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The gene that makes your mouth water

Ability to digest starch could have spurred human evolution.

Spit might have helped human evolution by enabling our ancestors to harvest more energy from starch than their primate cousins.

Read the story here.

Posted by Nicola Jones on September 10, 2007
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Very interesting theory.

But, is there any evidence that reduced amylase-levels lead to malassimilation of carbohydrates?

I was thought in physiology classes that salivary amylase is quite irrelevant for the digestion of carbohydrates, but rather gives some protection against caries.

So, are there any papers showing the importance of salivary amylase for carb digestion?

Posted by: Daniel Schneeberger | September 11, 2007 09:33 AM

Hi Daniel,

I wondered that myself. The researchers cite a couple references, showing that salivary amylase is important for energy absorption during diarrheal and that enzymatic activity persists further down the pipe.

Lebenthal, E. Role of salivary amylase in gastric and intestinal digestion of starch. Dig. Dis. Sci. 32, 1155–1157 (1987).

and

Fried, M., Abramson, S. & Meyer, J.H. Passage of salivary amylase through the stomach in humans. Dig. Dis. Sci. 32, 1097–1103 (1987).

Thanks for reading,

Ewen

Posted by: Ewen Callaway | September 11, 2007 11:27 AM

It makes me wonder about a possible link between this and diabetes....?

Posted by: Kirti Salunkhe | September 11, 2007 05:25 PM

Like Kirti, I was wondering too about any link between digestion of starch, and diabetes. Also... please tell me more about the connection between digestion of starch, and diarrhoea -- how are the two connected? Thanks.

Posted by: Joyce Gorsuch | September 11, 2007 06:18 PM

The findings are interesting, but the possible link with brain evolution seems quite speculative. Most physiology textbooks remark that although salivary alpha-amylase (a.k.a. ptyalin) is able to digest a substantial amount of cooked starch before being inactivated by gastric hydrochloric acid, it is not required for complete starch digestion. This is because the isozyme, pancreatic alpha-amylase, is able to perform the job very efficiently in the duodenum - both in cooked and non-cooked starch. Salivary amylase may be important in the neonatal period, when the pancreatic enzyme production is low. It will be interesting to know whether pancreatic amylase activity is higher in humans than in non-human primates.
An osmotic diarrhoea may be caused by lack of appropriate complex sugar digestion in the duodenum, because non-digested carbohydrates are then acted upon by bacteria in the hindgut, releasing large quantities of osmotically active molecules. On the other hand, a high amylase activity results in large post-prandial serum glucose levels because of enhanced absorption, and hence has a possible link with diabetes.

Posted by: Fernando Saravi | September 12, 2007 10:01 AM

And satiety? Obesity?

Posted by: Susan McGinty | September 12, 2007 10:49 AM

An interesting article. I wonder about the copy number variation of pancreatic amylase in humans.

In the article the authors mention that in the primate taxon cercopithecines the salivary amylase protein level is even higher than in humans. However, they do not report on salivary amylase copy number in any of these species. Surely an interesting topic for further studies.

With additional data the authors' hypothesis of the connection between the diet and evolution may turn out to be fully proven.

Posted by: Alexander Henke | September 13, 2007 10:47 AM

Very interesting. Fecal (pancreatic derived) amylase goes down during infections with rotavirus, the ubiquitous virus that is the commonest cause of childhood gastoenteritis. Even now it kills 600,000 children a year, suggesting it could have been a powerful evolutionary force. Rotavirus is not infectious in the mouth when it enters, but becomes so in the duodenum. Could children who can pre-process starch in the mouth have a selective survival advantage from such an acute and life -threatening illness?
Also what does the hypothesis mean for those with coeliac disease (gluten-sensitive enteropathy)? Are they likely to have high copy numbers, ie digesting more starch and revealing more of the the wheat's protein gluten? Would be interesting to look at copy numbers in coeliacs vs controls form the same population.

Posted by: Margo Honeyman | September 14, 2007 08:42 AM

"the rise of agriculture 150,000 years ago" ?? has to be a misprint. What did Dominy actually say?

Posted by: rosemary lewis | September 14, 2007 10:51 PM

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