How Cooking Affects The Nutrient Content of Foods
February, 2016
Eating nutritious
foods can improve your health and energy levels.
Surprisingly, the way you cook your food has a major
effect on the amount of nutrients in it.
This article will explore how the different cooking methods
affect the nutrient content of foods.
Nutrient Content is Often Altered During Cooking
However, several key nutrients are reduced with some cooking
methods.
Nutrients That May Decrease
The following nutrients are often reduced during cooking:
- Water-soluble vitamins: vitamin C and the B vitamins — thiamin (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), folic acid (B7) and cobalamin (B8).
- Fat-soluble vitamins: vitamins A, D, E and K.
- Minerals: primarily potassium, magnesium, sodium and calcium.
Nutrients That May Increase
These nutrients can increase with certain types of cooking:
- Antioxidants: molecules that protect other molecules from oxidation, which can damage cells.
- Phytochemicals: substances found in plant foods that can affect your health.
Bottom Line: Although cooking improves digestion and
the absorption of many nutrients, the levels of some vitamins and minerals may
decrease.
Boiling, Simmering and Poaching
Boiling, simmering and poaching are similar methods of
water-based cooking.
These techniques differ by water temperature:
- Poaching: less than 180°F/82°C.
- Simmering: 185-200°F/85-93°C.
- Boiling: 212°F/100°C.
Vegetables are generally a great source of vitamin C, but a
large amount of it is lost when cooked in water.
In fact, boiling reduces vitamin C more than any other
cooking method. Broccoli,
spinach and lettuce may lose up to 50% or more of their vitamin C when boiled (4, 5).
Because vitamin C is water-soluble and sensitive to heat, it
can leach out of vegetables when they’re immersed in hot water.
B vitamins are similarly heat sensitive. Up to 60% of
thiamin, niacin and other B vitamins may be lost when meat is simmered and its
juices run off.
However, when the liquid containing these juices is
consumed, 100% of the minerals and 70-90% of B vitamins are retained (6).
On the other hand, boiling fish was shown to preserve omega-3 fatty acid
content significantly more than frying or microwaving (7).
Bottom Line: While water-based cooking methods cause
the greatest losses of water-soluble vitamins, they have very little effect on
omega-3 fats.
Grilling and Broiling
Grilling and broiling are similar methods of cooking with
dry heat.
When grilling, the heat source comes from below, but when
broiling, it comes from above.
Grilling is one of the most popular cooking methods because
of the great flavor it gives food.
However, up to 40% of B vitamins and minerals may be lost
during grilling or broiling when the nutrient-rich juice drips from the meat (6).
There are also concerns about polycyclic aromatic hydrocarbons (PAHs), which are
potentially cancer-causing substances that form when meat is grilled and fat
drips onto a hot surface.
Luckily, researchers have found that PAHs can be decreased
by 41-89% if drippings are removed and smoke is minimized (8).
Bottom Line: Grilling and broiling provide great
flavor but also reduce B vitamins. Grilling generates potentially
cancer-causing substances.
Microwaving
Microwaving is an easy, convenient and safe
method of cooking.
Studies have found that microwaving is the best method for
retaining the antioxidant activity in garlic
and mushrooms (11, 12).
About 20-30% of vitamin C in green vegetables is lost during
microwaving, which is less than most cooking methods (5).
Bottom Line: Microwaving is a safe cooking method
that preserves most nutrients due to short cooking times.
Roasting and Baking
Roasting and baking refer to cooking food in an oven with
dry heat.
Although these terms are somewhat interchangeable, the term
“roasting” is typically used for meat while “baking” is used for bread, muffins,
cake and similar foods.
Most vitamin losses are minimal with this cooking method,
including vitamin C.
However, due to long cooking times at high temperatures, B
vitamins in roasted meat may decline by as much as 40% (6).
Bottom Line: Roasting or baking does not have a
significant effect on most vitamins and minerals, with the exception of B
vitamins.
Sautéing and Stir-Frying
With sautéing and stir-frying, food is cooked in a saucepan
over medium to high heat in a small amount of oil or butter.
These techniques are very similar, but with stir-frying the
food is stirred often, the temperature is higher and the cooking time is
shorter.
In general, this is a healthy way to prepare food.
Cooking for a short time without water prevents loss of B
vitamins, and the addition of fat improves the absorption of phytochemicals and
antioxidants (6, 13,
14).
One study found that absorption of beta-carotene
was 6.5 times greater in stir-fried carrots than in raw (15).
In another study, blood lycopene
levels increased 80% more when people consumed tomatoes sautéed in
olive oil rather than without (16).
On the other hand, stir-frying has been shown to
significantly reduce the amount of vitamin C in broccoli and red cabbage (5, 17).
Bottom Line: Sautéing and stir-frying improve the
absorption of fat-soluble vitamins and some phytonutrients, but they decrease
the amount of vitamin C in vegetables.
Frying
Frying involves cooking food in a large amount of fat,
usually oil, at a high temperature. The food is often coated with batter or
bread crumbs.
It’s a popular way of preparing food because the skin or
coating maintains a seal, which ensures that the inside remains moist and cooks
evenly.
The fat used for frying also makes the food taste very good.
However, not all foods are appropriate for frying.
Fatty fish are the best sources of
omega-3 fatty acids, which have many health
benefits. These fats are very delicate and prone to damage at high
temperatures.
Frying tuna has been shown to degrade its omega-3 content by
up to 70-85%, while baking caused only minimal losses (18, 19).
In contrast, frying preserves vitamin C and B vitamins, and
it may also increase the amount of fiber in potatoes by converting
their starch into resistant
starch (20).
When oil is heated to a high temperature for a long period
of time, toxic substances called aldehydes are
formed (21). Aldehydes have been linked to an increased risk of
cancer and other diseases.
The type of oil, temperature and length of cooking time
affect the amounts of aldehydes produced. Reheating oil also increases aldehyde
formation.
If you’re going to fry food, don’t overcook it, and use one
of the healthiest
oils for frying.
Bottom Line: Frying makes food taste delicious, and
it can provide some benefits when healthy oils are used. It’s best to avoid
frying fatty fish and minimize frying time for other foods.
Steaming
Steaming is one of the best cooking methods for preserving
nutrients, including water-soluble vitamins that are sensitive to heat and
water (4,
5, 6, 17).
Researchers have found that steaming broccoli, spinach and lettuce
reduces their vitamin C content by only 9-15% (5).
The downside is that steamed vegetables may taste bland.
However, this is easy to remedy by adding some seasoning and oil or butter
after cooking.
Try this easy recipe for steamed
broccoli with suggested additions to improve the flavor.
Bottom Line: Steaming is one of the best cooking
methods for preserving nutrients, including water-soluble vitamins.
Tips to Maximize Nutrient Retention During Cooking
Here are 10 tips to reduce nutrient loss while cooking:
- Use as little water as possible for poaching or boiling.
- Consume the liquid left in the pan after cooking vegetables.
- Add back juices from meat that drip into the pan.
- Don’t peel vegetables until after cooking them. Better yet, don’t peel at all to maximize fiber and nutrient density.
- Cook vegetables in smaller amounts of water to reduce loss of vitamin C and B vitamins.
- Try to finish cooked vegetables within a day or two, as vitamin C content may continue to decline when the cooked food is exposed to air.
- Cut food after rather than before cooking, if possible. When food is cooked whole, less of it is exposed to heat and water.
- Cook vegetables for only a few minutes whenever possible.
- When cooking meat, poultry and fish, use the shortest cooking time needed for safe consumption.
- Don’t use baking soda when cooking vegetables. Although it helps maintain color, vitamin C will be lost in the alkaline environment produced by baking soda.
Bottom Line: There are many ways to preserve the
nutrient content in foods without sacrificing taste or other qualities.
Take Home Message
It’s important to select the right cooking method to
maximize the nutritional quality of your meal.
However, there is no perfect m
ethod of cooking that retains all nutrients.
In general, cooking for shorter periods at lower
temperatures with minimal water will produce the best results.
Don’t let the nutrients in your food go down the drain.
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