Eating whole fruits linked to lower risk of Type 2 diabetes

Eating more whole fruits, particularly blueberries, grapes, and apples, was significantly associated with a lower risk of type 2 diabetes, according to a new study led by Harvard School of Public Health (HSPH) researchers. Greater consumption of fruit juices was 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. Our findings provide novel evidence suggesting that certain fruits may be especially beneficial for lowering diabetes risk," said 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 study appears online August 29, 2013 in BMJ (British Medical Journal).

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."

Source:

Harvard School of Public Health

Higher potato consumption associated with increased risk of high blood pressure

Higher intakes of boiled, baked, or mashed potatoes, and French fries is associated with an increased risk of developing high blood pressure (hypertension) in adult women and men.

The US-based researchers suggest that replacing one serving a day of boiled, baked, or mashed potatoes with one serving of a non-starchy vegetable is associated with a lower risk of developing hypertension.

But a linked editorial argues that studying overall dietary patterns and risk of disease is more useful than a focus on individual foods or nutrients.

Potatoes are one of the world's most commonly consumed foods -- and have recently been included as vegetables in US government healthy meals programs, due to their high potassium content. But the association of potato intake with hypertension has not been studied.

So researchers based at Brigham and Women's Hospital and Harvard Medical School set out to determine whether higher long term intake of baked, boiled, or mashed potatoes, French fries, and potato chips (crisps) was associated with incident hypertension.

They followed over 187,000 men and women from three large US studies for more than 20 years. Dietary intake, including frequency of potato consumption, was assessed using a questionnaire. Hypertension was reported by participants based on diagnosis by a health professional.

After taking account of several other risk factors for hypertension, the researchers found that four or more servings a week of baked, boiled, or mashed potatoes was associated with an increased risk of hypertension compared with less than one serving a month in women, but not in men.

Higher consumption of French fries was also associated with an increased risk of hypertension in both women and men. However, consumption of potato chips (crisps) was associated with no increased risk.

After further analyses, the researchers suggest that replacing one serving a day of boiled, baked, or mashed potatoes with one serving of a non-starchy vegetable is associated with a decreased risk of hypertension.

The authors point out that potatoes have a high glycaemic index compared with other vegetables, so can trigger a sharp rise in blood sugar levels, and this could be one explanation for the findings.

They also acknowledge some study limitations and say that, as with any observational study, no firm conclusions can be drawn about cause and effect.

Nevertheless, they say their findings "have potentially important public health ramifications, as they do not support a potential benefit from the inclusion of potatoes as vegetables in government food programs but instead support a harmful effect that is consistent with adverse effects of high carbohydrate intakes seen in controlled feeding studies."

In a linked editorial, researchers at the University of New South Wales argue that, although diet has an important part to play in prevention and early management of hypertension, dietary behaviour and patterns of consumption are complex and difficult to measure.

"We will continue to rely on prospective cohort studies, but those that examine associations between various dietary patterns and risk of disease provide more useful insights for both policy makers and practitioners than does a focus on individual foods or nutrients," they conclude.