Cholesterol-Lowering Effects of Probiotics and Prebiotics: A Review of in Vivo and in Vitro Findings

Probiotics are live microorganisms that promote health benefits upon consumption, while prebiotics are nondigestible food ingredients that selectively stimulate the growth of beneficial microorganisms in the gastrointestinal tract. Probiotics and/or prebiotics could be used as alternative supplements to exert health benefits, including cholesterol-lowering effects on humans. Past in vivo studies showed that the administration of probiotics and/or prebiotics are effective in improving lipid profiles, including the reduction of serum/plasma total cholesterol, LDL-cholesterol and triglycerides or increment of HDL-cholesterol. However, other past studies have also shown that probiotics and prebiotics had insignificant effects on lipid profiles, disputing the hypocholesterolemic claim. Additionally, little information is available on the effective dosage of probiotics and prebiotics needed to exert hypocholesterolemic effects. Probiotics and prebiotics have been suggested to reduce cholesterol via various mechanisms. However, more clinical evidence is needed to strengthen these proposals. Safety issues regarding probiotics and/or prebiotics have also been raised despite their long history of safe use. Although probiotic-mediated infections are rare, several cases of systemic infections caused by probiotics have been reported and the issue of antibiotic resistance has sparked much debate. Prebiotics, classified as food ingredients, are generally considered safe, but overconsumption could cause intestinal discomfort. Conscientious prescription of probiotics and/or prebiotics is crucial, especially when administering to specific high risk groups such as infants, the elderly and the immuno-compromised

Folate and Bifidobacteria

Folate is the generic term for a group of chemically related and biologically active forms of vitamin B9, needed by all organisms. Folic acid is the fully oxidized synthetic form of the vitamin. The chapter starts with nomenclature and chemical structure of folate forms followed by methodologies for extraction and chemical analysis of bacterial folate. Folates are unstable and susceptible to interconversion reactions so the special care needed to correctly determine folates in bacteria is discussed. Next follows folate biosynthesis, which happens commonly in plants and many microbes, including most bifidobacteria, but is absent in mammals, such as humans. Relevant genes, enzymes, and intermediate metabolites are described. Thereafter, the chapter continues to review folate metabolism, which describes cycling of different one-carbon units, using folate as vehicle, necessary for, for example, nucleic acid biosynthesis (purines and thymidine), amino acid homeostasis (glycine, serine, and methionine), and methylation of macromolecules, such as proteins and DNA, which includes epigenetic maintenance. Next follows a section on how biotechnology can be applied to produce high levels of microbial folate, to be used either as a food additive or as folate-producing probiotics. Finally, the main concerns and health implications from insufficient folate intake are described