What is it about Glucose that it elicits such strong opinions? Fear and loathing, love and kisses. Maybe cholesterol, but what other molecule brings out such passion? Is it a precious food or a poison? Let’s take a quick look at this fundamental molecule!
What is Glucose? Simply, it is a 6 carbon simple sugar. Alone it is called a “monosaccharide”, meaning “single sugar molecule.” There are lots of other monosaccharides with different numbers of carbon atoms: ribose and deoxyribose are 5 carbon sugars that form part of DNA and RNA. Galactose, Mannose, fructose, and Glucose have 6 carbons.
Where do we find Glucose? Glucose arrives in many of the foods we eat, but not so often as a free sugar. It tends to be linked to other sugars (for example, Sucrose or table sugar is Glucose linked to Fructose. This is two sugars, so is called a Disaccharide.)
Glucose polymers (several glucose molecules hooked together) exist in various forms in nature. Cellulose, the rigid structural component of plants, is a glucose polymer. Starch in potatoes is another, as is glycogen in our muscles and liver.
What does glucose do after we absorb it? Glucose, like any other food, can be burned as fuel, used as a structural component in glycoproteins, stored as glycogen, or converted to other molecules (most commonly fatty acids.)
What tissues NEED glucose? A persistent legend is that the brain requires glucose for all its energy. (PaleoMedicalSchool taught that to PaleoPathologist.) It is NOT true; after a short period of adaptation our brains do just fine on mostly ketone bodies. There may be some residual need for some glucose. Red Blood Cells seem to need glucose, and some parts of the kidney as well. That’s about it.
So, PaleoPathologist, why did you call it “sweet poison?” All molecules, even good ones, can go bad if there are too many of them. My blood volume is about 5 liters, so if my glucose level is 100 mg/dl (a bit high but still normal) then I have a total of only 5 grams of glucose in my bloodstream. If you add in extracellular fluid, maybe 15 grams of glucose circulating. If I have 30 grams instead, my blood level would be 200 mg/l which is way up in diabetic range. Just for perspective, one Snickers bar (PaleoPathologist LOVES Snickers bars but they don’t love him!) contains 27 gm of sugars. One potato has 63 grams. Our bodies have to put that sugar away and fast.
Why, Paleopathologist? Because high levels of glucose are toxic. When glucose levels go up a funny chemical reaction starts occurring and the glucose starts to bond to proteins in a nonspecific way. This causes the proteins to not work as well. We measure that in our lab by measuring Hemoglobin A1c, the percentage of hemoglobin that has hooked up with a glucose molecule. If glucose is hooking up with hemoglobin, it’s also hooking up with OTHER proteins forming AGE or advanced glycation end products. This may be one of the reasons people with diabetes get kidney disease (which PaleoPathologist sometimes has to diagnose in his lab.)
But doesn’t insulin just push the extra glucose into glycogen? What’s the big deal? PaleoPathologist has seen this argument on various message boards. The big deal is, we all are walking around with about as much glycogen as our bodies can possibly hold. The muscle and liver tank is totally full. There is no room at the Inn. (When was the last time most of us did any anaerobic exercise to burn glycogen?) The end result is the glucose becomes fat.
PaleoPathologist has a theory that we are really designed to have partially full glycogen tanks, not totally full/overflowing ones. He thinks that our muscles and liver should have some extra capacity to quickly take on some glucose excess as a safety valve, but we in modern times eat so much carbohydrate that the safety valve is useless.
So are you getting to insulin resistance? Yep. Eventually many of us push our glucose adaptation so hard that we get insulin resistant and blood sugars start to climb. Hemoglobin and other body proteins get glycated. We get sick, get heart disease, kidney disease, and go blind. It is not fun to watch and PaleoPathologist HATES to give that diagnosis to anybody.
What questions come to mind for you? Comment below and we’ll chat!