1. Introduction
Ghee is an integral part of Indian food and culture. Statistics indicate that 30–35 % of milk is converted into ghee in India [1]. The culinary use of ghee has grown in India over the centuries with its rich flavour positioning it as a health plus taste ingredient. As part of complex recipes ghee provides textural & food structuring properties such as in Indian sweets like ladoo, mysore pak and halwa, much like cocoa butter does in chocolate. It is used as a frying medium due to its relative stability on exposure to high temperatures and high smoke point (∼250 °C) compared to most other edible oils [2,3]. It is also used as a spread or topping on cooked food like rice, khichdi, daal, chappati and coffee [4].
The per capita consumption of ghee and butter in India has increased to 4.48 kg/yr (12.3 g/person/day) in the year 2020 from 2.7 kg/yr (7.4 g/person/day) in 2007 [5]. To put this number into perspective, clarified ghee and butter contributes about 110 calories/day/person or 5.5 % of the daily energy on a 2000 calorie diet comes from dairy fat. Though ghee is a culturally and commercially important food product, it remains a controversial food ingredient as the modern nutritionists and codified traditional medicinal knowledge systems view it differently. While traditional knowledge systems such as Ayurveda perceive ghee as a healthy food with therapeutic value, from the modern nutritionist’s perspective consumption of dairy fat should be limited due to the presence of saturated fatty acids. However, this single-point view of ghee’s impact on human health is beginning to get challenged [[6], [7], [8], [9], [10], [11]]. Research on the functional roles of lipids, their fatty acid constituents, association with maintaining energy balance in the body and reducing the risk of several diseases such as cancer, obesity, neurological, and cardiovascular disorders has led to a growing interest in ghee and its unique fatty acid profile amongst the world of edible fats and oils [12,13]. As interest in understanding the correlation between the components of ghee fatty acids grows, it is important to review the therapeutic value of ghee in Ayurveda literature as this may lead to generation of new hypotheses for testing in pre-clinical and clinical studies. This paper presents a comprehensive literature review on the role of ghee in Ayurveda. It also examines the complementarity between the focus of modern scientific research with that of Ayurveda.
1.1. What is ghee
Definitions of ghee in CODEX Alimentarius and Food Safety Standards Authority of India (FSSAI) are broad, and it has been defined as “a product exclusively obtained from milk, cream or butter, by means of processes which result in almost total removal of water and non-fat solids, with an especially developed flavour and physical structure” [14,15]. Accordingly, ghee is predominantly comprised of 99.5 % fat and less than 0.5 % moisture content. Furthermore, ghee is a source of fat-soluble vitamins including vitamin A (28.21 ± 0.142 IU/g), vitamin D (11.42 ± 0.425 IU/g), vitamin E (31.55 ± 1.109 IU/g), vitamin K, and phospholipids [16].
Food chemists further describe ghee by its fatty acid composition. The fatty acids are categorized in two ways – based on chain length and based on degree of unsaturation. Based on chain length, fatty acids are categorized as SCFA (Short Chain Fatty Acids), MCFA (Medium chain Fatty Acids) and LCFA (Long Chain Fatty Acids). Degree of unsaturation results in classes of fatty acids such as SFA (Saturated Fatty Acids), MUFA (Mono-unsaturated Fatty Acids) and PUFA (Poly-unsaturated Fatty Acids). Further sub-categorization includes the position of the double bond from the end of the hydrophobic chain classifying the fatty acids as omega-3 and omega-6, the conjugation of fatty acids, and phospholipids. The presence of SCFAs, conjugated linoleic acids (CLAs), omega-3 and omega-6 fatty acids and phospholipids make ghee unique in the world of edible fats and oils. These fatty acids are receiving attention from the scientific community for playing important roles in our body such as anti-inflammatory and antioxidant action as well as association with brain health and the discussion in modern science is beginning to broaden from the narrow focus on saturated fats to the wider benefits of the full spectrum fatty acid profile [17]. Initially, epidemiological observations of Greenland Eskimos established the potential health benefits of n-3 PUFAs and other dietary lipids [18]. Since then, researchers have paid substantial attention to the noncalorific roles of not just the n-3 PUFAs but also SCFAs, MUFAs and phytosterols and their impact on disease progression. Various studies have demonstrated that dietary intake of SCFAs and lipids like MUFAs, PUFAs, and phytosterols have significant therapeutic properties [19]. Consuming some of these fatty acids and lipids suppresses inflammation, Aβ production and deposition, hypercholesterolemia, and dyslipidemia [20]. Additionally, some of them play a crucial role in other cellular signaling pathways such as cell proliferation, programmed cell death, and cell survival [21]. While a detailed review of the benefits of the different fatty acid components of ghee are out of scope of this paper, a tabulation of the detailed composition has been included in supplementary material (S1).
2. Methodology followed for ayurveda literature review
To investigate ghee from Ayurveda perspective, a comprehensive review of relevant sections of eleven important Ayurveda texts was conducted to map ghee and its functional uses in Ayurveda. The referred texts included seven Samhitas, two lexicons (Nighantu), and two relatively recent classical texts, spanning a period of over 3000 years, from the 15th century BCE to the 17th century CE. The list of texts and the selected sections used in the review is given in the supplementary material (S3). Sections (vargas) in these texts explaining the milk and milk products were referred. References specific to ghee were found in the chapters on “Ghrita Varga” and related verses regarding the classification and properties of ghee, ghrita, ajya, and sarpi were compiled.
The selected sections were read manually and all mentions to ghee, milk, curd, butter, and buttermilk were curated to create a database. All the details such as source of milk, processing, Ayurveda pharmacological properties, rasapanchaka prosperities, tridoshik actions, therapeutic uses, health benefits and contraindications were recorded as metadata. Wherever multiple attributes were mentioned in a single sentence, each attribute was given a separate line in the database. A total of 4000 references to milk and milk-based products were curated through this process.
2.1. Literature review of ghee from Ayurveda texts
The review of traditional literature suggested that ghee is mentioned extensively in Ayurveda as a therapeutic on its own and as an ingredient in complex medicine formulations (ghrita). Ghee also finds mention as a food in Ayurveda and is listed in Caraka Samhita as one of the eleven food items recommended for daily consumption – Nityasevaniya Ahaara. This not only points to its goodness as a daily nourisher, but also that it was considered as a food that does no harm on daily consumption. Several of many Sanskrit & vernacular names for ghee are indicative of its goodness, such as pavitra indicating the purity of ghee, ajya portraying the long-lasting nature of ghee, amrita representing the life-giving qualities of a nectar, and tejas representing the potency of ghee.
Of the 4000 mentions to milk and milk-based products curated from the Ayurveda texts, 2913 references were in the context of functional benefits. Amongst the milk-based products, ghee finds the most mentions in context of functional benefits with 774 mentions (Fig. 1). While some mentions of ghee in Indian classical medicinal literature are without any classifier, many of the mentions had additional details such as manufacturing process, animal source of milk from which ghee was made, age of the ghee and the phase of the ghee.