As you probably know, glucose is the main sugar found in our blood. It is used by every cell in our body for energy. Glucose can be stored in our body, mainly as glycogen in the liver where it can be turned back to glucose if more energy is needed, via the gluconeogenesis process.
Fructose is found naturally in fruit. Only liver can metabolise fructose as it does not circulate in the blood and most tissues such as brain or muscles cannot use fructose directly. Table sugar, sucrose contains 50% glucose and 50% fructose and some manufactured sugar syrups such as high-fructose corn syrup around 55% fructose and 45% glucose.
Starches, the main carbohydrate in potatoes, wheat, corn and rice are glucose. When eaten, this glucose is rapidly broken down and absorbed into the cells. The glycemic index measures the blood glucose raising ability of different carbohydrates. Pure glucose causes the blood sugar (blood glucose level) to rise the most, so these foods have a high GI value. Bread (white flour) also has a very high GI value since refined starch from wheat is very quickly absorbed. Fructose and lactose (in milk) do not raise blood glucose levels so much and have lower GI values. Sucrose is half glucose and half fructose, so it has an intermediate GI value because only the glucose portion of sucrose raises blood glucose.
Fructose does not raise blood glucose or insulin, so it was considered healthier option previously. However, this is not the case because fructose being metabolised only in liver, causing an accumulation of fat in the liver, fatty liver. Fructose is therefore much worse than glucose. It causes fatty liver and that way insulin resistance.
Eating a bowl of rice is therefore not the same as eating a bowl of sugar. Rice contains no fructose. Of course if you are eating rice or other starchy foods, you will gain weight. But fructose is even more fattening because of it’s effects on liver so avoiding sugar is the most important thing when losing weight and staying healthy.
The metabolism if glucose and fructose are very different. Almost all cells are able to use glucose for energy, but no cell has the ability to use fructose, only liver. This places the liver under a lot of pressure as it is exposed to far higher levels of carbohydrates, both fructose and glucose that any other organ and so fructose is much more likely to cause fatty liver, the key problem of insulin resistance, compared to glucose. This explains why some people can tolerate quite high amounts of carbohydrates in their diet without developing insulin resistance, even when they are obese.
When you ear fructose, the excess is changed directly into liver fat which leads to a development of insulin resistance. You don’t necessarily have higher than normal blood glucose level, or blood insulin level when suffering from fatty liver and insulin resistance.
Fructose is of course a natural sugar found in fruit and berries. Our bodies can handle small amounts of fructose naturally, so the problem clearly is not consuming too much berries. What our bodies cannot handle, is the excess amount of fructose eaten today in the form of sugar. It is everywhere, from pre-prepared meals to breakfast cereals to sauces. You cannot find any processed food without sugar, not even sausages.
Glucose is a refined carbohydrate that directly stimulates insulin. Even when much of it can be burned for energy throughout your body, still high consumption of glucose may also lead to fatty liver. The effects of glucose are immediately obvious in the blood glucose and insulin responses.
The metabolism of alcohol in your liver is similar to that of fructose which is why excess alcohol combustion is known to cause fatty liver and also a risk factor for metabolic syndrome.
More on fatty liver later…