People are always going to argue over the stuff that is 5% of the equation while ignoring the actually important 95%. This debate between fresh, frozen, and canned produce is part of that 5%. Why? Because for the most part, a vegetable is a vegetable is a vegetable. While we may want to get all of our nutrition from fresh foods and be #healthy, that’s not always financially, practically, or geographically possible. Luckily, with the technological advancements in food processing (yes, I think processing can be a good thing), we are able to preserve foods and acquire foods we would never have gotten a chance to eat given our location. These developments have not come without criticism, however.
Many will claim that canned or frozen fruits and vegetables are not “as healthy” as their fresh counterpart. First off, please define healthy. You can’t measure something with healthy. “Oh, this food has 5 health”, this isn’t a freaking video game. Talk about nutrient density; that’s a good way to measure the healthfulness of a food. Nutrient density refers to the quantity and variety of nutrients (vitamins, minerals, fiber content, etc.) that are in a food. Obviously, fruits and veggies are extremely nutrient dense; but do they contain the same amount and types of nutrients across the board from fresh to frozen to canned? That’s the topic of discussion for today.
In 2007, there was a great literature review published in the Journal of the Science of Food and Agriculture that compiled a lot of the research conducted in this area over the last several decades from UC Davis1. This review was broken up into 2 main sections: Water-soluble & lipid-soluble. The difference here is that some nutrients dissolve in water while others dissolve in lipids (or fats). The properties of these nutrients change depending on their solubility. For example, water-soluble vitamins (C & B) are very susceptible to destruction from high temperatures while lipid-soluble vitamins (A, D, E, K) can tolerant high temperatures and still remain in food.
While it may come as no surprise that fresh produce was shown to have greater amounts of nutrients than frozen or canned, it may be interesting to know that fresh vegetables also degrade the quickest in terms of nutrient availability2. In one study, researchers found 56-100% decreases in Vitamin C content depending on the food item being tested. This was after storing the food at room temperature for 7 days3. Keep in mind, Vitamin C is a very unstable nutrient, so it’s sensitive and will be degraded the quickest of any nutrient, but for water-soluble vitamins, it’s a good estimation. Vitamin B losses were also found during storage, but not as dramatic as Vitamin C1.
Lipid-soluble vitamins had a different story. Vitamin A, in some cases, actually saw an increase in availability after a few days. This was seen in carrots refrigerated after 14 days4. Simultaneously, green beans experienced a small 10% decrease during refrigeration from 16 days4.
In part 2 of the review, minerals and fiber were tested in addition to lipid-soluble vitamins. What was seen there was that neither minerals or fiber saw significant losses during storage over many months, although I wouldn’t eat anything considered fresh produce after a couple months…yikes.
As mentioned previously, water-soluble vitamins can be quickly destroyed if exposed to heat such as from cooking while lipid-soluble vitamins are more tolerant of supa hot fiya. One study tested the Vitamin C content of produce straight from the supermarket after cooking and found that some foods had higher Vit. C levels when fresh and cooked while others had more of the vitamin when coming from a can and then cooked3! In addition, ascorbic acid (Vitamin C) has been shown to see decreases after cooking as high as 55%.
Thiamin, a B-Vitamin, has seen even greater losses from cooking at 66%. The cooking method will also be significant factor for how much of the nutrient is lost to cooking; unfortunately, the authors did not specify which methods are better than others for nutrient retention, but my guess would have to be whichever method utilizes heat for the least amount of time would be best.
Lipid soluble Vitamin A had an interesting outcome when exposed to heat; it increased! One study found a 26% increase in the amount of Vitamin A available after cooking fresh broccoli. Other studies did not find any increase but rather, a decrease .
Minerals and their quantity in foods are able to be reduced from cooking by leaching into the water or cooking liquid out of the food. If possible, use that cooking liquid again to get some of that nutrient back into a meal.
Fiber did not see any significant changes when exposed to heat. The primary way that you’re going to lose fiber from cooking is through processes like peeling, juicing, and removing parts of fruits and vegetables . For example, asparagus spears have the signature flower part to them and the annoying tough end to them. The reason why that end is tough is because it is loaded with cellulose/fiber. I’m not saying you need to eat all the hard parts of fruits and veggies, but save a little bit of it next time to get a little extra bit of fiber from your meal.
So far, we have only covered what the research has said about fresh fruits and vegetables, and haven’t really made a comparison with frozen and canned veggies. That will come next week when we talk about frozen produce and then the following week with canned products. For now, my takeaways are this:
- Fresh is not always the best option especially if the produce is going to sit for a couple of days.
- If possible, place fresh items in the fridge to slow the process of nutrient degradation
- Cooking can contribute to the greatest loss of nutrients, but don’t eat everything raw either. My point is focus more so on getting fruits and vegetables in the first place. Then, worry about cooking methods and other things.
I hope you found this information useful to you. As I said above, We’ll start actually comparing the three forms next week, then you may be able to make better decisions about what you select at the grocery store! Leave me your comments with your thoughts!
1Rickman, J., Barrett, D., & Bruhn, C. (2007). Nutritional comparison of fresh, frozen and canned fruits and vegetables. Part 1. Vitamins C and B and phenolic compounds. Journal of the Science of Food and Agriculture, 87(6), 930-944.
2Favell DJ, A comparison of the vitamin C content of fresh and frozen vegetables. Food Chem 62:59–64 (1998).
The antioxidant activity and composition of fresh, frozen, jarred and canned vegetables. Innov Food Sci Emerg Technol 3: 399–406(2002).and ,
β-Carotene and ascorbic acid retention in fresh and processed vegetables. J Food Sci 64: 929–936(1999)., , and ,
Nutritive value of fruits, vegetables, and their products, in Postharvest Technology of Fruits and Vegetables, ed. by VermaLR and JoshiVK. Indus Publishing, New Delhi, pp. 337–389 (2000).,
Comparison of vitamin losses in vegetables due to various cooking methods. J Nutr Sci Vitaminol 36: S7–S15(1990).and ,
Quantification of cis–trans isomers of provitamin A carotenoids in fresh and processed fruits and vegetables. J Agric Food Chem 45: 3728–3732 (1997)., and ,