Thursday, May 08, 2008

Dietary Fat Raises Insulin Levels

My previous post showed how high-protein foods can raise post-meal insulin levels higher than high-complex-carbohydrate foods (Beef Raises Insulin More Than Oatmeal).

This post shows how higher-fat diets raise post-meal insulin (and glucose) levels higher than lower-fat, higher-carb diets.

I'm finding more and more evidence for the benefits of eating a lower-fat, lower-protein, higher-complex-carbohydrate diet. This is not what I expected ... having read the rational for, and experimented with, low-carb Atkins-like diets.

Here's the study:
Effects Of Isoenergetic High-Carbohydrate Compared With High-Fat Diets On Human Cholesterol Synthesis And Expression Of Key Regulatory Genes Of Cholesterol Metabolism, American Journal of Clinical Nutrition, 2001

It was a small randomized crossover study that compared:
  • High-fat diet (40% carbohydrate, 45% fat) (HF)
  • High-carb diet (55% carbohydrate, 30% fat) (HC)
And found:
"During the oral-glucose-tolerance test, both glucose and insulin rose to higher concentrations after the HF diet than after the HC diet, showing lower glucose tolerance and insulin sensitivity with the HF diet."
(Insulin sensitivity was improved in the HC diet because it took less insulin to clear more post-meal glucose.)

Click for larger.
Above: Plasma glucose and insulin concentrations during oral-glucose-tolerance tests performed after 3 weeks of the high-fat (•) and high-carbohydrate (о) diets. * Significantly different from the high-carbohydrate diet, P < 0.05.

Improvements in Blood Lipids

The researchers also found improvements in blood lipids with the high-carb diet - although I was just looking at insulin and glucose levels. High-carb diets will sometimes show increased triglycerides. This study did not. Researchers attributed that to greater use of complex carbs and limited simple sugars.

Lipid findings:
  • Concentrations of total cholesterol were significantly lower after the HC diet than after the HF diet.
  • Both the HDL and LDL fractions were significantly lower after the HC diet than after the HF diet. The ratio of LDL to HDL was unchanged.
  • Plasma triacylglycerol concentrations did not differ significantly between the HF and HC diets.
A curious finding of this study ...

There was, in fact, increased synthesis of cholesterol in the HC diet. That might not be surprising since eating more carbohydrate presents more of the raw material for cholesterol synthesis (acetyl CoA), as I discussed in previous posts. There was also an increase in the expression of the gene for the enzyme HMG-CoA reductase. This is the enzyme that statins inhibit. And yet, even though there was more of this enzyme, and more raw material for making cholesterol, and more cholesterol made - there was a decrease in plasma cholesterol. (Perk up, statin makers.) The authors attributed this to better clearance of cholesterol (via LDL receptor) from the blood of people eating the low-fat high-carb diet.

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