茶叶中含有较多的鞣酸和茶碱。
鞣酸进入胃肠道后，会抑制胃液和肠液的分泌，而胃液和肠液都是消化食物所不可缺少的；鞣酸还会与肉类、蛋类、豆制品、乳制品等食物中的蛋白质产生凝固作用，形成不易被消化的鞣酸蛋白凝固物。吃的蛋白质越多，喝的茶越浓，这一情况就越严重。
大量的鞣酸对胃粘膜有较强的刺激作用，会引起胃功能失常，导致消化不良，还会刺激肠道粘膜，从而阻碍肠道对营养物质的吸收。此外，茶叶中的茶碱具有抑制小肠吸收铁的作用。
据科学家的实验证明，饭后饮用十五克茶叶冲泡的茶水，会使食物中铁的吸收量降低五十％。
有些人正是因为看中了饭后一杯茶具有影响人体消化和吸收食物营养的作用，所以才把它当作是一种减肥美容的有效方法。但是这也有引起胃肠功能失调和营养不良恶果的可能。
我们还常常可以看见有些人在饭前、饭后各喝一杯茶的习惯。
饭前喝茶不但和饭后喝茶一样，会影响胃肠道对食物的消化吸收，而且由于茶会刺激口腔里的味觉细胞，使味觉淡化，并减少唾液的分泌，从而使随后的饮食寡味。
细节提醒：
长期在饭前饭后饮浓茶，会造成消化不良、便秘、营养障碍和贫血等不良后果，因此，在饭前半小时和饭后一小时之内，都不宜喝茶。
译文:
Drinking tea after meals is equal to drinking poison
Tea cantains much acidum tannicums and theophylines.
After acidum tannicum enters in the gastrointestinal tract,it will refrain the secretory gastric juice and intestinal juice which are indispensable in digesting food;moreover,acidum tannicum will take a solidfication effect in the protein of meat,eggs,bean products and dairy products becoming the indigestible acidum tannicum protein coagulum.The more you have protein and thick tea,the more serious it will be.
A large amount of acidum tannicum may have so strong a stimulate effect on gastric mucosa that will not only cause the funciton of stomach be out of gear and indigestion but also stimulate the gut mucosa thus it will prevent the gut from absorbing nutrients.Besides,the theophlines in tea has the effect of refraining small intestine from absorbing iron.
The experiment by the scientist indicates that drink tea water with drawing fifteen grams of tea after meals will reduce half of the amount of iron absorbed in foods.
Somebody take it as a effective method of losing weight and facial beautification just for considering that drink a cup of tea after meals has the feature of affecting the body disgesting and absorbing nutrients in foods.However,it is possible to cause harmful consequence of disordering the function of stomach and intestine and malnutrition.
We often see somebody have the habit of drinking a cup of tea either after or before meals.
Similiarly,drinking tea before meals will also prevent digesting and absorbing foods. In addition , tea will stimulate the taste cell inside oral cavity, so it can weaken the sense of taste and decrease the secretory saliva ,therefore the following diet will be made tasteless.
Detail to warn:
Long time drink thick tea before and after meals will bring about harmful results of indigestion,constipation,dystrophy and anemia etc.Hence,it's not fit for drinking tea after meals within an hour and before meals within half an hour.