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.
Are Frozen and Canned Foods Inherently Less Primal?
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.
Frozen Vegetables and Fruit: As Good As Fresh?
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:
the particular nutrient in question,
the type of vegetable, including cultivar (what specific type of bean, apple, etc.),
growing conditions (soil, weather, and so on),
post-harvest handling and storage,
how you cook them.
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.
From Farm to Table
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.
Show Me the Data
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:
Twostudies from Bouzari and colleagues at UC Davis compared eight common fruits and vegetables that were either stored in a refrigerator for 3 or 10 days, or frozen up to 90 days. For vitamin C, riboflavin, alpha-tocopherol (a form of vitamin E), calcium, magnesium, zinc, copper, iron, fiber, and total phenolics, the researchers concluded that fresh and frozen were highly similar, with frozen sometimes outperforming fresh.
British researchers measured vitamin C, total polyphenols, total anthocyanins, and carotenoids (beta-carotene and lutein) in six common fruits and vegetables. Immediately after purchase from the grocery store, fresh and frozen were mostly similar. Levels of nutrients tended to decrease in the fresh vegetables over three days of storage.
Researchers from Virginia Tech and the USDA found that 5-methyltetrahydrofolate, the most bioavailable form of folate, did not decline in seven common vegetables over 12 months in frozen storage.
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.
Go Ahead and Hit Up the Freezer Section
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.
What About Meat and Seafood?
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.
Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.