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You are here: Experts > Health/Fitness > Eating Disorders > Nutrition & Dieting > Where and how carbohydrate and proteins are digested
Nutrition & Dieting - Where and how carbohydrate and proteins are digested
Expert: Tanya Zilberter, PhD - 10/24/2009
Question
QUESTION: Hello,
There is a theory out there about the human body not being able to efficiently digest animal proteins with any kind of starchy vegies or Carbs like rise, pasta.....Based on the assumption that Proteins are broken up easier in the stomach by acids and Carbs will be digested by alkalies. When you put them in the stomach together acids will mix with alkalies and will cancel each other out giving out indigestion. I'm suspecting there is a flaw in that assumption. What is your opinion?
Also if you could tell me. How does the digestive process vary in digesting complete and incomplete or complemented plant proteins.
Thank you.
ANSWER: Dear Robert,
In fact, proteins are digested by enzymes trypsin and chymotrypsin that break down a protein into single amino acids. If protein is consumed in quantities exceeding body needs, the excess is converted into glucose (carbohydrate), which, in its turn, if is not used for energy, goes into the body fat depots.
Very little carbohydrate digestion occurs in the stomach, with or without proten. When the sugars reach the small intestine, they are in dissacharide form and still too big for absorption by the small intestine. In the duodenum, the pancreas releases amylase, which breaks disaccharides down into monosaccharides.
The speed of starches' digestion depends on the chemical nature of the carbohydrate itself, on the activity of the enzymes, on the gastric juices. Gastric juice includes pepsin, gastrin, bicarbonates, and hydrochloric acid. The last fact makes me question the theory of carbohydrate digestion by alkaline - non-acid substance with a pH greater than 7. Compare with real Ph value of the gastric juice: it varies from 1 to 3.
More on acidity of foods:
http://en.allexperts.com/q/Nutrition-Dieting-939/2008/9/Acidity-apples.htm
http://atkinszone.com/faq/2008/10/which-foods-are-acid-and-which-alkaline.html
pH balance diet
http://en.allexperts.com/q/Special-Diets-768/PH-balance-diets-truth.htm
Protein digestion and absorption
http://en.allexperts.com/q/Nutrition-Dieting-939/2008/9/Protein-digestion-absorp...
Tanya Zilberter
---------- FOLLOW-UP ----------
QUESTION: Ok, But aren't the intestinal juices different from gastric juices? Plus the Carbs do not spend much time in the stomach where all the acids thrive, but in the small intestine. Could it be that the intestinal juices have a different pH than that of the stomach?
ANSWER: I cannot see how it changes my answer.
TZ
---------- FOLLOW-UP ----------
QUESTION: I'm trying to figure out whether there is a chance of our bodies creating both acidic juices like hydrochloric acid and alkaline juices possibly in the small intestine. So I'm trying to find out whether the intestinal juices are different than the gastric juices.
Answer
OK. First of all, secretion of intestinal juices is stimulated by the mechanical pressure of partly digested food in the intestine and not its chemical properties. Secondly, intestinal juice contains substances to neutralize hydrochloric acid coming from the stomach.
The most active, ten-feet long part of small intestine responsible for digestion (jejunum) May have pH varying from 4.0 to 7.6, but different foods strongly influences the pH. Without food, pH here is rather stable: from 6.5 to 7.5. The next part ten-feet long part is called ileum is responsible for absorption and here, pH varies more: from 5.4 to 8.0 with food but is neutral or slightly alkaline while empty (7 -8).
Food acidity, as we saw, influences the intestinal pH. You might want to refer to for the food acidity list:
http://atkinszone.com/recipes/2009/07/ph-of-common-acid-foods.html
TZ
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Authored 4 academic print books and two popular diet print books as well as about a hundred scientific and popular articles