Gretchen sent me the results of a little experiment she ran on herself. She measured blood glucose and triglycerides after 1) a low-fat diet and 2) a low-carb diet.
Gretchen describes her experience:
Several years ago I received a windfall of triglyceride strips that would expire in a week or so. I hated to waste them, so I decided to use them to test my triglyceride and BG responses to two different diets: low carb and low fat.
The first day I followed a low-fat diet. For breakfast I ate a lot of carbohydrate, including 1 oz of spaghetti cooked al dente and ¾ cup of white rice. For the rest of the day I ate less carbohydrate but continued to eat low fat.
The second day I followed a low-carb diet. For breakfast I ate a lot of fat, including a sausage, mushrooms fried in butter, 2 slices of bacon, and ¼ cup of the creamy topping of whole-milk yogurt. For the rest of the day I ate less fat, especially less saturated fat, but continued to eat low carb.
Both days I measured both BG and triglyceride levels every hour until I went to bed. On the low-carb day I had 3 meals. On the low-fat day, I was constantly hungry, had 4 meals, and kept snacking.
You can see the results in Figure 1. On the low-fat diet, after a “healthy” low-fat breakfast of low-glycemic pasta with low-fat sauce, my BG levels shot up to over 200 mg/dL and took more than 6 hours to come down. My triglycerides, however, remained low, and at first I thought perhaps the low-fat diet might be better overall. However, after about 6 hours, the triglyceride levels started to increase steadily, and by the next morning, they were higher than they had been the day before.
On the low-carb diet, my BG levels stayed low all day. However, after meals, the triglyceride levels skyrocketed. After meals they came down, and by the next morning they were lower than they had been the day before.
As I interpret these results, the high triglyceride levels after eating the high-fat meals represent chylomicrons, the lipoproteins that transport fat from your meals to the cells of your body. The high triglyceride levels the morning after eating the low-fat meals represent very low density lipoprotein, which takes the cholesterol your liver synthesizes when your intake of dietary cholesterol is low and distributes it to cells that need it, or again, to the fat for storage.
There are several interesting factors to consider here. First, when you have a lipid test done at the lab, it’s usually done fasting, which means first thing in the morning after not eating for 8 to 12 hours. It tells you nothing about what your triglyceride levels were all day.
Second, the low-carb diet resulted in lower fasting triglyceride levels, but much higher postprandial triglyceride levels. Which are more dangerous? I’m afraid I don’t know. You should also note that the high-fat, low-carb breakfast was extremely high in fat, including saturated fat. I don’t normally eat that much fat but wanted to test extremes.
Third, although the low-fat diet didn’t produce the very high postprandial triglyceride levels that the high-fat diet did, it produced extremely high BG levels that persisted for 6 hours. Some people think that it’s oxidized and glycated lipids that are the dangerous ones, so high BG levels and normal triglyceride levels might be more dangerous than very high triglyceride levels and normal BG levels. Note that high BG levels also contribute to oxidation rates.
Fourth, this shows the results of an experiment with a sample size of one. My physiology might not be typical. If you want to know how your own body’s lipids respond to different types of diets, you should get a lipid meter and test yourself. Unfortunately, your insurance is unlikely to want to pay for this, so it will be an expensive experiment.
The main point of this is that the results of different diets are complex. We have to eat. And what we eat can affect many different systems in our bodies. Finding the ideal diet that matches our own physiology and results in the best lipid levels as well as BG levels is a real challenge.
This was a lot of effort for one person. Thanks to Gretchen for sharing her interesting experience.
Gretchen makes a crucial point: Some of the effects of diet changes evolve over time, much as triglyceride levels changed substantially for her on the day following her experiment. Wouldn’t it be interesting to see how postprandial patterns develop over time if levels were observed sequentially, day after day?
The stark contrast in blood sugars is impressive–Low-carb clearly has the advantage here. Are there manipulations in diet composition in low-carb meals that we can make to blunt the early (3-6 hour) postprandial lipoprotein (triglyceride) peak? That’s a topic we will consider in future.
More of Gretchen’s thoughts can be found at:
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