The best and worst ways to cook vegetables
Did you know that the way you cook your vegetables could be leaching nutrients from them? In this blog post I discuss various ways of cooking and how they are affecting the nutrient quality of your food.
Steaming is probably the healthiest way to cook vegetables as opposed to boiling; it’s the steam that is used to cook the vegetables not the water itself. This helps to retain the texture, colour, taste of the vegetables and has been shown to be the best way to minimize nutrient loss. In a study by Xu et Al (2014) on carrots steaming resulted in only a 1.9% loss of Vitamin A boiling, which resulted in a 32.1% loss. In a separate study on broccoli done by Yuan et al, steaming caused the least percentage of nutrient loss compared to microwaving, stir frying and boiling. However the amount of nutrients lost increases with the cooking time so try to cook for as small amount of time as possible.
Boiling vegetables is a very popular method that has been around for a very long time. However this can cause many nutrients, mainly the water-soluble ones Vitamins B and C to be lost from the vegetables. All of these vitamins are quite unstable when exposed to high temperatures. There have been several studies that show that boiling causes the biggest losses of Vitamin C compared to other cooking methods. The amount of nutrients lost in cooking can also be affected by how long the vegetables are cooked for and how much water is used. The longer the vegetables are cooked, the greater the nutrient loses (and the soggier the veggies will be). On the health scales, boiling is great because you’re not using any excess fat or oil, however If you are going to boil veggies, try to use as little water as possible and avoid over boiling them. Try and separate them into separate vegetable categories and them steam each for a few minutes before taking out.
Blanching is a cooking method where food is plunged into boiling water, removed after a certain time and them put straight into cold water or under cold running water (shocked) to immediately halt the cooking process such as when boiling eggs. Blanching is mainly used to inactivate enzymes and is a prerequisite to the preservation of vegetables such as when they are canned. Nutrient losses during blanching differ according to the time interval of the food in the boiling water and the type of size of vegetable. Losses have been shown to be greater form vegetables with greater surface to volume ration and nutrient loss are not uniform throughout the process with the greatest losses happening in the beginning.
Microwaves cook food by agitating water and other small molecules to produce frictional heat. Meaning that compared to when you steam or fry your food it transfers the heat from outside in, but a microwave causes water within the food to vibrate, causing it to heat up. Microwaves heat food much quicker than boiling or steaming on a stove or cooking in an oven, however they can produce uneven heating within the food and extremely high temperatures can be reached. Like boiling many due to the high temperatures, many nutrients can be lost. If you are cooking your veggies in a microwave, it is best to use glass or microwave-safe plastic bowls. You can also add a little water and cover with a microwave safe lid to help create more of a steaming effect, which may help to preserve more nutrients. Once again, try not to overcook your veggies to help reduce these losses
Frying vegetables is often associated with deep fried chips or calamari and thus has gotten a bad rap over time. One of the positive aspects of frying, and probably the only one is that you are not submerging them in water or to high heat for a long period of time. It all depends on the way that you are frying the food. Frying in a pan with a dollop of coconut oil is great and won’t generally cause many nutrient losses and is a great way to add flavor and texture to the food especially when a few spices are added. However, with deep-frying, submerging your food in unhealthy oils is one sure fire way to increase the calorie and fat content of the food. The main thing when frying is to choose an oil that has a high smoke point such as coconut oil so that it doesn’t turn rancid.
Now most Australians are going to hate to hear this as there is nothing Aussies love more than a BBQ on a hot summers day but the charcoaled burnt edges of the steak and sausages are due to the pyrolysis of the fat in the food coming into contact with the flame. This produces greater amount of PAHs (polycyclic aromatic hydrocarbons) – that beautiful barbeque smoking smell – and studies have shown to be associated with an increased risk of several forms of cancer. My recommendations for BBQing is to not
Tips to minimize food loss when cooking
Store food properly such as keeping cold foods colds and in air tight containers.
Keep vegetables in the crisper section of the fridge.
Try washing and scrubbing vegetables rather than peeling them such as with pumpkin and sweet potato as the skin is where a majority of the nutrients are
Use the outer leaves of cabbage or lettuce unless they are wilted or unpalatable.
Steam vegetables rather than boil them and try to minimize deep-frying.
Cook foods quickly and use low temperatures.
Xu, F. 2014. Domestic cooking methods affects the nutritional quality of red cabbage. Food chemistry, Vol 161. Page 162-167.
Yuan, G et al. 2009. Effects of different cooking methods on health-promoting compounds of broccoli. Journal of Zhejang university science B.