Daily diet of fresh fruit linked to lower diabetes risk

"Eating fresh fruit daily could cut risk of diabetes by 12%," the Mail Online reports.

A study of half a million people in China found those who ate fruit daily were 12% less likely to get type 2 diabetes than those who never or rarely ate it.

It was also found that people with diabetes at the start of the study who ate fruit regularly were slightly less likely to die, or to get complications of diabetes, such as eye problems (diabetic retinopathy), during the study than those who ate fruit rarely or never.

Many people with diabetes in China avoid eating fruit, because they are told it raises blood sugar. However, the study suggests fresh fruit may actually be beneficial for people with and without diabetes.

Fruits which release sugars more slowly into the blood, such as apples, pears and oranges, are the most popular in China, according to the researchers. So this may be the preferred option if you are worried about diabetes risk, or have been diagnosed with diabetes.

The study doesn't show that fruit directly prevents diabetes or diabetes complications, as an inherent limitation of this type of study is that other factors could be involved. And it doesn't tell us how much fruit might be too much.

Overall, the research suggests fresh fruit can be part of a healthy diet for everyone.

Where did the story come from?

The study was carried out by researchers from the University of Oxford, and Peking University, Chinese Academy of Medical Sciences, China National Center for Food Safety Risk Assessment, Non-communicable Disease Prevention and Control Department, and Pengzhou Center for Disease Control and Prevention, all in China. It was funded by the Kadoorie Charitable Foundation.

The study was published in the peer-reviewed journal PLOS Medicine on an open-access basis, so it's free to read online.

The Mail's report was basically accurate, although it did not point out that this type of study cannot prove cause and effect. The report confused some readers by saying that fruit does not raise blood sugar because it is metabolised differently to refined sugar.

However, what the study found was that fruit-eaters' blood sugar was not on average higher than that of non-fruit eaters. Like most food, the rise in sugar levels after eating fruit is usually temporary.

The Sun's report was poorly written and contained some basic grammatical errors.

What kind of research was this?

This was a large-scale prospective cohort study. Researchers wanted to look for associations between fruit eating, diabetes and complications of diabetes.

However, while this type of study is good for spotting links, it cannot prove that one factor causes another.

What did the research involve?

Researchers used information from a big ongoing cohort study called the China Kadoorie Biobank Study, which recruited half a million adults aged 30 to 79 between 2004 and 2008.

Participants filled in questionnaires about their health, diet and lifestyle and had measurements taken of their blood sugar, blood pressure, cholesterol and other health-related factors. The diet questionnaires were repeated over the course of the study. After an average seven years of follow-up, researchers looked to see how fruit consumption related to diabetes.

Some people in the study (almost 6%) had diabetes at the start of the study. While not actually specified in the study, we assume the majority of these cases were type 2 diabetes. Type 1 diabetes usually begins in childhood and is less common than type 2.

About half of them had previously been diagnosed, and half were diagnosed due to their blood sugar readings taken during the study. China's Disease Surveillance Points system was used to identify any deaths and cause of death during the study. Disease registries and health insurance claims were used to look into diabetes-related health complications.

The researchers took the average responses from the diet questionnaires to establish how regularly people ate fruit, to account for possible changes in dietary habits.

They adjusted the figures to take account of potential confounding factors including age, age at diabetes diagnosis, gender, smoking, alcohol consumption, physical activity and body mass index. 

What were the basic results?

Only 18.8% of people surveyed reported eating fruit daily, and 6.4% said they never or rarely ate fruit. Some 30,300 people had diabetes at the start of the study, and there were 9,504 new cases of diabetes in the seven years of follow up, or 2.8 for each 1,000 people each year.

• People who ate fresh fruit daily were 12% less likely to develop diabetes than those who never or rarely ate fresh fruit (hazard ratio (HR) 0.88, 95% confidence interval (CI) 0.83 to 0.93).
• Of the people with diabetes at the start of the study, 11.2% died during follow up (16.5 for every 1,000 people each year).
• People with diabetes who ate fresh fruit on three days a week or more were 14% less likely to die of any cause, compared to those who ate fresh fruit less than one day a week (HR 0.86, 95% CI 0.80 to 0.94). They were also less likely to die from diabetes-related causes or cardiovascular disease, specifically.
• People with diabetes who ate fresh fruit daily were also 14% less likely to have complications of damage to their large blood vessels (such as heart attack or stroke) than those who ate fresh fruit never or rarely (HR 0.86, 95% CI 0.82 to 0.90). They were also 28% less likely to have small blood vessel complications, such as eye or kidney disease (HR 0.72, 95% CI 0.63 to 0.83).

How did the researchers interpret the results?

The researchers say their results "provide strong evidence in support of current dietary guidelines that fresh fruit consumption should be recommended for all, including those with diabetes."

They say that people with diabetes in China eat much less fruit than people without diabetes, because of concerns about sugar in fruit. They say the study shows that better health education is "urgently needed" in China and other Asian countries where diabetes is common, and many people misunderstand the effects of eating fresh fruit.

They speculate that "natural sugars in fruit may not be metabolised in the same way as refined sugars," although their paper did not investigate this.

Conclusion

The study findings – that eating fresh fruit every day does not raise the risk of diabetes, and may reduce it – are reassuring and in line with dietary advice in the UK. It's also helpful to see evidence that people who already have diabetes are likely to benefit from fresh fruit as well, because there has not been much research into fruit-eating for people with diabetes.

However, it's a step too far to say that fresh fruit prevents diabetes or diabetes complications. Fresh fruit is just one part of a healthy diet, and diet is just one of the things that may affect someone's risk of getting diabetes. This type of study can't tell us whether fresh fruit actually protects against diabetes, because it can't account for all the other health and lifestyle factors involved.

Though it would be expected that the results of this large scale study should be applicable to other populations, there may be differences between people from China and other populations. This could include differences in prevalence of diabetes and its risk factors, differences in healthcare (for example, diagnostic criteria and methods for coding health outcomes in databases), and other environmental and lifestyle differences, including fruit consumption.

The study didn't ask people which types of fruit they ate, but the researchers say the most commonly eaten fruits in China are apples, pears and oranges, which release sugars more slowly into the blood stream than bananas, grapes and tropical fruits.

It's important to make a distinction between whole fresh fruit, which contains lots of fibre, and fruit juice, which is very high in sugar. Previous research that we reported on in 2013 found that fruit may lower diabetes risk, but fruit juice may raise it.

The most effective method of reducing your diabetes risk is to achieve or maintain a healthy weight, through a combination of regular exercise and healthy eating. Read more about preventing diabetes.