Q&A: Fresh vs Frozen, Mercury Poison & Oil To Be Chosen

In the second Q&A episode of Nutrition Bites I am tackling three commonly asked questions: 1) Is fresh fruit better than frozen? 2) Should you be worried about mercury poisoning from fish? 3) Which cooking oil is the healthiest?

Tune in to hear the answers and learn how to eat what you want AND be healthy.

Want to recommend an episode topic? Send me a message on Instagram @nutritionbitespodcast

Credit to MonoSheep for the theme music.

Transcript

Welcome to Nutrition Bites. The no nonsense podcast where you get the truth about food so you can eat what you want and be healthy. I’m your host Maggie and welcome to the second Q&A installment, and final episode of this season! For this week I’m going to be answering 3 nutrition and food questions that I’ve received via my instagram @nutritionbitespodcast. So, let’s tuck in. On the menu today, Q&A!

Question 1

When it comes to fruits and vegetables, is fresh better than frozen?

With winter in full swing for those of us in the Northern Hemisphere, I’m starting to find the produce aisle in the grocery store to be a bit…sad… at least here in Canada. I do recognize of course how privileged we are to have an abundance of fresh produce - from bananas to bell peppers - even though we can’t harvest any of that locally right now. But in spite of this appreciation, there’s just something about fresh winter produce that kinda…sucks. I mean greenhouse tomatoes have this weird texture, and any kind of berries flown in from the South taste super bland. Even though bags of frozen spinach, green beans, mangos and pineapple are available year-round I usually forget about these options when shopping. 

Fruits and vegetables are powerhouse foods for a few reasons, and one of the most important is that they provide a colossal amount of micronutrients. But the moment that produce is picked from the ground or plucked from a tree, it begins to degrade and lose some of these valuable nutrients. The quicker produce can go from its source to your plate, the more nutritional value will be maintained. In a perfect world picking your veggies and fruits from your back garden is the optimal way to get the most micronutrients, but we all can’t afford, nor desire, to live this cottage-core lifestyle. I mean, just last summer I attempted to grow a variety of vegetables and it all backfired because I forgot to factor in the family of greedy raccoons who run my property.

Now when it comes to fresh produce available in the grocery store, which is how most people get their fruits and veggies, what you purchase may be days or even weeks old. From harvesting, to washing, packaging, transport and distribution, the fresh produce available to us often goes on a lengthy journey in order to wind up at the store. And once you pick it up, it can sit around for even longer before you get to eating it. All that to say is that by the time you crunch on your fresh kale salad, the quantity of some vitamins and minerals may be much less than what that veggie originally had. Frozen produce on the other hand, pauses the nutritional race against time. Freezing produce interrupts the process of oxidation - the chemical reaction that causes the cellular breakdown, and nutrient degradation, in fresh fruits and veggies. Many farms are able to flash freeze their produce mere hours after harvesting which helps these foods retain a larger quantity of their nutrients. But this does not always make frozen produce nutritionally superior over fresh. 

The exact micronutrients lost from the time of harvesting depend on the type of food and nutrient of interest. One study has shown that denser produce, like carrots, lose less nutrients than a thinner veggie with more surface area, like spinach. That’s because the density protects against moisture loss, and exposes less of the vegetable to elements that contribute to nutrient degradation, like heat and oxygen. When it comes to specific nutrients, water-soluble vitamins, like Vitamin C, tend to degrade more quickly, than fat-soluble vitamins like Vitamins A, E, D and K. With these two considerations in mind, frozen spinach is likely to have more Vitamin C than fresh spinach (sometimes over 100% more if that fresh spinach is a week old), but the Vitamin A levels in carrots don’t differ that much between fresh and frozen. 

Now, we could spend our time comparing each micronutrient level in the fresh vs frozen version of every fruit and veggie, but I got a life to lead. If we zoom out and look at the big picture of this topic, research has shown that there is no significant nutritional difference between the two. Which means that frozen produce is just as nutritious as the fresh stuff! What’s also interesting to think about is the seasonality of our food. If you are purchasing fresh broccoli out of season, it will likely have had to travel a longer distance to get to you, therefore losing more nutrients, so the frozen variety may be slightly more nutritious! But on the flip side, when broccoli is in season it may be a bit more advantageous to buy it fresh. Also keep in mind though that fruits and veggies are more than just vitamins and minerals. Fibre is one of the biggest benefits of this food group, and it’s quantity remains unchanged whether produce is fresh or frozen. 

Often people, myself included, forgo frozen fruits and veggies because their defrosted taste and texture can be a bit….yucky. But it’s all about using them in the right way, like frozen blueberries for a smoothie or frozen spinach in chilli. And remember that frozen produce has other benefits: it’s convenient, cheap, and provides out-of-season varieties all year round. Overall, it’s a great option to boost your intake of fruit and veg - especially during the off season. At the end of the day, it doesn’t really matter where you source your produce from in the grocery store, but rather that you’re making sure to eat your fruits and veg in the first place.

Question 2

How concerned should I be with the mercury levels found in fish?

The advantages of regularly consuming fish and seafood are astronomical.  It’s a lean source of protein, a significant source of Vitamin D, B12, and iron, and one of the richest sources of omega-3 fatty acids in our diet. But, there are of course, some health risks. The most common one is food poisoning from raw or undercooked seafood. And for most people this is more of a short-term consequence rather than a life-long health risk, and I would know having had to miss a Drake concert thanks to bad shellfish. True story, and I vow to never eat oysters again. But, the more scary and detrimental health risk from seafood is mercury poisoning. 

Now mercury is a metal that is naturally found in soil, water, and rocks, but it is also a byproduct from activities like metal mining and coal power generation. Thanks to our constant, and historic mistreatment, of the environment, mercury from these human-driven initiatives is now a common pollutant in our waterways. And because of this, most of the fish and seafood we consume contains some amount of mercury, in particular the toxic substance methylmercury. This molecule is so damaging to humans because it directly affects our brain and nervous systems, easily accumulates in our bodies, and is not readily eliminated. Which means that once we consume it, it kinda sticks around for a while. In adults, excessive methylmercury exposure can lead to vision changes, deafness, tremors and personality changes. To get this level of mercury from food is pretty rare, but there is a concern about accumulation of methylmercury in young and developing children, because of their small size and the fragility of their growing organs. Methylmercury exposure in a small child or fetus can result in permanent damage like a decreased IQ, poor memory function, blindness, and seizures.

Fortunately, the levels of methylmercury in many fish are relatively low. A general rule of thumb is that the smaller the sea creature, and the shorter its lifespan, the more safe it is to consume. Think things like shrimp, anchovies, scallops, salmon, and squid. Larger fish, which live for a long time, are more at risk of accumulating dangerous levels of mercury because they are at the top of the food chain - eating many smaller fish which contain mercury themselves. Here’s an example: swordfish, which is massive in size, has about 110x the average amount of mercury as shrimp. Other large species like shark, marlin, king mackerel, and albacore tuna are also generally regarded as having high levels of mercury. Many health authorities, including the FDA and Health Canada, advise against eating any of these species. Because of our global desire to continuously trash the planet, a lot of the fish and seafood we eat contains some mercury. But in general, most of these animals contain low enough levels that they are regarded as safe to eat. However, the list of safe species can vary drastically between regions because of different seafood consumption habits and local pollution of the waterways from which the food is sourced from. With that said, many government inspection agencies regularly test seafood products, both imported and local, to make sure that the supply is safe. So, unless you are pregnant, breastfeeding, or feeding a small child, I wouldn’t miss out on the amazing nutritional benefits, and taste, of seafood, because of fear of mercury poisoning. I hereby grant you the permission to order some sushi tonight. You’re welcome.

Question 3

Which cooking oil is the healthiest to use?

When it comes to choosing an oil to cook with there are two main criteria you should consider: smoke point and nutritional value. If you follow any chef or chef collective, like the pre-scandal Test Kitchen at Bon Appetit, you’ve probably heard of this term before. Smoke point is the temperature at which an oil starts to burn and smoke. Some chefs encourage getting your oil to its smoking point for very specific things like searing steak, but more often it is recommended to use an oil below its smoke point. That’s because if you cook food in an oil that has reached, or surpassed, it’s top temperature three things will happen: your food will have a burnt flavour, nutrients will be destroyed, and new harmful molecules, called free radicals, may be created. 

The smoke point of cooking oils vary widely - from 225℉ - over 500 (that’s 100 - 260℃). At the lower end of this smoke point spectrum are fats like flaxseed oil and extra-virgin olive oil. These low smoke point oils are best used as ingredients in lower-temperature cooking or cooking with no heat like for creating salad dressings or dips. At the higher end of the smoke point scale are products like peanut and vegetable oil. These highly refined oils are processed so they withstand high temperatures and are optimal for things like deep frying or a ripping hot wok. Oils that sit in the middle of the smoke point spectrum, like avocado and regular olive oil, should be avoided for deep frying, but are otherwise great for most of your everyday cooking needs.

While it’s important to pick the right oil based on how you are using it, it’s also valuable to think about it’s nutritional quality. When it comes to the health factor of cooking oils the focus is on the types of fat they contain. The majority of cooking oils are composed of unsaturated fatty acids - a category of molecules that causes fat to be liquid at room temperature. A diet high in these unsaturated fats is generally associated with good heart health. Animal-based fats like butter or lard, mostly contain saturated fatty acids - a molecule that causes a fat to be solid at room temperature, and is associated with poor heart health. The only plant-based fat that defies this categorization is coconut oil. Despite it’s incredibly high levels of saturated fats, this cooking oil has been deemed a superfood by many influencers, including our pseudoscience bestie,  Gwenyth Paltrow. But many health scientists are not convinced coconut oil is healthy because it’s sat fat levels are more than double the amount found in butter! This has caused organizations like the American Heart Association to advise against regularly consuming coconut oil. But the evidence of whether it’s good or bad for you is mixed - mostly because we’ve only studied the health effects of sat fat from animal products. But with the evidence we have today, it’s probably best to use coconut oil in dishes where it adds yummy flavour rather than for your everyday use.

Now for all the other types of cooking oils, the nutritional difference lies in the types of unsaturated fats they contain. Flaxseed oil is high in omega-3s - an essential unsaturated fat that is beneficial for your brain and heart. But, these same omega-3s make the product unstable in high-heat, so it’s not a great choice for everyday use. Sunflower oil on the other hand can be used in high heat cooking and is also a great source of Vitamin E. But this oil is high in omega-6s, a type of unsaturated fat that while healthy in moderate amounts, is thought to contribute to inflammation when overconsumed. Other popular oils, like canola and vegetable, also tend to be high in omega-6s. In addition, these oils are considered to be highly processed - which means that other beneficial nutrients have been removed in favour of a longer shelf-life and more uniform taste and appearance. 

Now none of these plant-based oils are necessarily unhealthy choices, many doctors  and dieticians will still recommend their use over butter or lard, but there is one amongst them who has been crowned as the chosen one: olive oil. This fat is high in monounsaturated fatty acids - a type of unsaturated fat known to reduce LDL, or “bad”, cholesterol. In addition, olive oil is one of the most studied fats in health science and so there is a ton of evidence to support that a diet rich in this oil can positively contribute to your health. The one thing you have to keep in mind though is the different types of olive oil that exist and how they should be used. Extra-virgin olive oil is a less refined product, which means it has a lower smoke point and retains more of a complex flavour profile. It should be saved for dressings and francy drizzles a la Masterchef. The more processed “regular” olive oil is better used for your everyday cooking needs - like pan fries, sautees and baking. Speaking of baking, I’ve got some cookies to make!

End

That’s been the bite for today. Stay hungry.