The Science Behind Tea
Tea, primarily Camellia sinensis, is renowned for its rich composition of bioactive compounds. The exact nutrient profile varies significantly depending on the type of tea (black, green, white, oolong) and its preparation. Tea is virtually calorie-free, with a single cup (240ml) containing less than 2 calories without added milk or sugar. It contains negligible amounts of macronutrients (protein, carbohydrates, and fats). The primary constituents of interest are micronutrients and phytochemicals.
Tea is abundant in polyphenols, particularly catechins, which are powerful antioxidants. Green tea, in particular, is rich in epigallocatechin gallate (EGCG). Clinical studies show EGCG possesses anti-inflammatory, anti-cancer, and cardio-protective properties. The amount of EGCG varies depending on factors like tea variety, growing conditions, and brewing methods.
Tea also contains the amino acid L-theanine, which promotes relaxation and focus. Nutrition research indicates that L-theanine works synergistically with caffeine to improve cognitive function and reduce anxiety. The caffeine content of tea ranges from 30-70mg per cup, depending on the type and brewing time. Black tea generally has the highest caffeine content, followed by oolong, green, and white teas.
Other micronutrients present in tea include trace amounts of minerals like manganese (important for bone health and metabolism), potassium (essential for electrolyte balance and blood pressure regulation), and fluoride (beneficial for dental health). However, the quantities are generally low and don't significantly contribute to daily nutrient requirements.
The GI index of plain tea is virtually zero due to its negligible carbohydrate content. Therefore, it does not cause a significant spike in blood sugar levels. However, adding sugar, honey, or milk will alter the GI depending on the quantities used. Digestion speed is rapid as tea is a liquid and primarily contains water and water-soluble compounds. The metabolic impact of tea is mainly driven by its antioxidant properties and its effect on energy expenditure. Some studies suggest that green tea extract can increase thermogenesis and fat oxidation, potentially aiding in weight management. However, these effects are generally modest and require consistent consumption in conjunction with a healthy diet and exercise.
It's important to note that tea also contains tannins, which can bind to iron and inhibit its absorption. This is particularly relevant for individuals with iron deficiency. Consuming tea with meals, especially those rich in iron, can reduce iron absorption. However, adding lemon juice to tea can help mitigate this effect as vitamin C enhances iron absorption.