I noticed that casein, while it suppresses hunger better than whey, tend to cause digestive issues.

So, here is my question: does eating large quantities of slow digesting protein down-regulates its absorption in intestines?

Chicks, it's a start

Journal of Nutrition Vol. 110 No. 5 May 1980, pp. 989-994
Copyright © 1980 by American Society for Nutrition This Article

Digestion and Absorption of Casein at Different Dietary Levels in the Chick: Effect on Fatty Acid and Bile Acid Absorption
D. Sklan1

The site of digestion and absorption of protein was determined in chicks fed diets containing 10, 30 and 45% casein as the protein source, 3% added oil with 91Y Cl3 added as a non-absorbed reference substance. Digestion of protein to low molecular weight (MW) peptides and amino acids was rapid in all diets with major absorption occurring between duodenum and lower jejunum. Increasing the dietary casein resulted in increases in low MW peptide levels in the duodenum. This increase was disproportionate with intake when 45% casein was fed, suggesting that absorptive capacity of the duodenum was exceeded. Overall nitrogen absorption was similar in all treatments reflecting the increased participation of the ileum in nitrogen absorption when high dietary casein levels were fed. Fatty acid and bile acid absorption was depressed when 45% casein was fed, mainly due to inhibition of absorption in the ileum, presumably by binding to undigested protein

There are several in vitro digestibility assays, some underestimate the digestibility of casein, that's as far as I'll get for now.

Or not...

Amount and fate of egg protein escaping assimilation in the small intestine of humans
Pieter Evenepoel, Dirk Claus, Benny Geypens, Martin Hiele, Karen Geboes, Paul Rutgeerts, and Yvo Ghoos

Department of Medicine, Division of Gastroenterology and Gastrointestinal Research Centre, University Hospital Leuven, B-3000 Louvain, Belgium

Studies attempting to evaluate protein assimilation in humans have hitherto relied on either ileostomy subjects or intubation techniques. The availability of stable isotope-labeled protein allowed us to determine the amount and fate of dietary protein escaping digestion and absorption in the small intestine of healthy volunteers using noninvasive tracer techniques. Ten healthy volunteers were studied once after ingestion of a cooked test meal, consisting of 25 g of 13C-, 15N-, and 2H-labeled egg protein, and once after ingestion of the same but raw meal. Amounts of 5.73% and 35.10% (P < 0.005) of cooked and raw test meal, respectively, escaped digestion and absorption in the small intestine. A significantly higher percentage of the malabsorbed raw egg protein was recovered in urine as fermentation metabolites. These results 1) confirm that substantial amounts of even easily digestible proteins may escape assimilation in healthy volunteers and 2) further support the hypothesis that the metabolic fate of protein in the colon is affected by the amount of protein made available.

protein fermentation; protein assimilation; stable isotopes; phenols

Nitrogen losses from the human small bowel: obligatory losses and the effect of physical form of food.
A Chacko, J H Cummings
MRC Dunn Clinical Nutrition Centre, Cambridge.

The amount and form of nitrogen lost from the human small intestine and the dietary factors which influence it have been studied in six ileostomists. Over a six day period the subjects were fed a series of diets including low nitrogen (LND) 0.17 g N/day, LND + soya beans (5.87 g N/day) and a high fibre diet (HFD) (10.6 g N/day). The soya beans were fed either whole or pureed to test the effect of physical form of food. Total N, protein, amino acids, urea, and ammonia were measured in ileostomy effluent which was collected throughout the study. Total N excretion was LND 0.91 (0.04) (SE) g/day; LND + whole soya beans (WSB) 2.26 (0.15) g/day; LND + pureed soya beans (PSB) 1.42 (0.12) g/day (WSB v PSB, p less than 0.001); and HFD 2.17 (0.11) g/day (HFD v PSB, p less than 0.001, HFD v WSB, NS). N losses as urea, ammonia, and free amino acids were less than 10-15% of total N, the remainder being protein (48-51%) and (by difference) peptides (20-30%). Eighty to 85% of effluent N was in the insoluble (pellet) fraction except on the low N diet where it was 66%. The physical form of food clearly influenced N digestibility in the soya beans whilst changes in dietary fibre seem not to have a significant effect.

What's that?

Hope this cannot be generalized to beef, as I enjoy mine essentially raw.

Bloody and still mooing is the only way to go!

I've read before that raw egg is not well absorbed. As for beef, well at least proponents of undercooked meat can feel good about ingesting fewer carcinogens. Not sure about protein assimilation - but where's that thread with the study posted about the absorption of well-masticated beef? Can't find it....

Regular mastication is key, it seems.

http://www.mindandmuscle.net/forum/index.p...st&p=459276