Grapes, wines and health

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

Grapes are consumed in fresh table form, as dried product (eg raisins and sultanas), as unfermented juice and in more recent times as dried powders for nutritional supplements. However, most of the world product is used to produce a variety of wines and other alcoholic beverages. Historically they've been part of cultural, religious, medical and celebratory practices for millennia. The following commentary on their place in our health and well-being is in two parts, the first briefly on the various non-fermented products, and the second in more detail on the fermented forms given this is how most product is consumed.

Fresh and dried grapes, juice and powdered supplements

These different products are very popular as snacks given their aromas and sweet flavour, particularly the seedless varieties, and they also make a valuable contribution to our total fruit and vegetable dietary intake which has been shown to have preventive benefits against a broad range of chronic diseases. The conventional nutrients in grapes are not especially superior to others, with high sugar content of 10-20% when fresh being the most prominent feature, while still having a glycaemic load classed as low-medium. Most of their positive health effects are thought to be due to numerous phytochemicals. Together, levels of these are also generally comparable to a number of other fruits (eg polyphenol and antioxidant activity is not clearly superior to others) but one component, resveratrol found in high concentration in grapes, has received particular attention. Study of the properties of individual compounds is indispensable in providing understanding of their fate and effects in the body and was pivotal in addressing historical nutritional deficiency states, but assessing their impact on preventive health effects and future well-being in real-life diets has been largely unproductive because so many ingredients all make their contributions. In this situation, the holistic approach considering total dietary patterns has proved more successful as ingredients can interact in synergistic and antagonistic ways.

There have been thousands of laboratory and animal-based studies on all these phytochemicals, documenting a great variety of positive effects. These have subsequently been further explored in human epidemiological studies to establish whether they have merit, but interpretation of results suffers from many limitations, including confounding factors not accounted for, patient and subject recall, and bias in completing diet questionnaires, comparability of subject controls etc. We still have relatively few prospective controlled trials in humans showing clinically significant outcomes under realistic conditions, but this could change dramatically in coming years as many studies are currently underway. As with many fruits and their components, there is considerable variation in their effects due to variations in horticultural conditions experienced during fruit production and which parts of the fruit are considered as skins are more often higher in nutrients than flesh. Dried forms have high glycaemic load with 80% carbohydrate. They may have been treated with sulphur dioxide and components may have suffered some degradation, juice may have almost no fibre content depending on processing technique, and the value of supplements will depend on appropriate dosing and reproducibility between batches. We also need to know much more about the active forms of these phytochemicals and their absorption, metabolism and excretion to understand the nature and magnitude of effects. A further complication is that many are extensively metabolised by gut microflora before being absorbed or excreted, and as we all have different microbiomes, this can lead to variation in effects between people.

Two studies with encouraging outcomes can serve as illustrations of the sort of work that has been undertaken to date on these products. In the first, an epidemiological case-control study examined the relationship between fruit, vegetable and soy intake on breast cancer risk in Korean women. There were 359 cases and 708 matching controls. No association was found between intake of total fruit, vegetables or soy food and cancer, but increased consumption of grapes, tomatoes and cooked soybeans reduced risk by 34, 38 and 33% resp after allowing for several confounding factors. In the second, the effect of daily consumption of a concentrated red grape powder for 12 weeks on blood pressure, flow-mediated dilatation (FMD, an important measure of arterial function) and oxidative stress was investigated in 50 subjects with pre- and mild-hypertension. Subjects were randomised into 3 groups that consumed 0, 200 or 400mg of the grape powder. They found a significant improvement in FMD, a significant decrease in lipid peroxidation, and diastolic blood pressure also decreased with the 200mg dose. No adverse effects were reported.

Wine, beer, cider and distilled liquor

We're all painfully aware that when any of these fermented alcoholic beverages are consumed in excess they can have devastating effects on individuals and societies. Consequently these habits should be avoided, managed or reversed if possible, and no more will be said on these high dose addiction problems. On the other hand, it's commonly believed and frequently promoted in the popular media that more moderate, low intakes can have beneficial effects on health and well-being, as might possibly be expected with a product derived from fruit, provided the beneficial ingredients have not been destroyed in processing and addition of other unhealthy chemicals has been minimised. As with un-fermented products there have been hundreds of studies addressing this phenomenon in laboratory, animal or epidemiological settings but few carefully controlled clinical trials in humans. The strongest general trait shown is in prevention or management of cardiovascular disease (CVD), still the biggest cause of morbidity and mortality in the developed world, and rapidly becoming so in developing countries. Moderate and regular wine consumption is thought to be the explanation for the 'French Paradox', where in France there's a high consumption of wine but lower incidence of CVD than elsewhere in Europe and the US, despite the population generally having increased risk in several of the classical disease markers. Further studies have led to the suggestion that red wine is better than white wine, beer, distilled products, grapes and grape juice etc because of the alcohol and polyphenol contents; white wines, beers and liqueurs have zero or very little polyphenols and grape products no alcohol . However these findings and conclusions are not universal or generally conceded, as summarised in the following 2008 review of the literature (Clinical Cardiology, 31, 347–351).

In a separate study, interview data collected from 12,958 young US adults who participated in the National Longitudinal Study of Adolescent Health were analysed to determine whether wine preference was related to educational, health and lifestyle characteristics that are predictive of long-term morbidity and mortality. Wine drinkers generally had more formal education, better dietary and exercise habits, and more favourable health status indicators (e.g., normal body mass) than other drinkers and non-drinkers. A larger proportion of wine drinkers were light-moderate drinkers compared to beer or liquor drinkers, and wine drinkers were less likely to report smoking or problem drinking than beer or liquor drinkers. These findings indicate that wine preference in young adulthood is related to educational, health and lifestyle characteristics that may help to explain the association between light-moderate wine consumption and morbidity and mortality risk in later adulthood so often reported in the epidemiological literature and public media.

Given the contentious nature of beneficial effects of low dose alcohol in CVD, is it sensible hoping to capitalise on these possible health outcomes when you consider the effects of such doses on other disease risks? For example, a large 2009 study of 1,280,296 middle-aged women in the UK examined the effect of moderate intake of alcohol and different types of alcohol on the risk of 21 site-specific cancers. A quarter of the cohort were abstainers and 98% of drinkers consumed an average of 10g alcohol/d; for a wine of 13% alcohol this is equivalent to 77ml, ie low intake. In the 7.2 years of follow-up there were 68,775 invasive cancers. Again, women who drank wine exclusively tended to be more affluent, to be leaner, take strenuous exercise more frequently and were less likely to be current smokers compared with other drinkers. For every extra 10g/d increase in alcohol intake, cancers of the oral cavity and pharynx increased by 29%, oesophagus 22%, larynx 44%, rectum 10%, liver 24% and breast 12%. In cancers of the upper aero-digestive tract the alcohol-increased risk was confined to current smokers with little or no effect on never or past smokers.

The nutritional summary of all this is that unfermented grape products can make a healthy contribution to your diet, whereas the benefits of grape-derived alcoholic beverages are more dubious, run the risk of habitual consumption escalating out of control, and there may be negative effects on some chronic diseases even at low intakes. If grape products form part of your diet, give preference to the former preferably fresh forms if possible.