Peter:

>  -  The plasma glucose-dependent insulinotropic peptide (GIP) concentration
> did not change after the pure carbohydrate meal yet the peak insulin and
> C-peptide levels did - though 60% less than when fat was added.  This seems
> to be contradiction to me.  How does GIP differ from insulin?

GIP, C-peptide and insulin are three different substances. I think that GIP
contributes to raising insulin levels.

Here is what Loren Cordain said on the Paleodiet list:

>>We need to clarify our terms on this one. The ingestion of fat with
>>carbohydrate results in lower blood glucose but higher insulin levels
>>compared to carbohydrate ingestion alone (1,2).   Fat ingestion
>>stimulates the secretion of glucose dependent insulino-tropic
>>polypeptide (GIP) and it is thought that the additional rise in insulin
>>is mediated by the effects of GIP (3).
>>
>>                                REFERENCES
>>
>>1.      Collier G, O'Dea K.  The effect of co-ingestion of fat on the
>>glucose, insulin and gastric inhibitory polypeptide responses to
>>carbohydrate and protein. Am J Clin Nutr 1983;37:941-45.
>>2.      Collier G. et al.  Effect of co-ingestion of fat on the
>>metabolic responses to slowly and rapidly absorbed carbohydrate.
>>Diabetologia 1984;26:50-56.
>>3.      Collier G et al.  The acute effect of fat on insulin secretion.
>>J Clin Endocrinol 1988;66:323-26.

>  -  It would be interesting to know how the six men were defined as
> "normal" and what form the carbohydrates and fats were in.

I suppose that "normal" means healthy, in particular don't have diabetes.

As far as the form of the carbohydrates and fats, in [Diabetologia 1984
Jan;26(1):50-54] it was 37.5 grams fat (type unspecified in the abstract) and 75
grams carbohydrates (lentils or potatoes). In [Am J Clin Nutr 1983
Jun;37(6):941-944] it was 50 grams fat in the form of butter and 50 g
carbohydrate in the form if potatoes.

Remark: An earlier article [Lancet 2:454, 1966] shows that mixing glucose with
tenderloin flattened the serum glucose curve but increased the production of
insulin. The meat contained slightly more fat than protein (by calories). The
author conjectured that there was a synergism between glucose with aminoacid,
but the studies by Collier et al. show that the fat was the real culprit.

>  -  Adding fat to a carbohydrate meal slows down the breakdown and entry of
> the carbohydrates into the blood stream.  I wonder to what extent the rise
> in the insulin response that seems to be associated with adding fat to
> carbohydrate is canceled out or overridden by the slower glycemic response.

Yes, but the articles mentioned show that despite a slower entry of
carbohydrates into the blood stream, MORE insulin is produced. A 30/30/40 Zone
meal produces the SAME effect on insulin than a 30/10/60 low fat meal. Protein
is neutral (on insulin). All of that suggest:

1] Western meals are usually high in fat and carbohydrate. The co-ingestion of
these two macro-nutrients, by inducing high insulin levels, may cause insulin
resistance.

2] Barry Sears is wrong when he claims that, to keep insulin levels low, EACH
meal should meet the Zone specifications. However, there are no good arguments
against having 30/30/40 proportions on a daily basis.

3] Proper food combining is important. The results of Collier give a good reason
not to combine avocado and fruit, in addition to the article that Tom has cited
(cf. avocados and "instant diabetes", posted on 12/8/1997).

Best wishes,

Jean-Louis
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