The Not So Sweet Side of Fructose
Fructose is a monosaccharide found in fruits, some vegetables, honey, table sugar (in form of sucrose, which is a combination of fructose and another monosaccharide glucose), and wheat (in the form of long chains known as fructans). Before agriculture began in 10,000 BC and even after, people depended on hunting and gathering for their food. To get through periods of a limited amount or lack of food, our bodies relied on glucose and fructose to store energy. Glucose is used by all our cells as their main source of energy and, if not used, is stored as glycogen, a chain or polysaccharide of glucose molecules in the liver and muscles. Any remaining glucose is stored as triglycerides (lipids) in adipose (fat) cells to be used as energy if needed. The energy stored as glycogen is readily available, which is why runners carbo-load on pasta before a marathon. Lipids were also very helpful to our ancestors when food was scarce because lipids additionally store energy and it can insulate our bodies keeping us warm during the long cold winter months. Fructose also provides energy, but to a lesser extent and is predominately used by liver cells. It additionally aids in the formation of glycogen and produces lipids via the process lipogenesis.
However, that was then and this is now. What once was a smart and strategic way for us to survive has become our Achilles heal with the easy access to food and the development of processed food. There is no question that the high amounts of sugar we are ingesting is affecting our heath and too much sugar overall, regardless of the type of sugar, can lead to obesity and diabetes. However, because of the food industry, we are ingesting a large amount of fructose, for example as crystalline fructose, which is 100% fructose found in “healthy” beverages, baked goods, and cereals and the high fructose corn syrup in sodas which is 55% fructose and 45% glucose. This excess of fructose can be especially harmful because (a) its role in lipogenesis can result in more lipids in the liver which can cause non-alcoholic fatty liver disease which untreated can lead to inflammation, scarring, and permanent liver damage. It can also increase visceral fat around organs, triglycerides, arterial plaques, and insulin resistance; (b) the way fructose is digested may result in digestive issues leading to gas, bloating, diarrhea, abdominal pain, and cramps; and (c) high fructose corn syrup does not signal insulin or leptin like table sugar does, so your body does not register that is full and you keep on eating.
The fructose found in fruits and vegetables is a necessary part of a healthy diet and should be eaten. But that is not all of the fructose we are eating. Far from it. On average, we are eating 49 g of fructose per day, but only 8 of those grams are coming from natural foods, like fruit. The other 41 grams are coming from processed foods. For example, sodas are made with the version of high fructose corn syrup with 55% fructose. A report in 2012 stated that almost half of Americans drink soda every day. One soda equals 10-12 teaspoons of sugar and according to the American Heart Association, men should have no more than 9 teaspoons a day and women no more than 6. Just for a visual, next time you are baking something, measure out 10-12 teaspoons of sugar in a bowl and see how high that pile is.
The rise of digestive issues we are seeing today can also be attributed to the increase of fructose in our diets. Glucose diffuses through the wall of the small intestine into the bloodstream where it is used as energy or stored for future use. If there are equal amounts or less fructose than glucose in food being digested, fructose will easily diffuse along with the glucose into the bloodstream. However, if fructose is by itself or there is an excess of fructose to glucose, as in the case of the high fructose corn syrup found in soda, then the fructose needs to be transported by specific proteins present in the wall of the small intestine. However, there is a limit to how much fructose these transporters can allow through the small intestine. What does not get absorbed will move along to the large intestine where bacteria sits and wait to feast on their favorite food, saccharides. As the bacteria feeds off the fructose, fermentation occurs, which leads to gas and bloating. More water will also be brought into the large intestine leading to diarrhea and the methane gas produced can cause cramping and slow the motility of the large intestine, which can lead to constipation. As someone with fructose malabsorption, this is a painful and uncomfortable situation that without being treated can lead to secondary symptoms, including fatigue, brain fog, joint pain, and headaches.
Overall, we should be eating our fruits and vegetables to stay healthy. Fructose in small amounts, especially along with the fiber present in the fruit, has a role in obtaining energy, storing glycogen, and forming triglycerides, which is needed by our body. However, the problem stems from the amount that we are eating and the source of the fructose. No one has ever said “You can never have too much fructose”.
Photo taken by Ashley Kirk on Unsplash