Green tea has mechanisms to inhibit protein, carbohydate, and fat uptake. However, it seems that when consuming green tea as part of a meal the 'inhibition of protein' is not a concern and the 'inhibition of fat', although present, is practically small. Only carbohydrate uptake is practically relevant in regards to calories, although cholesterol uptake is quite effectively reduced as well.
Green Tea possesses a ton of mechanisms which lead to the conclusion that it can inhibit a good deal of nutrient uptake.
It can inhibit the enzymes lactase, sucrase, maltase, amylase, a-glucosidase, lipase, trypsin, pepsin, and chymotrypsin.
However, the effects on the protein digestive enzymes (inhibition) are greatly alleviated when one salivates; proline-rich peptides are secreted in the saliva which can reduce the inihibitory effects on protein-digestive enzymes.
Studies on the matter, that try to examine caloric malabsorption, measure how many calories are in the feces of the subjects. Its not the most pleasant methodology, but it works. Fecal analysis is something that makes a primary researcher glad for graduate students and lab assistants.
In rats, studies analyzing feces note that fecal triglycerides increase from 3.5g daily to 5.8g daily with 1% Green Tea Catechins by weight of the diet. So the result is present, but it is minimal.
In regards to carbohydrates, after examining a test meal with 100mg Green Tea Catechins malabsorption of carbohydrates was seen to be 25% in human volunteers, whereas increases in fat malabsorption were again minimal.
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