Mean of plasma caffeine levels for all subjects after consumption of instant coffee or a guarana bar each containing 200 mg of caffeine. Fits according to an open one compartment model with 1st order absorption.
Fig. 2. Mean plasma glucose increments for all subjects after consumption of a guarana bar or white bread (reference) each containing 35 g of available CHO.
The psychostimulant effects of caffeine are well established and have been described in numerous reviews and publications. A threshold level of circulating caffeine (c.a. 2 mg/l although highly individual dependent) seems to be needed to observe stimulation, whereas at higher levels (> 10-12 mg/l) side effects such as excitation or gastric discomfort may appear. In order to safely prolong the stimulating effects of caffeine one way to maintain blood caffeine levels above a given threshold and to decrease peak values is to slow down caffeine absorption. Recently, a cereal bar was developed that is based on oat bran concentrate (OBC). OBC is rich in the soluble fibre beta-glucan, which, by developing a high viscosity in the intestine, slows down the absorption of glucose. It was hypothesized that beta-glucan could also slow down caffeine absorption by the same mechanism. The aim of the present study was primarily to determine the pharmacokinetics of caffeine when incorporated as guarana extracts in OBC-based bars in healthy volunteers. Blood glucose levels were also measured and glycaemic indices determined because caffeine may have an effect on glucose metabolism. A cereal bar containing ca. 6g of beta-glucan and 200 mg of caffeine as guarana extract was studied in 8 male volunteers (mean age: 35.3 (32-44) years, mean weight: 72.6kg (64-93), mean BMI: 22.7 (20-26)) after approval by the Nestle Ethical Committee. As reference treatments instant coffee (IC), white bread (WB) and IC + WB were also consumed. Because it is difficult to collect blood samples during long periods of time, plasma samples were collected during 3 h and saliva samples during 8 hours for caffeine alone. Plasma concentrations of caffeine and glucose were determined to obtain the pharmacokinetic variables of caffeine (one open compartment model with 1st order absorption according to Bateman function, Siphar/Simed Ltd software), the effects on glycaemia and eventual interaction of caffeine. Comparisons were analysed by either a paired t test or a repeated measures ANOVA test. Surprisingly, ingesting white bread together with caffeine from IC did not affect caffeine kinetics as compared with IC only. Absorption rate of caffeine from the cereal bar was 4 times lower than from IC and from 4 h onwards after consumption caffeine levels from the cereal bar were significantly above those from IC (Fig. 1). The glycaemic response and index of the cereal bar vs. WB confirmed what had been observed in previous studies (GI = 49, Fig. 2) and no effect of caffeine on the glycaemic response was observed. Incorporating caffeine from a natural source (guarana) in OBC-rich cereal bar did slow down its absorption (0.096 1/min. vs. 0.022 1/min, p<0.001), thus decreasing peak values (3.38 mmol/l vs. 2.71, p<0.01) and providing sustained levels presumably leading to prolonged stimulation.
Where applicable, experiments conform with Society ethical requirements