Fresh vs. frozen vegetables: which is more nutritious?

For years, even decades, it's been a tenet of nutrition professionals that frozen vegetables are just as good for you as fresh vegetables. Certainly frozen veggies are far more easily available, in both quantity and variety, to most people than fresh vegetables. I can clearly recall the (small) quantity and the (mediocre) quality of the fresh fruits and vegetables that were trucked in to the 20,000-soul town I lived in in the early 90's - but what's available there now, 30 years later, is light-years ahead.

It's still the case, however, that not everyone has access to fresh fruits and vegetables, even those who live in big cities: that fresh fruit and veg simply may not be sold in the small corner grocery stores that are easily accessible to those without a car, and even those who are determined to take public transportation to a comparatively well-stocked grocery store may face several hours and more than one transfer before they make the round trip from home to store to back to their homes. Add that transit time to a full-time job that also requires taking public transportation to and from, and it's no wonder that people find it a challenge to eat healthfully, let alone consuming fresh fruits and vegetables.

So if frozen fruits and vegetables are just as good as fresh, in terms of nutrition, it makes sense for nutrition professionals to recommend them: they keep well for far longer than fresh, as long as they are properly kept in the freezer (assuming you have one); easily cooked, and taste just as good as fresh.

So it's always good to find more and new (recent) research regarding such a well-received tenet of nutritional counseling: the relative nutritive qualities of fresh vs. frozen. In 2014 researchers from the Food Science and Technology Lab at the University of California at Davis (J Ag Food Chem 2014: doi:10.1021/jf5058793) analyzed 8 different fruits and vegetables for the amount of four important vitamins the fruits and vegetables contained.

The authors compared fresh versus frozen fruits and vegetables and were careful to control their growing and harvesting: the authors obtained seeds for each of 6 fruits and vegetables and grew each variety under the same conditions from seed to maturity. The items tested were: corn, carrots, broccoli, spinach, peas, green beans, strawberries, and blueberries.

The mature fruit or vegetable from each plant was harvested at the same peak ripeness based on experts' evaluation. Then half of the products of each fruit or vegetable plant were blanched and immediately frozen (as is typical in current harvesting processes), while the other half were transported to refrigerators at UC Davis and appropriately stored in the refrigerator. Equivalent, smaller portions of fresh or frozen were stored in identical circumstances for later analysis and comparison.

For each variety of fruit or vegetable, one fresh portion and one frozen portion were analyzed for vitamin content within 24 hours of harvest. Thereafter, another portion of the fresh (refrigerated, never frozen) was analyzed after 3 days of refrigeration and another portion after 10 days of refrigeration. Frozen portions were analyzed after 10 days of freezing and another portion was analyzed after being frozen for 90 days.

The authors analyzed the fruits and vegetables for the levels of 4 vitamins: ascorbic acid (Vitamin C), riboflavin (B2), alpha-tocopherol (Vitamin E), and beta-carotene (a Vitamin A precursor).

Their results support current advice:

Vitamin C (ascorbic acid): Frozen strawberries, carrots, spinach, peas, and broccoli did not contain significantly different amounts of Vitamin C as compared to fresh. Corn, green beans, and blueberries had significantly higher levels of Vitamin C in the frozen portions as compared to the portions stored fresh.

B2 (riboflavin): Fresh portions of carrots, corn, broccoli, blueberries, and green beans contained the same amount of B2 as frozen portions, while only peas lost B2 during storage in the freezer. Broccoli, on the other hand, actually had higher levels of B2 in the frozen portion than the fresh portion.

Vitamin E (alpha-tocopherol): Stored fresh, peas, carrots and corn lost significant amounts of their Vitamin E content. Green beans maintained their Vitamin E content better during fresh storage but still had lower Vitamin E content than frozen green beans. Blueberries, broccoli, green beans, spinach, and strawberries had no significant difference in Vitamin E content between fresh and frozen samples, but frozen peas, spinach, and corn contained almost twice the amount of Vitamin E than their fresh counterparts.

Vitamin A (beta-carotene): Interestingly, even fresh samples of blueberries, strawberries, and corn contained no "significant amount" of Vitamin A, and over the course of storage in the freezer peas, spinach, and carrots lost 50% or more of their beta-carotene content. Even keeping the fruits or vegetables in the refrigerator didn't help: peas, green beans, and carrots lost "at least 15% of the initial [beta-]carotene content" over the course of refrigeration.

What this means for you

For all that people tout "fresh" vegetables and fruits as healthier than frozen, overall this research just doesn't bear that out. Quibbling over small amounts of this vitamin or that vitamin is a waste of time when the important thing is to eat more vegetables and fruit, period.

Try a new vegetable side dish or a vegetarian main course dish and get some more vegetables (and fruit: fruits include tomatoes and eggplant) in your diet, and don't worry about whether fresh or frozen have the most vitamins.

First posted: June 6, 2018