Since we’re little, our moms always told us to eat our vegetables in order to be healthy. In the old days, little thought went into how food was prepared and the impact it would have on the nutritional value of it. Today, there is much controversy in the media about the nutritional content of cooked foods vs. raw foods, processed food, and other methods used when storing and transporting foods. With every TV show, newspaper article, and magazine telling you something different, it can get to be quite confusing what the science actually says about what we should do with our food before it is consumed. In this article we try to clear up some of the mystery surrounding food preparation.
Firstly, it must be mentioned that our body needs a variety of vitamins and minerals to be healthy (CDC, 2011), many of these nutrients are found in the fruits and vegetable servings recommended by the Canada Food Guide. People consume fruits and vegetables a number of ways: from frozen, dried, cooked, boiled and drained, and reheated after cooking.
Let’s talk about fruits and vegetables from frozen. Research shows that some vitamins and minerals (riboflavin, niacin, b6, b12, iron, magnesium and copper) are not lost at all during freezing; however certain vitamins like vitamin c can show as much as a 30 percent reduction after being frozen. In addition some minerals like copper and potassium are lost at a rate of 10 percent when frozen. Other vitamins and calcium are lost at a rate of 5 percent (Nutrition data, 2012) (Tu, 1998)
Next let’s discuss dried fruits and vegetables. Studies conducted on drying show that minerals aren’t typically lost during drying, but most vitamins are lost at a rate of 50 percent! In the case of vitamin c a typical loss during drying is 80 percent! (Nutrition data, 2012) (Tu, 1998)
The most common methods of preparing vegetables is probably cooking, or boiling then draining. Cooking your vegetables can cause you to lose as much as 40 percent of your minerals, and 70 percent of your vitamins. Boiling and draining can cause a loss of up to 70 percent of your minerals and 75 percent of your vitamins (nutritiondata.com, 2012) (Tu, 1998)! This means that if you buy frozen vegetables and then boil them, there is almost no nutritional value left in them at all! In addition to this reheating previously cooked vegetables can cause a loss of 10-40 percent of the remaining vitamins, although it does not seem to affect mineral content (nutritiondata.com, 2012).
So we should eat all of our fruits and vegetables raw then right? WRONG, studies show that while cooking vegetables shows a reduction in the mineral content, when eating fruits and vegetables raw makes it tough for our bodies to extract some vitamins in them, particularly beta carotene or vitamin A and other carotenoids (Nutritiondata.com, ND) (La Rock et al, 1998). Carotenoids are very important nutrients because they are anti-oxidants which neutralize free radical in the cells (electrons that cause damage) and fight some diseases like cancer (Tu, 1998). Research suggests that mildly heating or steaming of vegetables makes it easier to extract these carotenoids (Nutritiondata.com, ND) (La Rock et al, 1998). Since steaming still reduces some vitamins like vitamin C (Subramanian, 2009) it would make sense to eat fruits and vegetables BOTH cooked and raw in order to receive optimal nutrients.
The old saying goes “variety is the spice of life”, and as you can see this is true when it comes to food preparation. It is important that you not only have a variety of foods, but also that they are prepared in a variety of ways. In closing it should also be mentioned that the food preparation techniques discussed are for optimal nutrient absorption, however when certain barriers are present (time, access to fresh fruits and vegetables, etc.) the important thing is just that you are eating, because remember some nutrients are better than NO nutrients, however the more nutrients you absorb on a daily basis, the higher the chance that your body can fight off certain diseases like cancer.
Cheryl LeRock. (1998). Bioavailability of β-Carotene Is Lower in Raw than in Processed Carrots and Spinach in Women. Retrieved from: http://jn.nutrition.org/content/128/5/913.fullon Oct. 5 2012
Center for Disease Control (2011). Vitamins and Minerals. Retrieved from: http://www.cdc.gov/nutrition/everyone/basics/vitamins/on Oct. 5 2012
C. P. Stewart (1946). Loss of Nutrients in Cooking. Proceedings of the Nutrition Society, 4, pp 164-171 doi:10.1079/PNS19460031 on Oct. 5 2012
Jean-louis Tu. (1998). Looking at the science on raw vs cooked food. Retrieved from: http://www.beyondveg.com/tu-j-l/raw-cooked/raw-cooked-1a.shtmlon Oct. 5 2012
NutritionData (ND). Nutritional Effects of Food Processing. Retrieved from: http://nutritiondata.self.com/topics/processing on Oct. 5 2012
Sushma Subramanian (2009). Fact or Fiction Raw Veggies are Healthier Than Cooked Ones? Retrieved from: http://www.scientificamerican.com/article.cfm?id=raw-veggies-are-healthier on Oct. 5 2012
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