Does Cooking Food Really Hurt Nutritional Value?


The answer in this case is a resounding “it depends,” because some cooking methods hurt nutritional density (of some foods), while others can even improve the body’s access to said nutrients.

The raw-egg-swilling, beef-battering protagonist of the beloved Rocky franchise may have meant well, but as it turns out, the raw egg scene turned classic trope was all for not.

Were he to opt for more conventional means of getting a protein-rich breakfast in, i.e., cooking it, he would have actually had greater access to the protein content in the eggs because cooking them denatures tightly bound clusters of proteins that are harder to digest in raw form.

In some cases, yes, cooking hurts nutritional value, but in others, it actually helps.

In any case, there are much more appealing ways to minimize the loss of nutritional value caused by cooking – namely, choosing the least damaging cooking method (including not cooking at all).

But how does one go about this, and is it the same for all foods and/or nutrients?

The Problem with Ranking Cooking Methods

The effects of cooking on the nutritional value of a food are nutrient-specific and, thereby, food-specific; some cooking methods will severely affect one nutrient’s presence while barely affecting another.

For example, cooking method 1 may be much better than cooking method 2 for preserving the nutrients in broccoli, but this could be flipped around in the case of sweet potatoes.

As you’ll see, some cooking methods even increase the accessibility of certain nutrients when compared to leaving the food raw.

For example, beta-carotene and other carotenoids are easier to digest after being steamed, but boiling can leech these nutrients and others out.

These inconsistencies make for tougher decisionmaking in health-conscious dieters, but you can at least look up the effects of cooking on a few of the foods you find yourself eating most often (if not listed below) so you can make some healthy changes without sleuthing through volumes of research.

Cooking Effects by Nutrient

Here we will highlight how common cooking methods affect the nutritional composition and/or density of various vegetables and meats.

Because plant-based foods are typically more flexible in terms of available cooking methods (who wants to boil a steak?), and given their high nutritional density, we’re going to start with the effects of cooking on vegetables.

Studies have measured the effects of different cooking methods on the following nutrients – we’ll highlight boiling, steaming, and microwaving in the table below. 

This study from Chungbuk National University in Korea examined the effects of different cooking methods on “true retention” of vitamin C, vitamin E, vitamin K and beta-carotene in ten vegetables—we’ll keep it to four of the more commonly consumed vegetables for brevity.

Raw preparation is our baseline, or 100% value.    

Cooking and Nutrient Density (Vegetables)
Food and Method Vitamin C Vitamin E Vitamin K Beta-Carotene
Broccoli – boiled 52.85% 161.16% 98.89% 89.40%
Broccoli – steamed 111.21% 162.34% 123.08% 105.93%
Broccoli – microwaved 112.76% 144.86% 101.76% 109.71%
Sweet potato – boiled 67.70% 97.18% ND* ND
Sweet potato – steamed 59.44% 107.59% ND ND
Sweet potato – microwaved 100.21% 88.72% ND ND
Carrots – boiled 55.33% 69.46% 85.02% 47.36%
Carrots – steamed 70.51% 89.79% 69.87% 40.02%
Carrots – microwaved 92.02% 86.62% 85.35% 40.80%
Spinach – boiled 40.12% 158.37% 94.93% 114.67%
Spinach – steamed 44.75% 165.42% 87.70% 84.67%
Spinach – microwaved 91.10% 174.45% 121.21% 114.67%

*ND = not determined

As mentioned, many proteins are fragile enough in their structure to “unfold” back into their constituent parts when cooked, but just like vegetables, protein content increases in many cases of cooking.

Fats are also vulnerable to compositional changes when meat is cooked in different ways.

A finding from the Federal University of Paraiba’s Department of Food Engineering in Joao Pessoa, Brazil reported on these effects of cooking on meat as follows:

Cooking and Nutrient Density (Meat)
  Protein (g/100g ± SD)* Lipids (g/100g ± SD)
Jerk chicken – raw 32.43 ± 1.85 4.89 ± 0.42
Jerk chicken – grilled 34.59 ± 2.99 2.49 ± 0.21
Jerk chicken – roasted 36.37 ± 1.73 2.33 ± 0.45
Jerk chicken – fried 32.82 ± 0.62 4.02 ± 0.78

*Figures reported as grams of nutrient per 100 grams of food ± standard deviation

How Does Cooking Sap Nutrients?

In the above findings and others correlating cooking methods with nutritional changes, researchers have proposed a number of mechanisms that vary by nutrient as well as the food the nutrient is found in.

For example, even in usually heat-friendly broccoli, vitamin C doesn’t retain well when foods containing it are boiled because this nutrient is water soluble and sensitive to heat, so it gets “dislodged” and leached into the water.

In the case of more sensitive plant-based compounds called phytochemicals, enough heat applied for a long enough time can directly damage/destroy these nutrients without using water to extract them.

Finally, broiling or other high-heat methods can degrade key enzymes that allow access to vitamin B and some minerals.

These are just three of the more confidently established mechanisms among dozens.

The Raw Food Diet Paradox

This mostly plant-based approach to dieting is very healthy for what it provides – fiber, antioxidants, and tons of micronutrients – but can be problematic in its lack of protein and fats.

Because cooking usually degrades nutritional content to a significant extent, many people have transitioned to a raw food diet.

This mostly plant-based approach to dieting is very healthy for what it provides – fiber, antioxidants, and tons of micronutrients – but can be problematic in its lack of protein and fats.

By tempering the full-on raw food approach with just a few cooked protein sources, i.e., lean meat, fish, eggs, etc., you can cleanly fill in these gaps without dramatically affecting the nutritional impact.

In other words, keep the veggies raw (except broccoli/spinach per above), find plant-based sources of protein and fat, and if you eat meat, cooking it doesn’t count as cheating.

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