I previously posted Gretchen's postprandial diet experiment, in which she consumed a low-fat diet for a day, followed by a low-carbohydrate diet for a day. Grethen monitored blood glucose and triglycerides with fingerstick checks. (Blood glucose can be checked on any widely available glucose monitor; triglycerides can be monitored with the Cardiochek device.)
Let's now discuss what happened.
On the low-carb, high-fat day, there was an initial surge in triglycerides to 250 mg/dl late morning, followed by a secondary peak several hours following dinner. Because fat is mostly triglycerides, Gretchen's high-fat (sausage, bacon, butter, whole-fat yogurt) breakfast provided a large quantity of triglycerides that needed to be absorbed. This generally occurs over approximately 6 hours, varying depending on body weight, how accustomed you are to fat, activity level during the day, the kind of fat in the meal. The high content of saturated fat in Gretchen's high-fat breakfast likely caused the somewhat slower drop in triglycerides over approximately 7 1/2 hours.
As Gretchen herself had noted, triglycerides the following day were lower, a typical low-carb response. Blood sugar throughout showed only minor variation, with only small postprandial increases.
Thus, Gretchen experienced what we'd expect with a low-carb, high-fat diet: an initial high surge in triglycerides, followed by a decline in fasting levels, while blood sugar shows a normal contour.
Now, the more confusing low-fat experience:
Blood glucose makes a striking peak at 200 mg/dl after the low-fat breakfast of pasta and rice, in contrast to the low-carb breakfast. Triglycerides behaved very differently from the low-carb experiment: While there was no initial postprandial surge, there was a late surge developing 6-24 hours later. The late surge continued into the next day, with fasting levels the following morning (210 mg/dl) exceeding the starting triglyceride level (60 mg/dl).
The one potentially confusing aspect of all this is Gretchen's late rise in triglycerides on the low-fat diet. This phenomenon is due to something called de novo lipogenesis , or the liver's conversion of carbohydrates to triglycerides that occurs when an excessive carbohydrate load comes through diet. Because the human body cannot store anything beyond a minor quantity of carbohydrates (as glucose and glycogen), carbohydrates are converted to fats.
Another factor causing the late triglyceride increase is insulin resistance, given the high blood sugar response. When insulin resistance is present, the activity of the enzyme, lipoprotein lipase, is reduced. Less lipoprotein lipase activity allows slower VLDL degradation, allowing VLDL (and thereby triglycerides contained in VLDL) to "stack up" in the blood. Thus, the higher triglycerides late after eating and into the next morning.
One issue to be aware of: Acute responses can differ from chronic responses. In other words, had Gretchen had the luxury (and time and money) to conduct the experiment over, say, 4 weeks, rather than a single day, there would be somewhat different responses. The best data on this come from Dr. Jeff Volek of the University of Connecticut, in which 4 weeks of low-carbohydrate eating modify fasting and postprandial responses over time.
Several conclusions can be made from Gretchen's experience:
1) Low-carb, high-fat acutely generates extravagant postprandial triglyceride responses.
2) Low-fat causes a late triglyceride surge and higher fasting triglycerides.
3) Low-fat leads to high blood sugars and, by implication, diabetes.
Both the low-carb and the low-fat responses are undesirable, both leading to increased risk for heart disease. Which is worse ? I believe that low-fat is more destructive, since it leads over time to both high triglycerides and diabetes, while low-carb/high-fat only leads to postprandial triglyceride surges, at least acutely.
How to best balance the responses to reduce risk for heart disease? That's a discussion for future.
Again, my thanks to Gretchen and the substantial amount of effort that went into generating these numbers. More of Gretchens' own writing can be found on her blogs:
http://wildlyfluctuating.blogspot.com
http://www.healthcentral.com/diabetes/c/5068