By Dr. Marianna Pochelli
Fiber slows the rate that sugar is adsorbed into the bloodstream. When you eat foods high in fiber, such as whole fruits, the natural sugars are absorbed slower, which keeps your blood glucose levels from rising too fast and then falling rapidly. According to new research, published in the British Medical Journal, eating more whole fruit may help to lower your risk of developing type 2 diabetes, while increased consumption of fruit juices may be linked to higher risks.
Data was used from three large scale prospective longitudinal cohort studies to determine whether individual fruits are differentially associated with risk of type 2 diabetes. It is the first study to investigate how individual fruits might affect glucose and diabetes risk
Led by senior author Qi Sun from the Harvard School of Public Health (HSPH), USA, the research team analysed data from more than 180,000 people - consisting of more than 3,400,000 person years of follow up - examine the associations of individual fruit consumption in relation to risk of type 2 diabetes.
The study appears online August 29, 2013 in BMJ (British Medical Journal).
Specific Fruits Lower Risk
"Moreover, we estimated substitution effects of individual fruits for fruit juice in relation to risk of type 2 diabetes," explained the researchers.
"Greater consumption of specific whole fruits, particularly blueberries, grapes, and apples, is significantly associated with a lower risk of type 2 diabetes, whereas greater consumption of fruit juice is associated with a higher risk," they said.
Indeed, people who ate at least two servings each week of certain whole fruits -- particularly blueberries, grapes, and apples -- reduced their risk for type 2 diabetes by as much as 23% in comparison to those who ate less than one serving per month.
Conversely, those who consumed one or more servings of fruit juice each day increased their risk of developing type 2 diabetes by as much as 21%, revealed Sun and colleagues.
Fiber slows down the release of glucose into your blood stream, preventing blood sugar (glucose) spikes. While people with pre-diabetes and diabetes should be especially cautious if they opt for juice over a smoothie, everyone would benefit from a slow steady raise in blood glucose.
The team suggested that swapping three servings of juice per week for whole fruits would result in a 7% reduction in diabetes risk.
"While fruits are recommended as a measure for diabetes prevention, previous studies have found mixed results for total fruit consumption," said Sun.
"Our findings provide novel evidence suggesting that certain fruits may be especially beneficial for lowering diabetes risk." The researchers theorize that the beneficial effects of certain individual fruits could be the result of a particular component. Previous studies have linked anthocyanins found in berries and grapes to lowered heart attack risk, for example. But more research is necessary to determine which components in the more beneficial fruits influence diabetes risk.
"Our data further endorse current recommendations on increasing whole fruits, but not fruit juice, as a measure for diabetes prevention," said lead author Isao Muraki, research fellow in the Department of Nutrition at HSPH. “And our novel findings may help refine this recommendation to facilitate diabetes prevention.”
How Does Consumption of Fruit Juice Compare With Whole Fruit
Juicing separates the water in the fruit from the pulp and other solid parts of the fruit. You only drink the water and nutrients that dissolve in water. Although there are many reasons to juice your fruits and vegetables, the study serves as a valuable reminder to never exclude the importance of fiber from your diet.
Too many natural sugars from fruit without fiber to slow the digestion and absorption down will cause a spike in blood glucose. The pancreas secretes insulin to push glucose into the cells, and when the pancreas overcompensates as a result of a glucose spike, blood sugar will drop.
Overtime, if your pancreas secrets too much insulin often, your cells will stop responding, leading to a condition known as insulin resistance. Fruit juices alone won’t cause insulin resistance, but considering that most Americans eat more sugar and refined carbs than they should and not enough fiber, those juicing should ensure they consume as much fiber as they can if they over-consume refined processed foods.
The Benefits of Fruit Skins
The edible skins of many of the World's Healthiest Fruits - including apples, apricots, blueberries, figs, grapes, pears, plums, prunes, raisins, raspberries, and strawberries - are all sites of important biological activity in the life of the fruit. The skin is one of the places where the fruit interacts with sunlight, and forms a variety of colored pigments that absorb different wavelengths of light. These pigments, including carotenoids and flavonoids, are well researched as nutrients that protect our health and nourishment. The skins of whole fruits like grapes have actually been studied for their ability to help lower risk of cancer and help provide protection from ultraviolet light.
Unfortunately, when fruits are juiced, we don't always get to enjoy the fruit's skin. That is because many juicing processes remove the skin, and do not allow for its full benefits to get into the juice.
The Benefits of Fruit Pulp
In addition to the skin, which is an important source of fiber in most fruits, the pulpy part of the fruit is also a source of fiber (and other nutrients). Orange juice makes a good example of the health difference when you focus on the issue of its pulp. The white pulpy part of the orange is the primary source of its flavonoids. The juicy orange-colored sections of the orange contain most of its vitamin C. In the body, flavonoids and vitamin C often work together, and support health through their interaction. When the pulpy white part of the orange is removed in the processing of orange juice, the flavonoids in the orange are lost in the process. This loss of flavonoids is one of the many reasons for eating the orange in its whole food form (even if you only end up eating a little bit of the white pulpy part). Although many commercial products will say "pulp added" on their labels, the "pulp added" many not even be the original pulp found in the whole fruit, and it is highly unlikely to be added back in the amount removed.
Juicing Reduces the Fiber Content
How much fiber is lost in the conversion from whole fruit to fruit juice? Let's use apples and apple juice as an example.
A cup of apple juice that you can see straight through (pulp removed) contains no measurable amount of fiber. To create this 8-ounce glass of juice, approximately 3-4 apples are needed (depending, of course, on the size and density of the apples). Each of these 3-4 apples contains about 3.75 grams of dietary fiber, for a total of about 12-15 grams of dietary fiber. Virtually all of these 12-15 grams are lost in the production of clear apple juice! These 12-15 grams of lost fiber, if added back into the juice, would fully double our average daily fiber intake!
Is Fruit Juice Unhealthy?
The answer to this question depends on how it's consumed, and what foods it replaces. Fruit juice that has been robbed of its fiber and broad range of nutrients is basically just a concentrated source of sugar that lacks the supportive nutrients to help it digest and metabolize. Fruit juice elevates blood sugar more quickly than whole fruit, and the level of sugar that can be obtained from fruit juice is higher than the level found in whole fruit. For example, 120 calories' worth of whole apples contains about 24 grams of sugar, while 120 calories' worth of apple juice contains about 30 grams.
Additionally, many fruit juices that are sold in supermarkets contain only a small percentage of real fruit juice, and contain added sweeteners (sucrose or high fructose corn syrup). As a result, it is easy to consume a large amount of calories without getting any actual nutrition when you consume these beverages. Make sure you read fruit juice labels carefully! Turn over on the back of the jar or bottle, and look over the ingredient list - you may be surprised to see exactly where the fruit itself fits in!
Dr. Marianna Pochelli is a Doctor of Naturopathic Medicine specializing in the treatment of disease through superfoods and herbal strategies. She actively promotes detoxification, colon cleansing, and a vegetarian lifestyle using living foods as a platform to health.