Fructose is one of the most extensively studied sweeteners, but there are still a lot of misconceptions about it. This article will clear up most of the myths and clarify how it works as a sweetener, what foods contain it and some surprising health benefits of consuming high amounts of it daily.

Fructose is a naturally occurring substance that is present in all fruit. In recent years, fructose has been criticized for its role in causing metabolic diseases such as obesity and diabetes. However, studies have shown that the consumption of fruits and fructose itself are not the primary drivers of these diseases. In fact, a diet high in fruit and fructose has been shown to be a healthy and optimal diet.

What is fructose?

Fructose is a monosaccharide, the simplest form of carbohydrate. As the name suggests, a mono(on)saccharide (sugar) contains only one sugar group, so it cannot be broken down further.

Each carbohydrate subtype has a different effect on the body depending on its structure and source (i.e. the food it comes from). Chemical structure affects the speed and/or ease with which a carbohydrate molecule is digested/absorbed. The source influences the presence of other nutrients among the carbohydrates.

For example, high fructose corn syrup (HFCS) and fruit both contain fructose, but their effect on the body is different. HFCS is essentially a simple delivery system for fructose – it contains nothing else, whereas fruit contains additional nutrients and fiber that affect the digestion and absorption of fructose. Moreover, the amount of fructose in an average apple is much lower than that in, say, an average can of lemonade.

Fructose has a unique texture, sweetness, digestion speed and absorption rate that differs from glucose, the sugar into which most of the carbohydrates we eat are converted when they enter the bloodstream.

  • Fructose is absorbed in the gut through different mechanisms than glucose.
  • Fructose is absorbed more slowly
  • Unlike glucose, fructose does not stimulate a significant release of insulin.
  • Fructose is transported into cells by a different transporter than glucose.
  • Once fructose enters the liver, it can deliver glycerol, the basis of fat, and increase fat formation
  • Some people cannot fully absorb fructose when given in large doses – about 50 grams (note: this is an extremely large amount of fructose. We’re talking about 4-5 medium-sized apples. At the same time, 16 ounces of fruit juice with HFCS can contain about 45 grams of fructose).
  • The simultaneous consumption of glucose and fructose accelerates the absorption of fructose. This is one reason why many sports drinks contain a sugar mixture.

Why is fructose important?

500 years ago, before the mass production of sugar, our diet contained a minimal amount of fructose. Fructose was only offered as part of a complete diet.  Whole fruits, vegetables, grains, nuts/seeds and proteins contain a limited amount of fructose and can be consumed in moderation. As the food industry has processed fructose from sources such as corn and added it to various processed foods, fructose consumption has increased.

Fructose consumption increased significantly between 1970 and 2000. Although most people associate fructose with fruit, most of our daily fructose now comes from sources other than fruit.  A study in the 1990s found that the average person consumes about 80 grams of added sugars per day (equivalent to about 320 calories or 15% of energy intake); fructose makes up about half of this amount.

Fructose comes not only from HFCS, but also from sucrose (native sugar).  Sucrose is a disaccharide (double sugar) consisting of glucose + fructose.  HFCS and sucrose are found in processed foods, including candy, soft drinks and almost all edible food-like substances in a bag or box.

All About Fructose |

What you should know

Our liver is the main site of fructose metabolism.  In the liver, fructose can be converted into glucose derivatives and stored as liver glycogen.  The liver can only use and store a limited amount of fructose at a time as glycogen. The rest is deposited as fat, so a very high dose of fructose in one serving is more likely to find its way to the middle of your figure.  This phenomenon is more pronounced in people with high blood fat levels, insulin resistance or type 2 diabetes.

High consumption of fructose (as opposed to other carbohydrates in the diet) may not stimulate normal leptin production.  Leptin is a hormone involved in the long-term regulation of energy balance.  It increases when we get enough calories/energy and decreases when we don’t get enough to signal that it’s time to stop or start eating. The reduction in leptin production with chronic fructose consumption may have an adverse effect on the regulation of food intake and body fat.  In other words, when you consume HFCS, your brain never gives you the signal that I’m full, so you keep eating even though you have enough calories.

Since fructose is retained in the liver, it causes a low glycemic response.  While this is a positive feature of whole fruit consumption, it does not justify the use of fructose sweeteners.  Although fructose has a low glycemic index and can help replenish glycogen stores in the liver in physically active people, excessive consumption of fructose can lead to fat regeneration in the liver and short-circuit our energy balance and fat regulation systems. Consumption of large amounts of fructose sweeteners can therefore lead to central obesity (weight gain around the waist), low good cholesterol, high bad cholesterol, high triglycerides and poor appetite control.

Clinical evidence shows that people who eat lots of fruits (and vegetables) get slimmer, stay slimmer, and are healthier than those who don’t.

For additional credit

Are you worried about fruit? Just relax. The experts concluded: Consumption of naturally occurring fructose from unprocessed whole foods is low and unlikely to contribute to adverse metabolic effects.

Eating more fruits (and vegetables) can help prevent chronic diseases, including cancer.  See here.

Dr. Viok, author of a study that tracked adult fruit consumption for 10 years, believes that one need not worry about fat gain from overconsumption of whole fruit: There are no studies indicating significant long-term weight gain from excessive consumption of whole fruits.

If health and optimal body composition are important to you, eat that orange, but think twice before grabbing a bottle of orange juice (or worse, a can of orange juice).

All About Fructose |

Summary and recommendations

When it comes to fructose, the source is important. Eating whole, unprocessed fresh fruit is unlikely to contribute to an energy imbalance and increase in body fat. However, it is likely that regular consumption of fruit juices high in fructose, sweeteners and high-energy foods is the cause of these problems. Our bodies have a long and lasting relationship with fruit, which is not the case with fructose and fructose sweeteners.

Eating whole fruit provides a large amount of nutrients and helps control energy intake.  It takes more than 2 kg of most fresh fruit to provide 2,000 calories.  People don’t normally eat more than ~5 pounds a day.

Avoid buying foods/drinks that contain sweeteners with fructose.

Ask yourself: is my overconsumption of whole fruits leading to nutritional problems such as the development of chronic diseases and an increase in body fat?

References

Click here to see the sources of information referenced in this article.

American Institute for Cancer Research.  Called: 9/17/08

Berg CM, et al.  Dietary patterns and risk factors for cardiovascular disease: the Swedish research program INTERGENE.  Am J Clin Nutr 2008;88:289-297.

Bes-Rastrollo M, et al.  A prospective study of dietary energy density and weight gain in women. Am J Clin Nutr 2008;88:769-777.

Bray GA. Is fructose bad? Am J Clin Nutr 2007;86:895-896.

Elliott SS, et al. Fructose, weight gain and insulin resistance syndrome. Am J Clin Nutr 2002; 76: 911-922.

Ello-Martin JA, et al.  Nutritional energy density in the treatment of obesity: a one-year study comparing two slimming diets.  Am J Clin Nutr 2007;85:1465-1477.

Groff JL & Gropper SS. Advanced nutrition and human metabolism. 3. Traffic. Wadsworth Thomson Learning. 2000.

Havel PJ. Fructose in the diet : Implications for disruption of energy metabolism and fat and carbohydrate metabolism. Nutr Rev 2005;63:133-57.

Hung HC, et al.  Fruit and vegetable consumption and the risk of major chronic diseases.  J Natl Cancer Inst.
2004;96:1577-1584.

Liu S, et al.  Fruit and vegetable consumption and the risk of cardiovascular disease: a women’s health study.  Am J Clin Nutr 2000;72:922-928.

Savage JS, Marini M, Birch LL.  The energy density of the diet predicts women’s weight change over 6 years.  Am J Clin Nutr 2008;88:677-684.

Vioque J, et al.  Fruit and vegetable consumption in relation to weight gain over 10 years in Spanish adults.  Obesity (Silver Spring) 2008;16:664-670.

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Frequently Asked Questions

Why is fructose bad for you?

Fructose is a sugar that is found in fruits and vegetables. It is also found in honey, agave nectar, and high-fructose corn syrup. Fructose can cause weight gain, heart disease, and diabetes.

Why is fructose important to the body?

Fructose is important to the body because it is a simple sugar that can be used for energy.

What is fructose and its function?

Fructose is a simple sugar that is found in fruits, vegetables, honey and some other foods. It is also used as a sweetener in many processed foods.

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