Raw and processed fruit and vegetables – Impact on stroke

The expected lifespan in developing countries is much shorter than we experience in the industrialised world. These people generally suffer from ‘diseases of poverty’ caused by contaminated drinking water and poor sanitation, uncontrolled infections, malnutrition and famines, lack of medical facilities, civil unrest and so on. In developed countries such problems have largely been overcome and although living longer, we increasingly suffer from ‘diseases of affluence’. These follow from longer lifespans giving more time for chronic diseases associated with aging to develop, but also because our lifestyles are negatively affected through reduced physical activity, junk foods and generally poor dietary habits including over-consumption, stresses associated with work and modern urban living etc. Longevity is not necessarily sufficient in itself if quality of life in our senior years is poor.

Chronic diseases that have a major impact on our morbidity and mortality include cardiovascular and mental diseases, cancer, diabetes, osteoporosis etc, and the question is – what can we do about them preventatively, given waiting till they occur may be too late? This touches on perennial debates about nature versus nurture – at one extreme we can blame afflictions on our parents for the genes they passed on, and at the other it’s all about the environment and how we live our lives. Obviously nothing is ever as extreme as either of these two scenarios, and most if not all diseases of modern civilisation are multifactorial. So for those pre-disposing risk factors that we have some control over we can choose to favourably modify them.

Globally, the WHO estimates that by 2020 coronary artery disease and stroke together will be the leading causes of lost healthy life-years. In Australia, stroke is a major cause of death and disability, affecting more than 50,000 people each year. Incidence rates increase as we age, with more than half of all strokes occurring in those over 75. Mortality is significant with about 20% dying within a month of a first-ever event. Within 10 years the cumulative risk of a recurrent event is 43% and of being disabled or deceased is approx. 86%. The following Dutch study (Eur. J. Clin. Nutrition (2011) 65, 791–799) describes how increased consumption of fruit and vegetables significantly reduces risk. Given the very common practice of processing these foods, they considered whether fruit and vegetables eaten in these altered forms were as good as the raw foods in minimising stroke. We’re all exposed to numerous TV cooking shows, flash web sites and elegantly presented cook books where fruits and vegetables are turned into mouth-watering products progressively embellished over the years to the extent that it’s almost universal (eg apple pie, blueberry muffins….). These processed foods go way beyond the desire to convert them into forms with good storage properties and appeal primarily to our hedonistic preferences. Although some fruits and vegetables have improved nutritional properties after processing, generally there is deterioration. Moreover, many other poor nutrition ingredients such as sugar, saturated fats and salt may be included, often in copious amounts, with the result that the raw fruits and vegetables qualities can be severely compromised.

Prospective cohort studies have shown that high fruit and vegetable consumption is related to a lower risk of stroke. Whether food processing affects this association is unknown. We evaluated the associations of raw and processed fruit and vegetable consumption independently from each other with 10-year stroke incidence and stroke subtypes in a prospective population-based cohort study in the Netherlands. We used data of 20,069 men and women aged 20–65 years and free of cardiovascular diseases at baseline who were enrolled from 1993 to 1997. Diet was assessed using a validated 178-item food frequency questionnaire. Hazard ratios (HRs) were calculated for total, ischemic and hemorrhagic stroke incidence using multivariable Cox proportional hazards models. During a mean follow-up time of 10.3 years, 233 incident stroke cases were documented. Total and processed fruit and vegetable intake were not related to incident stroke. Total stroke incidence was 30% lower for participants with a high intake of raw fruit and vegetables (more than 262g/day in the top 25% consumption group (HR = 0.70), compared with those with a low intake (bottom 25% with less than 93g/day), and the trend across all four quartiles was borderline significant. Raw vegetable intake was significantly inversely associated with ischemic stroke (>27 vs <28 g/day; HR: 0.50), and raw fruit borderline significantly with hemorrhagic stroke (>120 vs <121 g/day; HR: 0.53). It was concluded that high intake of raw fruit and vegetables may protect against stroke. No association was found between processed fruit and vegetable consumption and incident stroke.

Ischemic stroke is more common than hemorrhagic stroke but the latter results in higher fatality within 1 month of the event. The study included dietary information on 178 foods, of which 35 were fruits and vegetables. There were 9 and 7 raw fruits and vegetables items resp, and 19 processed fruits and vegetables – 4 fruit juices and sauces, and 15 cooked vegetables, juices and sauces. Winter and summer consumption was assessed to take account of different seasonal diets. Fruit juices/sauces were mainly industrial products prepared from concentrates, and the processed vegetables were mainly home-cooked, canned or frozen foods and tomato sauce. Analysis of the data allowed for other possible confounders including age, gender, energy and alcohol intake, smoking, education, dietary supplements, family history of myocardial infarction, BMI etc. The biggest contributors to raw fruit intake were citrus fruit (25%) and apples (22%); for raw vegetables the main ones were cucumber (23%) and tomatoes (18%). Citrus and apple juices were the largest contributors to processed fruit intake (49 and 22% resp). The authors suggested that as citrus juice is low in fibre (0.3 cf 1.8g/100g raw) and apple sauce contains no fibre (0 cf 2.3g/100g raw) or the main antioxidant (quercetin) present in raw apples, that these components together with any added sugar could be principal factors in the loss of effect with processing. Processed vegetables were mainly cabbages and French beans (24 and 14% resp). They also commented that cooked cauliflowers, which figured strongly amongst the processed vegetables, have reduced fibre (1.5 cf 2.5g/100g raw) and vitamin C (40 cf 80mg/100g raw) and usually also have added salt, thus illustrating how cooking can compromise the nutrition of this group of foods. Plus it was noted that other health promoting vegetable phytochemicals normally acting synergistically with one another would likely be reduced, thus contributing to the null effects found in the study.

You may be eating fruits and vegetables for all sorts of non-nutritional reasons such as availability, convenience, cost, preparation time or pleasure, but if you want the benefit of their healthy qualities then when possible, you’re usually best off eating them in fresh form. Most fruit can be enjoyably eaten this way as they’re naturally sweet without tough, unpleasant fibrous material, but many vegetables need some processing to render them more palatable. The above study suggests that care should be exercised to get the best nutritional return on them, with similar considerations for those fruits you decide to process rather than eat fresh. The Australian Stroke Foundation recommends a balanced diet eating fresh foods where possible.