Best cooking method to retain nutrients

We are all aware that microwaving is an extremely easy and convenient way of preparing your food. What makes it even better is the fact that microwave-cooked food is the healthiest alternative in terms of nutritional value.

Short cooking times and reduced exposure to heat preserve the nutrients in microwaved food. Only 20–30% of the vitamin C in green vegetables is lost during microwaving, which is less than most cooking methods.

In fact, studies have found that microwaving is the best method for retaining the antioxidant activity of garlic and mushrooms.

Baking refers to cooking food in an oven with dry heat. Roasting can be done in an oven or on an open flame.

Even though baking and roasting are used interchangeably, they are somewhat different. Roasting is typically used for meat while baking is used for bread, muffins, cake, and similar foods.

Vitamin losses are minimal with this cooking method, including vitamin C. However, due to long cooking times at high temperatures, the vitamin B in roasted meat may decline by as much as 40%.

Longer duration of cooking at high temperatures in an oven is also associated with loss of fat-soluble vitamins like vitamin A.

Frying

While frying is the most beloved cooking technique there is, not all foods are appropriate for frying. Fatty fish are the best sources of omega-3 fatty acids, which have many health benefits. However, these fats are very delicate and prone to damage at high temperatures. For example, frying tuna has been shown to degrade its omega-3 content by up to 70-85%, while baking causes only minimal losses.

In contrast, frying preserves vitamin C and B, and it may also increase the amount of fibre in potatoes by converting the starch in them into resistant starch.

Stir-frying

Stir-frying comprises cooking food for a very short time over very high heat in a large wok—the food is stirred often, and cooked in oil or butter. (Read more: How to choose the right oil for cooking?)

This is a healthy way to prepare food. Cooking for a short time without water prevents the loss of B vitamins, and the addition of fat improves the absorption of plant compounds and antioxidants.

A study found that our body can absorb 6.5 times more beta carotene from stir-fried carrots than raw ones.

However, stir-frying has been shown to significantly reduce the amount of vitamin C in broccoli and red cabbage.

Steaming is one of the best cooking methods for preserving nutrients, including water-soluble vitamins, which are sensitive to heat and water. Researchers have found that steaming broccoli, spinach, and lettuce reduces their vitamin C content by only 9-15%. 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.

Boiling, simmering and poaching are all water-based cooking methods. These techniques differ in terms of the temperature of the water:

• 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 the vegetables are cooked in water. B vitamins are similarly heat-sensitive. Up to 60% of thiamine (vitamin B1), 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, which is why it is a wonderful idea to save up the vegetable and meat stock.

A sous-vide machine—though it uses water—does not let the food come in contact with the water or oxygen. That is why the food tends to preserve many of the nutrients. A study published in Food Science & Nutrition, a peer-reviewed journal, in May 2017 found that cereals and lentils prepared in a sous-vide machine had higher mineral content than the same foods cooked traditionally. However, the machine is expensive and the cooking method can be slow.

Fermentation is an old technique for processing foods that is seen in many cultures around the world. Think about fizzy and sour foods and drinks you might have consumed in the past; many of these are fermented. Some common examples include:

• Dhokla
• Idli
• Dosa
• Gajar kanji
• Kimchi
• Sauerkraut
• Gundruk
• Wine, including Mahua wine
• Beer

Fermented foods are basically those foods (or drinks) that have been prepared by adding yeast or another microbial culture. The food is then set aside, to allow the microbes to break down the sugars and other compounds to make the food slightly tart and very nutritious (you'll see bubbles rising as the food ferments). Research has found that fermented foods can be rich in vitamin B12, as well as improving gut microbiome and digestion.

Here are a few things to keep in mind while cooking, to reduce nutrient loss:

• Use as little water as possible when poaching or boiling.
• If you are cooking non-veg, collect any juices dripping from meat and add them back into the pan.
• Don't peel vegetables until after cooking them. Better yet, don't peel at all to maximize their fibre and nutrient density. For example, most of the vitamin C in potato is in the skin. So try not to peel potatoes before you cook them.
• Try to eat any cooked vegetables within a day or two, as their 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.

While cooking, it is important to abide by certain rules: to remember that the duration, temperature and technique of cooking are all important to get the most out of the food we eat (bioavailability of nutrients as well as the taste and texture of food).

Some cooking methods are generally healthier than others. For example, compared with deep-frying or shallow frying (used for paratha and patties, for example), stir-frying uses less oil and can preserve more nutrients in food. And compared with boiling, blanching vegetables can preserve more nutrients (and texture) as the duration of cooking is much less.

Some methods like fermentation enhance the nutritive value of food. Other methods like curing (for example, curing fish or meat in lots of salt) can improve their shelf life (and often taste) tremendously. Cooking improves the digestibility of food and kills microbes—some of which can cause food poisoning.

Certain recipes are also created with their nutritive value in mind. For example, adding amchur to food increases the body's ability to absorb zinc from it.

Cooking helps us break down foods more easily than eating them raw. The spices and condiments we add also help the body absorb the nutrients. That said, overcooking food, reheating it multiple times or storing it in the fridge for many days can erode its healthfulness—foods that are cooked or stored improperly can indeed do more harm than good.