Humble fruits that pack a powerful punch
Prunes, plums and peaches: delicious, cheap cancer-fighters
Posted Nov 15, 2010
For too long, plums, and especially their dried incarnations, prunes, have gotten a bum rap. This is mostly because of their unfortunate association with constipation, which they relieve quickly and naturally thanks to their high fiber content. However, as we feast on this year's crop of this delicious stone fruit, it's time to stop snickering and start appreciating this humble stone fruit's many other health benefits. For in addition to their laxative qualities, plums, and their cousins, peaches and nectarines, appear to have cancer-fighting properties.
Animal and test-tube experiments have yielded promising results. Most recently, scientists at Texas A&M University discovered that breast cancer cells died after being treated with peach and plum extracts. The researchers treated healthy cells and breast cancer cells (including an aggressive non-hormone-dependent strain) with extracts from yellow-fleshed ‘Rich Lady' peaches and red-fleshed ‘Black Splendor' plums - both commercially available varieties.
"These extracts killed the cancer cells but not the normal cells," reports Luis Cisneros-Zevallos, Food Scientist and Associate Professor at Texas A&M University. "Our studies in vitro show the potential for selective killing of cancer cells, and our studies with mice have confirmed that these compounds inhibit metastasis," he adds. (Metastasis is the spread of cancer cells to other parts of the body.) Indeed, the effect of the fruit extract was strongest on the aggressive, non-hormone dependent cancer cells that most commonly metastasize, he notes. The research was published in the Journal of Agricultural and Food Chemistry.
The two phenolic compounds largely responsible for plums' anti-cancer effect, chlorogenic acid and neo-chlorogenic acid, occur in many fruits and vegetables but are more prevalent in stone fruits than anywhere else - including blueberries with their impressive array of cancer-preventive phytonutrients. Whether these phenolic acids have similarly beneficial effects on other types of cancer is unclear. "We intend to study other types of cancers including prostate, colon and pancreatic," says Dr Cisneros-Zevallos.
What makes plums and prunes (coyly renamed ‘dried plums' by American prune marketers wishing to shake the stigma of geriatric constipation...) even more appealing is their low glycemic index (GI) ranking. (Anything below 55 is considered low.) According to the University of Sydney's Glycemic Index Database, prunes have a GI of 29, even below low-GI apricots (around 31) and half that of raisins (between 54 and 66). Foods with a high GI-value are thought to contribute to weight gain - a cancer risk factor - and the secretion of hormones such as insulin that can fuel cancer-cell growth.
Also in their favour, plums, prunes and peaches (ideally organically grown, to avoid pesticides: peaches and nectarines have among the hesviest pesticide residues, according to the Environmental Working Group's Shopper's Guide to Pesticides; plums fare better) are less expensive than many other fruits - especially imported tropical fruits or exiotic 'miracle foods' such as goji berries and acai fruit. This makes it easy to eat them on a daily basis, even for people with a tight food budget.
So what's the healthiest way to enjoy stone fruits? Straight off the tree. That's because phenolic compounds may be lost during processing, especially when subjected to heat, as in high-temperature canning and pasteurization for juice.
Alas, the plum season is short, so what can we do to get year-long protection from plum and peach compounds? Dried fruit is an option, as drying preserves a larger proportion of phenols than canning. "How much is lost will depend on the conditions of processing being used including temperature, air humidity and processing time," says Dr Cisneros-Zevallos. If you have a dehydrator, you may wish to experiment with fresh peaches and plums. Another option is frozen fruit - either bought fresh, pitted and frozen yourself, or bought ready-frozen.
Prune puree - which some call ‘prune butter' because of its thick, shiny texture - is quick and easy to make at home. Simply empty a packet of soft dried prunes into a bowl (making sure there's no stray pits left in any of them), pour warm water over them and leave to soak for an hour (or longer if they are very dry). Puree in a kitchen blender (you can add ginger or cinnamon for extra flavor) and transfer to a tightly sealed jar. This should keep for 3-4 weeks in the refrigerator.
In my house, we spread prune butter on toast, pancakes and waffles, mix it with plain yogurt and porridge or add it into fruit smoothies. We even serve it alongside roast meat (especially duck) as a sort of relish or chutney (adding a little salt, pepper and other spices). Lastly, one of my favorite recipes in Zest for Life is a chocolate-hazelnut spread that contains prune puree and tastes a lot like Nutella.
One excellent use of prune butter - which you can also buy in jars - is as fat replacement in baking. According to researchers at New York's Hunter College, pureed prunes can replace as much as 30 per cent of the fat by weight in chocolate cupcakes. The American Institute for Cancer Research's ‘Healthy Substitutions' page suggests replacing ½ cup of butter with ¼ cup prune purée and ¼ cup butter. As prune puree is dark and has a distinct flavor, this works best in spicy fruit cakes or chocolate cake (for example, Martha Stewart's ‘guilt-free' brownies - though I would reduce sugar content slightly and use whole grain flour). You can find dozens of other delicious prune recipes on the website of the California Dried Plums website.
Conner is a nutritionist and health writer and teaches health-cookery classes. She is the author of Zest for Life, The Mediterranean Anti-Cancer Diet, a cancer-prevention nutrition guide and cookbook published recently in the UK and soon to be available in the US.