General Introduction
Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847. The name “fructose” was coined in 1857 by the English chemist William Allen Miller.
Fructose is widely distributed in nature in fruits, beet root and honey. It is sweeter than glucose. We all know that consumption of fruits is beneficial for health. In earlier times, fruits were available during specific seasons only and in limited amounts. Now, thanks to increased production of fruits and technologies to preserve them, fruits or fructose is available throughout in abundance. If one has purchasing power, one can enjoy fruits through out the year. Industry has also come into play. Now fruit juices and fruit juices concentrates are commercially available at cheaper rates. Refined form of fructose are High Fructose Corn Syrup (55% fructose and 45% glucose), table sugar or sucrose (50% glucose and 50% fructose). The consumption of processed fructose in form of table sugar and High Fructose Corn Syrup (HFCS) has gone up tremendously. All of the these new changes has put an enormous challenge to the body.
Effects of Fructose on Body
Fructose is 100% metabolized in the liver, unlike glucose, which is 80% metabolized in peripheral cells and only 20% goes to liver. In this regard it is akin to alcohol, as alcohol is also 100% metabolized in liver. In the liver, fructose is usually either converted to glucose or fat directly by the liver. Excessive consumption of fructose has been shown to cause insulin resistance (IR) in liver, lipid abnormalities (hyperlipidemias) and NAFLD (non alcoholic fatty liver disease). It is seven times faster than glucose to cause glycation reaction or Maillard Reaction. One of the breakdown product of fructose, Methyl glyoxal, drives Milliard Reaction 250 times faster than glucose. Methyl glyoxal generates hundred times more oxygen radicals, that are responsible for tissue damage. Generally antioxidants takes care of oxygen radicals, but excessive consumption of fructose will overshoot the capacity of the liver to clear the load. Uric Acid is one of the side product of fructose metabolism. In gout people start restricting protein to reduce Uric Acid levels, whereas sugar (fructose) is the culprit. Fructose contributes to high blood pressure. It causes breakdown of intestinal barrier resulting in leaky gut. Leaky gut increases the exposure of body to inflammation and ROS (reactive oxygen species). Fructose as a sugar is highly addictive. It stimulates reward centers in brain giving a feeling of pleasure, that is why we always crave for sweet taste. It also blunts the ‘stop eating’ signals by the brain in response to satiety signals (generated by leptin and insulin hormones after meals). So thanks to fructose, even if we are full, we don’t mind eating an extra sweet or cake or ice cream.
How much Fructose is safe to consume
Safe limit of fructose consumption from all sources is up to 50 gm per day.
Should Fruits be Consumed or Not?
The adverse effects of fructose has been well publicized. It because of this publicity, few doctors advise people to refrain from fruits (must watch Fruits are evil by by Dr Boz, https://www.youtube.com/watch?v=A_m3UibHqGE), which is not correct. When fruits are taken in natural form with minimal processing, the absorbed sugar is released slowly due to the fiber in the fruits. Also, it is not possible to eat large number of fruits at one go. Fruit juices are problematic. To make a glass of an orange juice, we require four to six oranges. Normally we will not eat six oranges at one time. Each orange is around 140 gm with 12 gm of sugar. If we take juice of six oranges, then we have consumed 72 gm of sugar (much above the recommended safe level). During juice preparation, the fiber is lost. This 72 gm of fructose in this orange juice (well above the recommended safe dose of 50 gm per day)) will be absorbed quickly, creating a tsunami of fructose in liver, and liver will have to work on emergency mode to metabolize it. Each time you take a fruit juice, think about the torture faced by the liver. The commercial fruit juices are worst. In addition to fruit juice, it contains high amount of other sugars to act as preservative or taste enhancer. It increases the fructose load in the liver many folds. Apple and pear juices are of particular interest to pediatricians because the high concentrations of free fructose in these juices can cause diarrhea in children. The cells (enterocytes) that line children’s small intestines have less affinity for fructose absorption than for glucose and sucrose. Unabsorbed fructose draws water into the gastrointestinal tract, resulting in osmotic diarrhea. Fructose has a low glycemic index of 23. Due to low glycemic index, diabetics are allowed to use fructose as sweetener by some doctors which I feel is inappropriate, as fructose consumption will aggravate IR and deteriorate diabetics. But diabetics can take fruits in small amounts specially low fructose fruits (apples, oranges, etc).
In this post, effects of fructose have been discussed. Within the recommended level of consumption, it is safe and may be beneficial (Good) but excessive consumption may lead to number of metabolic arrangements (bad), and consumption of high doses of fructose in long term damages the liver akin to alcohol (ugly). Fruits juices including commercial fruit juices, and sugar sweetened beverages must be avoided.
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