Eat Two Fruits a Day, Ward Off Diabetes?

Marlene Busko

June 10, 2021

A new study supports the recommendation of eating two servings of fruit a day for health benefits — in this case a lower risk of diabetes.

Adults who ate two servings of fruit a day had a 36% lower odds of developing diabetes within 5 years compared to those who ate less than a half serving of fruit a day, after adjusting for confounders, in a population-based Australian study.

The findings by Nicola P. Bondonno, PhD, and colleagues, based on data from the Australian Diabetes, Obesity, and Lifestyle Study (AusDiab), were published online June 2 in the Journal of Clinical Endocrinology & Metabolism.

The study also showed that a higher fruit intake was associated with higher insulin sensitivity and lower pancreatic beta-cell function in a dose-response manner.

And a higher intake of apples — but not citrus fruit or bananas, the two other fruits studied — was associated with lower post-load serum insulin levels.

"This indicates that people who consumed more fruit [especially apples] had to produce less insulin to lower their blood glucose levels," Bondonno, from the Institute for Nutrition Research, Edith Cowan University, Perth, Australia, explained in a statement from the Endocrine Society.

"This is important since high levels of circulating insulin (hyperinsulinemia) can damage blood vessels" and this is "related not only to diabetes, but also to high blood pressure, obesity, and heart disease," she observed.

Fruit Juice Doesn't Have Same Effect

The study supports the recommendation of the Australian Dietary Guidelines — 2 servings of fruit a day, where one serving is 150 grams, which corresponds to a medium-sized apple, orange, or banana — Bondonno clarified in an email to Medscape Medical News.

However, fruit juice was not associated with better glucose or insulin levels, or lower risk of diabetes, possibly because of its relatively high glycemic load and fewer beneficial fibers, the researchers speculate, adding data suggest that even juice with added fiber does not trigger satiety.

The study findings "support encouragement of the consumption of whole fruits, but not fruit juice, to preserve insulin sensitivity and mitigate [type 2 diabetes] risk," Bondonno and colleagues summarize.

"Promoting a healthy diet and lifestyle which includes the consumption of popular fruits such as apples, bananas, and oranges, with widespread geographical availability, may lower [type 2 diabetes] incidence," they conclude.

Lower 5-Year Odds of Diabetes

It is not clear how eating fruit may confer protection against developing diabetes, the researchers write.

They aimed to examine how consumption of total fruit, individual fruit, and fruit juice is related to glucose tolerance, insulin sensitivity, and incident diabetes at 5 years and 12 years in participants in the nationally representative AusDiab study.  

They identified 7675 adults aged 25 and older without diabetes who had undergone blood tests and completed a food frequency questionnaire in 1999-2000.

Participants had indicated how often they ate 10 different types of fruit, any type of fruit juice, and other foods on a scale of 0 (never) to 10 (three or more times/day).

Researchers divided participants into quartiles based on their median fruit consumption: 62 (range 0-95) g/day, 122 (95-162) g/day, 230 (162-283) g/day, and 372 (283-961) g/day.

The most commonly consumed fruit was apples (23% of total fruit intake), followed by bananas (20%) and citrus fruit (18%). Other fruits each accounted for less than 8% of total fruit intake, so they were not studied separately.

Participants in each quartile had a similar mean age (54 years) and body mass index (27 kg/m2).

However, compared with participants in quartile 1 (low fruit intake), those in quartiles 3 and 4 (moderate and high fruit intakes, respectively) were more likely to be female and do at least 150 minutes of physical activity a week, and less likely to smoke. They also ate more vegetables and less red meat and processed meat, but they consumed more sugar.

Of 4674 participants who had 5-year follow-up, 179 participants developed diabetes.

Compared to participants with a low fruit intake (quartile 1), those with a moderate fruit intake (quartile 3) had a 36% lower odds of developing diabetes within 5 years (odds ratio [OR], 0.64; 95% CI, 0.44-0.92) after adjusting for age, sex, physical activity, education, socioeconomic status, income, body mass index, smoking, cardiovascular disease, parental history of diabetes, and consumption of alcohol, vegetables, red meat, processed meat, and calories.

Of the 3518 participants with 12-year follow-up, 247 participants had diabetes, but there were no significant associations between fruit consumption and this longer-term risk of diabetes, possibly due to the small number of participants and events.

The study was supported by grants from the National Health and Medical Research Council of Australia and the National Heart Foundation of Australia. Bondonno has reported no relevant financial disclosures. Disclosures of the other authors are listed with the article.

J Clin Endocrinol Metab. Article. Published online June 2, 2021. Full Text

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