"Eat to Live, Not Live to Eat"
John H Weisburger, 2000
Considering the thousands of edible tropical and sub-tropical fruits known worldwide, the USDA has suggested that only 300 of these are commercially important and less than 100 contribute to most production and consumption. Of fruits from Australia, the macadamia nut is the only one that makes these lists. Possible reasons for this laggard performance include firstly that our continent is the driest and has been relatively isolated botanically for a long time. As a consequence we don't have anything like the diversity and profusion of edible and palatable species found in Asia and the Americas. Secondly, our indigenous people have had a nomadic lifestyle for thousands of years that did not gradually improve the stock by selection of occasional superior trees as happened more often elsewhere. As a result, our limited native bush foods have remained in their original unimproved forms, and consumption of the best of them remains largely at the fringes of society.
However despite these negatives, numerous surveys and personal evaluation have usually judged the macadamia to be the tastiest of all the commercial nuts. They taste good raw and even better roasted, but most of the world's crop is eaten in more processed forms such as chocolate-coated kernels, nut-impregnated chocolates, muffins, pies etc. It was the Hawaiians who first realised their commercial potential, did the development work on them over several decades to produce superior cv's and then built up a successful industry. Only then did we belatedly decide to get operations going here on our own native plant!
Macadamias have an extremely strong shell which is more difficult to crack than other tree nuts. For the home user this usually means that many kernels are fractured during preparation. Like all nuts, un-broken kernels command higher retail prices than fragments and commercial crackers can give a better proportion of unbroken nuts than that achieved by the home-user. As with cashews which have a toxic oil removal problem, much of the high cost of purchase is due to quality kernel preparation. However, if you only want to savour a few a day, the high retail price provides a good incentive to grow your own, given a few broken kernels is really neither here nor there – you still get to enjoy these delicious things and they store quite well in-shell if kept dry.
So macadamias are almost universally recognised as strong players on the pleasure front. But do they also have favourable nutritional qualities that can be of benefit in our current Western dietary habits which underlie so many chronic disease problems, since many of these have progressed to epidemic proportions? The following is a summary of a study (J. Nutrition (2003) 133: 1060–1063) by a research group at the University of Newcastle NSW illustrating that macs have substance and aren't just a 'pretty face'. It concerns unhealthy blood cholesterol levels which predispose to cardiovascular disease (CVD), the biggest cause of mortality in Australia.
This study was conducted to assess the cholesterol-lowering potential of macadamia nuts. Seventeen hyper-cholesterolemic men (mean age 54 y) were given macadamia nuts (40–90 g/d), equivalent to 15% energy intake, for 4 wks. Plasma total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides and homocysteine (a CVD risk factor) concentrations and the fatty acid composition of plasma lipids were determined before and after treatment. Plasma monounsaturated fatty acids (MUFAs) were elevated after intervention with macadamia nuts. Essential polyunsaturated fatty acid concentrations(n-6 and n-3 PUFAs) concentrations in plasma were unaffected by macadamia nut consumption. Plasma total cholesterol and LDL-cholesterol concentrations decreased by 3.0 and 5.3% respectively, and HDL cholesterol levels increased by 7.9% in these hyper-cholesterolemic men after macadamia consumption. Plasma triglyceride and homocysteine concentrations were not affected by treatment. Macadamia consumption was associated with a significant increase in the relative intake of MUFA and a reduced relative intake of saturated fatty acids and PUFA. This study demonstrates that macadamia nut consumption as part of a healthy diet favourably modifies the plasma lipid profile in hyper-cholesterolemic men despite their diet being high in fat.
The quantity of nuts used in this study is higher than most people would consume per day but other studies since have considered more reasonable lower levels with comparable results. Although the 'bad' LDL-cholesterol only decreased by 5.3% on average, importantly the 'good' HDL-cholesterol increased by the larger margin of 7.9%, so that the more relevant ratio for predicting health benefits, namely LDL/HDL, changed to a far greater degree than either alone. Macadamias have the highest fat content of all the important tree nuts (76%) and 80% of this is MUFAs. Collectively, all these nuts have qualitatively similar effects on CVD and underlying risk markers, with the relative magnitude of effects depending on their particular makeup. No one of them is superior in all nutrient components so that the best strategy for health benefits is to eat mixed nuts rather than believing that any one of them is clearly superior. Three pillars of modern nutrition are balance, moderation and variety, and simplistic belief in the magic or sufficiency of 'super foods' that should be single-mindedly consumed is flawed.
To illustrate the varying strengths of nuts and the lack of any that are tops all round, consider how macadamias stack up against some of the others regarding familiar macro- and micro-nutrients (expressed per 100g edible fresh food): they have 7.9g protein cf 25.8g in peanuts, 6g fibre cf 10.4g in hazelnuts, 12.1g saturated fat cf 3.9g in almonds, 58.9g MUFA cf to 8.9g in walnuts, 1.5g PUFA cf 47.2g in walnuts, 1.3g n-6 essential fatty acids (eg linoleic acid) cf 20.6g in pecans, 0.2g n-3 (alpha-linolenic acid) cf 9.1g in walnuts, 11mcg folate cf 145mcg in peanuts, 0.54mg vitamin E cf 27.1mg in almonds, 85mg calcium cf 248mg in almonds, and 130mg magnesium cf 376mg in brazil nuts. With other less familiar plant phytochemicals, macadamias have roughly half the level of phytosterols cf pistachios and peanuts, and total antioxidant phenols in pecans is 28 times that in macadamias. All nuts including macadamias are very good nutrient-rich foods, and positive health effects that have been reported in addition to the study above on CVD risk factors include type 2 diabetes, reduction in overweight and obesity, gall stones, hypertension, cancer and inflammation.
Fruits and nuts may be processed into various forms for a number of reasons such as cultural practices, improved storage properties, improved palatability and taste, aesthetics and nutrition. If nutrition is important to you with the nuts you eat, then it should be recognised that preparation and processing can have a considerable influence. Most fruits have an unequal distribution of nutrients throughout the edible parts, usually with higher levels found towards the exterior. Simply removing apple skins before eating (eg for cooking in apple pie where heat/time causes its own additional losses) can result in loss of over 90% of phytochemical antioxidants.
With nuts this surface concentration can be similarly extreme eg in walnuts 95% of antioxidants are in the brown seed coat, almonds are often blanched to remove their brown coat for aesthetic reasons and so lose 80% antioxidant capacity, and peanuts minus their red-brown seedcoat lose 70%. Then once the kernel is isolated, simple dry roasting can further degrade nutrition (although usually enhancing flavour) eg with pistachios the loss can be 44%. More extensive processing into popular products such as peanut butter loses another 50%. As with many foods, raw is frequently best nutritionally unless there's a specific reason to modify, eg inhibit, microbial spoilage, reduce anti-nutrient factors or soften tough fibrous tissue.
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 favourable 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 ( fruits and vegetables) significantly reduces risk. Given the very common practice of processing these foods, they considered whether fruits and vegetables eaten in these altered forms was 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.
To minimise the onset of chronic diseases in aging populations, health authorities worldwide recommend we eat more fruit and vegetables and less animal-based foods. Plant-based diets are low in calories and saturated fats with good supplies of carbohydrate, fibre, vitamins and minerals. They also have no cholesterol and most importantly are rich sources of bio-active phytochemicals that have benefits beyond basic nutrition. These latter substances are usually produced by plants as secondary metabolites to help in their defence against predator and pathogen attack. Chemically they're mostly polyphenols, grouped into several classes such as flavonoids (eg anthocyanins, flavones and flavonols), stilbenes, phenolic acids and tannins, and many have strong antioxidant activity. There are thousands of them and in numerous laboratory, animal and human studies they've been found to be effective agents in preventing or ameliorating cardiovascular disease, cancer, diabetes and mental degenerative diseases amongst others.
An important process by which these diseases develop concerns the production of reactive oxygen species associated with normal physiological activities. When these pro-oxidative states are not kept in check by the body's own antioxidants and those supplied externally from the diet, damage can occur over time. Recent research indicates that adequate intake of foods with phytochemicals high in antioxidants is a principal and significant means by which the above-mentioned diseases can be positively impacted. But as an aside it should be realised that antioxidant activity is not the only positive health attribute of plant phytochemicals; different fruits have widely varying mixtures of these chemicals with a multitude of activities and these are thought to interact positively in several ways. Focussing just on antioxidant activity as a major player in this story, berry fruit have on average 4, 10 and 40 times the activity of other fruits, vegetables and cereals respectively. Much of this is due to anthocyanins, which give them their characteristically strong orange, red and purple colours. Many hundreds of anthocyanins have so far been identified.
The following is a summary of work published in Nutrition Reviews (2010, 68, 168-177) where the case for including a hearty amount of berry fruit in your regular balanced diet is made.
Berries are a good source of polyphenols, especially anthocyanins, micronutrients, and fibre. In epidemiological and clinical studies these constituents have been associated with improved cardiovascular risk profiles. Human intervention studies using chokeberries, cranberries, blueberries, and strawberries (either fresh, or as juice, or freeze-dried), or purified anthocyanin extracts have demonstrated significant improvements in LDL-cholesterol oxidation (a precursor to blood vessel adhesion and atherosclerosis), lipid peroxidation, total plasma antioxidant capacity, dyslipidemia (high LDL-cholesterol and/or fats) and glucose metabolism. Benefits were seen in healthy subjects and in those with existing metabolic risk factors. Underlying mechanisms for these beneficial effects are believed to include up-regulation of endothelial nitric oxide synthase (increasing production of nitric oxide which favourably modulates blood pressure and blood vessel function), decreased activities of carbohydrate digestive enzymes, decreased oxidative stress, and inhibition of inflammatory gene expression and foam cell formation (scavenger cells containing numerous cholesterol droplets). Though limited, these data support the recommendation of berries as an essential fruit group in a heart-healthy diet.
This study by US researchers refers to several berry fruits from colder climates not readily available to us, but we can nevertheless take on board the findings for ones we do know well, such as strawberries, blueberries, and blackberries/raspberries and their many hybrids. Benefits extend beyond the cardiovascular disease largely addressed in the above study. For example in a recent Finnish study on the effects of including fruit, berries and vegetables in the diet, it was found that those in the top 25% of consumption had a reduced chance of developing diabetes after allowing for several other risk factors such as obesity, family history etc. Berries are usually eaten in much smaller quantities than other fruit and vegetables, yet when the effects of berries were considered separately from the other two in this comparatively small study, it was found that they alone were responsible for a 35% reduction in incidence and the other fruits and vegetables had no significant effect.
Another feature to consider with berries is the common practice of processing them into jams, jellies and the like. Unfortunately, these products may contain up to 50% added sugar to achieve good storage properties. Consumption then results in a rapid and unwanted extra increase in blood glucose and insulin which can be deleterious to health in the long term (eg predisposing to type 2 diabetes). The only saving grace here is that the berry polyphenols do have an ameliorating effect, but the better pathway to adopt is to either eat them fresh, freeze as purees, dry etc rather than add all that nutritionally-empty sugar to your diet. Collectively we're all eating too much as it is, and it's compromising the nutritional value of the berries which start off with such excellent credentials. And to top it all off, the antioxidant activity in the fresh fruit generally declines in proportion to any heat (time and temperature) processing steps.