Pros And Cons Of Probiotics

Probiotics originate from Japan, where functional foods have been part of the normal diet for years. Doctors often recommend them to their patients, for example, to help treat gastrointestinal problems. Thanks to brands like Yakult, probiotics have become common across Asia. But in Europe and North America, interest in probiotics is relatively new.

Probiotics are mostly lactic-acid bacteria such as lactobacilli and bifidobacteria. They resist both gastric and bile and so can survive in the often bacteria-unfriendly conditions of the stomach.

This distinguishes them from other lactic-acid bacteria in fermented products such as yoghurt. Probiotics help to improve health by balancing the number of ‘good’ and ‘bad’ bacteria in the intestine. They’re the opposite of antibiotics—which kill bad bacteria.

(Probiotics should not be confused with prebiotics. Prebiotics are food ingredients that cannot be digested but affect in good ways— they selectively stimulating growth or activity of some strains of bacteria in the colon.)

New applications for probiotics are continually under development. The major end-user markets are dairy (nine percent), dietary supplements (44 percent), animal feed (46 percent) and, to a lesser extent, specialty nutrition products (one percent), such as infant formulae.

‘Most scientists believe they [probiotic bacteria] should be alive.However, there are indications that even dead bacteria may produce some probiotic effects.’

Some examples of probiotic foods are the yoghurt Danone Activia (to improve gastrointestinal transit), the fermented milk drink Yakult (to support natural resistance) and Nestlé LC1 Vitaldrink (to stimulate the ‘good’ bacteria in the gut and to reinforce the natural defence system).

The market research agency Frost & Sullivan mentions three key drivers for the development of the probiotics market: the development of targeted probiotic therapies for specific health conditions; new applications for probiotic ingredients; and bans on antibiotics in animal feed.

There are obstacles. Consumers may have little understanding or awareness of probiotics. Complicated regulations on health claims for food don’t help either. Did You Know? The name ‘probiotics’ was coined in 1989 by the British scientist Roy Fuller. In addition, health professionals outside Japan do not seem to be fully aware of the possible health benefits of probiotics. Another restraint is the limited stability of probiotics in foods. Some people believe that prebiotics may have a greater market potential than probiotics, as they do not have the same stability problems since they are not alive. In the last decades, scientists have discovered several promising probiotic applications, through both live and artificial studies. By now they are convinced that probiotics may decrease onstipation and both bacterial and viral diarrhoea. Dr Erika Isolauri leads a research group whose clinical studies focus on on probiotics in infants, especially in treating rota viruses. She is a professor of paediatrics at the Turku University Central Hospital in Finland. ‘In the last decades the treatment of this kind of diarrhoea has remarkably improved recovery from weeks into days,’ Prof Isolauri says. ‘We have found that probiotics can accelerate recovery even more, by one or two days.’ Prof Isolauri and her colleagues presume that probiotics reinforce intestinal defences in two ways: both by influencing the mix of bacteria in the intestine, and by stimulating the immune system. ‘For example, they may compete with “bad” bacteria by the production of enzymes and influence the local pH. In addition, they control the generation of pro- and anti-inflammatory cytokines— substances produced by our immune system as a protection against intruders,’ Prof says. She says clinical studies suggest probiotics help treat children with atopic eczema—an inherited form of the skin problem. But that doesn’t automatically mean that probiotics will help adults with the same condition, she says.‘Additional studies are needed, as probiotic effects are strain-specific and depend on several factors, including nutrition, age and composition of the intestinal flora,’ Prof Isolauri says. There are similar issues with probiotics and the prevention and treatment of health problems with lots of causes, such as gastric ulcers, irritable bowel disease, and colon and bladder cancer. ‘In these situations, both the underlying working mechanisms and the host-microbe interactions may be very different from those involved in viral diarrhoea, atopic eczema and allergy”, Prof Isolauri adds. Selecting a suitable probiotic bacteria for clinical studies is also complex. Several aspects must be considered. They include functional, safety and technological properties. ‘There is debate on the question if probiotics should be alive and viable to produce effects,’ says Dr Maria Saarela, a microbiologist at VTT Biotechnology. This Finnish research institute specialises in bioprocesses, food applications, systems biology, metabolic engineering and industrial biomolecules. Dr Saarela says: ‘Most scientists believe they [probiotic bacteria] should be alive; this is in line with the current definition of probiotics. However, there are indications that even dead bacteria may produce some probiotic effects.’ Safety is also important. ‘Rare cases have been reported of severe intestinal infections after consuming probiotics,’ says Dr Saarela, although she adds that was only in people who were already ill, and had malfunctioning immune systems. Then there’s the technological suitability of the probiotic strain. Careful screening allows selection of strains with the best manufacturing characteristics. Robust probiotic bacteria such as Bifidobacterium animalis, Bifidobacterium lactis, Lactobacillus rhamnosus and Lactobacillus plantarum can all survive passage through the gut. But they have a limited range of food applications. ‘Indeed, some bacteria with promising functional properties have been ruled out due to technological limitations,’ says Dr Saarela. Until now, dairy products have been the best medium for probiotics. They are usually stored at low temperatures and have a favourable pH and composition. ‘This in contrast to, for example, fruit juices, which are often more acidic and may contain ingredients that are harmful to probiotics.’ Dr Saarela says. Several substances can be added to food to make it friendlier to probiotics. They include energy sources, such as glucose; growth factors, such as yeast extract and protein hydrolysates; and antioxidants, minerals or vitamins. Sometimes other starter bacteria, Streptococcus thermophilus or yoghurt cultures, are needed. Another more difficult challenges are to increase shelf-life and allow storage at higher temperatures. One option is microencapsulation to add a protective layer around the probiotic bacteria. Intestinal Flora The gastrointestinal tract of a newborn baby contains no micro-organisms. But shortly after birth, contact with food and the mother help several kinds of ‘flora’ to start colonising the intestines. During the first months of life, the number and kind of bacteria may vary, depending on the kind of nutrition. For example, breast-fed and bottle-fed babies have different mixes of intestinal bacteria. In adults, the flora contains 400 to 500 different types. External factors such as nutrition may temporarily exchange the mix of bacteria in adults. But the composition of flora in grownups is remarkably stable over time. Consuming probiotics has short-term effects on the flora composition and thereby balances the number of ‘good’ (lactobacilli, bifidobacteria and so on) and ‘bad’ bacteria (such as Salmonella and E. coli) in the intestines. ‘However, encapsulation does not resolve all technological bottlenecks,’ Dr Saarela says. ‘The benefits of these techniques depend on several factors, including the type of bacteria and the food that they are applied to.’ Stress treatments to improve viability of probiotic bacteria show potential. ‘By gently exposing probiotics to acid or hot environments, the stress treatment activates genes in the bacteria that make them more resistant to acidity and heat,’ she says. The University of Helsinki and VTT Biotechnology have had promising results from their research on stress treatment—viability can be improved up to 10,000-fold. According to both Prof Isolauri and Dr Saarela, the most interesting future applications of probiotics are in specific target groups, such as children with allergies, and older people. ‘[The] elderly are more susceptible to infections and more sensitive to side-effects of medicines,’ Prof Isolauri says. She expects that in the next two decades most of the remaining questions on probiotics, such as host-microbe interactions, working mechanisms and long-term effects, will be answered. ‘By then, we may have a multifunctional “probiotic cocktail” with components that are released at optimum locations in the gastrointestinal tract.’ she says. *LISETTE DE JONG IS A REPORTER FOR OUR SISTER MAGAZINE, FOOD ENGINEERING & INGREDIENTS