In the hierarchy of vegetables, the best choices are fresh, in-season, and local.
Realistically, though, that’s not always going to happen. For one thing, you might live in a climate where access to a variety of local and in-season vegetables just isn’t a thing. It’s also well established that lower income areas have fewer supermarkets, so fresh produce is less available.
Although home-grown is the best of the best, I know that saying, “Just grow your own!” is presumptuous on a lot of levels. Assuming that you have the space and resources to plant a garden, time is a big consideration. Plus, once they’re grown, preparing fresh vegetables takes more time than preparing frozen or canned, which are already washed and chopped for you.
All this is to say, I’m sure many of you find yourself turning to frozen and canned vegetables—as well as fruit, seafood, and meat—for reasons of availability and convenience. You might wonder if you are sacrificing any health benefits or if I’m giving you the side-eye for eating vegetables that aren’t farm-fresh.
Let me put that concern to rest immediately.
True, Grok would not have frozen or canned foods. Food preservation as a concept is nothing new, though. Just because a technology is new does not mean it’s “un-Primal.” I am not now, nor have I ever been, opposed to using modern methods of food preservation and storage that make it safer or more convenient to eat healthy foods. I like safety and convenience.
So, if you’ve been avoiding frozen or canned foods because you think you’ll have to turn in your Primal card, rest assured that isn’t the case. That said, I have historically avoided canned vegetables in the store due to concerns over BPA in the can linings. (Home-canned in jars is different, of course. I’m all for home canning.)
Since people sounded the alarm about BPA in the past decade, industry reports suggest a significant number of manufacturers have moved away from BPA-lined cans, but not all of them. I still strongly favor frozen over industrially canned vegetables. If nothing else, the taste and texture is usually superior. Nutritionally, though, the data show that frozen and canned are comparable overall.
The frozen food industry dates back to 1925, when Clarence Birdseye began quick-freezing fish. It really took off after WWII as more homes had freezers. Since then, food scientists have worked to improve freezing, packaging, and transporting methods so that today (spoiler alert!) frozen foods are nutritionally comparable to their fresh counterparts. They also taste better and maintain a more pleasing texture and appearance compared to our grandparents’ frozen options.
Factors that affect nutrients in the produce you buy, whether fresh or frozen, include:
Frozen vegetables are typically blanched before freezing to halt enzymatic reactions. This step cleans the vegetables and preserves flavor and texture, but the heat also reduces the levels of some nutrients, notably vitamin C.
On the other hand, fat-soluble vitamins like vitamins A and E and carotenoids are released from their cellular matrices by heat. This might make them more bioavailable in frozen foods. The jury is still out on the bioavailability question according to Dr. Diane Barrett of the UC Davis Department of Food Science and Technology. Fiber is relatively impervious to processing and so isn’t affected by freezing.
Although there is an initial loss of some nutrients in the freezing process, this seems to even out by the time the vegetables make it to your plate.
At the very top of the nutritional hierarchy are vegetables that go from dirt to plate with the fewest stops in between. The best option is picking vegetables out of your garden and eating them more or less right away. That’s not usually how it works, though.
Supermarket produce might have been in the supply chain for several weeks before you even purchase it (and it was almost certainly not allowed to fully ripen before harvesting). Even if you buy your produce at a local farmer’s market, several days to a week might pass before you consume it.
During that time between farm and plate, nutrients are oxidizing and degrading. On the other hand, frozen vegetables are usually picked at the peak of ripeness and frozen as quickly as possible to preserve the nutrients.
Li and colleagues measured vitamin C, beta-carotene, and folate in broccoli, cauliflower, corn, green beans, green peas, spinach, blueberries, and strawberries that were fresh, “fresh-stored” (refrigerated for five days to mimic what happens when we actually buy produce), or frozen. They found a high degree of nutritional similarity overall and further concluded, “In the cases of significant differences, frozen produce outperformed ‘fresh-stored’ more frequently than ‘fresh-stored’ outperformed frozen.”
These findings are typical. Compared to fresh vegetables, frozen compare favorably in study after study. For example:
I could go on, but you get the picture. Note that across all the studies, results varied somewhat between different types of produce and nutrients. Dr. Barrett also points out that there is little research beyond that looking at key vitamins. More is needed to examine other nutritive compounds, as well as to explore the bioavailability question.
Don’t get caught up in the minutiae, though. Looking at the big picture, researchers consistently agree that taking everything into consideration, frozen is on par with fresh-stored. Frozen vegetables also have favorable nutrient-to-price ratios.
The fact is, you can’t stand in a grocery store with a head of fresh cauliflower in one hand and a bag of frozen florets in the other and know for sure which has more nutrients. There’s no reason to feel bad about choosing frozen over fresh, especially when fresh seasonal and local options are lacking.
Consider, too, that if convenience is key, and your choice is between a frozen meal containing vegetables, or grabbing a drive-thru meal, the frozen food is often the better choice.
Using data from the National Health and Nutrition Examination Survey (NHANES) longitudinal study, researchers compared adults who reported eating frozen meals or “restaurant fast food/pizza.” Using the standardized Healthy Eating Index, the frozen meal eaters scored higher overall and specifically for total vegetable intake and total protein food. They also had lower intake of refined grains and empty calories.
A separate analysis of NHANES data showed that people who eat frozen vegetables eat more total vegetables and get more fiber, potassium, calcium and vitamin D, than those who don’t.
In terms of covering your nutrient bases, your best option is to choose a wide variety of produce, fresh and local when possible, and frozen when needed. If you can grow some fresh herbs and a tomato plant outside your window, all the better.
The expert consensus is that frozen meat and seafood is also nutritionally on par with fresh.
For fish in particular, freezing is the only viable way besides canning for many consumers to access safe products. According to the Seafood Storage Guide from the National Fisheries Institute, most fresh fish (not shellfish) should be eaten within 36 hours of catching.
As a final note, if you opt for frozen food products, check out the USDA Freezing and Food Safety fact sheet and USDA guide to Safe Defrosting Methods to make sure you are maximizing safety and quality.
Composition of Foods Raw, Processed, Prepared. USDA National Nutrient Database for Standard Reference, Release 28 (2015) – Documentation and User Guide.
Kmiecik W, Lisiewska Z, Korus A. Retention of mineral constituents in frozen brassicas depending on the method of preliminary processing of the raw material and preparation of frozen products for consumption. Eur. Food Res. Technol. 2007; 224:573–79.
Li, M. Ho, K., Hayes, M. Ferruzzi, M. G. The Roles of Food Processing in Translation of Dietary Guidance for Whole Grains, Fruits, and Vegetables. Annual Review of Food Science and Technology. 2019; 10:569-596.
MacTavish-West, H. Vegetables: is fresh best? The Journal of the Institute of Food Science and Technology. 2014.
Miller SR, Knudson WA. 2014. Nutrition and cost comparisons of select canned, frozen, and fresh fruits and vegetables. Am. J. Lifestyle Med. 2014; 8:430–37.
Produce for Better Health Foundation. State of the Plate: 2015 Study on America’s Consumption of Fruit & Vegetables.
Rickman JC, Barrett DM, Bruhn CM. Nutritional comparison of fresh, frozen and canned fruits and vegetables. Part 1. Vitamins C and B and phenolic compounds. 2007; J. Sci. Food Agric. 87:930–44.
Rickman JC, Bruhn CM, Barrett DM. Nutritional comparison of fresh, frozen, and canned fruits and vegetables. II. Vitamin A and carotenoids, vitamin E, minerals and fiber. J. Sci. Food Agric. 2007; 87:1185–96.
Villa-Rodriguez, J.A., et al. Maintaining antioxidant potential of fresh fruits and vegetables after harvest. Crit. Rev. Food Sci. Nutr. 2015; 55: 806–822.