"Eat to Live, Not Live to Eat"
John H Weisburger, 2000
This series of occasional articles on nutrition is intended to complement the horticultural information, providing a rationale for why we might bother to grow our own plants instead of buying fruit at commercial outlets. Producing your own fruit has its advantages: the pleasure of growing your own, lower cost, convenience, confidence in pesticide history, superior flavour when the fruit is picked at the right time, and increased likelihood of improved nutrition. Relevant scientific publications are used to provide information on recent advances and understanding.
In recent years there's been increased world-wide emphasis on prevention of health problems rather than what has been the more traditional practice of medicine, viz. attempting to cure or ameliorate them once they've developed. Lifestyle plays a large part in the prevention story, and diet is one factor that can be modified. However identifying life-long healthy diets is a complex affair, and application of the reductionist strategy that has been so successful in drug therapy and nutritional deficiency states has usually been found to be ineffective. So although vitamins, minerals, fibre, essential fatty acids, antioxidants etc all play a role in long-term well-being, adding particular compounds or supplements into the diet is not the way to go.
Even individual foods with their many contained nutrients have been found inadequate, and nowadays there's a recognition that it's only whole dietary patterns that can provide the full spectrum of required nutrients. The Mediterranean Diet which focusses on fruit, vegetables, nuts, cereals, legumes, fish and olive oil and minimises consumption of red meats, saturated fats and dairy is one such proven approach. The thousands of nutrients in plant foods, which we still do not fully understand, can act synergistically in the body to produce their beneficial effects, so selecting a few of them for supplementation is virtually doomed a priori. Consequently prudent diets embrace diversity of nutritious foods as a guiding principle. Research over several decades has convincingly shown that fruits and vegetables (F&V) are very important components of healthy diets, but consumers in developed countries generally eat so few of them that public health promotion programs have concentrated mainly on encouraging people to increase their total intake with choice of which food types make up the servings largely left to the consumer. As a consequence, studies on the importance of F&V variety as opposed to quantity have been of lower priority, resulting in less being known on this question.
The following study (American Journal of Clinical Nutrition (2011) 93, 37–46) on Puerto Rican adults from a USDA Nutrition group is one of the few that has specifically addressed the question of F&V variety. They used a semi-quantitative Food Frequency Questionnaire (FFQ) specifically developed and validated for this population, to assess dietary intake over a 12-month period. The food list for the questionnaire was developed using the format of the National Cancer Institute/Block food frequency, but with data from the Hispanic Health and Nutrition Examination Survey (HHANES) dietary recalls for Puerto Rican adults and tested in Puerto Rican participants aged more than 59 years in Massachusetts.
The Puerto Rican population has a typical diet that differs considerably from both the general US population and from Mexican Americans, so foods such as plantains and specific soup and rice-dish recipes were added to the FFQ. Reported servings of individual F&V were summed to obtain the mean servings consumed per day. Variety in F&V intake was defined as the total number of unique F&V consumed at least once per month over the past 12 months. Fruit included apples, pears, bananas, oranges, grapefruit, peaches, apricots, nectarine, plums, grapes, avocado, kiwi fruit, papaya, mangoes, prunes, cantaloupe, honeydew melon, watermelon, cherries, strawberries, blueberries, raspberries, cranberries, pineapple, olives, and 100% fruit juice. Vegetables included lettuce, spinach, tomato, carrots, string beans, peas, corn, peppers, broccoli, cauliflower, cabbage, beets, asparagus, mushrooms, eggplant, onion, squash, cucumber, radish, celery, cilantro, garlic, parsley, zucchini, basil, and 100% vegetable juice. Starchy vegetables (including potato, plantains, and cassava), beans, and legumes (including lima beans, pinto beans, white beans, black beans, pink beans, kidney beans, cowpeas, soybeans, split peas, and lentils) were excluded.
Before reading the summary of their findings, a few words on inflammation might be helpful. It's a normal response to injury/infection and the subsequent healing/repair process, provided it's not excessive or uncontrolled. Localised and transient inflammation, such as from a bee sting, is very different to chronic systemic inflammation, which if sustained over time can increase the risks of almost all of the non-infectious chronic diseases increasingly found in Western societies. There are a number of valuable markers of systemic inflammation and one of these is C-reactive protein (CRP). Its importance can be gauged by just considering the cardiovascular diseases (CVD) where it's also a mediator, is independent of the traditional risk factors of age, smoking, cholesterol levels, blood pressure and diabetes, and is a stronger predictor of future risk than elevated levels of LDL-cholesterol and most other markers. Results from studies in >15 different populations and >40,000 people (when transient inflammation can be excluded) have shown that the top tertile of CRP levels is associated with a 2-fold relative increased CVD risk. Weight loss, diet, exercise and cessation of smoking all reduce CRP levels and reduce vascular risk.
Puerto Rican adults have prevalent metabolic abnormalities but few studies have explored F&V intake and coronary heart disease (CHD) risk in this population. We tested the hypothesis that greater F&V intake and variety are associated with a lower 10-y risk of CHD and CRP concentrations. In a cross-sectional study of approximately 1200 Puerto Rican adults aged 45–75 y, we assessed F&V intake with an FFQ. The 10-y risk of CHD was assessed with the Framingham Risk Score (FRS, a long running US public health study) in participants free of cardiovascular disease. CRP was measured in fasting serum. Variety, but not quantity, of F&V intake was significantly associated inversely with FRS after adjustment for the following: sex; waist circumference; perceived stress; alcohol use; intakes of energy, trans and saturated fatty acids, use of supplements, cardiovascular medications, and diabetes medications. However, the association was attenuated just above the significance level after adjustment for income. Variety, but not quantity, was significantly associated with a lower serum CRP concentration after adjustment for age, sex, smoking status, alcohol use, servings of F&V, white blood cell count, diastolic blood pressure, diabetes, nonsteroidal anti-inflammatory medication use, intakes of energy and vitamin B6, waist circumference, perceived stress, and income. The adjusted odds of a high CRP concentration for those in the highest compared with the lowest tertile of F&V variety was 0.68. F&V variety, but not quantity, appears to be important in reducing inflammation. Although the results are suggestive, larger studies are needed to confirm a possible association with CHD risk score.
Public media reports of individual 'magic or super foods' or 'the 5 fruits you must eat' that purportedly engender superior health should not be blindly followed to the extent where they unduly dominate others, but instead should be considered in the context of possibly making a contribution to the wide variety of healthy foods in your balanced diet.
There is archaeological evidence showing pomegranates have been cultivated as a source of food and medicines in the Middle East for millennia. It's so highly valued in some cultures it features in their religious history and has been called the 'fruit of paradise', the 'fruit of love' because of their many seeds representing fertility, and more recently 'nature's power fruit'. In traditional folk remedies it's been used for just about everything - eliminating parasites, improving libido and skin problems, relief of menopausal symptoms, as an antipyretic, contraceptive, vermifuge and anti-helminthic, and to treat ulcers, snake bites, diabetes, rheumatoid arthritis, mental diseases, cardiovascular, respiratory, fertility and hormonal problems, diarrhoea, acidosis, dysentery, haemorrhage and microbial infections. In many impoverished countries with limited access to modern medicines and vaccines, it still finds use in these various treatments. Historically in Western countries it's really not been more than a curiosity fruit, valued mainly as an ornamental tree with beautiful glossy green foliage and bright red flowers, and for use of the fruit as an adornment in a dining room setting.
As often happens in the development of world-wide interest in nutritional and medicinal fruit qualities, the early scientific work came from indigenous areas where pomegranates are strongly embedded in local cuisines and lifestyles. These isolated studies reported a range of positive features mainly centred on polyphenolic (PP) antioxidant activity. For example, one study found that pomegranate juice (PJ) had more PPs than juices from (in decreasing order) red plum, grape, cranberry, kiwi fruit, orange, grapefruit, apple, pineapple, pear and peach, with the range from PJ to peach being 5-fold. Others found antioxidant activity in PJ was 3 times that of red wine and green tea, and in another it was greater than that in 22 other commonly eaten fruits. These reports then led to more widespread interest from the global research community that has grown remarkably in the last 20 years. The increase in research can be gauged from a literature search conducted in November 2012 for published studies on pomegranates that retrieved 677 studies, of which 619 had been published in the last 10 years and 425 in the last 5. The usual approach to addressing nutritional questions on foods is to begin with laboratory work, as compared to human studies, it's much easier and faster to perform without exorbitant costs, has fewer ethical and logistical restraints and concerns over possible toxicities, and can suggest future promising lines of investigation and appropriate dosage for desired effects together with some understanding of possible mechanisms. Identification of the important and different active chemicals present with suitably specific and sensitive assays, their bioavailability, metabolism and excretion also needs study in the lab. This process has been largely followed with pomegranate fruit, and while many favourable results have been forthcoming in the last decade there have so far been relatively few randomised clinical trials at doses that can reasonably be expected to be consumed, which would allow assessment of cause and health effects in humans.
As an aside, all this research activity has led to pomegranates becoming quite trendy in developed countries of late, with considerable marketing hype on their ability to prevent many of the chronic diseases currently causing so much concern. The food processing industry has jumped on the bandwagon, producing all manner of PJ extracts and supplements for the health conscious, at specialty prices of course. If you believe pomegranates are good for you and wish to regularly include them in your diet, a 2009 study emphasises how you might be better off growing your own or at least purchasing the whole fruit rather than more convenient juice, tablet or capsule forms. One of the metabolites of PJ is the PP ellagic acid, and it's commonly been used to standardise PP concentration in these extract products as it's easier to assay than many others. In this 2009 study they found that only 5 out of 27 commercially-available products in the US had the natural distribution of PPs, 17 had been adulterated with added cheaper sources of ellagic acid, and 5 had almost no antioxidant activity at all as a result of how they were processed. Ellagic acid is an antioxidant, but these compounds almost always exert their effects in synergistic interactions with the many other PPs in whole fruit rather than being effective alone, so inadequate or improper quality control on these supplements may mean they have very little value.
The following review of the published literature by a German and Swiss group (Phytotherapy (2015), 29: 501–508) considered just one area where pomegranates are purported to have beneficial health effects, namely cardiovascular disease, still the biggest cause of morbidity and mortality world-wide. It was concluded that the evidence available as of 2015 was not sufficiently strong to be convincing, but they acknowledged with all the studies currently in progress this evaluation could become more positive in future. It illustrates the very large gap between promising lower level scientific studies (laboratory, animal and epidemiological) and those that are relevant and properly controlled in the realistic human setting, let alone those that rely solely on centuries-old traditional practices and beliefs based on essentially zero real knowledge.
This study attempts a critical evaluation of the clinical evidence behind the use of dietary pomegranate preparations in the prevention and treatment of cardiovascular diseases. A search of PubMed on August 10, 2014 identified 228 references, which yielded extractable data from 24 clinical studies of pomegranate preparations. Hand searching identified two further studies. The quality of the studies and evidence of effectiveness of pomegranate were assessed by an established set of conventional criteria. Overall, the study quality was poor. Even in the best studies, indications of benefit did not reach the conventional levels of statistical significance. The only study with a definitive design had a biochemical rather than a clinical endpoint: it showed the expected difference in blood concentrations of myeloperoxidase (a marker for cardiovascular mortality risk) after a single dose of either pomegranate or placebo. Only 10 of the 26 studies provided HPLC data (a sensitive and specific assay technique) on the amounts of co-active ingredients in the preparations that were consumed by the subjects. If pomegranate has a role in the prevention and treatment of cardiovascular diseases, there is a pressing need for dose-finding and long-term confirmatory studies. The ultimate endpoint for definitive studies would be mortality, but reductions in blood pressure or demonstrable decreases in atherosclerotic plaques would be useful surrogates. Sample sizes for various assumptions are provided. Future studies need to prove the clinical benefit.
So we have a cautionary tale here. Enjoy the fruit if flavour, good storage properties, taste, availability etc make them appealing to you, but keep your feet on the ground regarding hyped-up claims about their magical qualities, and buy whole fruit or grow your own if this feeling is strong enough, instead of relying on costly and maybe dubious extracts. Pomegranates have a place in a varied diet by providing their own mix of valuable nutrients, not above all else but together with other delicious fruits. And let's see what is scientifically established for them in coming years regarding their promise (eg with prostate cancer) in being able to make a distinct contribution to human health and well-being.