Research

Ingestion of all three bars produced a significantly lower peak BG concentration compared with dextrose. All three bars produced a BG value that was higher than dextrose when measured at 2-hours. There were fewer occurrences of hypoglycaemia (BG≤3.9 mmol/l) over the 2-hour period under all bar conditions compared with dextrose meal (CON 8/10 participants, RED 3/10 participants GREEN 4/10 participants YELLOW 4/10 participants). There was no within bar differences in BG concentration at any time point.

Foods with a low glycaemic response have significant health benefits because from a public perspective, a lower glycaemic response is related to greater feelings of satiety and fullness which prevents the need to eat additional foodstuffs and may aid in weight loss. Low glycaemic index (GI) foods are correlated to a lower insulin demand and may improve long-term blood glucose control and blood lipids for those at risk of developing or already with diabetes. Additionally, knowledge of the GI of a food may help maintain good glucose control and avoid hypoglycaemic incidents. The lower (but not absent) occurrences of clinical hypoglycaemia under the bar ingestion trials compared to dextrose is a positive finding.

It must be stated that we did not determine the glycaemic index of the Human FoodTM bars in this experiment as to do so would require larger amounts of dextrose and necessitate consumption of ~4 bars to match carbohydrate intake. This project sought to determine the glycemic impact of a typical serving size.

Different carbohydrate foods are digested in vitro at different rates which are, in turn, directly related to the blood glucose and insulin responses they elicit (Wolever et al., 1988). The incorporation of low glycaemic response foods into mixed meals reduces glucose and insulin concentrations in normal and diabetic subjects (Chew et al., 1988; Indar-Brown et al., 1992). Wolever et al., (2002) demonstrated that high carbohydrate-low GI dietary advice over 4 months improved β-cell function in impaired glucose tolerance (IGT) subjects. Several meta-analyses have demonstrated that low GI diets reduce HbA1c or fructosamine in subjects with or without diabetes (Brand-Miller et al., 2003; Kelley et al., 2004; Opperman et al., 2004).

A long-term (1 year) multicentre, randomised control trial compared the potential of an alteration in the source of carbohydrate with the effect of reducing the amount of carbohydrate on glycosylated haemoglobin and secondary endpoints such as blood glucose, lipids and CRP in 162 patients with T2DM managed with diet alone. There were sustained reductions in post-prandial glucose and CRP in the low-GI diet group compared to high GI or low carbohydrate content groups. In the low GI group after the 1 year intervention, 2-h post-OGTT glucose concentrations were ~1 mmol.l-1 lower than those seen in the other two diets – a difference that, in prospective studies represents a 6-15% reduction in cardiovascular events (Coutinho et al., 1999; Meigs et al., 2002). Additionally, the results demonstrated improved CRP concentrations, insulin sensitivity and β-cell function in the low GI diet group. Therefore, these results demonstrate that a low GI diet might be an option for dietary management of T2DM.

Performance of physical exercise increases the demand for energy. Compensation for energy expenditure comes from ingestion of carbohydrates, fat and protein. Regarding carbohydrate, energy release is three times as fast as from fat but is limited to stores in the muscle and liver. Adequate carbohydrate ingestion before, during and after exercise replenishes carbohydrate stores and prevents increased use of protein for energy production (Waganmakers et al., 1991). The choice of specific low-, medium- or high-GI carbohydrates may be dependent on the functional outcome to be gained i.e. pre-exercise preparatory carbohydrate ingestion to provide energy during exercise or post-exercise replenishment of muscle and liver carbohydrate stores.

It is evident from the literature that an increase in fat oxidation (and reduced carbohydrate oxidation) occurs during exercise after consumption of a pre-exercise low-GI carbohydrate compared to an isocaloric high GI carbohydrate (Stevenson et al., 2005 and 2006; Wee et al., 2005; Wu et al., 2003 and 2006). Therefore, the role of consumption of a low GI carbohydrate source in maintaining blood glucose carbohydrates for longer might preserve exercising glucose concentrations and extend prolonged endurance performance. Interestingly, a high GI CHO 3 h before exercise was more effective in increasing muscle glycogen concentrations compared to a low GI carbohydrate (Wee et al., 2005). More muscle glycogen stores were also used during exercise in the high GI trial whereas the low GI meal demonstrated an increased fat oxidation rate, potentially demonstrating how low GI pre-exercise meals preserve muscle glycogen concentrations and allow for more sustained carbohydrate availability over the endurance exercise.

Wu et al., (2008) have demonstrated that consumption of a low GI meal 2 h before exercise results in better endurance running performance compared to high GI meals. Additionally, Wong et al., 2008 demonstrated all subjects ran faster over 16 km following consumption of a low GI meal 2 h before exercise compared with a high GI meal. Muscle glycogen sparing was thought to be the working mechanism evidenced by a higher fat oxidation rate.

Several studies have reported that the GI can play a significant role in exercise recovery (Erith et al., 2006; Stevenson et al., 2005a; 2005b; Siu et al., 2004). Carbohydrate ingestion has repeatedly been shown to increase post-exercise glycogen replenishment (Ivy et al., 1988; Tsintzas et al., 2003). The amount and timing have of post-exercise carbohydrate have been widely examined and standard guidelines produced (Hawley et al., 1997; Burke et al., 2001). The recommended type of carbohydrate is still a matter of debate. In relation to resistance exercise, standard nutritional guidelines recommend ingesting a combination of carbohydrate and protein to maximise recovery (Manninen et al., 2006). The timing of post-exercise recovery is important as studies have shown positive carbohydrate replenishment of high GI in the immediate post-exercise period whereas low or high GI can be consumed if recovery extends beyond 24 h if sufficient amounts of carbohydrate are consumed (Kiens et al., 1990; Burke et al., 1993; Pitsiladis et al., 1999; Lambert et al., 1997).