Sun, Jun-03-07, 14:53
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Don't Call Me Sugar
Posts: 4,209
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Plan: Atkins
Stats: 293/287/230
BF: :^( :^| :^)
Progress: 10%
Location: Auburn, WA
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Thanks for the research, NancyLC. 
I admit I'll be happier if milk is safe, since people drink so much of it in this country. But I am trying to keep an open mind here. If I had to guess, I would guess that it's no good for some people, and fine for some people.
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The effect of bovine casein and synthetic ß-casomorphins on the motility of rat gastrointestinal tract was studied by noninvasive techniques using the nonabsorbable marker 141Ce.
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This is interesting, but it only shows that colon motility was slowed down due to the casomorphins triggering opiod receptors in the colon, and that it didn't happen with whey. As far as I can tell, that is - I only can see the abstract. It's well known that (a)opiate drugs slow intestinal motility - I was prescribed some painkillers after my c-section that certainly had that affect - and (b)casein is slow to digest and gives a long feeling of satiety. Apparently, casomorphins trigger the same receptors in the colon and slow down the digestion just like opiates do.
That's interesting stuff, but it doesn't discuss effects to the brain other than messages of satiety. And to be honest, I see an upside - long-term satiety is helpful when you're dieting. Casein is a favorite evening food for weightlifters as the slow trickle of protein goes on most of the night. I eat cottage cheese before bed sometimes for the same effect (instead of a shake of casein powder).
I did pop casomorphin brain into the search tool on the Journal of Nutrition site, and I got four results:
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Catherine Sandré, Aude Gleizes, Françoise Forestier, Roseline Gorges-Kergot, Stefan Chilmonczyk, Joëlle Léonil, Marie-Christiane Moreau, and Colette Labarre
A Peptide Derived from Bovine ß-Casein Modulates Functional Properties of Bone Marrow-Derived Macrophages from Germfree and Human Flora-Associated Mice
J. Nutr. 131: 2936-2942.
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This one was hard to read, but it was a test whether some casein peptides had a helpful effect on the immune system without causing inflammation. The answer was a yes, but it was only in vitro and using mice.
Grant money - This work was funded in part by Action Incitative Programmée nutrition et immunité (Convention AIP 96/383/P00156 Institut National de la Recherche Agronomique).
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Jelena Pupovac, and G. Harvey Anderson
Dietary Peptides Induce Satiety via Cholecystokinin-A and Peripheral Opioid Receptors in Rats
J. Nutr. 132: 2775-2780.
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This is a good read. Check it out:
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The results of this study support the hypothesis that the digestion of food proteins gives rise to peptides that initiate a multiplicity of satiety signals from the gut. We showed that suppression of food intake by casein and soy protein involves peptides released from their digestion and is mediated through both CCK-A and opioid receptors. When the receptor antagonists were combined, their effect on food intake in h 1 of feeding was greater than the effect of each alone, suggesting that their effects were additive.
Mediation of satiety signals induced by casein and its hydrolysate through these mechanisms was expected. Previous in vivo studies have shown the presence of opioid activity in casein (11Citation ). Also, it was demonstrated recently that intact casein promotes premature meal termination in meal-fed rats, most likely through the mechanism that involves peripheral opioid and CCK receptors (15Citation ). However, there are no reports describing opioid activity of soy protein.
(...)
Some early work showed that soy protein inhibited the adenylate cyclase activity in hybrid cell homogenates, but, unlike wheat or milk proteins, this inhibition was not naloxone-reversible (19Citation ), suggesting the lack of opioid peptides in soy protein. Our study suggests, however, that there is opioid-like activity arising from both proteins, and that these are involved in food intake regulation. Naloxone increased food intake by 83% when given with CH, by 58% with SH, by 21% with intact casein and by 59% with intact soy protein in h 1 of feeding (Table 2).
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(bolding mine)
They suggest a possible opioid action of soy peptides.
Grant money - Supported by the National Sciences and Engineering Research Council (NSERC) of Canada.
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Xi Lin, Mark R. Chavez, Richard C. Bruch, Gail E. Kilroy, Linda A. Simmons, Ling Lin,, H. Douglas Braymer, George A. Bray, and David A. York
The Effects of a High Fat Diet on Leptin mRNA, Serum Leptin and the Response to Leptin Are Not Altered in a Rat Strain Susceptible to High Fat Diet-Induced Obesity
J. Nutr. 128: 1606-1613.
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Not directly relevant. The keywords only appeared in cites at the bottom.
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M. A. Froetschel, M. J. Azain, G. L. Edwards, C. R. Barb, and H. E. Amos
Opioid and Cholecystokinin Antagonists Alleviate Gastric Inhibition of Food Intake by Premeal Loads of Casein in Meal-Fed Rats
J. Nutr. 131: 3270-3276.
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Again with the satiety:
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The similar effects of the antagonists, which are incapable of crossing the blood-brain barrier, suggest that intake and digesta retention responses associated with casein ingestion are peripherally mediated in a synergistic fashion involving both opioid and CCK receptors.
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Also interesting - effects on insulin:
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Although premeal loads of casein increased insulin compared with amino acids, the effects of the antagonist treatments were similar in rats given either casein or amino acids. Postprandial insulin release in dogs due to dietary casomorphin or a peptic digest of casein was blocked by the opioid antagonist naloxone but not in those fed a liver extract-sucrose meal (14Citation ). Finding that opioid antagonists lowered insulin in rats treated with premeal loads of amino acids to a similar extent as rats treated with premeal loads of casein indicates that casomorphins are not likely the only stimulus of insulin release after ingestion of milk protein. In the present experiment, naltrexone, which blocks both peripheral and central opioid receptors, had a greater effect at lowering postprandial insulin than naloxone methiodide, which specifically blocks peripheral opioid receptors. This suggests that a central opioid mechanism that is related to dietary amino acids may exist in addition to the peripheral influence of casomorphins that mediates this effect on postprandial insulin. Furthermore, the changes in circulating insulin without corresponding changes in glucose may also contribute to a central effect of insulin on satiety (15Citation ).
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That worried me until I read that the preparation included skim milk. That could smack someone's insulin around.
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The lack of an antagonist effect in rats given premeal loads of amino acids compared with casein supports the overall hypothesis that peptide fractions of casein, known as casomorphins, are responsible for a reduction in intake. The only definitive method to determine whether casomorphins are responsible for the intake-suppressive effects of casein is to administer these peptides directly. However, postabsorptive delivery of free peptides and their susceptibility to intestinal hydrolysis may influence their relative activities compared with peptides within intact casein (10Citation ). Another concern is related to the potential opioid and CCK bioactivity of isolated soy protein, used as the protein source in the basal diet. Pepsin hydrolysates of other protein sources including wheat and bovine serum albumin may contain peptides with opioid activity as indicated by naloxone reversible inhibition of adenylate cyclase activity in cell homogenates (3Citation ). However, a fraction of soy protein did not exhibit opioid activity with this procedure compared with these other protein sources (3Citation ). In this experiment, premeal loads of 0.25 g of casein resulted in effects that were reversed by opioid and CCK-A antagonists even though the rats were receiving >1.5 g of isolated soy protein from their diet. Others have found that premeal loads of albumen, another intact protein source, will cause CCK-A antagonist reversible intake suppression compared with premeal loads of amino acids, carbohydrates or fat (24Citation ,25Citation ). Comparisons between different protein sources in relation to their effects on CCK or opioid-antagonist reversible-inhibition of intake suppression would help determine whether opioid activity is specific to a few identified protein sources such as casein, albumen or wheat.
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Opioid activity from albumen (egg white)? This is news to me.
Grant money - Supported by a grant from the National Dairy Council.
Nothing in any of these about direct travel of casomorphin into the brain. Perhaps instead of a nutrition journal, we'd have to dig around in some neurology journals. |
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