Yerba Maté (Ilex paraguariensis A.-St.-Hil), a plant from the Aquifoliaceae family, is wide-spread in tropical regions of South America (Southern Brazil, Northern Argentine, Paraguay, and Uruguay) [1]. From its leaves and branches, Maté extract can be produced by steeping in hot or cold water. Maté consumption, as an alternative to coffee or tea, is a traditional element of social life in its native countries. The Ilex family comprises approximately 600 species. Some of them, Kudingcha (Ilex kudingcha C.J. Tseng and Ilex latifolia Thunb from China), Yaupon (Ilex vomitoria from the Southeast USA) and Guayusa (Ilex guayusa Loes from South America) can be used to produce medicinal and stimulating beverages [2]. Yerba Maté, as well as its relatives, contains large amounts of caffeine polyphenols, alkaloids (mainly caffeine and theobromine), tannins, and saponins [1-4]. The content of these molecules in Yerba Maté is similar to that in coffee and tea, but Yerba Maté contains more polyphenols [1] with stronger antioxidant capacity [2,5,6] than green tea.

Yerba Maté has antioxidant, antibacterial, anti-inflammation, and antitumor properties. The most known are the metabolic effects of Yerba Maté. In traditional medicine, it is used as a diuretic drug. Biomedicinal research validated the ability of Yerba Maté to reduce the levels of insulin, glucose, lipids, and cholesterol in blood of animals and humans [3,7]. It prevents diseases of cardiovascular system as well as bone thinning in menopause women. It improves gastrointestinal microbiota [2,6,8,9].

In addition, Yerba Maté is a mild stimulator of the nervous system, which can increase exercise performance and mood [9].

Kudingcha, a relative of Yerba Maté, has in addition to these properties also can counter diabetes and neurodegenerative diseases [2], therefore it is possible, that Yerba Maté could have this effect as well.

The likely medicinal properties of Yerba Maté and its related species are explained by the presence of polyphenols and alkaloids, which have antibacterial, antioxidant, anti-inflammatory, and phytoestrogenic properties [2,10]. When phenols were eliminated from the Yerba Maté extract, its ability to decrease the level of lipids in human blood was eliminated as well [11].

Yerba Maté extract reduced obesity (accumulation of fat, levels of lipids in blood and body weight) in rats and mice [1-3,8,12-14]. On the other hand, consumption of Yerba Maté did not alter their body mass in rabbits [15] and even increased it in lambs [16]. These observations suggest species-specific differences in metabolic effects of Yerba Maté, which could be explained by different regulators of body weight targeted by Yerba Maté.

Andersen and Fogg [17] demonstrated reduction of body weight in patients with obesity after consuming a mixture of extracts from Yerba Maté, Guarana seeds (Paullinia cupana) and leaves of Damiana (Turnera diffusa). Other authors, however, did not report any data on changes in body weight of patients under the influence of Yerba Maté, Guarana and Damiana [18]. Kim et al. [19] studied the effect of pure Yerba Maté extract on patients with obesity and determined reduction of fat stores and body weight. Studies by other authors did not confirm the effect of Yerba Maté consumption on body weight and other anthropometric parameters [7], levels of lipids [11] and a marker of obesity (leptin) [10] in patients. Although the main studies were performed on patients suffered from obesity, the reported differences in Yerba Maté effect on human body weight could be due to initial state of patients, doses, duration of plant administration and variability in source and quality of Yerba Maté teas used in the reported studies.

The action of Yerba Maté on lipid metabolism of animals and humans can be facilitated by several mechanisms. Yerba Maté is capable of:

• Suppressing appetite and reducing food intake. The long-time diet containing Yerba Maté reduced consumption of food by rats and mice [3,13,18]. These effects are probably performed by altering the level of nonapeptide Y, which is a regulator of appetite, in brain (rat: [3]). Some data indicate the influence of Yerba Maté on leptin concentration in rodent’s brain [13]. Other data do not validate the effect of chronic dietary intake of Yerba Maté on leptin concentration in murine blood [3,10].
• Slowing the rate of food’s passage through the intestines and fecal output in overweight patients [17].
• inhibiting the differentiation and growth of adipose cells isolated from obese rats and cultured in vitro [2,20]. The in vivo and in vitro studies on obese rats demonstrated, that Yerba Maté can down-regulate the expression of a number of genes that promote adipogenesis and up-regulate the expression of genes related to the inhibition of adipogenesis, which can mediate the plant effect on rat adipogenesis [20].
• Reducing the activity of enzymes of lipid synthesis and lipids’ accumulation in adipose cells and liver of obese rodents [2].
• Stimulating lipolysis [4].
• Increasing burning (oxidation) of fat in human sportsmen and healthy volunteers [21-24] and mice [25] and energy expenditure in mice [3]. On the other hand, the antioxidant properties of Yerba Maté polyphenols [6,25] and their ability to reduce oxidation of lipids in humans [4] has been reported. The reported differences in plant effects could be explained by differences in experimental models and treatments used in different studies.
• Increasing energy expenditure during exercise in humans [2,3,21-23].
• Affecting microbiota in human digestive system which play an important role in food digestion and fat metabolism [2,26,27].

The majority of the performed studies determined no negative effects of Yerba Maté consumption on health of animals [15,28] and human beings [17-19]. Yerba Maté is a very popular drink in some countries, and its production and consumption is not limited by any legislative or medicinal regulations. Nevertheless, the epidemiological studies provided indirect evidence that Maté consumption could be associated with development of cancers of the oral cavity and oropharynx [29]. Few cases of toxic effects of consuming preparations containing Yerba Maté on humans including ischemic stroke have been reported [30].

The adverse effect of Yerba Maté could be explained not by the plant itself, but presence of benzo[α]pyrene and other molecules with toxic, irritating [4] and carcinogenic [31] activity.

Yerba Maté indisputably belongs to the category of efficient functional food (food with added value). Despite their potential adverse side-effects, Yerba Maté has many positive effects on health. At present more than 60 patents for products at the basis of Yerba Maté constituents related to the pharmaceutical area, food supplements and beverages, cosmetics, and nutraceuticals have been issued [8]. 

Simultaneously, Yerba Maté is a promising candidate for a natural product which could be used to manage lipid metabolism and in prevention and treatment of obesity. Existing data on the effect of Yerba Maté on weight reduction are currently limited, indefinite, and contradictory. The animal studies demonstrated the species-specific character of Yerba Maté effect. At present, the positive effect of Yerba Maté on weight loss in humans was validated only by one clinical study [19] and one successful experiment [17], in which Yerba Maté was only one component in the tested mixture. Other studies have not confirmed this effect. The reported studies remain contradictory probably because of the variability in initial state of patients and methodology of treatment (see above) including quality and dose of administrated plant (see below). Therefore, further, and more profound human studies are needed to identify the characteristics of Yerba Maté on health including fat storage, its positive and adverse effects. At present the clinical application of Yerba Maté on weight loss requires further validation and is premature.

Clinical experiments demonstrated that Yerba Maté can be efficient at a large spectrum of daily doses – 0.112 g [18], 1 g [21,24], 3 g (corresponding 107 mg of phenols and 84.24 mg of chlorogenic acid; [11]), 50 g or 100 g [7,19]. Recommended dose is consumption of 0.5 l [23] to 1 l [10] of the beverage a day. Cold Maté beverage stimulates fat oxidation and dissipation of heat more than warm [23]. An extract from a fresh plant is preferable. Fermentation of the Yerba Maté plant, similarly as in black tea and oolong, leads to reduction of its antioxidation capacity [32].

Taken together, the available reports indicate the positive effects of Yerba Maté on human health. Moreover, there are indications that this plant could be promising for phytotherapy of obesity. Nevertheless, there is currently insufficient data of the clinical studies for conclusion concerning applicability of this plant as an anti-obesity drug.