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Rate of glucose/insulin changes with macronutrient changes


Zeta

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Hey everyone,

 

I've been greatly enjoying my high-fat nut-based diet, and my cholesterol numbers are great, and my blood pressure is actually better than I'd thought (I'm pretty sure I've been taking it with my arm too low!), but I don't like my fasting glucose numbers, which tend towards the mid- or even high-80s mg/dL.

 

I want to trial a low-fat run of X days -- isocaloric with my current diet -- to see how the fasting glucose might change.

 

Anyone have any thoughts -- or even guesses -- about X, about how long I'd have to do it to see whatever changes are likely to occur? I expect there'd be an immediate lowering, if minor, simply because overnight gut transit/glucose absorption/clearance time would be altered. But, beyond that, would a week be long enough to see all the changes I'm going to get, or might the body's entire adjustment period -- various genes turning on or off -- be longer? I want to minimize the length of the experiment, given that there's a risk of an IBD flare-up.

 

Thanks,

Zeta

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Zeta,

I want to trial a low-fat run of X days -- isocaloric with my current diet -- to see how the fasting glucose might change.

 

Anyone have any thoughts -- or even guesses -- about X, about how long I'd have to do it to see whatever changes are likely to occur?

 

It looks like in as little as 2 weeks fasting glucose may be reduced, insulin sensitivity increased and cholesterol numbers improved by a low-fat, high-carb diet in healthy men [1]. Of course the diets weren't ideal for this comparison, so YMMV.

 

--Dean

 

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[1] Hypertension. 1999 Oct;34(4 Pt 1):580-5.

 
Hypotensive effect of low-fat, high-carbohydrate diet can be independent of
changes in plasma insulin concentrations.
 
Straznicky NE(1), O'Callaghan CJ, Barrington VE, Louis WJ.
 
Author information: 
(1)Department of Clinical Pharmacology , Austin and Repatriation Medical Centre, 
Heidelberg, Victoria, Australia.
 
To examine the relationship between diet, blood pressure, and plasma insulin
concentrations, we studied 14 healthy males who were prescribed low-fat and
high-fat diets. The low-fat diet contained 25% (of energy intake) fat and 54%
carbohydrate; the high-fat diet was 45% fat (predominantly saturated fat) and 36%
carbohydrate. The diets were consumed over consecutive 2-week periods in random
sequence, separated by a 2-week washout period. Resting supine systolic and
diastolic blood pressures decreased significantly by 7 and 3 mm Hg, respectively,
and plasma total cholesterol, LDL cholesterol, and HDL cholesterol concentrations
all fell (by 21.6%, 25.7%, and 18.0%, respectively; all P<0.001) on the low-fat
compared with the high-fat diet. Fasting glucose and the glucose area under the
curve during the frequently sampled intravenous glucose tolerance test (300 mg/kg
glucose load with blood sampling for 180 minutes) were significantly lower, and
the glucose disappearance rate tended to be faster after the low-fat diet. In
contrast, fasting insulin concentrations and the insulin response (insulin area
under the curve) to glucose challenge were unchanged. Insulin sensitivity
(defined as the rate of glucose disappearance per unit of insulin increase during
the period 0 to 40 minutes after the glucose load) was significantly higher on
the low-fat diet. These results suggest that the hypotensive effects of a
low-fat, high-carbohydrate diet, although associated with an improvement in
insulin sensitivity, are not mediated by changes in plasma insulin concentration.
 
PMID: 10523330
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All:

 

I'm not aware of the kind of time-course study you'd really want to see to answer this question (let alone a time-course study using ultra-healthy diets for both arms and subjects who are very lean and with great bloodwork to begin with), but to give the best material into which to dig I identified a bunch of crossover studies (ie, studies in which the same subjects are randomly administered one of 2 or more diets for some time period and then "cross over" to the other, with or without a "washout" period returning them to baseline in between) comparing high-MUFA to high-carb diets with different aspects of glycemia other than just acute postprandial effects. Several studies report improvements on the high-MUFA diet within 4-6 weeks, but others find no effect; however, the studies vary in many regards (metabolic, adiposity, and energy balance of  participants; source of MUFA (EVOO, refined OO, nuts, high-oleic sunflower); quality of carbs (in both or in one diet vs. the other), etc. Most of them are available as free full-text articles, so you can dig in and see if you can come to any conclusions. If you do, please report back!

 

There is certainly also some hint of a possible genetic interaction (PMIDs 15671101, 26203360), and this could also be a confounder in studies carried out in subjects predominantly of one ethnicity (which is probably most or all of them tho' I'm guessing it's unreported in most).

 

It looks like in as little as 2 weeks fasting glucose may be reduced, insulin sensitivity increased and cholesterol numbers improved by a low-fat, high-carb diet in healthy men [1]. Of course the diets weren't ideal for this comparison, so YMMV.

Here "the high-fat diet was 45% fat (predominantly saturated fat)" (per the free full text, "3% as polyunsaturated, 15% as monounsaturated, and 25% as saturated fatty acids")  which is explicitly not Zeta's real-world crossover. "Daily energy intake was calculated at 10.5 MJ (2500 kcal) for both diets and was adjusted when necessary to keep body weight constant," so that's 69.4 g of SaFA/d!

 

Moreover, "Mean energy intake was significantly higher (by 1880 kJ [=449 Calories!]) on the high-fat diet, which is best explained by the higher than prescribed fat intake by subjects"; I think everyone will agree that this is likely to have affected insulin sensitivity....

 

The high-SaFA diet also had substantially less magnesium (338 vs 434 mg/d), which might have affected insulin sensitivity.

 

One thing that might on its face be thought to make the low-fat diet in this study look worse is that "Main fat sources were sunflower oil and polyunsaturated margarine on the low-fat diet." Since they don't say otherwise, and since the study was published in 1999, I think it's safe to assume that this margarine would have had the usual significant presence of trans-fatty acids (tho' it would make a significant difference even whether it was commercial tub or stick margarine). However:

 

(a) because this was a (relatively!) low-fat diet (25% fat), the level would not likely have been not crazy-high; and more importantly

 

(b) while one is always tempted to assume that trans-fats must cause All Things Bad (my Mom can't be convinced that there is no credible evidence that trans-fat intake causes cancer (and yes I know there are some unreasonable animal studies suggesting this)), meta-analysis of controlled trials finds "Increased [trans-fatty acid] intake did not result in significant changes in glucose or insulin concentrations,"(2) and several studies I looked at (including (3) and (4) in normoglycemic subjects and others in various states of dysglycemia) find no effect on insulin sensitivity per se.

 

On the other hand, they do seem to have done a pretty good job in their selection of carbs: "Carbohydrate sources were fruit, wholemeal bread, brown rice, white pasta, and potato. The ratio of sugars to starch was identical (0.44:0.56) in the 2 diets. Diets were balanced for sodium and potassium content." The problem, of course, is that if you have teh same ratio of sugars to starch in a high- and a low-fat diet, the implication is that there's less fruit and veg in the high-fat diet; there was certainly less fiber, tho' it was respectable in both (40 vs. 29  g/d).

 

------------

[1] Hypertension. 1999 Oct;34(4 Pt 1):580-5.

Hypotensive effect of low-fat, high-carbohydrate diet can be independent of

changes in plasma insulin concentrations.

Straznicky NE(1), O'Callaghan CJ, Barrington VE, Louis WJ.

PMID: 10523330

 

2: Aronis KN, Khan SM, Mantzoros CS. Effects of trans fatty acids on glucose homeostasis: a meta-analysis of randomized, placebo-controlled clinical trials. Am J Clin Nutr. 2012 Nov;96(5):1093-9. doi: 10.3945/ajcn.112.040576. Epub 2012 Oct 10. Review. PubMed PMID: 23053553; PubMed Central PMCID: PMC3471197.

 

3: Lovejoy JC, Smith SR, Champagne CM, Most MM, Lefevre M, DeLany JP, Denkins YM, Rood JC, Veldhuis J, Bray GA. Effects of diets enriched in saturated (palmitic), monounsaturated (oleic), or trans (elaidic) fatty acids on insulin sensitivity and substrate oxidation in healthy adults. Diabetes Care. 2002 Aug;25(8):1283-8. PubMed PMID: 12145222.

 

4: Louheranta AM, Turpeinen AK, Vidgren HM, Schwab US, Uusitupa MI. A high-trans fatty acid diet and insulin sensitivity in young healthy women. Metabolism. 1999 Jul;48(7):870-5. PubMed PMID: 10421228.

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  • 2 weeks later...

Dean and Michael, thanks!

 

Most of [some studies showing changes in metabolic parameters with changes in macronutrient ratios] are available as free full-text articles, so you can dig in and see if you can come to any conclusions. If you do, please report back!

 

I most assuredly will. Preliminary report: nothing conclusive yet, but I've only begun digging into the material. I'm going to wait to dig in further partly because I decided to wait to try the low-fat diet experiment until closer to the time of my trip back to the US (mid-March or so), so I can test more than glucose and insulin (if I even could test insulin here, on my schedule).

 

Zeta

 

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