The manner in which you cook your vegetables can have a drastic effect on the nutritional value of fresh produce. Some cooking methods for vegetables enhance the content and bio-availability of their vitamins, minerals, and antioxidants. Still other ways of prepping produce can bring about a significant loss to the fruit or vegetable’s core nutrients.
We’ve rounded up some of the more popular cooking techniques and discovered some surprising things about how cooking affects food. Read on to learn more about the 7 best (or in some cases, the worst!) cooking methods to maximize the nutritional value of your veggies.
As one of the quickest and easiest methods of preparing raw vegetables, boiling water has the unfortunate tendency to degrade nutrition. Water-soluble nutrients like vitamins C and B, as well as disease-fighting antioxidants such as polyphenols, are often significantly reduced through the cooking process of boiling. This is because boiling water actually leaches said nutrients out of the vegetable and into the water.
That said, boiling water doesn’t damage every fruit or vegetable that comes in contact with it. Other research shows that boiling actually boosts the antioxidant properties of carrots, spinach, tomatoes, mushrooms, peppers, cabbage, asparagus, and pumpkin.
While these may be the exceptions to the rule, you don’t want to lose out on 60% to 70% of the vegetable’s nutritional value when boiling your fresh produce. To reduce losses:
- Add a pinch of salt to the water
- Add raw vegetables to the pot once the water is at a full boil, then reduce heat to a simmer
- Cook for the shortest amount of time possible
- Stow the nutrient-rich water in the fridge or freezer to make soups and stews
Since steaming is such a gentle way of cooking, it is often considered to be the best way to retain nutrients since the vegetable never touches the water. And indeed, water soluble vitamins and nutrients are not leached into the water as with boiling, but some nutrition is lost with heat.
For example, a study on broccoli which compared five different cooking methods found that, overall, steaming was the most favorable option. Tests on steamed broccoli did show some losses in chlorophyll, vitamin C, and soluble proteins and sugars. However, broccoli that is microwaved, boiled, or stir-fried saw the most dramatic decreases in these areas.
Because they heat food via electromagnetic radiation, microwave ovens are perhaps the most controversial of kitchen appliances; and they have long suffered from a reputation for destroying nutrients in your food.
Yet, if the enemies of nutritional content are liquids, heat, and cooking duration; a quick zap in the microwave may prove to be among the better ways to retain nutrients. According to a Spanish study published in 2009, veggies that were heated up without being immersed in water – including microwaved vegetables – enjoyed the least amount of nutrient loss. By using as little liquid in the container as possible and heating for as short a time as possible, microwaved veggies won’t degrade nearly as much as boiled vegetables.
4. Roasting and Grilling
Like microwaving, cooking vegetables in the oven or on the barbecue grill exposes them to dry heat. Of course, roasting takes longer for veggies to become tender, and prolonged exposure to heat does result in some nutrient loss. Still, this method does not result in the same leaching losses that occur with boiling veggies in water.
Some vegetables are better candidates for the oven. Artichokes, asparagus, leeks, broccoli, eggplant, green beans, celery, onions, and peas were able to keep all of their antioxidants (per the same Spanish study). The antioxidants in green peppers, on the other hand, did not hold up nearly as well after dry roasting.
5. Pressure Cooking
Capable of cooking food ridiculously fast, the science behind pressure cooking resides in the locking lid. Because excess heat is lost when water vaporizes into steam and escapes into the air, other cooking methods are restricted by a boiling point of 212?F. Pressure cookers, on the other hand, trap heat inside by increasing the atmospheric pressure within the pot to 15 pounds per square inch. This, in turn, allows the internal temperature to rise to 242?F.
Though this cooking method requires a very small amount of water, pressure cooking reduces cooking times significantly (many veggies need only a minute or two). A study on the effects of pressure cooking on spinach and amaranth found that vitamins A and C were better retained than cooking in the oven, boiling, or pan frying. Broccoli, too, was able to retain 90% of its nutrients when prepped in the pressure cooker.
This method of cooking also promotes the Maillard reaction, a chemical transformation that results in the creation of hundreds of new and different flavor compounds. In other words, pressure cooking produces tastier veggies. If you’ve yet to do so, you’ll definitely want to give this one a try!
Much maligned for causing obesity and heart disease, the data on fried foods is far from complete. And many studies on the topic have found no direct link between eating fried foods and premature death. Though the jury is out on the health risks of frying overall, there is some positive news about the nutritional effects of frying vegetables.
The main concern with frying is the addition of unhealthy fats. However, pan frying vegetables with just a touch of olive or coconut oil can help retain nutrients like vitamin C much better than boiling. This is because fried veggies are cooked quickly on high heat, without water to leach out nutrients.
Whether the pan was lightly oiled (as with sautéing) or if veggies were fully submerged in oil (aka deep frying) made little difference for the results of a 2015 study that investigated the antioxidant properties of tomatoes, potatoes, eggplant, and pumpkin post-frying.
Using extra virgin olive or coconut oil to deep fry and sauté, researchers found that, although these methods unsurprisingly increased fat content, they also increased the total phenolic compounds in the vegetables. Boiling with plain water or water with extra virgin olive oil added had no such effect. The extra virgin olive oil was able to boost antioxidants by conferring its own unique phenols to the food being cooked.
7. No Cooking
By now you might be thinking that it’s probably best not to cook your vegetables at all. It seems that practically every cooking method has its drawbacks. And yes, raw veggies do maintain all of their intrinsic vitamins, minerals, and phytochemicals. However, cooking provides the important function of increasing the variety and availability of nutrients in vegetables. It also improves the human body’s ability to digest them.
For example, researchers analyzed blood samples from 198 volunteers who had subsisted entirely on a raw food diet for at least two years. As long as their diets were enriched with fats, the participants’ vitamin A and carotene levels were high enough to provide protection against chronic disease. However, their levels of the potent antioxidant lycopene were well below the threshold to derive any disease-fighting benefits. One way to enhance lycopene levels is to cook tomatoes, which will increase the bio-availability of lycopene and improve overall antioxidant activity, at the cost of diminished vitamin C lost through the cooking process.
It’s clear that when it comes to cooking vegetables, there is almost always a trade-off. Every time you add heat or liquid, fruits and vegetables lose some of their nutritional value. The same goes for extra long cooking times. (Though sometimes degradation in one area means an increase of other healthful elements in some other aspect.)
Because there is no single best way to cook them, always employ variety with your fresh produce. Eat your veggies raw or baked one day. Then boil or steam them the next. This will help foster a balance between lost nutrients and increased antioxidants.
Every fruit and vegetable has its own unique cooking requirements that can help maximize its nutrition. (Or at the very least, minimize the damage.) Unless you’re ready and willing to stay on top of the latest food science, here are some general tips:
- Keep cooking time, temperature, and liquids to a bare minimum
- Don’t pre-soak your veggies in water before you cook them
- Cook fruits and vegetables whole whenever possible, or cut them into large pieces
- Wait to chop up veggies until just before cooking them
- Increase the bio-availability of nutrients by including healthy fats into your meals, like extra virgin olive oil, nuts, and seeds
- Keep the peel on fruits and vegetables to add even more nutrition to your meals