Fruit variety and the big C

The WHO predicts deaths from cancer will rise from the current level of around 8 million lives a year to more than 13 million by 2030. The 2013 Global Burden of Disease study estimated that the number of years lost through premature death and disability (DALYs) due to cancers was 197 million worldwide. The economic cost of this situation has been estimated at US$2 trillion dollars pa through reduced output and medical care costs, separate from quality of life questions.

Different forms of cancer have different causes, incidence, screening, diagnosis, symptoms, treatments and outcomes, and consequently they each have to be considered as individual diseases. But what is common to most in addition to genetic factors (5-10% causation) is that lifestyle and environmental factors are considerable risk factors (90-95%). Adverse lifestyle factors include cigarette smoking, diet (fried foods, red meat), alcohol, sun exposure, environmental pollutants, infections, stress, obesity and physical inactivity. The evidence indicates that of all cancer-related deaths, almost 25–30% are due to tobacco, as many as 30–35% are linked to diet, 15–20% to infections, 10-15% to obesity and the remaining percentage to other factors like radiation, stress, physical activity, environmental pollutants etc.

The 2013 global DALYs for oesophageal cancer was 9.8 million years. As one of the relatively low incidence cancers it has been less studied than many others, but fatality rates are very high. More than half of all patients have metastases at the time of diagnosis and surgical removal of all cancerous tissue is not possible. Chemotherapy and radiotherapy, alone or in combination, don’t greatly improve prospects. The overall 5-year survival rate is currently only about 14%. So the main focus is on prevention, and several studies have considered the importance of diet, including fruit and vegetable (F&V) intake. The following summarises a study published in the international Journal of Cancer ((2012) 131, E962-E973) by a large European research group on this topic.

Diets high in F&V have been suggested to be inversely associated with risk of gastric cancer.  However, the evidence of the effect of variety of consumption is limited.  We therefore investigated whether consumption of a variety of F&V is associated with gastric and oesophageal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC) study.  Data on food consumption and follow-up on cancer incidence were available for 452,269 participants from 10 European countries.  After a mean follow-up of 8.4 years, 475 cases of gastric and oesophageal adenocarcinomas and 98 oesophageal squamous cell carcinomas were observed.  Diet Diversity Scores were used to quantify the variety in F&V consumption. We used multivariable Cox proportional hazard models to calculate risk ratios.  Independent from quantity of consumption, variety in the consumption of F&V combined and of fruit consumption alone were statistically significantly inversely associated with the risk of oesophageal squamous cell carcinoma (continuous hazard ratio per 2 products increment 0.88 and 0.76 respectively) with the latter particularly seen in ever-smokers. Variety in F&V consumption was not associated with risk of gastric and oesophageal adenocarcinomas.  Independent from quantity of consumption, more variety in F&V consumption combined and in fruit consumption alone may decrease the risk of oesophageal squamous cell carcinoma.  However, residual confounding by lifestyle factors cannot be excluded.

Explanatory comments on terms used and conduct of the study are:

Squamous cell carcinoma and adenocarcinomas account for about 90% of all oesophageal cancers.
EPIC is an on-going 23-centre European study investigating the relations between diet, lifestyle, metabolic and environmental factors and the incidence of chronic diseases. The participants are adults aged 35-70 years who were recruited from 1992 to 2000.
Country-specific questionnaires for Germany, The Netherlands, Sweden, Denmark, UK, Norway, France, Italy, Spain and Greece were used to obtain data relevant to differing national dietary intakes and habits. Lifestyle data on education, occupation, medical history, lifetime history of tobacco use and physical activity were also collected. Four different Dietary Diversity Scores were considered. For F&V together there was a range of 0-40 for the number of individual F&V products eaten at least once in the past 2 weeks. 26 vegetables eaten at least once in the last 2 weeks were included in a vegetable-only group, and a further sub-group for vegetables was also constructed where these 26 were categorised as leafy, fruiting, root, grain, pod and stalk vegetables, cabbages, mushrooms, onions and garlic (range 0-8). 14 fruit products (including fresh, dried and canned) were similarly considered for the fruit-only group. The dietary scores were divided into 3 categories (eg for F&V – 0-11, 12-19 and 20-40), and effects were also calculated if participants were to increase their diversity scores by 2 (1 in the vegetable sub-group).
Observed fruit and vegetable intake for all participants was 195 and 177g/d resp.
The risk of oesophageal squamous cell carcinoma was reduced by 12% in the F&V group for an increase of 2 different products per fortnight, independently of quantity consumed, age at recruitment, gender, study centre, smoking status, duration of smoking, lifetime number of cigarettes, energy intake from fat and non fat sources, red and processed meat, body mass index and alcohol. There was a non-significant reduced risk for vegetables alone, whereas for fruit it was significantly reduced by 24%.
The fruit effect was stronger for people who had smoked at any time in their life, and the authors suggested a possible mechanism could involve the damaging oxidant effects of tobacco smoke being offset by the well known antioxidant effects of fruits, usually stronger than for vegetables (by an average five-fold according to other studies).
Excluding the first 2 years of data following diagnosis did not change results.

The above is supportive of our club interest in growing and eating a whole range of fruits, not just the few like apples, pears, citrus and bananas that many Australians limit themselves to in their diet. Even with these more common fruits, Australian studies have shown that people on average don’t eat enough.. As a consequence this inadequacy will be even more pronounced in terms of diversity – if you eat very little fruit there is less opportunity to embrace a greater range. In 1997 the World Cancer Research Fund–American Institute for Cancer Research concluded that there was convincing evidence that high intake of F&V decreases the risk of oesophageal cancer, and the UK Committee on Medical Aspects of Food and Nutrition Policy reached similar conclusions.

A 2003 meta-analysis of 13 studies also found a significant protective effect of F&V for each additional 100g/d consumed, and this effect was stronger for fruit than for vegetables (28% and 11% lower risks resp). The present study advances these findings by considering the additional dimension of F&V variety on beneficial effects in this cancer, and suggests that the positive effect of F&V variety combined could be due entirely to the fruit variety part alone. The participants who remained free of the cancer during the study period were consuming on average 4-14 different fruit products in a two week period – a far cry from only eating the few commons, and even more so for those who concentrate on a few ‘super fruits’ that may be promoted in health magazines.

It is an important contribution as it was a prospective study, whereas the majority in this area have been of the case-control type. The former enter healthy people at the start of the trial and collect data on lifestyles and diets, uninfluenced by disease diagnosis that may have led people to dramatically change their habits. They also avoid the problem of people recalling without bias what they may or may not have eaten some years earlier. In case control studies, people who have already contracted the disease are compared with matching healthy controls and differences in diet/lifestyle are then analysed. However there is the ever-present possibility that the 2 groups may differ in ways not recorded or studied, and this can confuse interpretation.

These considerations suggest it’s sensible to take off the blinkers and enjoy the full range of fruit that we can grow. It could also help you keep at bay the ravages of chronic diseases associated with our busy and often stressful modern lifestyles.