Let me summarize the confusing picture :-)
Compared to 50 g carbohydrates alone, co-ingestion of 50 g fat induces a
dramatically improved blood glucose response, but only a slight improvement of
the insulin response [1,2]. The likely explanation is that fat stimulates GIP
secretion [3].
When carbohydrates and fat are ingested together at breakfast, carbohydrate
tolerance is impaired a few hours later at lunch. The effect is significant but
not spectacular [4].
Let's compare two situations:
A: 50 g carb and no fat at breakfast, 50 g fat and no carb at lunch
B: 25 g carb and 25 g fat at each one of those meals.
To make the comparison easier, take the situations
C: 50 g carb and no fat at breakfast, no lunch
D: 25 g carb and no fat at breakfast, same at lunch
Obviously, C will induce a similar response than A. D is better than C
(advantages of "nibbling versus gorging [5]"). And B will produce a greatly
improved serum glucose response than D and possibly a slightly worse insulin
response than D, due to the effects of [1,2,4].
Overall (and I am revising my initial opinion here), mixed meals seem very
beneficial on serum glucose levels and moderately beneficial on insulin levels.
Moreover, there is evidence that, in addition to the deletious effects of high
blood glucose on the kidneys, it can cause insulin resistance or exacerbate an
underlying insulin resistance state [6-13].
Of course, a non-vegetarian will generally ingest a significant amount of
protein. Westphal et al. [14] found that adding protein doesn't, or only
minimally, increase insulin secretion, which is not consistent with other
studies [15,16].
Overall, I think there is a lot of uncertainty, but carbohydrate moderation and
mixed meals seem to be a good choice.
Peter:
> It is becoming clearer and clearer to me how so many
> scholars selectively pick the research they need to confirm their already
> preconceived notions. When Loren Cordain posted his message on Paleodiet a
> couple of months ago about how mixing fats and carbohydrates caused insulin
> levels to rise, I was already suspicious. Supplying scientific references
> can be a very effective way of shutting up any possible critics, for only
> the smallest minority is going to check them anyhow or even check in the
> literature to see what else has been published on the subject.
Someone said (approximately) that scientific papers are like the Bible: whatever
opinion you might have, you will always find a citation to support it.
But when you look more closely at the sources, there are so many variables that
the picture is not quite as simple as what you read in best-seller books (I am
not only talking about "The Zone").
Best wishes,
Jean-Louis
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1. Collier et al., The effect of co-ingestion of fat on the glucose, insulin
and gastric inhibitory polypeptide responses to carbohydrate and protein,
Am J Clin Nutr 37:941
2. Collier et al., Effect of co-ingestion of fat on the metabolic responses
to slowly and rapidly absorbed carbohydrates, Diabetologia 26:50-54
3. Collier et al., The acute effect of fat on insulin secretion, J Clin
Endocrin. Metabolism 66:323 (1988)
4. Collier et al., Concurrent ingestion of fat
and reduction in starch content impairs carbohydrate tolerance to
subsequent meals, Am J Clin Nutr 45(5):963-9, 1987
5. Jenkins-David et al. Nibbling versus gorging: metabolic advantages of
increased meal frequency, New England J of Medicine, 1989, 321(14):929-34
6. Yki-Jarvinen H. Acute and chronic effects of hyperglycemia on glucose
metabolism, Diabetologia 1990(33):579-585
7. Yki-Jarvinen H. Glucose toxicity, Endocrine Rev. 1992(13):415-431
8. Anderson CM et al., Relative expression of insulin receptor isoforms does not
differ in lean, obese and NIDDM subjects, J Clin Endocrinol Metab
1993(80):1037-1044
9. Rossetti L et al., Effect of chronic hyperglycemia on in vivo insulin
secretion in partially pancreatomized rats, J Clin Invest 1987(80):1037-1044
10. Rossetti L et al., Correlation of hyperglycemia with phlorizin normalizes
tissue sensitivity to insulin in diabetic rats, J Clin Invest 1987(79):1510-1515
11. Garvey WT et al., The effects of insulin treatment on insulin secretion and
action is type II diabetes mellitus, Diabetes 1985(34):222-234
12. Henry RR et al., Diabetes 1986(35):990
13. Kolterman OG et al., The acute and chronic effects of sulfonylurea therapy
in type II diabetics, Diabetes 1984(33):346
14. Westphal et al., Metabolic response to glucose ingested with
various amounts of protein, Am J Clin Nutr 1990 (62):267-272
15. Spiller et al., Effect of protein dose on serum glucose
and insulin response to sugars, Am J Clin Nutr 1987 (46):474-80
16. Lancet 2:454, 1966
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