Sunday, July 5, 2009
Protein Intake and Blood Glucose Levels
Low-carbers know that when a person eats foods that contain carbohydrates, his blood glucose will rise. As the pancreas releases insulin in response, the blood glucose levels will gradually return to normal.
What happens when a person eats protein? Insulin is released in response to protein as well, enabling the amino acids to be removed from the blood and stored in the tissue. The cells don't know the insulin is there to remove amino acids from the blood, so they will take up glucose from the blood as well. To prevent hypoglycemia, the liver gradually releases glucose into the blood to replace the glucose that has been stored.
In the graph above, the white lines show us that when a normal person eats 50 grams of protein, the blood glucose remains the same out to five hours after the meal, even though a significant amount of insulin has been released. The person with type 2 diabetes is represented by the yellow lines. His blood glucose levels start out at a much higher level, but when he eats 50 grams of protein, his blood glucose levels also stay steady out to two hours and then actually begin to drop because a great deal of insulin has been released. These graphs are found at Metabolic response of people with type 2 diabetes to a high protein diet.
It is important to realize that the response to protein in both the diabetic and non-diabetic person are happening in people who are not low-carb-adapted. Low-carbohydrate-adapted people are able to make all the carbs they need through gluconeogenesis. Their brains and muscles have switched over to the use of ketones and fatty acids for fuel, and the 40 or so grams of glucose they need for glucose-requiring tissues are readily converted from glycogenic amino acids and the glycerol backbones of triglycerides. So, what happens when a person who eats very low carbs has a meal of protein? For a rather extreme example, look at the graph below.
Lex Rooker is a very dedicated and meticulous individual who posts at the Raw Paleo Forum. (In no way do I either support or condemn what Lex does regarding his diet, but his journal certainly makes fascinating reading.) For about two years, Lex ate a single daily meal in the afternoon, at the time marked by an asterisk on the graph. This meal contained 150 grams of protein and consisted of 68% fatand 32% protein. As you can see, his blood glucose remained rock-steady at about 106 mg/dl throughout the day. But a couple of hours before he ate, it would drop to 95 mg/dl. After he ate a meal consisting solely of meat and fat, his blood glucose would rise about 25 mg/dl, returning to baseline in about four hours. (The graph shows a rise of 15 mg/dl, but he refers to the amount of the rise several times, so this may be an error in the graph.)
At one point Lex decided to switch things up a bit. He kept his calories the same, but ate only 90 grams of protein per day, making the ratio 80% fat and 20% protein. His baseline blood glucose dropped into a range between 68 and 78. After his single daily meal of meat and fat, his blood glucose would rise about 15 mg/dl, though it would take longer than before to come down to baseline. It appears that decreasing the amount of protein intake also decreases the amount of glucose released into the blood of a low-carb-adapted person.
People who are not low-carb-adapted do not do much gluconeogenesis because they get plenty of glucose from their diet. People like Lex Rooker who eat no carbs at all, apparently do quit a bit of gluconeogenesis. Low-carbers fall somewhere in between those two points. This provokes a question to which I do not currently have an answer: What does a normal blood glucose curve look like in a low-carber? If he chooses to eat only meat and fat at a particular meal, does his blood glucose rise or does it stay steady? If he eats a few carbs with each meal, does it rise less, or does it rise more than it would without the carbs?
In other words, this time it's not a blog, it's a bleg. If anybody has data on what a normal (or abnormal) daily blood glucose curve looks like in a low-carber, would you please share that information in the comments? Thanks!
(If any of the graphs are too fuzzy to read, just click on them and you'll get a clearer version.)