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There has certainly been a buzz about prebiotics in recent years. Our interest was initially piqued following the Michael Mosely programme on TV. Since then, an increasing number of studies have looked at the various effects prebiotics have on our gut microflora, and consequently their link with issues such as weight management, stress, and sleep. As inulin and Fructooligosaccharides (FOS) pop up in many of these research studies, it might lead to questions about choosing one over the other.
So let’s take a closer look at these two common and well-researched prebiotics, inulin and FOS.
The principal difference between these two prebiotics is their structural difference. Fructooligosaccharides are shorter-chain molecules and are linear in their molecular structure, whereas inulin is slightly longer and has more cross-links in its structure1.
Both inulin and FOS are effective prebiotics that stimulate the growth of intestinal Bifidobacteria, without leading to a rise in serum glucose or stimulate insulin secretion. However, it is believed that long-chain inulin is fermented a little more slowly because bacterial enzymes find it more difficult to access the interlaced cross-linked structure.
A number of clinical studies have shown that high doses of inulin given over a considerable period of time, may help to reduce fat, notably fat around our internal organs. This enables the organs and the body as a whole to work better, and reduce premature ageing. The mechanism of action for this is not fully understood, but is thought to be related to short-chain fatty acid (SCFAs; glossary definition: short-chain fatty acid) production resulting from the gut microflora fermenting the inulin. These SCFAs then regulate hormones and signals involved in regulating the appetite.
In one trial, 44 participants with pre-diabetes took either 30g inulin, or a cellulose placebo each day, for 18 weeks (6 months). They were put on a diet for the first 3 months, but were not on a diet for the last 3 months. Fat loss around the organs and under the skin dropped significantly more in the inulin group compared to on those in the cellulose group2.
In another trial, dosages of 35g or more per day of inulin were shown to decrease appetite3. A further study showed that 21g per day caused greater weight loss compared to placebo, and the authors proposed that a possible mode of action could be that inulin is able to regulate the appetite4.
Despite this, European Food Safety Authority (EFSA) has yet to approve a health claim for inulin associated with weight management. The following health claims have not (yet) been approved:
Since we know that FOS also increases production of SCFA (through stimulation of lactobacilli and Bifidobacteria growth), can we say that it could regulate appetite in the same way as inulin?
One trial found cookies enriched with FOS were more likely to increase satiety than those not enriched, when given to obese volunteers at a daily dose of 9g FOS5. However, as with the inulin trials, other FOS studies looking at weight management used different doses, e.g. 16g/day over 2 weeks6.
This inconsistency in the recommended dose for healthy weight management is partly due to the complex nature of weight management; which involves a number of different regulatory pathways in the body, as well as individual variability. Along with the lack of understanding of the mode of actions, it also highlights the need for further trials and undoubtedly an appreciation that it is very difficult to find a magic solution for weight management or other health issues.
In a nutshell:
Have a look at the following links for more information about prebiotics: