I’ve written many times about added sugar, but what about consuming fruits, and the fructose that they contain? Are fruits considered to be added sugar? The good news is that they are not — except for smoothies and processed fruit juice. But let’s look at what exactly fructose is.
Fructose is a carbohydrate, or simple sugar, that’s found in fruits and honey and gives them their sweet and delicious taste. In whole fruits it serves as a marker for foods that are nutritionally rich. It plays an important role in lipogenesis — which means that it may increase weight gain, even with the small impact of fructose on insulin compared with glucose. About 50 percent of a fructose load is converted into glucose (sugar), 25 percent into lactate, and around 15 percent into glycogen (stored sugar).
Whole fruit contains soluble and insoluble fibers. These two fibers together prevent the majority of the fruit’s sugar from being absorbed early on during the digestive process, which limits the rate of sugar absorption in the liver.
The biggest source of fructose is actually sucrose, or table sugar, which is a man-made product that’s derived from sugar cane and sugar beets. Sucrose is a disaccharide that is comprised of fructose and glucose. After consuming sucrose, it is degraded in the gut by sucrase, releasing fructose and glucose that are then absorbed.
The other major source of fructose is high fructose corn syrup (HFCS), which consists of fructose and glucose mixed in a variety of concentrations, but most commonly as 55 percent fructose and 45 percent glucose.
In the United States, HFCS and sucrose are the major sources of fructose in the diet, and HFCS is a major ingredient in soft drinks, pastries, and processed foods, which have a very low (or zero) nutritional value.
Despite the similarity in their chemical structures, fructose and glucose are metabolized in completely different ways and utilize different GLUT transporters. Most cells have only low amounts of the glut-5 transporter, which transports fructose into cells. Fructose cannot enter most cells, because they lack glut-5, whereas glucose is transported into cells by glut-4, an insulin-dependent transport system. Once inside the liver cell, fructose can enter the pathways that provide glycerol, the backbone for triacylglycerol.
Also, fructose is absorbed from the gastrointestinal (GI) tract by a different mechanism than that for glucose. Glucose stimulates insulin release from the pancreas, but fructose does not. High fructose consumption can induce insulin resistance and other types of metabolic syndrome. And some people can not absorb the natural fructose sugar in fruits, which is the common symptom of irritable bowel syndrome (IBS).
Low fructose fruit means there’s a more even ratio of glucose to fructose. High in fructose means that there is much higher ratio of fructose to glucose. Fruits with more than 4 grams per serving of fructose are considered high in fructose.
Examples of higher fructose fruits include dried fruits, mangos, grapes, watermelon, cherries, and bananas. Lower fructose fruits include tomatoes, avocados, lemons and limes, melons, raspberries, blackberries, strawberries, clementines, kiwis, and grapefruit.
Here’s a few suggestions to help you lower the fructose in your diet.
w Try berries instead of banana, try kiwi instead of mango.
w Use only half a banana in a smoothie.
w Measure your portions, especially grapes and watermelon — it’s so so easy to consume too much of them.
w Eat some nut butter or nuts, together with your fruits, to slow down the sugar release from the fruit. You can also add some other types of protein too, together with your fruit, such as full fat yogurt.
Lowering your carbohydrate consumption is the best strategy for avoiding or reversing obesity, diabetes, and metabolic syndrome. So make sure you watch how much carbohydrates you consume each day. If you keep a log or journal of your food, recording everything that you eat — even just for a single day — you will be surprised, probably even shocked, at how much you are eating without even realizing it!
Ayda Ersoy is a nutrition and fitness director at The Diet Doc Hawaii. She can be reached at DietDocHawaii.com, Ayda@DietDocHawaii.com or (808) 276-6892