Diabetes Nutrition: Low Carbohydrate Diet, Cholesterol before Insulin Discovery
A few days ago I was browsing through an old physiology textbook, the one I used when I was in college, because I was curious to read what they said about diabetes way back then.
The book, Textbook of Medical Physiology, second edition, by Arthur Guyton, was copyright in 1956, more than 50 years ago. And I came across this statement:
"In the early days of treating diabetes it was the tendency to reduce the carbohydrates in the diet so that the insulin requirements would be minimized. This procedure kept the blood sugar level down to normal values and prevented the loss of glucose in the urine, but it did not prevent the abnormalities of fat metabolism. Actually, it exacerbated these. Consequently, there is a tendency at present to allow the patient a normal carbohydrate diet and then to give simultaneously large quantities of insulin to metabolize the carbohydrates. This depresses the rate of fat metabolism and also depresses the high level of blood cholesterol which occurs in diabetes as a result of abnormal fat metabolism."
Because most people today find that low-carbohydrate diets do not "exacerbate" high cholesterol levels, I was curious to see what more current editions of the book had to say. The 10th edition, copyright in 2000, says,
"In the early days of treating diabetes, the tendency was to severely reduce the carbohydrates in the diet so that the insulin requirements would be minimized. This procedure kept the blood glucose from increasing too high and attenuated the loss of glucose in the urine, but it did not prevent many of the abnormalities of lipid metabolism. Consequently, the current tendency is to allow the patient an almost normal carbohydrate diet and to give large enough quantities of insulin to metabolize the carbohydrates. This decreases the rate of fat metabolism and depresses the high level of blood cholesterol."
So in almost 50 years, the author has decided perhaps a low-carb diet doesn't exacerbate lipid abnormalities, but he and his coauthor still think a higher-carbohydrate diet (now "almost normal" instead of "normal") will have a better effect on cholesterol levels.
Why is this exactly the opposite from what Dr. Richard Bernstein writes? He's the doctor who has type 1 diabetes and as a teenager was put on a high-carb diet and had cholesterol levels in the stratosphere. It was only after he worked out a low-carb way of eating and got his blood glucose (BG) levels into normal ranges that his cholesterol levels came down.
Was there actually good evidence in 1956 that low-carb diets "exacerbated" lipid abnormalities? Or was this simply something that people assumed and wrote in textbooks as fact and then passed on to students?
Sometimes one finds interesting information in older texts. For example, this same 1956 book also says, "Most factors that are known to destroy the beta cells are especially likely to destroy these cells when an animal is on a high carbohydrate diet, for such a diet stimulates the beta cells."
This statement is absent from the 10th edition. Because they no longer think it's true? Or because they no longer think it's important and didn't have extra room? Or because high-carb diets are now recommended by so many people and they don't want to contradict that point of view? One doesn't know.
Sometimes older texts have interesting information that has been omitted from more modern books because knowledge has exploded so much and there's not room to include everything. Other times it's been omitted from newer books because they've learned it's not true. But it's very difficult to check the information we find in older books, because the journal articles presenting the evidence are not online. Many of us have become so accustomed to using Internet resources to find information that if it's not online, it seems as if it doesn't exist.
Sometimes we can find the titles and authors of older articles, but the text is not available. Some journals are slowly putting more and more of their archives online (I recently discovered that my undergraduate thesis, which was published, is now online), but many of them are not. So only someone with time and access to a good academic library is able to read the details about research performed decades ago.
Gary Taubes was able to spend almost 5 years researching questions like these and concluded that dietary fat was not the cause of heart disease, but most of his research did not focus on people with diabetes.
So without being able to read the journal articles that led Guyton to suggest in 1956 that low-carb diets elevated cholesterol levels, I can only guess why his conclusions were so different from those of Bernstein.
In the 1950s, BG meters were not available to patients (Bernstein got one in the 1960s only because his wife was a physician), and the only clue about BG levels was spilling glucose in the urine, a very crude measure of glucose levels in the blood. So patients in those days, despite low-carb diets, were most likely not maintaining truly normal BG levels, just levels that weren't superhigh.
Also, in those days, the common treatment was to use one or two shots a day of a combination insulin, 70:30, which can never give as good control as the multiple daily injections or insulin pumps that people use today. Their BG levels were mostly likely rollercoasting around all day, despite the restriction in carbohydrates in the diet.
Furthermore, to prevent low blood sugar, which can be fatal, patients were advised to be cautious and to keep their BG levels on the high side, rather than on the low. When you have type 1 diabetes, your BG levels will go high even on a low-carb diet when you don't inject enough insulin. In other words, back then, people with diabetes who followed low-carb diets did not have normal BG levels.
And a low-carb diet on a background of close-to-normal BG levels may improve lipid levels when the same diet with poor control may not.
Also, in the early days, researchers didn't distinguish between the beneficial HDL and the dangerous LDL, so a diet might increase the good cholesterol (HDL) and be criticized because the total cholesterol level went up.
The main reason I've cited these "ancient" writings, however, is not so much to say that they're not true as to note that many doctors practicing today have been taught that they are true. The Guyton book was considered the classic physiology text and was used in physiology courses at many top-notch medical schools, including Harvard.
Some people think that low-carb diets have only recently been discovered and that until recently doctors didn't realize that it's carbohydrate that makes BG levels go up. That's not true. It's been known for a long time that you get better BG control if you don't eat a lot of carbohydrate. At the turn of the 20th century, before insulin was discovered, that was the only treatment available that had any success at all, and then it only worked short term for people who were unable to produce any insulin of their own. In the long run, type 1 diabetes was always fatal.
But after the discovery of insulin, biochemists and physiologists told doctors that a low-carb diet would make the lipid abnormalities found in most people with diabetes worse, and the doctors went along with the then-current dogma and prescribed high-carb diets instead.
Today, with better tools to ensure that BG levels stay in good ranges and better tools to measure lipid levels, it's worth trying the older approach of carbohydrate restriction and learning what it can do for your BG levels, at the same time also keeping a close watch on lipid levels to make sure that the higher-fat diet doesn't cause problems in that area.
Most people find that their triglycerides go down a lot on a low-carb diet. Many find their LDL cholestrol levels also decrease, although this effect can vary, depending on a number of factors, including your age.
We have so many good tools today. Use them, and find out what works for you.