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By Dr. Maiko Ochi, N.D., L. Ac.
Sugar, or sucrose, is a disaccharide, meaning that it is made of two monosaccharides. When we eat sugar, it gets broken down into the monosaccharides glucose and fructose.
Glucose, also known as blood sugar, is used as fuel by our cells to create energy. When our blood glucose levels increase after eating sugar, our pancreas releases insulin, a hormone that tells our cells to absorb that glucose and lower blood sugar levels back to within a normal range. When we eat a high-sugar diet for an extended period of time, our insulin levels stay elevated and our cells become deaf to the hormone’s signals, resulting in a state called insulin resistance or pre-diabetes. Chronically elevated blood glucose and insulin develop into diabetes over time.
Fructose, the other monosaccharide that makes up sucrose, is also known as fruit sugar because it’s found in fruit. It’s also present in high-fructose corn syrup, fruit juice, and agave syrup (more on that later).
It used to be regarded as a healthy sweetener even for diabetics because it doesn’t raise blood glucose levels. However, the only organ in the body that can metabolize fructose is the liver. Normally, your liver converts some fructose to glucose to be used as energy by the rest of the body. Some of the fructose also gets stored as glycogen, which is a form of carbohydrate stored in our muscles. Any excess fructose that the liver can’t handle gets packaged as triglycerides, which is a form of fat. If you get your cholesterol levels checked and discover that your serum triglyceride levels are high, cut out fructose in all its forms.
Now, the liver can normally handle the amount of fructose in whole unprocessed foods such as fruit, because it is bound to fiber, which slows down its absorption into the bloodstream. However, when it is in the form of high-fructose corn syrup in processed food and drinks, or “healthy” alternatives like fruit juice, fruit juice concentrate, dried fruit, or agave syrup, it is a huge fructose overload. Your poor liver gets overwhelmed and has no choice but to convert it to fat. This is how kids these days are becoming obese, developing non-alcoholic fatty liver and even diabetes, because they are consuming packaged foods that have been sweetened with high-fructose corn syrup (or agave syrup or fruit juice if their moms shop at Whole Foods).
Not only does fructose make you fat, but the more you eat, the better your body gets at absorbing it and creating more fat! GLUT-5 is the transporter on your liver cells that helps them absorb fructose, and its expression on cell surfaces increases the more fructose you eat. However, the good news is that once you reduce fructose consumption, less GLUT-5 gets expressed on cell surfaces, meaning less fructose is absorbed and less fat is created.
If you’re looking to lose some fat, the quickest way is to stop eating fructose in all its forms. A note on agave syrup – it contains 70-90% fructose, which is even more than high-fructose corn syrup! Although it was initially thought of as a healthy alternative to sugar because it doesn’t raise blood sugar, now it’s known that that’s because it goes straight to your liver to get converted to fat. Also be wary of fruit juice (even, or especially, 100% fruit juice) or items sweetened with fruit juice or fruit juice concentrate – these are high in fructose and will be a huge load on your liver.
So what about fruit? Should you avoid it altogether? If you’re trying to lower your serum triglyceride levels or lose weight, you may want to avoid all fruit temporarily. Even though fruit has vitamins, minerals, and fiber, it still contains fructose, as well as glucose. Fructose absorption actually increases when there’s glucose around, so when you eat fruit, you absorb even more fructose than if you were just eating fructose alone.
However, not all fruit is equal. Some fruit contain more fructose than glucose, others have equal amounts, and the rest have more glucose than fructose. You’ll want to avoid the ones that are higher in fructose than glucose, such as apples, black currants, cherries, grapes, pears and watermelon.
If you don’t have any major health issues and just want to reduce fructose consumption to prevent any chronic health issues in the future such as cancer, hypertension, diabetes, gout, heart disease, liver disease, and obesity, avoid any foods or drinks containing high-fructose corn syrup, agave syrup, fructose, fruit juice, or fruit juice concentrate. You’ll also want to steer clear from dried fruit and fruit juice, or enjoy them on occasion. When you eat fruit, concentrate on ones that have relatively low fructose to glucose content, such as: acai berries, avocado, blueberries, cantaloupe, cranberries, grapefruit, guava, lemons, limes, nectarines, olives, oranges, peaches, persimmons, raspberries, starfruit, strawberries, and tomatoes. Fruit to limit would be apples, apricots, bananas, cherries, dates, fig, grapes, honeydew, kiwi, mango, papaya, pears, pineapple, plums, pomegranate, sun-dried tomatoes, tangerines, tomato juice/paste/sauce, V8 juice and watermelon.