Preliminary reports of a prebiotic potential of almonds are promising and intriguing, and impending human trials may reveal if the benefits can be translated from the lab to the layperson.
Dr Martin Wickham, from the Model Gut Platform at the Institute of Food Research (IFR) in Norwich, England, told NutraIngredients that surprising results from their in vitro lab results indicated that almonds possess prebiotic potential, interesting linked to the lipid content of the nuts.
However, human studies are needed before we may see almonds challenging inulin and oligofructorse - the established masters of the prebiotic universe. Prebiotics are currently defined as "nondigestible substances that provide a beneficial physiological effect on the host by selectively stimulating the favourable growth or activity of a limited number of indigenous bacteria".
“We’ve looked at this on the bench, in vitro. We now have to take this into human volunteers. Will we still see an effect and to what extent?” said Dr Wickham.
The wheels have been set in motion for the human study, he added, noting that the team is at the proposal stage, and putting together the study protocol.
The researchers subjected almond matter to a simulation of the digestive system, starting with gastric digestion which mimics the biochemical environment of the stomach, including the appropriate enzymes and acidic nature. This is followed by passage through the small intestinal environment, with the relevant adjustments to pH and enzymes. Finally, a model of the colon is used that itself is divided into three sections representing the ascending, transverse, and descending colon. Each vessel is inoculated with faecal material,
“The advantage of this model is that you can get a very good mechanistic understanding. It allows you to know exactly what is going on,” said Wickham.
Dr Wickham went on to point out the differences between almonds and the established or traditional prebiotics of inulin and oligofructose. These fibres are resistant to the gastric and small intestinal environments, but “almonds are kind of interesting because they do change on the way through the stomach and small intestine. There are still a lot of nutrients present when the almonds reach the large intestine, including lipids and polysaccharides.”
In fact, Wickham said that as much as 60 per cent of the nutrients are still potentially available by the time the almond reach the large intestine (J. Agric. Food Chem. 2008, Vol. 56, Pages 3409-3416).
IFR scientists, in collaboration with researchers the University of Messina in Sicily, used two almond products for their experiments: almond flour, or defatted almond flour. With the former, Wickham said they observed a “very good prebiotic effect, but remove the lipid and the prebiotic potential disappears”
“This was a huge surprise. There shouldn’t have been any change,” he said. “In fact, the presence of the lipids should have diluted the carbohydrates present.”
Writing in the journal of Applied and Environmental Microbiology (Vol. 74, pp. 4264-4270), Wickham and his co-workers reported that the whole (lipid-containing) almond material in the colon model significantly increased bifidobacteria and Eubacterium rectale numbers.
“More-detailed studies on the digestibility of almonds and the role played by lipids in the potential prebiotic effect need to be performed using human volunteers,” they concluded.
Commenting independently on the research, Professor Glenn Gibson, a prebiotic expert from the University of Reading, agreed with the conclusions and emphasized that human studies are needed to support the indicative in vitro results.
Regarding the potential lipid effect, Prof Gibson told NutraIngredients.com: “I'd be very surprised if it is the lipid content [that is responsible for the prebiotic effect].
“The common prebiotic targets are carbohydrate metabolisers not lipid ones. Also, the end products from CHO metabolism are benign/beneficial while those from lipid fermentation are not known to be so the bacterial groups they analysed are not known for their ability to reduce lipid, this also relates to the two groups that increased the study is an in vitro batch culture approach. As such, it can only be seen as a very early indicator of prebiotic potential,” said Prof Gibson.
“The batch approach can only apply one pH value, bacterial growth rate and substrate level. So, it is a straightforward approach usually used before more complex fermentation studies. Following these, a human trial would be necessary to give the definitive proof - only then can the prebiotic effect be confirmed,” he added.
West coast nuts
About 80 per cent of the world’s 1.7 million tons of almonds (Amygdalus communis L.) are produced in California. The Almond Board of California provided the funding for Dr Wickham’s research.