This debate has been going on for years.
In the grand scheme of a well-balanced, nutrient-dense, varied, whole foods diet, the cooked vs. raw debate isn't that critical for most people. This becomes more of a consideration for those with vitamin and mineral deficiencies (or "insufficiencies”), caused by digestion or absorption issues, or avoidance of certain foods (due to allergies, intolerances, or choice).
The answer isn't as simple as "raw is always better" or visa versa. As with most nutrition science, it depends on several factors, including your health status and the season.
While some vitamins are destroyed in cooking, others become easier to absorb (a.k.a. more "bioavailable").
Here is the skinny on vitamins and minerals in raw foods versus cooked foods.
Foods to eat raw
As a general rule, water-soluble nutrients (vitamin C and the B complex vitamins) are best eaten raw. These vitamins/minerals are found in fruits, vegetables and grains. This may not be a big surprise, but do you know why?
The reason is two-fold.
First, when we cook fruits and vegetables, we lose much of the vitamin content. When these nutrients are heated, vitamins tend to degrade. This will happen with any heat - be it steaming, boiling, roasting, or frying.
Vitamin C and the B vitamins are a bit "delicate" and more susceptible to heat than other nutrients. This is important to consider as vitamin C protects the immune system, cardiovascular health and is important for eye and skin health. The B vitamins are key in energy metabolism (feeling tired?), brain health, mood regulation, cellular metabolism, and is integral in the development of health red blood cells.
Vitamin C is found in high amounts in guava, bell peppers, kiwi fruit, strawberries, oranges, papaya, broccoli, tomatoes, kale and snow peas. In produce, B vitamins are most plentiful in grains, mushrooms, nuts, seeds, dark leafy vegetables and citrus fruits.
Of course, the obvious way to combat these nutrient losses is to eat foods high vitamin C and B vitamins in their raw form as much as possible (like in an awesome salad or overnight soaked oats). But that’s hard to do all the time, so try cooking them for as short a time as possible (like quickly steaming or blanching).
But wait! B vitamins are found in grains. Very few people I know actually eat raw grains, so in theory, they are losing a lot of the vitamin content from grains. Commercial baking also strips the germ and bran when making refined white flours (the germ and bran contain ALL the nutrients), so all the nutrients are lost. This is why manufacturers re-inject B-vitamins into their products (called "enriched").
Another reason why foods high in vitamins C and B are best eaten raw is that they're "water soluble." Guess where the vitamins go when they're cooked in water? They dissolve into the water. This is particularly true for fruits and veggies that are boiled and poached, but the same will happen with steaming.
How much loss are we talking about? It ranges, but can go from as low as 15% to over 50%.
But don’t despair – sometimes cooking vegetables is necessary. And, you’re still left with the mineral content of the vegetables and fruit.
TIP: Save the liquid from your steaming/poaching/boiling to use in your next soup or sauce! This is something my mother-in-law taught me (she saves the water from the vegetables to make the gravy at Thanksgiving). It also adds a nice flavour to your next dish. Just don’t overheat it or you may lose what you were aiming to keep.
Foods to eat cooked
When you cook tomatoes (i.e., tomato sauce), you may lose its vitamin C content, BUT you increase its vitamin A content and other compounds like lycopene, which is an another antioxidant present in red coloured fruits and vegetables.
Cooking certain orange and red “beta-carotene rich” veggies (e.g. tomatoes, carrots, sweet potatoes, squash) can help make this pre-vitamin A compound more absorbable. And vitamin A is a powerhouse antioxidant – it is the first to go in to help, lending support to vitamins C and E along the way.
Vitamin A is commonly known for its role in eye health, but also helps with skin. Symptoms of vitamin A deficiency include: dry skin, dry eyes, night blindness, infertility (trouble conceiving), poor wound healing and acne.
One study found that absorption of beta-carotene was 6.5 times greater in stir-fried carrots than in raw carrots!
Eating your fat-soluble vitamins (vitamins A, D, E and K) with a bit of fat will help you to absorb more of them, so that’s one more factor to consider.
One vegetable that’s best eaten both raw and cooked?
And I’m not just saying this to get everyone to eat it any way possible (although, I would love for this to happen). Spinach contains so many beneficial compounds that it's great eaten both raw and cooked.
Eating raw spinach preserves the water-soluble vitamins C & the B vitamins. In fact, raw spinach can contain three times the amount of vitamin C as cooked spinach.
Eating cooked spinach allows the pre-vitamin A, as well as some of the minerals like iron to be better absorbed. Not to mention how much spinach reduces in size when it’s cooked, so it’s easier to eat WAY more cooked spinach than raw spinach. If you're low in iron, consider this approach.
What about nuts and seeds?
Technically, nuts and seeds are from plants, so we could call them produce. They too, have their own insights for maximum health.
For maximum benefit, you need to soak your RAW nuts and seeds in room temperature water with a little salt. Sounds weird, but it’s true. This helps increase their nutritional value AND breaks down phytic acid and enzyme inhibitors (found in most plant foods). Phytic acid can interfere with digestion and absorption.
Don’t panic – not all phytates are bad. Do not stop eating nuts and seeds, even if you don’t soak them. This is simply to make you aware about how to increase nutritional value of your already healthy diet.
The old nutrition philosophy of making sure you get a lot of nutrient-dense whole foods into your diet holds true. Feel free to mix up how you eat them, whether you prefer raw or cooked just make sure you eat them. A combination will give you the best health!
Raw fruits and vegetables – preserve vitamins
Cooked Fruits and vegetables – gently steamed or braised
Orange coloured vegetables – cooked increases beta-carotene content
Raw spinach – higher in vitamin C
Cooked spinach – you can eat WAY more and it is higher in iron