QUESTION: “Does freezing fruits cause a loss of nutrition?”
DR. NEAL: Today’s question came to me via Spotify!
Thank you so much for your question. It’s hard to believe, but scientists have been studying whether freezing fruits and vegetables leads to a loss in their nutritional quality for over 75 years!
This means that we have some pretty definitive answers to this question.
What we know is that refrigeration and freezing foods helps prevent them from spoiling. Foods spoil when bacteria grow and spread.
By lowering the temperature at which foods are stored, we prevent the growth and spread of many harmful bacteria.
But besides the growth of bacteria, there’s another process that happens to produce as well – something called oxidation. When foods are exposed to the air, well specifically the oxygen in the air (which is why it’s called “oxidation”), they start to lose some of their nutritional value.
This is a natural process because, if you think about it, just like us fruits and vegetables are exposed to the air all the time!
Luckily, again though, keeping produce at lower temperatures helps slow down this oxidation process.
Fruits and Vegetables: Prior to Freezing
Now, I should mention that sometimes, before produce is frozen, it’s blanched first. What this means is that the food is briefly placed in boiling water before being placed in a freezer.
The purpose of this is to help preserve the food even more by destroying some of the enzymes naturally found in the food, that may contribute to it spoiling.
This process is usually performed with vegetables, not with fruits.
Fruits are much more delicate and so blanching them would actually make them less likely to survive the freezing process.
The Dietary Guidelines
Given all of this, both the Dietary Guidelines for Americans and Centers for Disease Control and Prevention say that we should aim to consume all types of whole fruits and vegetables, whether they are fresh, dried, canned, or frozen just so long as they don’t have added fats or sugars.
When we look at the trends among Americans, we find that most of us consume processed fruits and vegetables most often as opposed to fresh. For example, we’re much more likely to eat a canned tomato product instead of using a whole tomato.
This highlights the importance of your question. If we’re not eating as many whole, unprocessed fruits and vegetables, are we still getting enough nutrients?
Nutrient Quality of Frozen Produce
Studies have found that freezing fruits and vegetables tends to preserve vitamin C, for example. Now there are differences depending on which fruit and vegetable we’re talking about, but again, for the most part freezing preserves vitamin C.
When it comes to the B-vitamins, like thiamin, niacin, and folate, the results aren’t as clear. We know that freezing does lead to losses of some of these B-vitamins but more studies are needed to know whether this is significant.
Now, what about those oh-so-important antioxidants? Antioxidants are found in basically all plant-based foods, like fruits and vegetables, and are believed to protect us from many chronic diseases – everything from dementia to cancer.
When it comes to both fruit and vegetables, the great news is that freezing does seem to preserve many antioxidants. Again, this does differ depending on the fruit but for the most part, antioxidants are preserved when frozen.
When The Real Nutrition Losses Happen
The real nutrition losses happen during the reheating and cooking process. Sadly, it’s difficult to say which method is truly best for ALL forms of produce, but in general light and oxygen tend to be produce’s worst enemies.
So, when you’re reheating frozen vegetables or fruit for example, the trick is to be sure they are heated with water. For example, adding ¼ cup of water to your frozen produce when heating them in the microwave can still preserve many of the nutrients.
Here’s another trick. Even after heating, don’t throw out the water. Instead, that same water you used to reheat the frozen fruits and vegetables in to flavor some of your other dishes, or in the case of vegetables, make a soup out of it. This is because any nutrients lost during the heating process get submerged in the water.
So, if you end up consuming that water you will still get those nutrients!
If you don’t like the idea of microwaving, steaming, stir-frying and boiling are also good alternatives. In fact, steaming leafy greens can make their vitamins and minerals more absorbable, too. I realize that steamed vegetables may bring up images of hospital or cafeteria food, but that’s only because those places didn’t get creative with their cooking methods.
For example, instead of using water as the source of steam, use vegetable, chicken or beef stock. This will help bring in some extra flavor. Don’t forget, you are allowed to season after your vegetables are done cooking, too! One of my favorites is to give them a little drizzle of olive oil and a generous dusting of dried Italian herbs on top.