In the ongoing debate over whether it’s fat or carbohydrate restriction that leads to weight loss and health, here’s another study from the Oxford group examining the postprandial (after-eating) effects of a low-fat vs. low-carbohydrate diet. (Roberts R et al, 2008; full-text here.)
High-carbohydrate was defined as 15% protein; 10% fat; 75% carbohydrate (by calories), with starch:sugar 70:30.
High-fat was defined as 15% protein; 40% fat; 45% carbohydrate, with starch:sugar 70:30. (Yes, I know. By our standards, the “high-fat” diet was moderate-fat, moderate-carbohydrate–too high in carbohydrates.)
Blood was drawn over 6 hours following the test meal.
Roberts R et al. Am J Clin Nutr 2008
The upper left graph is the one of interest. Note that, after the high-carbohydrate diet (solid circles), triglyceride levels are twice that occurring after the high-fat diet (open circles). Triglycerides are a surrogate for chylomicron and VLDL postprandial lipoproteins; thus, after the high-carbohydrate diet, postprandial particles are present at much higher levels than after the high-fat diet. (It would have been interesting to have seen a true low-carbohydrate diet for comparison.) Also note that, not only are triglyceride levels higher after high-carbohydrate intake, but they remain sustained at the 6-hour mark, unlike the sharper decline after high-fat.
It’s counterintuitive: Postprandial lipoproteins, you’d think, would be plentiful after ingesting a large quantity of fat, since fat must be absorbed via chylomicrons into the bloodstream. But it’s carbohydrates (and obesity, a huge effect; more on that in future) that figure most prominently in determining the pattern and magnitude of postprandial triglycerides and lipoproteins. Much of this effect develops by way of de novo lipogenesis, the generation of new lipoproteins like VLDL after carbohydrate ingestion.
We also see this in our Track Your Plaque experience. Rather than formal postprandial meal-testing, we use intermediate-density lipoprotein (IDL) as our surrogate for postprandial measures. A low-carbohydrate diet reduces IDL dramatically, as do omega-3 fatty acids from fish oil.
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