We are often lead to believe that using sweeteners high in fructose is better than using ordinary table sugar (which consists of fructose and sucrose in equal proportions) as fructose has a low GI (glycaemic index) and does not affect our blood glucose levels nearly as much as table sugar. Low GI foods such as agave syrup, containing a high fructose content, have risen in popularity as a sweetener in favour of other, higher GI sweeteners.
The problem with fructose is that it cannot be metabolised by the cells in our bodies, as opposed to glucose which can be used as energy by our cells. Instead it can only be metabolised by the liver. The problem we run into with our modern diets is that we consume enormous amounts of fructose, particularly through the drinks on offer on the supermarket shelf in the form of “healthy” fruit juices, smoothies and soft drinks.
Our livers are designed to cope with small amounts of fructose and this is why eating fruit is not harmful to us. Fruit also contains a host of vitamins and minerals and fibre. By virtue of the fibre content, the fructose is released more slowly to the liver, not having such a heavy impact.
When we ingest more fructose than our liver can handle, the excess fructose turns into fat. A dire picture starts to be painted when we are seeing children diagnosed with non-alcoholic fatty liver disease, which is becoming increasingly prevalent in the United States where soft drinks are sweetened with high fructose corn syrup instead of table sugar. There is also emerging evidence that that a high fructose intake leads to insulin resistance and cardiovascular disease.
Reasons why you should limit consumption of fructose:
Only the liver can metabolise fructose and fructose cannot be used for energy by other cells in our body. Fructose therefore does not contribute positively to the body’s function (i.e. by creating cellular energy) and is toxic when the amounts are so high that the liver is unable to process it.
Excess fructose damages the liver resulting in insulin resistance and non-alcoholic fatty liver disease.
Fructose reacts with proteins and polyunsaturated fats in our bodies creating advanced glycation end-products, which create oxidative damage in our cells contributing to inflammation and chronic disease.
Fructose increases uric acid production, which can cause gout, kidney stones and precipitate or aggravate hypertension.
Our body’s cells can’t use fructose as a source of energy, but our gut microflora can, and excess fructose can create gut flora imbalances and promote overgrowth of pathogenic bacteria.
Chronic excess fructose causes dyslipidemia (elevation of the "bad" low-density lipoprotein (LDL) cholesterol and the triglyceride concentrations, and a decrease in the "good" high-density lipoprotein (HDL) cholesterol concentration) increasing your risk for heart disease.
Fructose can causes leptin resistance. Leptin is a hormone that controls appetite and serves as a regulator to ensure that you maintain a stable and normal weight. Leptin resistance is very common among overweight and obese people.