Part 1 reported on a BARLEYmax® consumption trial that found a link with feelings of hunger and net energy intake. In this follow-up we examine three scientific questions:
- How do our findings fit with our existing knowledge of the effects of dietary fibre consumption on appetite?
- What might be the physiological mechanisms causing these effects?
- What are the implications for BARLEYmax® consumption?
Results investigating the consumption of high fibre foods on satiety, hunger and food intake have not been consistent.
Amongst the reviews on the subject are:
Slavin and Green in 2007 reported that a range of different dietary fibres promoted satiety decreased hunger. However, some dietary fibres demonstrated no effect. These seem to be the less-viscous fibres.
Wanders et al. (2011) concluded that for appetite, acute and long-term energy intake and body weight there were clear differences between the dietary fibres. The more viscous fibres were found to be more effective in reducing appetite than the less viscous fibres. The effects on energy intake and body weight were small and a dose response relationship was not observed.
Saleh et al. in 2020 concluded that different types of soluble fibre had different effects on parameters in this area. The most effective were guar gum followed by beta glucan, pectin and polydextrose. However, the appetite effects were not uniformly observed.
As well as the fact that different dietary fibres will have different physiological effects, other possible explanations for the inconsistencies are:
- the duration of the trial,
- the amount of the food consumed,
- the characteristics (e.g. obese or not) of the participants or the way in which the parameters were measured;
- potentially a small sample size leading to insufficient statistical power in the trial.
Maybe meta-analyses of fibre effects should not treat dietary fibre as one entity but divide the category as Saleh et al did.
A variety of mechanisms have been suggested to account for the effect of dietary fibre consumption on measures of appetite. These include:
- Greater time chewing high fibre foods
- Lower energy density
- Greater distension of the stomach
- Delayed gastric emptying
- Lower glycaemic index (low GI meals are associated with greater satiety or reduced hunger in 15/31 studies but not in 14/31)
- Appetite hormones
- Effects of gut microbiome metabolites
Disentangling these effects and trying to work out which dietary fibre may provide the desired effect on appetite is going to be very complex.
Such a diversity of mechanisms could also help explain the inconsistent results.
Previous trial with BARLEYmax® consumption.
A 2007 trial undertaken by CSIRO with BARLEYmax® consumption reported no effect on satiety or energy intake or a range of similar measures, though the glycemic response and insulin response was reduced compared to control. This was a one day trial. It is possible that a longer period of BARLEYmax® consumption is required in order to have a statistically significant difference on these parameters.
Anecdotally, BARLEYmax® consumption has been reported to have an immediate effect on feelings of hunger, which also suggests that this earlier CSIRO trial design in some way masked the effects of BARLEYmax® consumption.
Implications for BARLEYmax® consumption.
BARLEYmax® consists of a unique blend of dietary fibres and prebiotics. Would this result in differences compared to other trials in which only a single fibre was consumed (in addition to the fibre in the regular diet)?
BARLEYmax® contains relatively high levels of fructans, typically 10%, and thus the similar effects to those observed with other fructans is not a surprise. Despite containing fructans, BARLEYmax® would probably be considered a less-viscous fibre. BARLEYmax® flour does not gel or become viscous on standing in cold water. Maybe this is why there was no observed effect on satiety/feelings of fullness and is consistent with the previously noted CSIRO trial.
In summary, our small trial adds support to the importance of not considering dietary fibre as a homogeneous grouping. It still leaves open the question of how to best categorise dietary fibres to understand their effects on appetite and associated measures.
Intended as general advice only. Consult your health care professional to discuss any specific concerns.