Having been diagnosed with type 1 diabetes in 1992, I spent a lot of time in and out of doctors visits. Now, at the age of 25 my childhood endocrinology visits at Children’s Hospital San Diego all seem to run together in a giant blur of carbohydrate counting games and insulin doses.
As I recall, I saw a number of physicians and a rotating cast of dietitians and diabetes educators from the age of two to the age of thirteen. I remember very clearly the utterly blank stare of one dietitian as I asked why a serving of pasta containing 40 g of carbohydrates caused a spike in blood sugar two hours after ingestion, but a serving of other starches with the same amount of carbohydrates ,such as sushi rice, hit immediately. She told me that I must be imagining it. I, as a twenty-five year old studying nutritional biochemistry, already have some guesses as to the answer, but I can understand why this question could stump many RDs, CDEs, and physicians.
Nutrition for diabetes has been simplified to the very basics, carbohydrate counting. I understand that it makes sense in theory to simplify food down to only its carbohydrate content when dosing insulin, as carbohydrates are the macronutrient that has the greatest effect on blood glucose. In fact, carbohydrate counting is the first thing taught to those diagnosed with type 1 diabetes. I can understand why it is a good place to start, but carbohydrate counting does not account for everything, and that’s where education is often lacking. There are too many other factors that affect metabolism and therefore affect your blood glucose.
Glycemic index is a scale that measures starch digestibility. Many of the carbohydrates we commonly consume are composed of different starches of the amylose family. In order for starch to enter the blood stream and be used for energy, it must first be converted to glucose. The scale measures how a carbohydrate containing food raises blood glucose in comparison to a reference food (often glucose or white bread).
This is where that dietitian went wrong with her six year old patient. As not all calories are created equal, so are starches created unequal. There is an explanation to my body’s reaction to pasta and it boils down to basic chemistry. Pasta that is al dente has a lower glycemic index than pasta that is cooked until it is soft. Most of us know from high school chemistry or just playing in the kitchen that heat can change the chemistry of something, and so it would make sense that heat changes the structure of the starches in pasta rendering the grain softer and easier to digest. I have no idea if I was eating my pasta al dente as a six year old; however, rather than dismissing my question as irrational, there are a number of questions I could have asked my six year old self if I was that dietitian.
Glycemic index can change the way a certain food is digested and therefore change the effect it has on blood glucose. This means that something that has the same number of carbohydrates can affect your blood sugar in different ways, say causing a more gradual rise rather than an immediate spike. Simply counting the grams of carbohydrates in a food therefore proves a less than perfect method when considering glycemic index.
Fat also has an unexpected effect on blood glucose levels. Fat slows glucose uptake, meaning it slows down the digestion/absorption of carbohydrates as it delays gastric emptying. High triglyceride levels in the blood stream can also cause insulin resistance, often causing the liver to secrete more glucose. This means that when you eat something high in fat, say french fries, you most likely won’t immediately see a rise in blood sugar. Instead, you may see a spike in blood sugar over 2-4 hours, a rather different response than if you had simply eaten a plain baked potato with no added fat. Carbohydrates tend to cause an immediate rise in blood glucose, generally an hour, while fat will delay that rise, and sometimes even make it harder to treat (insulin resistance)
People also often forget to consider the basic structure of a fat. A triglyceride is made up of a glycerol backbone and three fatty acids. A little biochemistry will tell you that glycerol is a major substrate in gluconeogenesis, which is the biosynthesis of new glucose. This means that fat itself can actually affect blood glucose, a fact that is often forgotten. My endocrinologist actually pointed this out in a group session the other day. Just because the carbohydrates in a stick of butter are negligible, it doesn’t mean that butter will not have any effect on blood sugar.
As diabetics, we need to stop ignoring the fat in our diets, because it does play a role. Fat may not raise blood glucose to the extent that carbohydrates do, but its effect is not always negligible. The fat in ones diet should always be considered when calculating insulin ratios.
” As diabetics, we need to stop ignoring the fat in our diets, because it does play a role in blood sugar control.”
Does carbohydrate counting have a place in diabetes treatment?
Certainly! I think that it is useful for someone who has little or no background in nutrition. It can give you a sense of the number of carbohydrates in the foods you are eating and help gage how much insulin you require. I think that it can be a great starting point for those who are recently diagnosed, but I think that it should not be the primary form of nutrition education given during diagnosis. It is important to note that counting carbohydrates is not an exact science and that other factors should not be ignored when striving for better treatment and control.
I personally never count carbohydrates. Having lived with diabetes for almost 24 years, I can pretty accurately gage how the fat, protein, fiber, and carbohydrates and my meals will affect my sugar levels. I of course make mistakes all the time, but am fortunate to have a Dexcom CGM to warn me when I’ve over or under calculated my insulin doses. There is still so much to learn when it comes to nutrition and diabetes, so the best advice is to take it one bite of pasta and one bolus at a time.