Fruit intake in perspective

Collectively, peoples of the world are not eating enough fruit, even though in many countries there have been public health advocacy programs such as ‘two and five’ fruit and vegetable servings a day for many years now. How do we know this is so? It’s all been reported in an update of the Global Burden of Disease study (GBD, Lancet (2015) 386, 2287–2323) and covering the years 1990-2013. This has been an ambitious and monumental research effort undertaken by more than 500 of the world’s leading scientific and medical authorities from 300 institutions and 50 countries, documenting the effect of 79 risk factors on 306 disease outcomes in 188 countries. Even at the 2010 update stage it was by far the largest such global database, consisting of more than 3 terabytes of data on 800 million deaths, risk factors and analyses, and it will continue to expand exponentially as new studies are reported and additional diseases and risks are incorporated.

Before reading a summary of their summary, a description of some features of the study design and methods used, basic data and terms might be helpful.

Disability-adjusted life years (DALYs) is the quantitative metric they used for assessing how many healthy years of life people may lose due to health risks, first through premature mortality (years of life lost, YLL), and before that, the number of healthy years that may be lost through disability (morbidity, YLD). DALYs are the total of YLL and YLD. Different diseases can typically be associated with different ratios of YLL and YLD eg mental disease and low back pain can have small YLL but large YLD, and aortic aneurysm the reverse. Developing countries have a greater relative contribution of YLLs to their DALYs than in those that are more developed, and if their development status improved from 1990 to 2013, DALYs become more dependent on YLDs. During this period, the YLD proportion of global DALYs rose from 21 to 31%. With increasing age in developed countries, the proportion of people with co-morbidities increased markedly, from 36% with none in the 0-4yr age group to <0.03% in 80+ yr olds.
Diseases were grouped at the highest level into 3 categories – communicable (maternal, neonatal and nutritional), non-communicable, and injuries.
The theoretical minimum risk exposure level (TIMREL) is the threshold above or below which the factor has no negative health impact. For example with asbestos it is zero and levels above this cause increased risk, and for fruit, it is estimated as 200-400g/d and levels below this increase risk.
Many variables influence health outcomes. GBD 2013 has considered three of these – behavioural, environmental and occupational, and metabolic, all of which are modifiable and provide scope for improved health outcomes if addressed at the individual and/or population levels. In future GBD updates it is the intention to progressively include other important health outcome factors, namely social, cultural and economic, medical interventions, genes, microbiome and host, and pathogens.
Counterfactual risks examine the effects of a risk compared to the no-effect risk level eg non-smokers compared to smokers.
Glomerular filtration rate is a measure of kidney function.
The quality and strength of evidence for particular risk-disease outcomes reported in the literature varies greatly, and GBD graded them all into 4 categories – convincing, probable, possible and insufficient according to well-established criteria. Only those in the 1st two were considered, and this left >35,000 distinct data sources for analysis. There were more data in some countries and for various risk factors and diseases than others.

The Global Burden of Disease, Injuries, and Risk Factor study 2013 (GBD 2013) is the first of a series of annual updates of the GBD.  Risk factor quantification, particularly of modifiable risk factors, can help to identify emerging threats to population health and opportunities for prevention.  The GBD 2013 provides a timely opportunity to update the comparative risk assessment with new data for exposure, relative risks, and evidence on the appropriate counterfactual risk distribution.

Attributable deaths, years of life lost, years lived with disability, and disability-adjusted life-years (DALYs) have been estimated for 79 risks or clusters of risks using the GBD 2010 methods.  Risk–outcome pairs meeting explicit evidence criteria were assessed for 188 countries for the period 1990–2013 by age and sex using three inputs: risk exposure, relative risks, and the theoretical minimum risk exposure level (TMREL).  Risks are organised into a hierarchy with blocks of behavioural, environmental and occupational, and metabolic risks at the first level of the hierarchy.  The next level in the hierarchy includes nine clusters of related risks and two individual risks, with more detail provided at levels 3 and 4 of the hierarchy.  Compared with GBD 2010, six new risk factors have been added: handwashing practices, occupational exposure to trichloroethylene, childhood wasting, childhood stunting, unsafe sex, and low glomerular filtration rate.  Attributable burden for clusters of risks and all risks combined took into account evidence on the mediation of some risks such as high body-mass index (BMI) through other risks such as high systolic blood pressure and high cholesterol.

All risks combined account for 57.2% of deaths and 41.6% of DALYs.  Risks quantified account for 87.9% of cardiovascular disease DALYs, ranging to a low of 0% for neonatal disorders and neglected tropical diseases and malaria.  In terms of global DALYs in 2013, six risks or clusters of risks each caused more than 5% of DALYs: dietary risks accounting for 11·3 million deaths and 241·4 million DALYs, high systolic blood pressure for 10·4 million deaths and 208·1 million DALYs, child and maternal malnutrition for 1·7 million deaths and 176·9 million DALYs, tobacco smoke for 6.1 million deaths and 143·5 million DALYs, air pollution for 5.5 million deaths and 141.5 million DALYs, and high body mass index (BMI) for 4·4 million deaths and 134·0 million DALYs.  Risk factor patterns vary across regions and countries and with time.  In sub-Saharan Africa, the leading risk factors are child and maternal malnutrition, unsafe sex, and unsafe water, sanitation, and handwashing.  In women, in nearly all countries in the Americas, north Africa, and the Middle East, and in many other high-income countries, high BMI is the leading risk factor, with high systolic blood pressure as the leading risk in most of Central and Eastern Europe and south and east Asia.  For men, high systolic blood pressure or tobacco use are the leading risks in nearly all high-income countries, in north Africa and the Middle East, Europe, and Asia.  For men and women, unsafe sex is the leading risk in a corridor from Kenya to South Africa.  Behavioural, environmental and occupational, and metabolic risks can explain half of global mortality and more than one-third of global DALYs providing many opportunities for prevention.  Of the larger risks, the attributable burden of high BMI has increased in the past 23 years.  In view of the prominence of behavioural risk factors, behavioural and social science research on interventions for these risks should be strengthened.  Many prevention and primary care policy options are available now to act on key risks.

As could be expected, the series of GBD studies have become and will continue to be very influential in directing governmental policies for improving public health worldwide. What they illustrate is that across all races, genetic backgrounds, societal cultures, practices and cuisines, stages of economic development, climates, environment etc, we’re all capable of substantially modifying the risks of unwanted health outcomes given where evolution has delivered the human species to the present day. With 57% of all deaths and 42% of DALYs due to the behavioural, environmental and occupational, and metabolic risk clusters studied, there is substantial opportunity for improvement. We can expect when additional factors are included in future GBD studies that ever-increasing proportions of premature mortality and morbidity will be explained, but at best these extra factors can only account for roughly half of all disease outcomes. Excusing all poor personal health on for example family genes is consequently defying the evidence and jettisoning chances of improvement, with some diseases offering greater opportunity than others.

What’s the significance of these findings in Australia and more pointedly regarding our club interest in fruits? As the authors point out, the importance of different diseases and risks varies greatly between countries and regions, with DALYs generally made up more strongly from YLDs than YLLs in developed countries, and the reverse in the developing world. The diet risk cluster included 14 individual risks and globally the 8 most important of these in descending order were diets low in fruit, high in sodium, low in whole grains, low in vegetables, low in nuts and seeds, low in seafood omega-3 fatty acids, and low in fibre. Insufficient fruit was roughly twice as important as low vegetable intake, and our general interest in eating fruit also addresses the low nuts, seeds and fibre risks. In developed and developing countries worldwide, low fruit intake ranks as one of the 10 most important of the 79 risk factors studied.

A majority of primary research reports on diet and health outcome relevant to us comes from the highly developed nations with prestigious research institutes such as the US, Western Europe and Japan, and so the question is to what extent do findings for their populations, which are taken up by the GBD in their analyses, apply to us? Do we as a nation have more optimal dietary habits or worse, knowing that in many societal behaviours we may trail them but nevertheless show the same trends? Well the US, UK, Scandinavia and Japan all have low fruit intake as a top 10 risk factor amongst the total of 79. So in these countries, increased fruit intake can be expected to have significant effects on health. But although Australians are generally going down the same road with a common top 4 across all risks (high BMI, smoking, high systolic blood pressure and high fasting blood glucose), low fruit intake is not one of our top 10.

So the GBD provides context. It’s one thing to become aware of a study from one of the advanced countries showing that increased fruit may reduce the risks of a particular disease by some percentage. But is this potential improvement greater or less than the myriad other risks that may also have impact – which ones may matter more than others? Without context to allow a wise and balanced conclusion regarding their relative importance, effort in changing lifestyle. habits etc may not be as successful as imagined. The GBD is also important in allowing people to see through popular media reports and promotions on this or that diet, food, herb etc that ‘çan change your life’, ‘give you boundless energy’, ‘eliminate aches and pains’ and so on. No matter how much substance may be in these claims, often very little, on average in our country they can never even approach resolving maybe a few percent of all poor health. We know from studies conducted on the Australian population that we’re still not eating enough fruit, but it’s not amongst our biggest health risks. Of course all these health considerations are independent of our simple enjoyment in eating them!