Eat Whole Fruits, Not Juice, to Lower Your Risk of Type 2 Diabetes

by Diane, M.P.H, M.S.

The best six doctors anywhere
And no one can deny it
Are sunshine, water, rest, and air
Exercise and diet.
These six will gladly you attend
If only you are willing
Your mind they’ll ease
Your will they’ll mend
And charge you not a shilling.
(Nursery rhyme quoted by Wayne Fields, What the River Knows, 1990)

Eat more whole fruit:

A new study led by Harvard School of Public Health (HSPH) researchers and published online in the British Medical Journal (BMJ) August 29, 2013, has reported that eating more whole fruits, especially blueberries, grapes, and apples, is significantly associated with a lower risk of type 2 (maturity-onset) diabetes. However, consumption of fruit juices is associated with a higher risk of type 2 diabetes. The study is the first to look at the effects of individual fruits on diabetes risk.

“While fruits are recommended as a measure for diabetes prevention, previous studies have found mixed results for total fruit consumption. While total fruit consumption is not consistently associated with a lower risk of type 2 diabetes, certain fruits may be especially beneficial for lowering diabetes risk,” according to senior author Qi Sun, assistant professor in the Department of Nutrition at HSPH and assistant professor at the Channing Division of Network Medicine, Brigham and Women’s Hospital.

The researchers examined data gathered between 1984 and 2008 from 187,382 participants in three long-running studies (Nurses’ Health Study, Nurses’ Health Study II, and Health Professionals Follow-up Study). Participants who reported a diagnosis of diabetes, cardiovascular disease, or cancer at enrollment were excluded. Results showed that 12,198 participants (6.5%) developed diabetes during the study period.

The researchers looked at overall fruit consumption, as well as consumption of individual fruits: grapes or raisins; peaches, plums, or apricots; prunes; bananas; cantaloupe; apples or pears; oranges; grapefruit; strawberries; and blueberries. They also looked at consumption of apple, orange, grapefruit, and “other” fruit juices.

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%. The researchers found that swapping three servings of juice per week for whole fruits would result in a 7% reduction in diabetes risk.

The fruits’ glycemic index (a measure of how rapidly carbohydrates in a food boost blood sugar) did not prove to be a significant factor in determining a fruit’s association with type 2 diabetes risk. However, the high glycemic index of fruit juice — which passes through the digestive system more rapidly than fiber-rich fruit — may explain the positive link between juice consumption and increased 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.”

Avoid drinking juice: 

Type 2 diabetes risk increases with greater consumption of fruit juice. The juicing process causes some of the beneficial natural fiber and phytochemicals in fruit to be lost. Also, since fruit juices are fluids, they can be absorbed more rapidly into the gastrointestinal system than whole fruits, and subsequently lead to more dramatic changes in blood sugar and blood insulin levels.

Scientific evidence exists that large changes in blood sugar and blood insulin levels after meals may in the long run increase the risk of type 2 diabetes. More research is needed to determine if other factors in fruits could further explain their different effects on diabetes risk.

Qi and his colleagues are conducting several studies to further explore the associations between phytochemicals such as resveratrol, flavonoids, and chlorogenic acid, and diabetes risk. “We also hope to extend these associations to persons with chronic conditions such as cardiovascular disease, and to other patient populations such as diabetic patients.”

 Increase your consumption of a variety of whole fruits, especially blueberries, grapes, and apples, to help reduce your risk of diabetes.

  1. Fields, Wayne. What the River Knows: An Angler in Midstream.  A memoir written by Dr. Fields, Lynne Cooper Harvey Distinguished Professor of English, American Literature and American Culture Studies at 1 Brookings Drive, Washington University, St. Louis, MO 63130-4899. 1990.
  2. Muraki, Isao (research fellow); Fumiaki Imamura (investigator scientist); JoAnn E Manson (professor of medicine); Frank B Hu (professor of nutrition and epidemiology); Walter C Willett (professor of epidemiology and nutrition); Rob M van Dam (associate professor); Qi Sun (assistant professor). “Fruit consumption and risk of type 2 diabetes: results from three prospective longitudinal cohort studies.” British Medical Journal (BMJ). 2013; 347 doi: Published 08/29/13.

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