Cooking clean and healthy meals can be confusing. Not only is the quality of ingredients important but how we prepare them can significantly alter their nutritional content. We all know that a piece of broccoli is nutritionally rich and may protect against some cancers, however; that same piece of broccoli smothered in batter and deep fried as tempura suddenly becomes toxic. Most cooking methods for broccoli, other than steaming, can significantly modify the chlorophyll, soluble protein, vitamin C, and glucosinates in broccoli. Similarly, a study published in April of this year found that the phytochemical and antioxidant capacity of purple fleshed potatoes was dramatically reduced after stir frying while steaming these vegetables was able to retain the health promoting compounds.
Let’s review different methods for preparing food and how to optimize your meals:
Type of Food Prep |
How Does it Work? |
What Foods Work Best? |
When Should I Avoid this Method? |
Steaming |
Using steam from boiling water to cook rather than directly from the hot liquid. Studies have found there are minor losses in carotenoid content though glucosinolates found in brassica vegetables are preserved best with steaming. Steaming also has the best phenolic retention of many of the cooking methods examined in a 2013 review. |
Fish, shellfish Leafy greens Broccoli Asparagus Artichoke Legumes Potatoes Watercress |
Tough fibrous meats or grains that require tenderising may not cook through using this steam methodology. While microwaving food can be an effective form of steaming, there may be some risks associated with excessive use of the microwave light to heat food. |
Boiling |
Unlike the above process, ingredients are fully submerged in liquid. This allows for the breakdown of cellulose structures of plants, enabling powerful carotenoids to be extracted. Therefore boiling can be beneficial in vegetables with a tight fibrous structure. The length of boiling time was also linked to a proportional loss in polyphenols. |
Brussel sprouts Artichokes Pumpkin Millet Fonio Red Rice |
The liver supporting phytochemicals known as glucosinolates found in broccoli and cauliflower tend to leach or degrade when boiled in large volumes at high temperatures. |
Blanching |
Food is cooked by submerging warmed food into cold water. This disrupts the cell membrane allowing for extractability of the nutrients. This may also be done to prepare vegetables for freezing. |
Asparagus Green beans Spinach Broccoli cauliflower | |
Frying |
Frying involves the application of high heat usually with some sort of oil or wine. It has been shown to increase degradation of carotenoids after longer periods, of exposure. Increases the oxidative potential. |
Cooking with certain oils or marinating foods can mitigate some of these side effects- stay tuned for our blog post on finding the right oils for your cooking needs. |
Brassica family: broccoli, cauliflower etc.Leafy greensLycopene containing vegetables such as tomatoes |
Baking |
Applying heat over a period of time for thorough and complete cooking. This has been shown to provide the least loss of polyphenols in berries. |
Potatoes Rhubarb Berries Sweet potatoes | |
Raw food |
Raw food can increase susceptibility to infection by microorganisms, or poor bioavailability. |
Carotenoid rich foods-orange/yellow fruits and vegetables as well as dark leafy greens. |
Chicken Red meat Raw fish if an individual is susceptible to gout as it increases risk for hyperuricemia. |
A note on frozen foods: as frozen vegetables are often blanched before freezing their cell membranes are disrupted,allowing for easier extraction. That being said,they are often more susceptible to heating upon defrosting.
References:
Heywood Taylor, B. Cancer Prevention Cooking. United Kingdom: Anness Publishing, 2004
Palermo, M., Pellegrini, N. and Fogliano, V. (2014), The effect of cooking on the phytochemical content of vegetables. J. Sci. Food Agric., 94: 1057–1070. doi:10.1002/jsfa.6478
Tian J, Chen J, Lv F, Chen S, Chen J, Liu D, Ye X. Domestic cooking methods affect the phytochemical composition and antioxidant activity of purple-fleshed potatoes. Food Chem – April 15, 2016; 197 Pt B (); 1264-70
Yuan GF, Sun B, Yuan J, Wang QM. Effects of different cooking methods on health-promoting compounds of broccoli. – J Zhejiang Univ Sci B – August 1, 2009; 10 (8); 580-8
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