Frozen vs. Fresh? Which Vegetables Are Best

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With so many options lining the grocery store aisles, choosing how to buy veggies (and then prepare them once at home) can be mind boggling. But when nutrition is the deciding factor, what’s the best way to get the biggest bang per nutritional buck?

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Photo by Caitlin Covington

Uncooked, fresh produce is typically thought to be the most nutritious— but it does vary from food to food. One study showed higher levels of lutein, a carotenoid that can prevent macular degeneration and eye problems, in uncooked spinach when compared to cooked^[1]. Foods with high amounts of vitamins B and C are best fresh because the vitamins are water-soluble, meaning some nutrients are usually dissolved in food processing. But the nutritional quality in fresh versus frozen varieties also depends on the type of veggie. Brassica veggies— like cabbage, kale, Brussels sprouts and cauliflower— are typically better fresh than frozen because they retain more phytochemicals and antioxidants, which studies suggest may actually help prevent certain cancers^[2].

But this doesn’t mean that fresh produce isn’t immune to some nutrient loss— and the farm-to-grocery store process may be to blame. The freshness of a ripe tomato or strawberry isn’t based on when it hits the grocery store shelf— it begins right after harvesting. Once a fruit or veggie is harvested, it begins to release heat and lose water (a process called respiration), impacting its nutritional quality. Between pest-controlling sprays, transportation, handling, and plain ol’ time, fresh produce at the store might have lost roughly half it’s original amount of nutrients.

Fortunately for those who rely on convenient bags from the freezer aisle, studies suggest frozen veggies have just as many nutrients (if not more) as their fresh counterparts^[3][4]. Fresh fruits and veggies produce enzymes (trypsin and chymotrypsin) that cause loss of color, flavor, and nutrients just after harvest. But the reaction can be stopped by deactivating the enzymes— which freezing can do— leaving the frozen veggies with more nutrients^[5][6]. (When done right, that is— the storage process can also cause some nutrients to be lost because of oxidation.) Foods that are best frozen are those with high amounts of fat-soluble nutrients, like vitamin A, cartenoids, and vitamin E, because they’re more stable during food processing and storage (like blanching and freezing). However, be careful with the prep: Studies suggest thawing frozen veggies before cooking can actually speed up vitamin C losses in frozen peas, spinach, okra, and green beans^[7].

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The bag is mixed on whether cooked veggies are any “worse” nutritionally. Some research suggests cooking bright veggies (like tomatoes, carrots, and sweet potatoes) can also zap out essential nutrients (specifically, carotenoids)^[8]. But other studies show the overall nutritional quality of a cooked veggie depends on the type of cooking. Despite the common notion that cooking kills nutrients, boiling or steaming some veggies (like broccoli and carrots) may actually boost levels of free radical-trapping antioxidants and phytochemicals like carotenoids and polyphenols^[9]. However, methods like stir-frying have been found to deplete key nutrients like chlorophyll, protein, and vitamin C in broccoli^[10].

The best bet for cooking veggies to get the most nutrients for your buck? Go easy on the temperature and cooking time, and cook with little water for veggies loaded with vitamin B and C (remember, water soluble vitamins will quickly vanish in the presence of H2O).  And here’s some good news for the microwave chef: Studies suggest microwaves have little effect on the nutritional quality of fruits and veggies, much like conventional ovens^[11].

1. Cellular transport of lutein is greater from uncooked rather than cooked spinach irrespective of whether it is fresh, frozen, or canned. O’Sullivan, L., Ryan, L., Aherne, S.A., et al. Department of Food and Nutritional Sciences, University College Cork, Cork, Ireland. Nutrition Research, 2008 Aug;28(8):532-8. [↩]
2. Effect of different cooking methods on color, phytochemical concentration, and antioxidant capacity of raw and frozen brassica vegetables. Pellegrini, N., Chiavaro, E., Gardana, C., et al. Department of Public Health, University of Parma, Parma, Italy. Journal of Agricultural and Food Chemistry, 2010 Apr 14;58(7):4310-21. [↩]
3. Effect of home freezing and Italian style of cooking on antioxidant activity of edible vegetables. Danesi, F., Bordoni, A. Research Center on Nutrition and Vitamins, Dept. of Biochemistry G. Moruzzi, Univ. of Bologna, Via Irnero, Bologna, Italy. Journal of Food Science, 2008 Aug;73(6):H109-12. [↩]
4. Polyphenols and antioxidant capacity of vegetables under fresh and frozen conditions. Ninfali P, Bacchiocca M. Istituto di Chimica Biologica, G. Fornaini Università di Urbino, Urbino (PU), Italy. Journal of Agricultural and Food Chemistry, 2003 Apr 9;51(8):2222-6. [↩]
5. Nutritive value and effect of blanching on the trypsin and chymotrypsin inhibitor activities of selected leafy vegetables.Mosha, T.C., Gaga, H.E. Sokoine University of Agriculture, Department of Food Science and Nutrition, Morogoro, Tanzania. Plant Foods for Human Nutrition, 1999;54(3):271-83. [↩]
6. Effect of blanching on the content of antinutritional factors in selected vegetables. Mosha, T.C., Gaga, H.E., Pace, R.D. et al. Sokoine University of Agriculture, Department of Food Science and Nutrition, Morogoro, Tanzania. Plant Foods for Human Nutrition, 1995 Jun;47(4):361-7. [↩]
7. Vitamin C losses in some frozen vegetables due to various cooking methods. Nursal, B., Yücecan, S. Hacettepe University, Department of Nutrition and Dietetics, TR-06100 Sihiye, Ankara, Turkey. Nahrung/Food, 2000 Dec;44(6):451-3. [↩]
8. Micellarisation of carotenoids from raw and cooked vegetables. Ryan, L., O’Connell, O., O’Sullivan, L., et al. Department of Food and Nutritional Sciences, University College Cork, Cork, Republic of Ireland. Plant Foods for Human Nutrition, 2008 Sep;63(3):127-33. [↩]
9. Customized cooking method improves total antioxidant activity in selected vegetables. Ng, Z.X., Chai, J.W., Kuppusamy, U.R. Department of Molecular Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia. International Journal of Food and Science Nutrition, 2011 Mar;62(2):158-63. [↩]
10. Effects of different cooking methods on health-promoting compounds of broccoli. Yuan, G.F., Sun, B., Yuan, J., et al. Department of Horticulture, Zhejiang University, Hangzhou, China. Journal of Zhejiang University Science, 2009 Aug;10(8):580-8. [↩]
11. The effect of microwaves on nutrient value of foods. Cross, G.A., Fung, D.Y. Critical Reviews of Food Science and Nutrition, 1982; 16(4):355-81. [↩]