Fructose Sugar: A major driver of obesity, diabetes and hypertension, By Mukaila Kareem

Counting calories on nutrition fact labels pasted on packaged food may not be as helpful as we think. The overconsumption of fructose in sedentary life is the main threat to human health. Therefore, count the health costs when you routinely have a bottle of soda or fruit juice on your desk job, not calories!

Glucose and fructose sugars are respectively a combination of nutrients of life and survival. Whether in mama’s milk, tubers, or the tree trunk, glucose is found almost everywhere, and all parts of the human body can use it for energy (ATP) and growth. Contrary to common perception, glucose is not all that sweet and certainly not the reason why we are hooked on sugar. On the other hand, fructose is sweet and occurs seasonally in fruits and honey, where it links with glucose as sucrose. Fructose cannot be directly used for energy but true to form, as a nutrient of survival, sperm cells are the only known cells that directly use fructose to fuel their five-day life span, to avoid glucose competition with bacteria and other cells in order to survive in the female body for successful fertilisation.

Just as the words “art” and “rat” have the same alphabets but different arrangements, glucose and fructose have the same chemical formula (C₆H₁₂O₆) and equal calorific values. However, the body uses them differently, for the same reason that “art” and “rat” are not the same. In the fasting state or during prolonged strenuous exercises, fructose can be quickly converted into glucose to replenish glycogen stores and prevent “hitting the wall” in competitive sports. Perhaps because glucose is abundant in nature and available for immediate energy needs, its metabolism or usage is highly controlled and solely dependent on the amount of chemical energy (ATP) available in the body. Therefore, in the absence of hunger, excess glucose is converted into fructose through what is termed the sorbitol pathway. As in scrabble, based on the state of play, “art” and “rat” could be swapped on the scrabble board.

In preparation for winter, grizzly bears go into a yearly feeding frenzy, called hyperphagia, to pack as much fat on as possible, before hitting the winter dens for a three- to five-month period of hibernation. Contrary to the occasional headline grabbing stories of bear attack on humans, grizzly bears are not true carnivores. In late summer and fall, when they are in a state of hyperphagia, grizzly bears are not known for hunting rabbits or scavenging but have been documented while eating more than 200,000 buffalo berries in a single day. Also, before the advent of agriculture, when finding food was wildly unpredictable, our human ancestors took advantage of easily digestible ripe fruits to build up thier body fat at the end of the summer/rainy season, in anticipation of scarce food supply in winter or the dry season. By way of lived experience, those of us who grew up in the village know that farmers can store tubers for up to a year before the next harvest season but ripe fruits that are not eaten are destined to rot under the trees, which is a reason why you never expect to have fruit juice in any rural African setting.

The question is, given that fructose is now cheaply available, what has it got to do with obesity and chronic diseases? First, as a nutrient of survival against impending scarcity, fructose is extremely sweet and does not trigger insulin or leptin secretion and therefore can be consumed excessively, especially in refined foods, without a sense of fullness.

The question is, given that fructose is now cheaply available, what has it got to do with obesity and chronic diseases? First, as a nutrient of survival against impending scarcity, fructose is extremely sweet and does not trigger insulin or leptin secretion and therefore can be consumed excessively, especially in refined foods, without a sense of fullness. While all cells can process glucose, only the liver processes most of the fructose consumed. Following meals, we often talk of a glucose spike in the bloodstream but the fructose deluge on the liver is never mentioned. The extraction and uncontrolled trapping of fructose in the liver cells trigger alarm signals due to the sudden depletion of ATP, as the body goes into “safety mode” towards energy storage and water retention. The depletion of ATP results in the accumulation of uric acid, a metabolic product, which causes the constriction of blood vessels by blocking the enzyme that produces nitric oxide, a potent gas that relaxes and widens blood vessels to protect us against hypertension.

The rapid depletion of ATP with a “panic” consequence also triggers the brain to initiate whole body insulin resistance, which reduces glucose uptake by other organs and keeps the blood glucose available for the “selfish” brain, possibly leading to diabetes in the long run. In the abnormal state of excessive blood glucose, the kidney is not only able to convert glucose to fructose, but able to breakdown fructose exactly like liver cells do, also causing the formation of uric acid with the increased reabsorption of sodium and water, leading to a rise in blood pressure. Uric acid is also known to cause gout and high levels of uric acid in the kidneys, which may result in acute kidney injury, kidney stones and chronic kidney disease, a condition that often coexists with diabetes.

A renowned endocrinologist described fructose sugar as a “toxin” and because the body metabolises fructose in about the same way as alcohol, he also referred to it as “alcohol without the buzz”. Therefore, when fructose is chronically consumed in a sedentary state, it is obligatorily converted to fat, which reminds me of a 2013 article titled “F Stands for Fructose and Fat”.

More importantly, the unregulated breakdown of fructose results in a overwhelmingly high level of citrate production. This is exacerbated by uric acid action, which blocks the enzyme that converts citrate into iso-citrate and therefore diverts metabolism away from ATP formation to unfettered fat making in the liver. These fats are transported to fatty tissues and other organs as triglycerides, and the consumption of foods rich in fructose may therefore results in high triglycerides (hypertriglyceridemia) and obesity. By the way, triglycerides are transported by a carrier called VLDL, which is also made in the liver but converted to small dense LDL particles in the blood, the real “bad cholesterol” compared with large bouyant LDL that carries dietary fats from the small intestines. A renowned endocrinologist described fructose sugar as a “toxin” and because the body metabolises fructose in about the same way as alcohol, he also referred to it as “alcohol without the buzz”. Therefore, when fructose is chronically consumed in a sedentary state, it is obligatorily converted to fat, which reminds me of a 2013 article titled “F Stands for Fructose and Fat”.

Fructose occurs in fruits during the time of abundance in raining season and summer. Fortunately, nature sweetens it for voracious seasonal consumption to build fat and protect against starvation and dehydration in the dry season. In that context, fructose is not a toxin but overexposure to fructose in the modern time is the problem. With cheap man-made fructose, its availability is no longer seasonal, even though the human body continues to treat it as a storage nutrient for a time of scarcity that no longer exists for the most part. We should, therefore, endeavour to limit its consumption, be it in ketchup, fruit juice, soda drinks, barbecue sauce, buns, bread, desserts, cookies, salad dressings, pastries and all other refined foods.

Counting calories on nutrition fact labels pasted on packaged food may not be as helpful as we think. The overconsumption of fructose in sedentary life is the main threat to human health. Therefore, count the health costs when you routinely have a bottle of soda or fruit juice on your desk job, not calories!