I read in 快猫短视频 that raw eggs are 65 per cent digestible, versus 94 per cent for cooked eggs. Similarly, uncooked potatoes are 32 per cent digestible, but the figure rises to 98 per cent when cooked. But how much of the nutritional value in these foods is destroyed in the cooking process?
鈥� The answer depends on the nutrients of interest and whether you are referring to the overall levels in a food or the amounts we can actually absorb, known as bioavailability.
One measure of how much nourishment a food provides is its . This is based on the mean percentage of the recommended daily intake for 16 key nutrients contained in 2000 kilocalories of that food. Using data from the , the NNR of raw egg equates to 146.8. Scaling this value to 1, the relative values for cooked egg equate to 0.95 for poaching (a loss of 5 per cent), 0.89 for boiling (a loss of 11 per cent) and 0.78 for frying (a loss of 22 per cent). But raw egg white contains a that inhibits our protein-digesting enzymes. Cooking inactivates it, making the egg protein more digestible, and because the amino acids resulting from cooking are key nutrients, this makes the protein more nutritious. Eggs are also rich in sulphur and selenium. Since these are found in the amino acids methionine, cysteine and selenocysteine, their bioavailability is increased too.
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鈥淗umble spuds, when raw, are rich in vitamin C and fibre as well as vitamin B6 and energy from starch鈥�
So, which egg nutrients are lost? This depends on the cooking method but, luckily, most nutrients 鈥� including those that people are more likely to lack 鈥� are largely unaffected. Poaching cuts vitamin B2 (riboflavin) by about 20 per cent because it is soluble in water. Boiling increases measured vitamin B9 (folic acid), but frying reduces it because it is unstable at higher temperatures. However you cook them, it is best to avoid using iron or copper-bottomed pans because these metals degrade vitamins E and B12.
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As for the humble spud, it has an NNR of 128.2 when raw, but is rich in vitamin C and fibre, which eggs lack, as well as vitamin B6 and ready energy from starch. Considering the flesh and skin combined, the nutrition loss due to cooking is 25 per cent through baking and 28 per cent when microwaved. Discard the skin and 95 per cent of their iron content is lost. If you do want to take the skin off, do so after cooking. This is because the flesh of unpeeled boiled potatoes is 31 per cent less nutritious than when raw and has 33 per cent less vitamin C, whereas if you peel them first, the loss rises to 44 per cent overall and 63 per cent for vitamin C.
鈥淏oth weight for weight and by calorie, oven-ready French fries beat the avocado for vitamin C鈥�
French fries, unsurprisingly, fare worst, losing 54 per cent of their original nutrition because they are bulked up by absorbed cooking fat. This also contributes to reduced ratios of vitamin C and B6 to calories. Yet both weight for weight and by calorie, oven-ready French fries beat even 鈥渉ealthy鈥� avocado (NNR = 124.8) for vitamin C and almost match it for potassium. Complement egg and chips with salad and you鈥檙e set.
Len Winokur, Leeds, UK
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