More fruit and nuts, please

"Eat to Live, Not Live to Eat"
John H Weisburger, 2000

The following is a summary of a comparative risk assessment of the burden of disease and injury attributable to 67 risk factors and risk factor clusters in 20 age groups and both sexes in 187 countries grouped into 21 worldwide regions that was conducted by the WHO and published in 2012 (Lancet, 308, 2224-2260) as part of The Global Burden of Disease Study 2010. 

Quantification of the disease burden caused by different risks informs prevention by providing an account of health loss different to that provided by a disease-by-disease analysis.  No complete revision of global disease burden caused by risk factors has been done since a comparative risk assessment in 2000, and no previous analysis has assessed changes in burden attributable to risk factors over time.  We estimated deaths and disability-adjusted life years (DALYs, the sum of years lived with disability and years of life lost through premature death) attributable to the independent effects of 67 risk factors and clusters of these risk factors for 21 global regions in 1990 and 2010.

We estimated exposure distributions for each year, region, sex, and age group, and relative risks per unit of exposure by systematically reviewing and synthesising published and unpublished data.  We used these estimates, together with estimates of cause-specific deaths and DALYs from the Global Burden of Disease Study 2010, to calculate the burden attributable to each risk factor exposure compared with the theoretical-minimum-risk exposure.  We incorporated uncertainty in disease burden, relative risks, and exposures into our estimates of attributable burden.  In 2010, the three leading risk factors for global disease burden were high blood pressure (7.0% of global DALYs), tobacco smoking including second hand smoke (6.3%), and alcohol use (5.5%).

In 1990, the leading risks were childhood underweight (7.9%), household air pollution (HAP) from solid fuels (7.0%), and tobacco smoking including second-hand smoke (6.1%).  Dietary risk factors and physical inactivity collectively accounted for 10.0% of global DALYs in 2010, with the most prominent dietary risks being diets low in fruits and those high in sodium.  Several risks that primarily affect childhood communicable diseases, including unimproved water and sanitation and childhood micronutrient deficiencies, fell in rank between 1990 and 2010, with unimproved water and sanitation accounting for 0.9% of global DALYs in 2010.  However, in most of sub-Saharan Africa childhood underweight, HAP, and nonexclusive and discontinued breastfeeding were the leading risks in 2010, while HAP was the leading risk in south Asia.  The leading risk factor in Eastern Europe, most of Latin America, and southern sub-Saharan Africa in 2010 was alcohol use; in most of Asia, North Africa and Middle East, and central Europe it was high blood pressure.  Despite declines, tobacco smoking including second-hand smoke remained the leading risk in high-income north America and western Europe.  High body-mass index has increased globally and it is the leading risk in Australasia and southern Latin America, and also ranks high in other high-income regions, North Africa and Middle East, and Oceania.

There were more than 200 world experts who contributed to this study, and together they reviewed all relevant published and other data sources such as census and health surveys that provided convincing or probable evidence on disease and injury risk factors according to criteria specified in the widely-used grading system of the World Cancer Research Fund.  The relative impact of different diseases on disability and healthy living can vary greatly (eg from dental caries and eczema through to major depression and multiple sclerosis) and allowance was made for these different degrees of severity.  As part of their analysis they determined the theoretical minimum risk exposure for all risks.  In some like tobacco smoking this was 100% of the population being life-long non-smokers.  In others like systolic blood pressure it was 100-115mm Hg, ie they found evidence for progressively increased disease risk at levels above this.  Their corresponding best estimates for some of the dietary risk factors were - fruit intake below 300g/d, vegetables below 400g/d, whole grains below 125g/d, fibre below 30g/d, seafood omega-3 fatty acids below 250mg/d, nuts and seeds below 114g/wk, red meat above 100g/wk, trans fatty acids above 0.5% of energy and  sodium above 1000mg/d.  The minimum risk levels for processed red meat and sugar sweetened beverages were zero.  In many countries there is an unsatisfactory state of affairs where government and health authority recommendations can be more conservative than those above for all kinds of reasons, not least being powerful lobbying by commercial interests.  The compromise goal may be to recommend what is potentially doable rather what may actually be required.   To illustrate with two examples, until recently the goal was to get sodium intake below 2300mmg/d and for antihypertensive therapy to get systolic blood pressure below 140mm Hg, but for some time now there has been evidence that unwanted risks are still present below these targets.

A recent study published this week in the Journal of the American Medical Association found that only 1.5% of the US population consumes an ideal healthy diet, eg adequate fruit, nuts and seeds, vegetables, whole grains and  fish, and less red meat and low sodium.  Collectively we don’t eat enough fruit, nuts and seeds, and the relative global importance of this trait in 2010 was compared to the other risk factors in this study.  The top ranked (rank shown in parentheses) dietary-related risk factors causing the largest DALYs due to all diseases were as follows - low fruit consumption (no. 5), high sodium intake (no. 11), low intake of nuts and seeds (no. 12), iron deficiency (no. 13), low intake of whole grains (no. 16), vegetables (no. 17), and omega–3 fatty acids (no. 18), high processed meat intake (no. 22), low fibre intake (no. 24) and vitamin A and zinc deficiencies (nos. 29 and 31 resp).

Ischemic heart disease was ranked as the number 1 global DALYs health problem and stroke was ranked number 3; in the US these two diseases were ranked 1 and 2 resp for premature deaths.   Cardiovascular diseases have several important risk factors (age, gender, physical inactivity, diabetes, family history and tobaccos smoking, and high blood pressure, total cholesterol, BMI…) which can act independently and conjointly.  As a consequence the combined effect of multiple risk factors is not a simple addition of the individual effects and often is smaller than their sums.  When the effects of individual factors are estimated by holding others constant (eg grouping people into age brackets to allow for the effects of age) then dietary and physical inactivity risks for ischemic heart disease DALYs were - low nut and seed intake 40%, low physical activity 31%, and low fruit and vegetable intake 30 and 12% respectively.

All sobering findings.  However, with our interest in fruits and nuts we should be in a good position to ensure we’re not amongst the majority out there with less than adequate intake as these risks are modifiable if we choose.  And maybe with infectious enthusiasm we might even be able to spread the word about their pleasures and benefits as after all, eating a piece of fruit is enjoyable and far removed from having to take some unpleasant medicine that may be good for you.

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