Fruit Juice

There is little controversy as to the overall healthfulness and benefits of eating whole fresh fruits, especially those that are locally and organically cultivated and eaten as part of a balanced diet. The story is a bit less clear when it comes to drinking fruit juices however, even those that market themselves as 100% juice. Frequently consuming fruit juice may actually raise the risk of developing type 2 diabetes.

There are three principle reasons why fruit juices are often less healthful than consuming a whole fruit; glycemic load, fiber content and lower satiation.

The first reason involves the difference between two rating systems based on the carbohydrate content of foods, known as glycemic index and glycemic load. These rating systems and their differences are particularly important for diabetics and those at risk for developing diabetes.

Glycemic index is a numeric index (0-100) assigned to each food based on how large an effect that food has on blood glucose levels, with pure glucose (sugar) having a glycemic index of 100. Generally speaking, processing a food raises its glycemic index, and foods with higher fiber content lower glycemic index because fiber helps slow the absorption of sugar into the bloodstream.

Glycemic load goes a step further and accounts for real-life portion sizes and the amount of carbohydrate content within each serving, and in turn is considered more accurate in predicting how much a serving of a particular food or drink will affect blood-glucose levels. Glycemic loads below 10 are considered low, while those above 20 are considered high.

Because fruit juices often are the result of the blending or processing of many whole fruits, the amount of carbohydrates within a glass of fruit juice is typically much higher than the carbohydrates within a typical serving of the whole fruit. So fruit juice has a higher glycemic load than whole fruits, and therefore a larger and faster impact of blood-glucose levels.

The second reason that fruit juice is less healthful than whole fresh fruits has to do specifically with fiber. In the process of juicing (especially for processed and packaged juice drinks made from fruit concentrate, but for fresh fruit juices as well) dietary fiber, which is abundant within most whole fruits, is broken down and mostly lost when consumed in liquid form. Fiber is essential for healthy digestion, and in slowing the absorption of sugar into the bloodstream. The loss of dietary fiber in juices exacerbates the impact that fruit juices have on blood sugar, and also diminishes the absorption and utilization of certain nutrients that may pass directly through the body before providing any healthful benefits (this last point is one reason that dietary supplements often do not provide much value).

The conclusions from a recent study published in the BMJ helps to illustrate the differences between whole fruits and fruit juices: “the relatively high glycemic load values of fruit juices along with reduced levels of beneficial nutrients through juicing processes (for example, the glycemic load values per serving are 6.2 for raw oranges and 13.4 for orange juice, and fibre levels per serving are 3.1 g and 0.5 g, respectively) may explain the positive associations between fruit juice consumption and risk of type 2 diabetes. Moreover, the difference in the viscosity of foods is also an important factor affecting postprandial blood glucose dynamics. Fluids pass through the stomach to the intestine more rapidly than solids even if nutritional content is similar.”

Furthermore, as with other beverages with caloric content, drinking fruit juice is less satiating (feeling of fullness) than consuming the same number of calories from the whole fruit. This can potentially lead to increased caloric intake throughout the day, which without proper lifestyle adjustments such as increased physical activity, leads to weight gain. Overweight and obesity is perhaps the most important risk factor in the development of type 2 diabetes. 

Fruit juices can still be loaded with many important micronutrients, especially vitamins and minerals, that are not broken down during the process of juicing, and this is especially true when blended from whole fruits. However, though fresh fruit juices with no added sugar are certainly recommendable in comparison to sugary drinks like sodas and packaged and processed fruit beverages with added sugar or made from concentrate, the main conclusions to take away from this post are that fruit juices overall have less fiber and a significantly higher glycemic load than the whole fruits they are derived from, and are often consumed in addition to solid foods, not in substitution. Therefore, their frequent consumption can potentially increase the risk for developing type 2 diabetes.

For diabetics and those at high risk for developing diabetes, as well as individuals looking to maintain overall health, eating whole fresh fruits, and drinking healthful beverages like water and unsweetened coffee and tea, are the best options for regulating blood glucose levels and maintaining a healthy weight.

Resources and Further Reading

2013 study revealing many aspects of why fruit juices increase risk of developing diabetes as opposed to whole fruits: 
http://www.bmj.com/content/347/bmj.f5001

A study about sugar-sweetened beverages, including fruit juices and sodas and incidence of type 2 diabetes: 
http://ajcn.nutrition.org/content/97/3/517.long

A guide that gives some solid recommendations on diabetes prevention, including limiting fruit juice intake and explanations about glycemic index and load: 
https://www.hsph.harvard.edu/nutritionsource/diabetes-prevention/preventing-diabetes-full-story/#references

Glycemic and Glycemic Load guide from Harvard: 
https://www.health.harvard.edu/diseases-and-conditions/glycemic-index-and-glycemic-load-for-100-foods

Sugar-sweetened beverages such as packaged and processed fruit juice, and diabetes incidence in African American women: 
https://www.ncbi.nlm.nih.gov/pubmed/18663160?dopt=Citation