With increasing public health awareness worldwide, demand for functional food with multiple health benefits has also increased. The use of medicinal food from folk medicine to prevent diseases such as diabetes, obesity, and cardiovascular problems is now gaining momentum among the public. Seed from Salvia hispanica L. or more commonly known as chia is a traditional food in central and southern America. Currently, it is widely consumed for various health benefits especially in maintaining healthy serum lipid level. This effect is contributed by the presence of phenolic acid and omega 3/6 oil in the chia seed. Although the presence of active ingredients in chia seed warrants its health benefits, however, the safety and efficacy of this medicinal food or natural product need to be validated by scientific research. In vivo and clinical studies on the safety and efficacy of chia seed are still limited. This paper covers the up-to-date research on the identified active ingredients, methods for oil extraction, and in vivo and human trials on the health benefit of chia seed, and its current market potential.

1. Introduction

Salvia hispanica L. (Figure 1), a biannually cultivated plant, is categorized under the mint family (Labiatae), superdivision of Spermatophyta, and kingdom of Plantae. Prominently grown for its seeds, Salvia hispanica also produces white or purple flowers. The seed (Figure 2) contains from 25% to 40% oil with 60% of it comprising (omega) ω-3 alpha-linolenic acid and 20% of (omega) ω-6 linoleic acid. Both essential fatty acids are required by the human body for good health, and they cannot be artificially synthesized. Chia can grow up to 1 m tall and has opposite arranged leaves. Chia flowers are small flower (3-4 mm) with small corollas and fused flower parts that contribute to a high self-pollination rate. The seed color varies from black, grey, and black spotted to white, and the shape is oval with size ranging from 1 to 2 mm [14]. Wild and domesticated chia differs little. Currently, only Salvia hispanica but not other species of the genus Salvia can be grown domestically. To prevent the misidentification of Salvia hispanica and other species of Salvia, clear understanding of the morphological and genotypical differences among them had been proposed as solutions [4, 5]. Locally known for its medicinal uses, Salvia hispanica L. acquired the common name chia from the indigenous South American people of the pre-Columbian and Aztec eras [6]. Owing to the fact that it can grow in arid environments, it has been highly recommended as an alternative crop for the field crop industry [7].

Chia seed is composed of protein (15–25%), fats (30–33%), carbohydrates (26–41%), high dietary fiber (18–30%), ash (4-5%), minerals, vitamins, and dry matter (90–93%). It also contains a high amount of antioxidants [8]. Heavy metal analysis showed that chia seed contains them at safe levels, not exceeding the maximum metal levels for food safety, and the seed is also free from mycotoxins [1]. Another key feature of chia seed is that it does not contain gluten [9]. Recent studies on chia seeds have focused on phytochemicals and their extractions from the seed. Only very little studies have focused on in vivo or clinical bioactivities and the safety aspects of chia seed. The aim of this paper is to critically evaluate the health benefits, phytochemical contents, methods of oil extraction, and the current market potential of chia seed as a health food supplement.

2. Phytochemicals in Chia Seed

Various active ingredients including essential fatty acids and phenolic compounds have been identified in chia seed. These active compounds which contribute to the health benefits of chia seeds are summarised in Table 1.

There are many factors that may cause variations in the concentrations of the active compounds in chia seed. One of them is the cultivation area of the plant itself. Differences in the environment, climate changes, availabilities of nutrient, year of cultivation, or soil conditions play crucial roles to the variations [17, 22]. For example, the protein content tends to decrease as the temperature increased [23]. Furthermore, an inverse relationship between altitude and the content of saturated fatty acids (SFAs) had been observed whereby, at low elevation, an increase in fatty acid saturation was noted in areas where the temperature was high [7, 24]. In Argentina, Ayerza [25] demonstrated that temperature largely contributed to the type of fatty acid found in the oil. They found that, during seed development from April to May, an increase in the temperature of the environment brought about a decrease in the polyunsaturated fatty acid (PUFA) content.

Another factor that may contribute to differences in the chemical compositions of chia seed is the developmental stage of the plant. It was shown that the (α-linolenic acid) ALA content decreased by 23% from the early stage to the matured stage of the seed. This concurrently resulted in the increase of linolenic acid (LA) and lignin content [7].

3. Health Benefits of Chia Seed-Animal Studies

Several crops have been commercially recognized as being good sources of oil for dietary use including flaxseed, rapeseed, sunflower seed, soybean seed, maize, evening primrose, and chia seed. A comparative study using flaxseed, rapeseed, and chia seed as chicken feed had been conducted. Eggs from hens fed with chia had the highest ω-3 ALA content as compared to hens fed with flaxseed or rapeseed [26]. Due to the easier availability and lower price of flaxseed over chia, an attempt to replace chia with flaxseed in laying hen’s feed was carried out. The incorporation of flaxseed in the diet resulted in a slight decrease of the ω-3 ALA content of egg yolk [27]. However, the high antinutritional content of flaxseed affected the poultry meat quality.

Besides the utilization of chia in poultry animal targeted for human consumption, it had also been used for animal nutrition by itself. Other than chia seed oil, studies had been done using other grain oil such as flaxseed in broiler feed which also resulted in an increase of fatty acid quality level in broiler’s meat [16].

Ayerza and Coates [28] and Fernandez et al. [29] conducted studies concerning the effects of chia seed feeding on rat plasma. Their findings indicated that serum triglycerides (TG) and low-density lipoprotein (LDL) were significantly decreased whereas high-density lipoprotein (HDL) and ω-3 PUFA levels were increased. They also noted that no adverse effects were observed on the rat’s thymus and IgE serum level. Furthermore, chia seed feeding was tested in pigs and rabbits, which resulted in an increase of PUFA in meat fats as well as aroma and flavor [3032]. These are desirable characteristics of human food. In summary, the incorporation of chia seed into animal feed results in an increase of ALA and a decrease of cholesterol levels in meat and eggs. Hence, it is a good substitute source of PUFA to fish and other seed oils. Moreover, atypical organoleptic characteristics such as flavor and smell from marine sources were not found in chia [33]. This showed the superiority of chia seed against other nutritional sources.

4. Health Benefits of Chia Seed-Human Clinical Trials

Correlation between high SFA and low PUFA intake with diseases such as cardiovascular diseases, diabetes, and metabolic syndrome were widely reported [20, 34]. Besides, the additive effect of ALA and n-3 long chain PUFA was observed to exhibit cardioprotective effects in women [35], which led to consequent human clinical studies of chia on disease risk factors. To date, four clinical trials have been carried out, and the details are summarised in Table 2. Among these trials, only that of Nieman et al. [19] showed no health benefits from chia seed. This difference could be due to the treatment durations employed and also the actual biochemical components of the dietary chia seed used in the various studies. Nevertheless, later studies [18, 20, 21] demonstrated well the benefits of chia on human health. However, studies of chia’s intake in human diet which take into consideration factors such as lifestyle and genetic variations are still limited. Hence, studies which target these factors should be done in the future.

5. Extraction of Chia Seed Oil

Chia seed is mainly valued for its oil. Thus, many oil extraction methods had been utilized. Differences in the extraction methods caused variations in the oil yield, quality of fatty acids, fatty acid contents, total dietary fibers, and also antioxidant content. Table 3 summarises the current methods used in the extraction of chia seed oil.

6. Market Potential and Commercial Application of Chia Seed

Functional foods have gained tremendous attention worldwide over the past few years due to the wave of healthy lifestyle changes. One of the reasons for the interest to shift to a healthier lifestyle is the increasing number of people suffering from cardiovascular diseases (CVDs), high blood pressure, obesity, diabetes, and other related diseases. These conditions are commonly due to inactive lifestyle and poor diet where the food consumed daily contains high amounts of saturated fatty acids (SFAs). There are numerous studies which reported on the correlation between high SFA, particularly palmitic acid, and low PUFA intakes with CVD [34]. Traditionally, the now so-called functional foods have been consumed based on their availabilities as daily staple foods. At present, many studies have been done to increase their functionality as high nutrient food supplements. The benefits of functional foods primarily come from the presence of active ingredients and bioactivities of compounds originally present in the plant being still present in the food products after they have been processed to make them suitable for human consumption.

Recently, chia has regained its popularity by becoming one of the main oil sources that contains high levels of PUFA. Chia, which used to be the major food crop of the indigenous peoples of Mexico and Guatemala, is now widely cultivated and commercialized for its (omega) ω-3 alpha-linolenic acid (ALA) content and antioxidant properties. Today, its cultivation is not only limited to the Americas but is also extended to other areas such as Australia and Southeast Asia [6].

At present, chia seed is used as a healthy oil supplement for humans and animals. Table 4 presented a summary of the current commercial usages of chia seed. Human consumption of chia in diet is mainly from the extracted oil through its incorporation into cooking oil, confections, or supplements. In 2000, the US Dietary Guidelines recommend that chia seed can be used as a primary food not exceeding 48 g/day. Chia is commonly consumed as salad from chia sprout, in beverages, cereals, and salad dressing from the seed, or it is eaten raw [41, 42]. The European Commission approved the use of chia seed in bread products with a limit of not more than 5%. Other than bread, the food industry of various countries around the world including US, Canada, Chile, Australia, New Zealand, and Mexico has widely used chia seeds or its oil for different applications such as breakfast cereals, bars, cookie snacks, fruit juices, cake, and yoghurt [43, 44].

Despite of its well-known antioxidant activities and healthy fatty acid profile, consumers are not very aware of chia’s benefits until recently. Chia seed production is a major contributor to the Argentine economy being responsible for 24% of its agricultural industry. In 2008, Argentina contributed approximately 4% of the world grain production [52]. Although chia seed has been commercialized for a long time in Argentina, however, due to the comparatively small-scale production there, problems in its availability and sustainability as an edible oil source in the global market exist. The current planting and production of chia seed oil are yet to fully meet the world market demand [17, 53, 54].

7. Summary

Based on the current research findings, chia seed is a good choice of healthy oil to maintain a balanced serum lipid profile. However, unlike vitamin E and coenzyme Q10, in vivo clinical bioactivity and safety evaluation of chia seeds are still limited. Furthermore, details on the mechanisms of chia seed’s hypolipidemic effects need to be studied and compared with those of the isolated omega 3 and omega 6 fatty acids.