Green tea, black tea, white tea, yellow tea, and puerh all come from the same plant (Camellia sinensis). The classification depends on how its processed more so than how it's grown or what subspecies is used.
By going through varying levels of oxidation, the leaves change flavor, color, and chemistry. This is why black and green tea taste so different from each other, and in fact, even have some differences in medicinal use.
This plant has been used by humans for thousands of years. Its use dates back to at least the Shang dynasty in China 3000 years ago.
It has a wide range of health benefits from antioxidant, stimulant, cardioprotective and general tonic effects. Tea is great to drink daily, and aside from water is the most popular drink in the world.
There are several varieties of tea, grown in many different countries around the world, but the vast majority of tea come from the Assam variety in India, or the Sinensis variety in China.
Japan, Korea, and Taiwan are also large producers of tea and each country has its own signature style of growing, and preparing tea.
Leaves, unopened buds, stems
- CNS Stimulant
- ACE inhibitor (mild)
+ Cardiovascular System
- Congestive heart failure
- Cardiac arrythmia
+ Neurological System
- Parkinson's disease
- To aid concentration and focus
- As an antioxidant
- Viral infection
- Bacterial infection
- Dental carries
- Athletic performance enhancement (mild)
Camellia sinensis has recently been shown to produce a wide variety of positive effects on health including antioxidant, antimicrobial, antiviral, and antitumor, preventative effects on obesity, leukemia, Parkinson’s disease, and cardiovascular disease .
It has been argued, that the therapeutic dose for effects noted in vitro, especially from catechin (polyphenol) constituents, are not reached in vivo due to poor absorption issues. Therefore it should be noted that actions that are tested in vitro, should be considered and reviewed more closely. .
Camellia sinensis is used as a preventative in such diseases as tooth decay, cardiovascular disease, diabetes, atherosclerosis, obesity, cancer, stress, diabetes, hypertension, and hypercholesterolemia.
Also used for colds/flu, to reduce fatigue, to increase mental alertness during meditation or studying, useful for reducing stress, and mildly improving athletic performance (through stimulant actions).
- Green tea
- Black tea
- Red tea
- Pu erh
- Oolong tea
- Yellow tea
- C. sinensis var. sinensis
- C. sinensis var. Assam
- C. sinensis Var. cambodiensis
The earliest clear reference to the medicinal use of tea was during the Tang dynasty (750 AD). Through the coming ages, tea became more popular, and in the 800s The Classic of tea (written by Lu Yu), was written, which incorporated both Taoism and Confucianism and outlined the ceremonies associated with teas consumption. In the 17th century tea found its way to Europe, where it was widely accepted, and although arriving to Europe around the same time as coffee, it dominated the market .
Green tea is considered to prolong life, and has been used to treat headache, body ache, indigestion, depression, low energy, obesity, and hair loss .
Commonly used ceremonially in many cultures, as a form of meditation, or social events. Such ceremonies include the Chinese gongfu ceremony, Japanese tea ceremony using matcha tea (also called “the way of the tea”), or various other cultural versions of the ceremonial consumption of tea. The ceremony is often designed to produce both high quality tea extraction, as well as offering a form of meditation to lower stress, and promote awareness.
The flowers of Camellia sinensis have also been considered healthful since ancient times, though is less talked about today. Chinese folk remedies using tea flowers includes inflammatory diseases .
Even in modern times tea is considered the most popular beverage in the world aside from water .
+ Traditional Chinese Medicine
Taste: Bitter and sweet .
Energy: Cold .
Channels: Heart, liver, Kidney, stomach, spleen .
Actions: Cools heat, drains damp-heat, drains fire .
Contraindications: Cold or spleen deficiency .
Taste: Bitter and sweet .
Energy: Warm .
Camellia sinensis is a small evergreen tree, reaching 16m in height, though is often pruned much shorter in cultivation. Leaves are lanceolate to obovate, and are 4-15cm long depending on variety. The flowers are white to pink .
Green tea, white tea, oolong, and black tea all differ in how they are processed. That is how much they are allowed to oxidize before the process is stopped by the addition of heat to kill the enzymes catalyzing the oxidation process. The polyphenol oxidases condense the polyphenols in the leaves, changing the qualities of the tea as it oxidizes. Green and white teas are minimally oxidized, oolong is in the middle to varying degrees, and black tea is allowed to oxidize the most, resulting in polyphenols condensing and forming polyphenol dimers, and polymers .
Once the leaves are subjected to heat, this oxidation process stops, and the leaves are then dried or processed further, which will maintain the polyphenol content as is, without further oxidation taking place. The main difference between Japanese style teas, and Chinese teas, are the way this heat is added. Chinese style processing (usually) includes pan frying, whereas Japanese processing mostly involves steaming [6, 13].
Other differences in these famous teas as well as other teas from different parts of the world, are due to local climate, and soil conditions, which have a profound effect on the flavor profile of the teas. The variety used also plays a part (sinensis, assamica, or cambodiensis are the main ones but there exists others as well).
Pu Erh tea is another kind of tea, that has had its oxidization process halted, but is allowed to ferment via separate organisms, through either natural processes (raw puerh), or in a modern, cultured environment (cooked puerh). This process adds another set of qualities and chemical constituents to the leaves, and produces a very unique flavor profile, and health effects when compared to unfermented teas.
Habitat, Ecology, Distribution:
Tea, originates from Southeast Asia, Sri Lanka, India, and China, but is widely cultivated worldwide in tropical, and subtropical regions. Cultivation occurs up to about 2000m in altitude. To cultivate this plant effectively, there needs to be consistently warm, humid, frost free conditions. [3, 12]. It is thought that tea originated in China, and only after it became popular in India was it discovered that a separate variety grew naturally there, which has since become heavily cultivated in the region due to better adaptability to that hot, and inconsistently wet region of the world.
Harvesting, Collection, Preparation:
Camellia sinensis is usually grown between 300 and 2000 m in altitude, and tea grown at higher levels is generally considered to produce a better flavour. Other considerations are rainfall (200-230cm/year), and temperature (10-24C) .
When preparing Camellia sinensis as an infusion (tea), it has been noted that higher temperatures (100C) have been shown to extract more of the polyphenol content from the leaves and buds , however traditionally this has been frowned upon, as it is considered to negatively affect taste, likely due to the increased absorption of such bitter constituents as tannins and xanthine alkaloids. Generally tea should be infused with water at temperatures of between 50-80C to maintain the best possible flavour, although this varies mildly with different teas (ex black teas and puerh do well in higher steeping temperatures such as 90-100C). Steeping time also varies, but generally between 1-5 minutes is best. Lighter, less oxidized teas such as green and white teas would be best on the lower end of this range, while darker, more oxidized teas like black and dark oolongs would do well with a longer steeping time, however personal preference plays a large role, here as the infusion will in fact become more bitter in flavour the longer it steeps. Some cultures and traditions (such as gongfu tea ceremony) recommend steeping for only a few seconds, but reuse the leaves many times. If the health effects are considered most important, it may be beneficial to use higher water temperatures, higher infusions (standard medicinal infusion ratio for any herb is 1:20 for 5-30 mins) and longer extraction times in order to extract more of these constituents. It will however be quite bitter and astringent this way.
Ontioxidant Content of Green Tea Constituents
About 70% of green tea's polyphenol content is catechins . EGCG (Epigallocatechin-3-gallate) (EGCG) is one of the most abundant catechins in green tea, and is considered one of the most active constituents of green tea as well, accounting for about 32% of the plants antioxidant profile (AP). One cup of green tea is suggested to contain 20-200mg of EGCG .
Other catechins contained in green tea include epicatechin ((-)-EC)(5-7% AP), epigallocatechin (EGC)(9-12% AP), and epicatechin-3-gallate (ECG)(9-12% AP). Comparatively, black tea generally has about 30% of the catechins found in green tea, and is found mostly in the form of thearubigins, theaflavins, and other complex condensation products .
Catechins are mostly absorbed in the intestine, specifically in the ileum and jejunum. Peak absorption is about 1.5-2.5 hours after consumption, however absorption is quite low (about 5% of consumed catechins will appear in blood plasma on average), however during microbial interaction in the colon, catechins are often broken down into compounds such as valerolactones, which are absorbed much later (about 7.5-13.5 hours later) .
Generally, catechin metabolites have been shown to produce limited activity compared to their pure form, however a select few of the metabolites are noted to have similar, higher, or a completely separate activity. These polyphenols have been discovered not to accumulate in blood plasma, or urine, and have been suggested to be excreted via the biliary duct . Catechins can also be found in red wines, grapes, apples, and chocolate , as well as guarana (Paullinia cupana).
The caffeine content of Camellia sinensis varies from <0.02-3%. The young leaves of the first shoots contain fairly high caffeine concentrations, whereas the stems and roots contain very little .
Green tea leaves have a higher caffeine content than black tea leaves, and about the same (very slightly less) as white, though confusingly, the infusion is often recorded as the opposite. See below under black tea for the reason behind this conflicting information in caffeine content.
Other comparisons include green teas higher quercetin, flavonoid (catechin), and kaempferol contents, than white and black teas, but has the lowest gallic acid .
The chemical composition of green tea by dry weight is as follows: 15-20% proteins (enzymes), 1-4% amino acids, 5-7% carbohydrates, 5% minerals/trace elements and xanthic bases (caffeine, theophylline), pigments, sterols, vitamins, and volatile compounds, though these levels can vary greatly depending on growing conditions, strain, and processing techniques .
Gyokuro, is a specific style of tea that involves covering the tea plants in shade for the final 2 weeks before harvest, this results in lowered catechin content in the leaves, while increasing theanine, and caffeine. This will result in a less bitter tea, and allows the sweetness of the leaves to appear more intense. The increased theanine may also provide psychological effects based on its pharmacology. Theanine is an amino acid and is mildly psychoactive. It has been regarded highly as a nootropic substance.
White tea is considered semi-fermented (semi-oxidized) and contains about the same caffeine content as green (in the leaves and the infusion), and a similar catechin content as well [3, 5, 12].
Caffeine Contents of Different Tea Leaves
Black tea is considered fully-fermented (fully oxidized) and has higher gallic acid and higher caffeine in its infusion, when compared to both green and white teas. This information is controversial however, in that caffeine is often listed as being highest in white tea, and lowest in black, as Barceloux et al., (2009) lists; the levels of caffeine are highest in white tea (140mg/L), then green (130 mg/L), then oolong, then black (89 mg/L). It should be noted that because black tea is generally steeped hotter, and longer, this may play a role in why the caffeine content of this tea is usually recorded as higher. This is why dry weight constituents, as well as average infusion levels of these chemicals are equally important. For someone drinking green tea for its suggested lower caffeine content, but uses boiling water and prolonged steeping times, may in fact be receiving more caffeine instead of less. For example matcha (Japanese powdered green tea), is mixed into a solution, and the whole leaf is consumed including fibre and all of its constituents. This tea is often considered to have the highest caffeine content as a result of all of the constituents being consumed. Caffeine (and other purine alkaloids) have a low solubility in water, and therefore when consumed as an infusion, avoid extracting a lot of the caffeine content in the leaves, and therefore less concentrations will be measured in the liquor. As the temperature increases, it improves as a solvent, and allows more caffeine to extract into solution, longer steeping times will also increase this. When preparing black tea, the higher temperatures, and longer steeping times will directly affect this.
Due to the oxidization process black tea goes through, constituents like therarubigins, theoflavins, and other oxidized phenolic compounds, are included, and a relatively higher concentration of fluoride is noticed [3, 5].
Puerh is a special tea, with an extra fermentation process. This process is a true fermentation, compared to black or oolong teas oxidization process that is often referred to as fermentation misleadingly (because it is not fermentation by definition). Puerh however is truly fermented. There are generally two ways to go about doing this. “Cooked” puerh is a newer process developed to speed the process to a few months (rather than years), where the leaves are piled and cultured in a controlled environment. “Raw” puerh is the traditional method of aging the tea leaves (often in caves or other moderately humid locations), for decades. Some consider the older the puerh, the better the flavor.
In a study investigating the organisms responsible for this fermentation , researchers found a huge variety of organisms. A few includes fungi such as Absidia, Arxula, Aspergillus, Blastobotrys, Cladosporium, Corynascus, Dictyuchus, Emericella, Eurotium, Eutypella, Gliocladium, Fusarium, Hypocrea, Leptosphaeria, Mucor, Neurospora, Penicllium, Peziza, Phanerochaete, Plectosphaerella, Pichia, Rhizopus, Saccharomyces, Septogloeum, Stemphypium, Syncephalastrum, Talaromyces, Trametes, and Trichoderma, as well as bacteria from such genera as, Actinoplanes, Streptomyces, Paenibacillus, and Bacillus. The most dominant species were noted to be very closely related to Bacillus coagulans. The sample used in this study went through the “cooked” processing style .
Due to this secondary fermentation that takes place during processing, by this huge variety of organisms, this tea contains an abundant source of GABA , and statins [need more reputable source] that the other processing techniques simply will not provide. The colour is more of a velvety red, and the flavour is much smoother as well. More research is needed to get a better idea of what changes are taking place under different cultures of microorganisms during fermentation, and how this changes the medicinal value of this amazing plant.
It would be interesting to see some research investigating what strains of bacteria and fungi produce higher GABA, or statin levels for different medicinal benefit, or flavour.
Pharmacology and Medical Research:
+ ACE Inhibition
Catechins from Green tea (primarily EGC), have been shown to significantly inhibit angiotensin converting enzyme (ACE), however the absorption of these polyphenols are poorly understood. It is possible that not enough of these polyphenol dimers, and trimers are absorbed to produce therapeutic effects .
Green tea catechins have been shown to produce positive effects on endothelial, and overall vascular function. This effect is likely to do with the ACE inhibitory effects also noted .
Due to poor absorption of catechins, more research is needed on the metabolites of these polyphenols, to further understand the mechanisms taking place.
The antibacterial activity in Camellia sinensis aqueous extract was noted to be highest in green tea, and lowest in black tea, but present in all samples. This effect is likely due to the catechin content. Its action has been reported to be effective on gram positive bacteria .
The anti-cholesterol effects of green tea were suggested to be due to the catechins in long term cholesterol lowering actions, through both reduced cholesterol absorption, and increased cholesterol excretion through fecal matter. “Green tea catechins have also been shown to increase the gene expression of bile acid synthesis” . These effects on cholesterol would have a positive impact on the long term health of the vascular system, however the short term improvements are likely due to other constituents.
Puerh tea has a different method of lowering cholesterol. This style of Camellia sinensis processing allows secondary fermentation to change the chemical makeup of the plant. One of the changes, involves the addition of statins. Synthetic statins are commonly used in hypercholesterolemia, and as a life long treatment option after cardiovascular events (heart attacks). The addition of these chemicals have significantly reduced morbidity and mortality associated with cardiovascular disease, however often produce such adverse effects as myopathy or rhabdomyolysis , as well as some more recently discovered side effects such as neurological dysfunctions.
Therefore it is crucial that new, safer statin medications are discovered, and puerh offers an interesting alley to investigate further. It is one of the most common tea styles available, and due to the new techniques in processing, the tea only takes a few months to process rather than a few years. this allows the price to stay affordable, and sourcing is easy.
Puerh tea has very low toxicity, and can be drunk throughout the day, and over long periods of time, which may suggest this style of Camellia sinensis a very viable option for prevention of hypercholesterolemia, and its associated pathologies such as atherosclerosis, and cardiovascular disease. More research is needed on the safety of this product, and its effectiveness in vivo on cholesterol levels.
EGCG (a catechin), as well as tannins and theoflavins (to a lesser extent than EGCG) were shown to produce anti-diabetic effects through an improvement in insulin sensitivity (reported to be as much as 13% in some cases), both in vitro, and in vivo .
The catechin EGCG found in high amounts in green tea, has been shown to produce anti inflammatory effects through cytokine inhibition. Other catechins in green tea have been noted to regulate NADPH oxidases which are related to the pathophysiology of stress related processes. .
In a study done investigating the effects of Camellia sinensis flowers on inflammation found that the aqueous extract was able to produce significant anti-inflammatory effects on acute inflammation, as well as immunological liver inflammation in vivo. these actions were suggested to be due to polyphenol content .
Green tea has been shown in vitro and in vivo to produce geno-protective effects on DNA through its antioxidant profile . This supports the daily use of green tea as general health enhancer.
Camellia sinensis leaves and flowers have been shown in multiple studies to provide strong antioxidant effects in vitro and in vivo. Both oxidized, and unoxidized leaves (green, oolong, and black) have been shown to produce these effects in various studies [2, 6].
The antioxidant effects of Camellia sinensis have been suggested to be mostly due to its polyphenol (catechins, and related metabolites) content .
Chunjian Zhao et al, (2014), investigated the correlation between various polyphenol contents of various levels of processing in Camellia sinensis leaves (Black, oolong, white, yellow, and green teas), and found that as the catechin EGCG was broken down during the oxidization process, ECG levels increased. This same study noted that total polyphenol level in black tea was the lowest at 14%, with green containing the highest at 23% (the study did not include white tea), oolong varied greatly in its samples but researchers reported the mean value at 17% polyphenol content. This correlated with the studies findings for oxygen radical absorbance capacity (antioxidant profile), showing that green tea produced the highest, followed by oolong, and finally, black teas.
The cardioprotective effects in Camellia sinensis, especially white, and green teas, are likely due to the inhibitory effects the tannins and related gallotannins produce on Ca2+ activated Cl- channels (CACC) (C. da Costa Krewer et al., 2011).
Sri Lankan black tea Camellia sinensis L. has been shown to produce pharmacologically safe, mild diuretic activity. This effect has been noted to be due to multiple mechanisms: increased urinary Na+ output, inhibition of aldosterone secretion, inhibition of carbonic anhydrase activity, and through thiazide-like diuretic action. Interestingly, these effects seemed to correlate with the elevation with which the plants were grown, with higher elevation plants producing less diuretic effects, and low grown plants producing higher diuretic effects, however all can be used effectively as a diuretic .
Green tea extracts have been shown to produce neuroprotective effects in such neurodegenerative disorders as Parkinson's disease. Its effects were suggested to be due to the anti inflammatory, and antioxidant profile of green tea's catechins . It is possible that the theanine content played a role in these effects as well, however more research is needed.
This herb contains xanthines in its many forms, though, due to low saturation during infusion, and low solubility of xanthine alkaloids, the caffeine content is much lower than a cup of coffee (roughly 50%). Nevertheless, this alkaloid (and other purine alkaloids) are present, and those sensitive should use care, or avoid consuming altogether. Caffeine has been shown to cause acute hypertensive effects, but does build tolerance after prolonged intake, however if serious hypertension is present, it is advised to avoid this botanical in all its forms (there is decaffeinated versions, however these still contain very small amounts of this chemical).
Pharmacy and Dosage:
Generally the infusion ratio of this plant is 1:85, for 1-5 mins, with temperatures ranging from 50-90C. Various traditions have different ideas on how to make tea, and personal preference plays a big part as well. The lower the temperature, and shorter the infusion, the less of the catechins, caffeine and other bitter principles are extracted. This is especially true in green, and white teas due to their more raw, and delicate nature. Black, and pu Erh teas can handle longer and hotter infusions before releasing their bitter and astringent principles. Chinese traditional preparation (Gongfu) involves more infusions of the same leaves, but a higher leaf ratio used (such as a 1:30), and the steeping times are generally only a few seconds long (5-15 sec). With Japanese green tea, a similar process is used traditionally, more often for slightly longer however (1-2 minutes), but with a lower temperature. These methods are to avoid extracting the bitter constituents of this herb. For medicinal purposes, these bitter principles are desired, this means that higher temperatures, and longer infusion times will produce a stronger, more medicinal, and bitter tea as compared to the weaker, sweeter, and less astringent infusions traditionally prepared in asian cultures.
Medicinally, to obtain the powerful medicinal actions of the bitter and astringent constituents, the standard 1:20 infusion can be used, and drunk at the dose of 1 cup, 3 times per day.
Capsules can also be used, and are often marketed for weight loss, or energy producing effects. Follow the label when using these products.
There also exists green tea extracts, which vary greatly in concentration. Follow the label when using these products.
Suggested to have synergy with Juglans regia in use against Multidrug-resistant bacteria .
Shown to produce synergy with guarana (Paullinia cupana) in powdered, capsule form to increase energy expenditure (F.C. Schimpl et al., 2013).
The Sunlight Experiment
Updated March 2017
Recent Blog Posts:
- Amber Farooqui, Adnan Khan, Ilaria Borghetto, Salvatore Rubino, Bianca Paglietti, Shahana U. Kazmi. (2015). Synergistic Antimicrobial Activity of Camellia sinensis and Juglans regia against Multidrug-Resistant Bacteria. PLOS ONE. DOI:10.1371/journal.pone.0118431
- Bang-Tian Chen, Wei-Xi Li, Rong-Rong He, Yi-Fang Li, Bun Tsoi,Yu-Jia Zhai, and Hiroshi Kurihara. (2012). Anti-Inflammatory Effects of a Polyphenols-Rich Extract from Tea (Camellia sinensis) Flowers in Acute and Chronic Mice Models. Oxidative Medicine and Cellular Longevity. Vol 2012. doi:10.1155/2012/537923
- Barceloux, D. G. (2012). Medical Toxicology of Drugs Abuse : Synthesized Chemicals and Psychoactive Plants. Somerset, NJ, USA: John Wiley & Sons. Retrieved from http://www.ebrary.com
- Chien-Wei Hou. (2011). Pu-Erh tea and GABA attenuates oxidative stress in kainic acid-induced status epilepticus. Journal of Biomedical Science. 18. 75.
- Chunjian Zhao, Chunying Li, Shuaihua Liu, and Lei Yang. (2014). The Galloyl Catechins Contributing to Main Antioxidant Capacity of Tea Made from Camellia sinensis in China. the Scientific World Journal. Vol 2014. doi.org/10.1155/2014/863984
- Eric W.C. Chan, Eu Ying Soh, Pei Pei Tie, Yon Peng Law. (2011). Antioxidant and antibacterial properties of green, black, and herbal teas of Camellia sinensis. Pharmacognosy Res. 3(4): 266-272. DOI: 10.4103/0974-8490.89748
- K. C. Han, W. C. Wong and Iris F. F. Benzie. (2011). Genoprotective effects of green tea (Camellia sinensis) in human subjects: results of a controlled supplementation trial. British Journal of Nutrition, 105, 171–179 doi:10.1017/S0007114510003211
- K. R. W. Abeywickrama, W. D. Ratnasooriya, A. M. T. Amarakoon. (2010). Oral diuretic activity of hot water infusion of Sri Lankan black tea (Camellia sinensis L.) in rats. Pharmacogn Mag. 6(24): 271-277. DOI: 10.4103/0973-1296.71788
- M. Bláha, H.Vlckova, L.Nova kova, D.Solichova, P.Solich, M.Lanska,J. Maly, and V. Bláha. (2011). Use of Ultra High Performance Liquid Chromatography-Tandem Mass Spectrometry to Demonstrate Decreased Serum Statin Levels after Extracorporeal LDL-Cholesterol Elimination. Journal of Biomedicine and Biotechnology. doi:10.1155/2011/912472
- Ming Zhao, Wei Xiao, Yan Ma, Tingting Sun, Wenxia Yuan, Na Tang, Donglian Zhang, Yongxia Wang, Yali Li, Hongjie Zhou, Xiaolong Cui. (2013). Structure and dynamics of the bacterial communities in fermentation of the traditional Chinese post-fermented pu-erh tea revealed by 16S rRNA gene clone library. World Journal of Microbiol Biotechnol. 29. 1877-1884.
- Natália Bitu Pinto, Bruno da Silva Alexandre, Kelly Rose Tavares Neves, Aline Holanda Silva,1 Luzia Kalyne A. M. Leal,1 and Glauce S. B. Viana. (2015). Neuroprotective Properties of the Standardized Extract from Camellia sinensis (Green Tea) and Its Main Bioactive Components, Epicatechin and Epigallocatechin Gallate, in the 6-OHDA Model of Parkinson’s Disease. Evidence-Based Complementary and Alternative Medicine. Volume 2015. doi.org/10.1155/2015/161092
- Rosalind J. Moore, Kim G. Jackson and Anne M. Minihane. (2009). Green tea (Camellia sinensis) catechins and vascular function. British journal of Nutrition. vol 102. 1790-1802. doi:10.1017/S0007114509991218
- Saberi, H. (2010). Tea: A global history. London: Reaktion.
- Shing-Tack Fung, Cyrus K. Ho, Siu-Wai Choi, Wai-Yuen Chung and Iris F. F. Benzie. (2013). Comparison of catechin profiles in human plasma and urine after single dosing and regular intake of green tea (Camellia sinensis). British Journal of Nutrition (2013), 109, 2199–2207 doi:10.1017/S0007114512004370
- Hempen, C. H., & Fischer, T. (2009). A Materia Medica for Chinese Medicine: Plants, Minerals, and Animal Products. (pg. 122-123).