Blanching. Before a food is canned or frozen, it is usually heated very quickly with steam or water. The water-soluble vitamins, including vitamin C and B-complex, are sensitive and easily destroyed by blanching.
Thus, the cooking method that results in the greatest loss of nutrients is boiling.
The sooner you eat the food, the less chance of nutrient loss. The water-soluble vitamins, especially thiamin, folic acid and vitamin C, can be destroyed during improper storage and excessive cooking. Heat, light, exposure to air, cooking in water and alkalinity are all factors that can destroy vitamins.
Cooking damages the chemical structure of the nutrient, to some degree. However, there are plenty of nutrients left. And cooking kills many microbes that might have contaminated the food—and might have caused health problems.
Slow cooking does not destroy more nutrients. In fact, the lower temperatures may help preserve nutrients that can be lost when food is cooked rapidly at high heat. What's more, food cooked slowly often tastes better.
The fact is that all forms of cooking can destroy some of the nutrients (such as vitamin C and B vitamins) in vegetables.
Stir-frying and stir-frying/boiling, the two most popular methods for most homemade dishes in China, cause great losses of chlorophyll, soluble protein, soluble sugar, vitamin C, and glucosinolates, but the steaming method appears the best in retention of the nutrients in cooking broccoli.
That's why steaming is one of the best ways to maximize nutrients. It turns out that's especially true for broccoli. When in doubt, microwave. That's because microwaving uses little to no water, and can heat the vegetable quickly, thus preserving nutrients such as vitamin C that break down when heated.
Baking is a healthy option, as you generally need little or no oil – for example, chicken, fish and vegetables can be baked in greaseproof paper or foil parcels with a little water or reduced-salt stock. However, sometimes large amounts of oil or fat are used, such as when roasting potatoes.
If we compare baking to boiling microscopically, boiling helps thin out the cell walls and gelatinize the starch, which may enhance the bioavailability of nutrients.
Baked dishes offer fewer calories, and are great for weight loss. It saves time and maintains the natural vitamins to an extent. This makes it a good option for those trying to avoid heart diseases and live a healthy lifestyle.
If you want to be at an increased risk of heart disease at all times, deep frying is for you. Not only this, frying also adds saturated fat, cholesterol and sodium. High temperatures end up destroying the nutrient value of your food.
Steaming veggies can preserve nutrients, color, shape, and texture, without having to add any unnecessary fats through ingredients like oils or butter. To steam, place food into a steam basket and cover over simmering water. Since food is not directly touching the water, vegetables retain more of their nutrients.
So if you often eat deep-fried foods, switching to an air fryer could be helpful. If you're cooking a food that you wouldn't normally add fat to when you cook it, whether that's ready-made oven chips, bacon, sausages or breaded chicken, being cooked in an air fryer is unlikely to make it healthier.
Not surprisingly, steaming is the healthiest way to cook vegetables. Steaming vegetables is also the most efficient. A gentle steam is best; it allows vegetables to maintain their nutrients because the vitamins and minerals don't leak out into the water you end up discarding.
Steamed broccoli may be one of the healthiest ways to cook broccoli because it's quick and nutrients and vitamins won't be lost in the cooking water, as can be the case with boiled broccoli.
Boiling leaches out the vegetable's water-soluble vitamins in these vegetables, such as vitamin C and folate, as well as many of the glucosinolate compounds, which are water-soluble, too. Moreover, too much exposure to high temperatures destroys the enzyme that converts the inactive glucosinolates to active compounds.
Cooking in olive oil means you'll get the health benefits of olive oil, plus you'll absorb the healthy components. In addition, olive oil makes vegetables taste so much better than plain. I find people eat more vegetables when they use olive oil to prepare them.
Across the board, steaming retains the most nutrients. That's because all veggies contain folate and vitamin C—which don't like heat—so they “tend to keep most nutrients when cooked quickly and not in water,” Pine says.
TL;DR: If making smoothies or blending fruits and vegetables in any other form feels good to you, keep it up. There is no significant nutrient loss, and in fact you truly may be positively impacting your overall nutrition and health.
Cooking in an “instant pot” or pressure cooker is a great method for preparing your food on many levels — including the nutritional level, according to registered dietitian Beth Czerwony, RD. “Instant pot recipes are absolutely healthy as long as what you put in the recipe is healthy,” she says.
Pressure cooking is a cooking method that uses a combination of heat and steam. It is the steam and pressure and not the high heat that actually cooks the food. Therefore, it is considered safe to cook food in a pressure cooker as long as cooking time is carefully regulated.