10 a day

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    Ten a day of fruit and veg: how good is the evidence?

    24 February 2017

    Eating more than five portions of fruit and vegetables a day greatly reduces the chance of heart attack, stroke, cancer and early death, according to a study at Imperial College London. (See our analysis below.)

    The researchers found that although five portions of fruit and vegetables a day reduces the risk of disease, the greatest benefits are derived from eating 800g a day, or roughly 10 portions.

    The study, published in the International Journal of Epidemiology, suggests that 7.8 million premature deaths could be prevented annually if everyone followed this advice.

    The global meta-analysis included health data from up to two million people, gathered during 95 separate studies.

    The researchers found that the greatest protection against heart disease, stroke and cardiovascular disease was provided by apples and pears, citrus fruits, salads and spinach, lettuce and chicory.

    They also found that green vegetables, such as spinach or green beans, yellow/orange vegetables such as peppers and carrots, and cruciferous vegetables like broccoli provide the best protection against cancer.

    When compared with zero intake of fruit and vegetables, eating 10 portions of fruit and vegetables a day was associated with a 24 per cent reduced risk of heart disease, a 33 per cent reduced risk of stroke, a 28 per cent reduced risk of cardiovascular disease, a 13 per cent reduced risk of total cancer and a 31 per cent reduction in dying prematurely.

    Dr Dagfinn Aune, the study’s lead author, said: ‘We wanted to investigate how much fruit and vegetables you need to eat to gain the maximum protection against disease and premature death.

    ‘Fruit and vegetables have been shown to reduce cholesterol levels, blood pressure, and to boost the health of our blood vessels and immune system. This may be due to the complex network of nutrients they hold. For instance they contain many antioxidants, which may reduce DNA damage, and lead to a reduction in cancer risk.

    ‘It is clear from this work that a high intake of fruit and vegetables holds tremendous health benefits, and we should try to increase their intake in our diet.’

    Instant analysis
    Recommendations of fruit and vegetable intake have varied over the years. Research has yielded a mixed picture, with some studies showing the benefit of more than the definitive five-a-day, and others not.

    This new study suggests there is strong evidence for advising a higher intake of fruit and vegetables.

    This was a systematic review of 142 prospective studies on specific health outcomes related to intake of fruit and vegetables. A systematic review is a critical review of all relevant study types on a particular subject with relevant results presented but not pooled, as they would be in a meta-analysis.

    Results were stratified by overall fruit and vegetable intake, by amount and also by individual fruit/vegetable and group, in terms of effect on cardiovascular health, stroke, cancer and all-cause mortality (death from any cause).

    The authors found that for every 200g fruit/vegetables consumed a day, there was an eight per cent decrease in coronary artery disease, 16 per cent decrease for cardiovascular disease, three per cent decrease for cancer and 10 per cent decrease for all-cause mortality.

    A total intake of 550-600g a day (seven servings) of fruits and vegetables was associated with the lowest risk for cancer; for lowered risk from coronary artery disease, stroke and all-cause mortality the lowest risk was associated with 800g or 10 servings a day.

    We should be clear that this refers to consumption of whole fruit and vegetables. Fruit smoothies, which can contain higher levels of fruit, lower levels of fibre but also more sugar, were not assessed and neither were ‘green’ smoothies. Consumption of canned fruit was not found to be protective, and we can speculate that this might be linked to the higher sugar levels, which by themselves have been implicated in disease.

    The foods that showed the most benefit — apples, pears, tomatoes, green, leafy or cruciferous vegetables or those rich in vitamin C and beta-carotene — were mostly lower on the glycemic index, which might partly explain why their consumption was so beneficial.

    When one considers the vitamins, antioxidants, fibre and other constituents of fruit/vegetables, it is extremely plausible that their consumption will be useful to human health, and it makes perfect sense at first glance that higher levels will result in better health.

    Correlation is not causation, though, even if the results seem to be ‘obvious’.

    We must remember that increased consumption of fruit and vegetables is often associated with other factors that are themselves markers for lowered incidence of disease and mortality.

    As various papers have established, people who eat more fruit and vegetables also do more exercise, have a healthier diet and healthier BMI and make other healthy decisions which significantly alter risk, thus confounding any apparent direct link between fruit and vegetable consumption and health.

    As a result, we cannot conclude from this paper that simply increasing fruit and vegetable intake, in isolation, will result in lowered risks from the outcomes considered.

    Human health is more complex than the simple sum of its parts and, in order to optimise it, we need to adopt various good habits, not just one.
    Research score: 3/5