And we’ve replied that most published evidence shows that freezing or canning fruits and vegetables preserves their nutrients pretty well.
Now, two studies show that frozen produces often provides more of certain vitamins and antioxidants, compared with fresh produce refrigerated for three days or more.
While local produce may be consumed within three days of harvest, most produce is bought in supermarkets with lengthy supply chains that stretch across the country and overseas.
The vast majority of supermarket produce was picked anywhere from a week to a month before being presented to consumers, why often delay another day or more before consuming fresh produce.
It’s well established that nutrient levels in fresh produce drop fairly rapidly, to the extent that they can have lower nutritional value than their frozen equivalents.
Although fresh apples, pears, and blueberries are marketed as “just-picked” products straight from harvest, most have spent several weeks in storage.
Conversely, frozen foods retain most of their antioxidants and vitamins, as they are chilled almost immediately upon harvest.
Wild beats cultivated
There are exceptions, such as onions, which retain their nutrients during lenghty storage at room temperature.
That fact and many others are featured in veteran health writer Jo Robinson’s great new book, Eating on the Wild Side: A Field Guide to Nutritious Food.
Robinson’s book is the fruit of a decade of research collecting everything known about the nutrient levels in wild and cultivated strains of fruits and vegetables.
She shows that our prehistoric ancestors picked wild plants far more nutritious and healthful than the heavily hybridized produce we buy today … including super-fresh plant foods at farmers’ markets.
For example, compared with spinach, a dandelion has twice as much calcium, three times as much vitamin A, five times more vitamins K and E, and eight times more antioxidants.
Some common produce items – such as arugula, colorful “gourmet” lettuces, and culinary herbs or spices – are genetically “wild” and relatively high in nutrients and antioxidants.
Frozen produce can surpass fresh for certain vitamins and antioxidants
The two independent studies from Britain measured the nutritional content of frozen versus “fresh” produce.
Separate research teams from Leatherhead Food Research and the University of Chester conducted 40 different tests.
The sampled frozen produce items and fresh equivalents that had been stored in a refrigerator for three days.
In two out of three cases, frozen fruit and vegetables tended to exhibit higher levels of vitamin C and polyphenol antioxidants (e.g., flavanols and carotenoids).
The nutritional advantages of quick-freezing produce within hours of harvest were most noticeable in soft fruits, such as berries.
That said, it wasn’t always a clear win for frozen versus fresh produce … for example:
- Frozen sprouts scored higher on all nutrient measures.
- Frozen spinach beat fresh spinach in some but not all nutrient tests.
- Frozen raspberries and peas were about equal to their fresh counterparts.
- Frozen cauliflower and baby sweetcorn showed no major advantages over fresh.
- Frozen blueberries and green beans had much higher levels of vitamin C and polyphenols.
- Frozen carrots had more vitamin C, more polyphenols, three times more lutein, and twice as much beta-carotene.
- Frozen broccoli had more vitamin C and lutein and four times more beta-carotene, while fresh broccoli had more polyphenols.
Rachel Burch, who led the Leatherhead Food Research study, told the Daily Mail that the results should prompt rethinking:
“We must disregard the mistaken opinion that ‘fresh’ food is always better for us than frozen food. These results demonstrate that frozen can be nutritionally comparable to ‘fresh’ produce.”
Polyphenols may extend lifespan
Coincidentally, a new study shows that higher intakes of polyphenol-type antioxidants from plant foods may cut the risk of early death in older adults by up to 30 percent.
Researchers from the University of Barcelona conducted a 12-year study in 807 men and women aged 65 or older from Tuscany, Italy (Zamora-Ros R et al. 2013).
The Spanish investigation was the very first epidemiological or clinical study in which researchers measured levels of these compounds’ breakdown products people’s urine.
This is a far more accurate way to estimate people’s polyphenol intake, versus the far more common reliance on diet questionnaires.
Hence, the Spanish team’s approach allowed a more reliable gauge of how people’s health outcomes may be affected by high or low polyphenol intakes over time.
The results fit perfectly with the positive outcomes of thousands of cell, animal, and population studies, which indicate that these compounds are wildly healthful.
- Auborn KJ, Fan S, Rosen EM, et al. Indole-3-carbinol is a negative regulator of estrogen. J Nutr. 2003;133(7 Suppl):2470S-2475S. (PubMed) Liu RH. Potential synergy of phytochemicals in cancer prevention: mechanism of action. J Nutr. 2004;134(12 Suppl):3479S-3485S. (PubMed)
- McNaughton SA, Marks GC. Development of a food composition database for the estimation of dietary intakes of glucosinolates, the biologically active constituents of cruciferous vegetables. Br J Nutr. 2003;90(3):687-697. (PubMed)
- van Poppel G, Verhoeven DT, Verhagen H, Goldbohm RA. Brassica vegetables and cancer prevention. Epidemiology and mechanisms. Adv Exp Med Biol. 1999;472:159-168. (PubMed)
- Verhoeven DT, Goldbohm RA, van Poppel G, Verhagen H, van den Brandt PA. Epidemiological studies on brassica vegetables and cancer risk. Cancer Epidemiol Biomarkers Prev. 1996;5(9):733-748.
- Zamora-Ros R, Rabassa M, Cherubini A, Urpí-Sardà M, Bandinelli S, Ferrucci L, Andres-Lacueva C. High concentrations of a urinary biomarker of polyphenol intake are associated with decreased mortality in older adults. J Nutr. 2013 Sep;143(9):1445-50. doi: 10.3945/jn.113.177121. Epub 2013 Jun 26.
- Zhang Y. Cancer-preventive isothiocyanates: measurement of human exposure and mechanism of action. Mutat Res. 2004;555(1-2):173-190. (PubMed)