# Probiotics and Paraprobiotics--New Proposal for Functional Food
## 1 Introduction  
Health-promoting food, along with the increase in the health consciousness of consumers, is gaining worldwide acceptance. Increased demand for functional foods, mainly from the probiotics segment, and expectations of new varieties of products are driving the development of this market. It is estimated that the functional food segment will grow by USD 53.14 billion between 2023 and 2028 [1]. The idea of functional food was first presented in 1984 in Japan. The \"third\" function of food, except the nutritional and hedonic value, was proposed. The added \"tertiary\" function was attributed to the influence of food on human physiology [2]. In Japan, functional food was approved by the Ministry of Health and officially named \"foods for specified health uses\" (FOSHU) [3]. The rapid development of this food industry segment, along with extended research, created the need for a new, redefined comprehensive concept. In 2012, the Functional Food Center (US), according to the current knowledge, proposed a new definition: \"Natural or processed foods that contains known or unknown biologically-active compounds; which in defined amounts provide a clinically proven and documented health benefit for the prevention, management, or treatment of chronic disease.\" [4]. For more than 20 years, evidence was gathered confirming that both alive and dead probiotic cells can generate biological responses conferring health benefits on the host. Traditionally, widely recognized probiotics are the core group of microorganisms with proven human health benefits. Healthy populations, as well as various groups of sick people, benefited from probiotic implementation. According to the International Scientific Association for Probiotics and Prebiotics (ISAPP), probiotics are \"live microorganisms that, when administered in adequate amounts, confer health benefits on the host\" [5]. To ensure health benefits, it is recommended that a high number of living probiotics be provided (at least more than \(10^{6}\) CFU). However, regardless of the type of administration, i.e., food products or capsules, living microorganisms, dead cells, their fragments, and secondary metabolites are also supplied. Therefore, due to the simultaneous coexistence of all these forms in a single food product, an assessment of their health effects is complex and sophisticated. Considering that bacterial viability is not essential for retaining diverse bioactive properties, a new, broader approach to the probiotic concept should be implemented. The biological response of non-viable cells was called by some authors the \"probiotic paradox\". The extension of biological response generation beyond the probiotic cell viability contradicts the general assumption that the health-promoting effects only result from the viable cells' bioactivity [6]. Both populations, living as well as dead probiotic cells, can trigger or modify host biological reactions. In this regard, it seems more reasonable to replace the term \"probiotic paradox\" with \"probiotic advantage\" [7]. However, according to the FAO/WHO definition, non-viable microorganisms or bacterial-free extracts, despite their health benefits, cannot be further classified as probiotics [8]. In 2011, [PERSON] and [PERSON] [9] proposed a new category called paraprobiotics as \"non-viable microbial cells (intact or broken) or crude cell extracts (i.e., with a complex chemical composition), which, when administered (orally or topically) in adequate amounts, confer a benefit on the human or animal consumer\". The terms \"non-viable probiotics\", \"inactivated probiotics\" or \"ghost probiotics\", refer to inactivated (non-viable) microbial cells, which, when administered in sufficient amounts, confer benefits to consumers\".