"Eat to Live, Not Live to Eat"
John H Weisburger, 2000
We’ve all heard the saying that an apple a day keeps the doctor away, probably beginning way back when you were a youngster and your parents were trying to get you to eat some fresh food. Is there any truth in it?
A recent study in the 30th March 2015 edition of the Journal of the American Medical Association attempted to address the question by conducting a cross-sectional study of a nationally representative sample of the noninstitutionalized US adult population. A total of 8728 adults 18 years and older from the 2007-2008 and 2009-2010 National Health and Nutrition Examination Survey completed a 24-hour dietary recall questionnaire and reported that the quantity of food they ate was reflective of their usual daily diet. Daily apple eaters were taken as those who consumed the equivalent of at least one small apple (about 150g) daily. The primary outcome measure was success at "keeping the doctor away," measured as no more than one visit to a physician during the past year. Secondary outcomes included successful avoidance of other health care services, ie no overnight hospital stays, visits to a mental health professional, or prescription medications. Of 8399 eligible study participants who completed the questionnaire, there were 753 apple eaters (9.0%) and 7646 non-apple eaters (91.0%). Without considering any other contributing factors, the apple eaters were more likely to keep the doctor (and prescription medications) away, but after adjusting for socio-demographic and health-related characteristics, this association was no longer seen. There were also no differences between the two groups in overnight hospital stay or mental health visits, but the apple eaters were marginally more successful at avoiding prescription medications. The authors concluded their data did not support the 'apple a day keeps the doctor away' belief, but did note that the small fraction of US apple eaters appear to use fewer prescription medications.
Questionnaire studies are always subject to the reliability of information gathered. In this case, how well does a 24-hour snap-shot represent what someone consumes on a yearly basis, and do participants report or remember accurately. Nevertheless, such information is still better than the unfounded cultural beliefs of the past. The small proportion of US adults who regularly eat apples is interesting, but this ties in with another 2015 study where it was found that more than 60% of the daily calorie intake in US households came from processed foods. If taken literally, the advice regarding apples would be expected to produce a negative result in any properly conducted study, as no single food, no matter how favoured, could hope to provide all the necessary nutritional components to ensure long-term well-being. If, however, it is more loosely interpreted to simply mean 'eat more fruit and vegetables', then it's excellent.
Traditional methods for extending the storage life of perishable foods such as fruit, vegetables, milk, meat and fish were based overwhelmingly on techniques available at the time, eg salting, smoking, fermentation and solar drying with little knowledge of the effects these processes had on nutritional properties. Nowadays we have a far wider range of techniques including freezing, high pressure, spray and drum drying, and vacuum and microwave drying, but the question for each remains – how do they affect healthful nutrients and are some techniques better than others? The answers vary greatly depending on what is intended, the particular fruit and cultivation conditions, its state of maturity, how pre-treatment may influence processing, storage conditions etc, so let's just consider one example – thermal drying of apricots.
This product is commonly known and enjoyed everywhere as about half the total world crop is sold dried, usually by solar heating. Most consumers prefer them when in a çhewy rather than crisp state and this means they are processed to a moisture content that is higher than that required to totally prevent microbial spoilage. This is prevented usually by 'sulphuring', where either burning sulphur or bisulphite is used as a preservative. However some people are hypersensitive to the resultant SO2 and have unwanted inflammatory reactions. Plus, SO2 totally destroys vitamin B1. Leaving this as a separate issue, to what extent does the solar or hot air drying cause breakdown of valuable nutrients?
All fruits have high moisture content, usually around 90%, and as a result their nutritional qualities depend mainly on vitamins and similar acting phytonutrients, fibre type and content, and to a lesser degree, minerals. Minerals are the least affected by drying, fibre properties are changed because cellular structure is compromised as the fruit dries out, and vitamins/phytonutrients are the most sensitive to processing conditions. It should be realized that in achieving extended storage life with drying, products are subjected to longer, possibly degrading conditions, than they ever would be in the fresh state. Storage losses, due for example, to oxygen and light can then sometimes outweigh those from the processing operation itself. Most breakdown of vitamins and phytonutrients in drying occurs enzymatically or thermally, the latter often by oxidation. Pre-treatment blanching (eg 100°C for 1-3 minutes followed by rapid cooling) is one way to inactivate enzymes and minimise losses from this source.
Carotenoids are responsible for the yellow colour of many fruits and vegetables, and are a major nutritional feature of apricots. Many of these can be converted into vitamin A in the body, ie they are pro-vitamins. In a recent Italian study (Plant Foods & Human Nutrition, 2013, 68, 241-246) it was found that apricot halves dried in a dehydrator at 60°C or 70°C with no other pre-treatment took 21 and 15hrs respectively to reduce moisture content from 87% to 20%. Carotenoids are regarded as being relatively heat stable whereas many of the other common vitamins, vitamin C in particular, are notoriously more prone to degradation. Nevertheless, in this study carotenoids still decreased by 28 and 43% respectively compared to the fresh fruit.
In general, newer techniques such as freeze-drying lead to better nutrient retention than that obtained in hot air or sun dried products. Solar drying is still a major process in the developing world because it doesn't involve large capital costs and it's energy-free. But sufficient space is needed, labour is required to turn and rake fruit, processing is not well-controlled and needs warm sunny weather, fruit have to be protected from rain and over-night moisture, there can be foreign matter (eg dirt) contamination, and fruit need protection from insects, birds and microbial spoilage given the process can take several days. There is also a risk of aflatoxins being produced which are carcinogenic. In addition, it involves exposure of fruit to strong light which can cause breakdown of phytonutrients such as vitamins B2and C.
Surveys show that, on average, consumers place hedonic qualities of fruit, ie taste, flavour, aromas, appearance and texture before nutrition. And dried fruits are normally most desirable because their sweetness etc has been concentrated through loss of moisture. However, if nutrition is important to you then fresh is almost always best. Dried products do serve a valuable role in providing important out-of-season foods which can also be distributed to locations other than where they're grown. The challenge to the modern processing industry and the home processor, is to adopt those techniques that provide the tastiest, healthiest and safest products.
Selenium (Se) is an essential micro-nutrient but more than a billion people worldwide, mainly in undeveloped countries but also many parts of Europe, have deficient intakes. The Australian NHMRC recommends a daily intake (RDI) of 70 and 60 mcg/day for adult men and women respectively. In the average Australian diet, most of this comes from two food groups, cereals and meats. These two main groups are not particularly rich in Se but as staples in the diet, sufficient amounts are consumed to add up. Se levels in all foods are greatly influenced by the particular plant species and the soil content. For example in one study, pasta products made from US wheat contained 57mcg/100g Se, whereas an Italian equivalent had only 6mcg/100g. For comparison, Australian sourced pasta has 1-10mcg/100g.
There are many geographic areas worldwide that have low soil Se (some regions in China are extreme), and the south west of WA is one of them. So for example, wheat grown here does not have good Se content. Depending on the makeup and source of individual dietary components, people can become deficient and this may lead to Keshan's disease, compromised reproductive, immune and brain function and decreased resistance to viral infections. The average adult intake in the UK is only 30-40mcg/d. Australians have fared better in the past (57-87mcg/d) but this has been in decline over the last 20 years. Although acute deficiency states are not usually seen here, many recent studies have shown that intakes at or above the RDI can have positive effects on the above-mentioned conditions as well as reducing total cancer incidence and mortality.
How can we ensure we're consuming sufficient to avoid deficiency problems and hopefully also benefit from amelioration of chronic diseases? One broad approach in deficient areas such as Finland, is for the government to mandate that all agricultural fertilizers be supplemented with Se so more is taken up by plants, and these are then richer sources whether subsequently used as human foods or livestock fodder. Unlikely or at least years away for us, given we don't have severe deficiency problems. Tablet supplementation is less than ideal as Se exists in many forms and the availability, action and fate of these in the body varies - which form/s should a tablet contain?
The following study by Yang (LWT- Food Science & Technology, 2009, 42, 1573-1580) makes the case for regularly including brazil nuts in your diet:
Epidemiological studies have shown an inverse relationship between nut intakes and chronic diseases such as cardiovascular diseases and cancers. Brazil nuts contain abundant dietary antioxidants, especially Se. One single Brazil nut provides 160% of the US Recommended Daily Allowance – probably the best source of Se from plant-based foods. Brazil nuts possess phenolics and flavonoids in both free and bound forms and are rich in tocopherol, phytosterols, and squalene. The possible beneficial effects of these compounds are due to their antioxidant and anti-proliferative activities, which are linked to a reduced risk for developing atherosclerosis and cancer.
The NZ population is Se deficient and a 2008 study suggested that two brazil nuts a day could help ensure adequate intake. However as with many nutrients, adequate is good but when taken to excess, toxicity can develop. The NHMRC recommends an upper intake limit of 400mcg/d. While over-zealous use of tablet supplements with the goal of minimising future chronic disease can all too easily occur, this is also the case with brazil nuts, as they can be such a rich source of Se depending on their provenance (average 1920mcg/100g). Accordingly, their consumption should be limited and not gorged.