Carbohydrates contain only around 4kcal per gramme.
There are two primary fuel sources your body needs – glucose and ketones (from the breakdown of fats). Your body can run pretty much completely on either, and this is something that been a part of our genome for millenia. However, you cannot quickly switch from one fuel to another, but this is explained in the Understanding Ketosis page.
Carbohydrates offer the body the most accessible energy in the form of glucose. From a metabolic point of view, carbohydrates are the most quickly and easily digested foods, and therefore have the most immediate effect on blood sugar and insulin levels. There are three primary sugars we encounter in natural foods, glucose, sucrose and fructose.
- Glucose – The most accessible sugar is glucose as this is the same thing as our own blood sugar. Glucose stimulates insulin release.
- Sucrose – Table sugar to you and me. This is the stuff we get from sugar beet, fruit and vegetables. Sucrose is digested via an enzyme, beta-fructosidase, which separates it into glucose and fructose. The glucose is taken up by the body, and stimulates insulin release. The fructose… well, read on.
- Fructose – Fructose has a very different metabolic pathway, and cannot be converted by our body to glucose. Although, like glucose, fructose is a 6-carbon sugar, it has a completely different metabolic pathway and ends up being broken down into 3-carbon fragments in the liver and then contributed to lipogenesis (the conversion of sugars to fat), and that is a one way street to your already overcrowded fat cells. I could (and probably will) write a whole article on Fructose, corn syrup (otherwise known as high fructose corn syrup) and its association with a whole host of metabolic problems, but suffice to say it’s best to avoid anything that contains it if you can.
How much sugar do I contain?
A healthy adult should have no more than around a couple of teaspoons of glucose in the bloodstream – about 40 Calories worth, or just 10g. Add to this that fact that the liver can only store between 1000 and 2000 calories as glycogen, which can be released if required on demand, and you can see that your total carbohydrate “fuel tank” is limited to around a day’s energy needs. Not much, is it?
The role of insulin
So, what happens when we eat a bowl of rise or a bag of chips. A tasty bag of chips weighing in at 100g of sugars has to be digested and metabolised quickly to avoid potentially lethal consequences. To keep your blood sugar under control at around 10g of glucose, the hormone insulin is produced in the pancreas and released into your bloodstream.
The insulin activates receptors in your muscle cells, and to some extent you liver, allowing them to absorb the excess glucose from the blood, and store it as glycogen inside of the cell membrane, where it can later be used (or released by the liver again to maintain your blood sugar level during exercise, for example).
Insulin also opens the gates to your adipose tissue (your fat) cells allowing them to soak up glucose and to store it as fat. Sadly for many of us, we are simply unable to store glucose efficiently as glycogen in our muscles because our cells become insulin resistant. This means that the glucose has no other place to go but to our fat cells – which we know is a one way street.
Insulin resistance, also known as metabolic syndrome, is believed by many to be the main reason for the burgeoning obesity epidemic sweeping the developed world. There are various theories as to the cause of insulin resistance, but we know one thing for certain – if you consume less carbohydrates, then you produce less insulin. This is of great importance to Type-2 diabetics, or people who have been diagnosed as pre-diabetic.
In most cases, a ketogenic diet leads to complete withdrawal of diabetic medication provided carb intake is carefully managed.