Ad
Get special offers, recipes, health news, PLUS our FREE seafood cooking guide!
Got it, thanks! Click here for your FREE seafood cooking guide & recipes e-booklet.
Food, Health, and Eco-news
When is Oil Better than Water?
Versus water, cooking veggies in extra virgin olive oil yields two big benefits 03/09/2016 By Craig Weatherby
We all know it's important to eat plenty of vegetables. 

That's very clear … but does it matter whether they're raw or cooked?

Comic Dick Gregory advocated raw-food diets in the 1970s … but his skeletal appearance was pretty off-putting.

In the 1980s, raw-food diets got a huge boost from advocacy by TV's vibrant, vivacious "Juiceman” (Jay Kordich), and they've been adopted by Hollywood stars like Woody Harrelson.

Advocates make strong claims about the benefits of eating veggies raw, but generally offer dubious explanations for those alleged effects.


However, cooking makes some nutrients more "bioavailable", and eating vegetables along with fats enhances absorption of carotenoids.

Carotenoids are the healthful, antioxidants in red/yellow/orange vegetables like peppers and squash, and in dark green vegetables such as spinach, kale, and chard.

So cooking makes sense from a nutritional standpoint, but what's the best way to cook vegetables?

What's the healthiest way to cook vegetables?
Many health authorities advise steaming vegetables.

Steaming minimize nutrient losses versus boiling in water, and avoids the calories added by cooking foods in oil.

And exciting findings show that cooking vegetables in extra virgin grade olive oil (EVOO) does two very good things:
  • Boosts vegetables' antioxidant power
  • Instantly improves people's blood sugar and fat/cholesterol profiles
Although other vegetable oils contain small amounts of antioxidants, such as carotenes, only extra virgin olive oil is truly rich in antioxidants.

Crucially, the uncommon antioxidants in EVOO – such as oleuropein and tyrosols – are virtually unique to olives, and deliver particularly powerful, clinically proven cardiovascular benefits.


Quick cardiovascular and metabolic benefits from EVOO
Rome's Sapienza University just reported more encouraging findings from a small clinical trial in 25 people (Violi F et al. 2015).

The results showed that eating a Mediterranean-style meal with extra virgin olive oil (EVOO) brought immediate blood sugar and cholesterol benefits.

The Roman researchers divided the subjects into three groups:
  1. No Oil Group - Mediterranean lunch with no added oil
  2. EVOO Group - Mediterranean lunch plus 10 grams of added EVOO
  3. Corn Oil Group - Mediterranean lunch plus 10 grams of added corn oil
The team conducted blood tests before each meal and two hours after the meals.

In all groups, blood sugar levels rose after eating, which is normal.

But blood sugar rose much less after a meal with olive oil, compared to either of the other meals.

The blood tests also found lower levels of LDL ("bad”) cholesterol in the EVOO-meal group, compared to the two other meals.

EVOO differs sharply from corn oil, which may explain the trial results:
  • Corn oil is low in antioxidants and extremely high in polyunsaturated omega-6 fats
  • EVOO is extremely rich in antioxidants and monounsaturated fat, and quite low in omega-6 fats
The heart-healthy reputation of cooking oils high in omega-6 fats (e.g., corn, soy, cottonseed, and safflower) has suffered a series of scientific blows: see Heart Risks Raised by Omega-6 Excess.

So choose oils lower in omega-6s, such as canola oil, extra virgin olive oil, macadamia nut oil, coconut oil, and avocado oil.

The effects of cooking methods on antioxidant content
Ten years ago, researchers at Italy's University of Parma tested various cooking methods to see how each affected the antioxidant power of vegetables.

The Italian team noted that standard antioxidant-content data comes from tests on raw, uncooked vegetables (Pellegrini N et al. 2009).

But cooked vegetables might provide substantially more or less antioxidant power, depending on cooking method and duration.

So they tested the effects of boiling, pan-frying and deep-frying on the "total antioxidant capacity” of potatoes, artichokes, eggplant, mushrooms and onions.

Total antioxidant capacity or TAC is a measure of how much antioxidant power a given chemical (such as vitamin C) or substance (such as a bit of puréed vegetable) displays in a test tube experiment.

In line with other studies, they found that boiling reduced the TAC of every vegetable (except artichoke).

In contrast, vegetables pan-fried (sautéed) in EVOO had substantially higher TACs, while foods deep-fried in EVOO had dramatically higher TAC values.

If you're going to cook with water, the results suggest you should steam vegetables instead of boiling them.

If you must boil veggies, be aware that antioxidant losses in them rose along with the volume of water used, so minimize the amount.

And the water used to boil veggies contains some of their lost antioxidants, so keep it to cook beans and grains or to make broths and sauces.

Spanish studies give extra-virgin olive oil a boost
Spanish researchers have performed some of the best studies in this realm.

For example, twin studies from Spain's University of Mucia found that cooking vegetables in water reduced antioxidant levels much more than cooking them in oil, and that cooking them in EVOO resulted in the highest antioxidant content (Moreno DA et al. 2007; Jiménez-Monreal AM et al. 2009).

As the authors of one of those studies wrote,"... griddling, microwave cooking, and baking produced the lowest losses, while pressure-cooking and boiling lead to the greatest losses; frying occupies an intermediate position. In short, water is not the cook's best friend when it comes to preparing vegetables." (Jiménez-Monreal AM et al. 2009)

Recent studies from two other Spanish universities echo the results of their countrymen's earlier investigations, and of the 2009 Italian study.

#1 - Effect of cooking time and added EVOO
Researchers from the University of Barcelona prepared tomato sauce from scratch.

They cooked it using four different durations (5, 30, 45, or 60 minutes) and with or without extra virgin olive oil (EVOO), with these results:
  • The TAC of tomato sauce dropped the longer it was cooked.
  • Adding EVOO to tomato sauce boosted its TAC (antioxidant power).
As the Barcelona team wrote, "Higher levels of virgin olive oil in tomato sauce seemed to enhance the extraction of phenolic [antioxidant] compounds from the tomato, leading to higher phenolic contents in the sauces.” (Vallverdú-Queralt A et al. 2014)

Of course, addition of EVOO to tomato sauce would boost its antioxidant content, aside from any extraction effect on the polyphenol-type antioxidants in the tomatoes.

#2 - Effects of different cooking methods
Scientists from Spain's University of Granada joined with Mexican scientists to test the effects of four common cooking methods on the antioxidant capacity of vegetables.

They tested the raw vegetables before cooking to determine the variety and baseline levels of their antioxidants .

The researchers cooked about 4 ounces of potato, tomato, eggplant, and pumpkin in 4 different ways: deep-fried, sautéed, boiled in water, or boiled in a mixture of water and extra virgin olive oil (EVOO).

So that their test would mimic actual household cooking methods, they used the proportions of vegetable to either water or oil found in traditional recipes.

Across all three methods, the vegetables were cooked for 10 minutes, which produced results that resembled the findings from the University of Barcelona study and the prior Italian and Spanish studies:
  1. Cooking the vegetables in water invariably cut their antioxidant capacity.
  2. Deep-­frying raised antioxidant capacity dramatically, while sautéing raised it substantially.
  3. Vegetables cooked in EVOO retained their original antioxidants, and gained antioxidant capacity, thanks to several particularly powerful types they absorbed from the EVOO.
As the Spanish-Mexican team wrote, "Deep frying and sautéing led to increased fat contents and total phenolic content, whereas both types of boiling reduced the same.” (Ramírez-Anaya Jdel P et al. 2015)

As the research results show, a deep-fried vegetable is likely to absorb more oil than a vegetable sautéed in oil.

And when you sauté absorbent veggies like pumpkin or potato, they will retain more oil than smooth, hard vegetables like carrot or peppers.

The evidence suggests these are the best ways to cook vegetables, in descending order of nutritional preference:
  1. Sauté veggies in EVOO, and use minimal oil to minimize calories.
  2. Sauté veggies in minimal amounts of any low-omega-6 oil, such as macadamia nut, canola, coconut, avocado, or hi-oleic sunflower.
  3. Steam your vegetables for the minimum time needed to soften them sufficiently.
  4. Boil veggies in minimal water, for the minimum time required to soften them sufficiently.
By the way, many Internet sources provide misinformation about the "smoke point" of olive oil.

The smoke point (temperature) of an oil matters, because smoke signifies the degradation of an oil's fats ... a bad thing for taste and health.

In reality, EVOO resists damage even when heated to 400 degrees, as you would for deep-frying foods (see Can Extra Virgin Olive Oil Stand Your Kitchen's Heat?). 

Of course, using EVOO for deep-frying is far from the ideal culinary use of a top-quality extra virgin olive oil!

What's the bottom line?

First, the idea that it's always healthier to steam vegetables than to cook them in oil isn't necessarily correct.

And when you cook with oil, you probably can't do better than extra virgin olive oil.


Sources
  • Andlauer W, Stumpf C, Hubert M, Rings A, Fürst P. Influence of cooking process on phenolic marker compounds of vegetables. Int J Vitam Nutr Res. 2003 Mar;73(2):152-9.
  • Andrikopoulos NK, Dedoussis GV, Falirea A, Kalogeropoulos N, Hatzinikola HS. Deterioration of natural antioxidant species of vegetable edible oils during the domestic deep-frying and pan-frying of potatoes. Int J Food Sci Nutr. 2002 Jul;53(4):351-63.
  • Bayram B, Esatbeyoglu T, Schulze N, Ozcelik B, Frank J, Rimbach G. Comprehensive analysis of polyphenols in 55 extra virgin olive oils by HPLC-ECD and their correlation with antioxidant activities. Plant Foods Hum Nutr. 2012 Dec;67(4):326-36. doi: 10.1007/s11130-012-0315-z.
  • Carnevale R, Pignatelli P, Nocella C, Loffredo L, Pastori D, Vicario T, Petruccioli A, Bartimoccia S, Violi F. Extra virgin olive oil blunt post-prandial oxidative stress via NOX2 down-regulation. Atherosclerosis. 2014 Aug;235(2):649-58. doi: 10.1016/j.atherosclerosis.2014.05.954. Epub 2014 Jun 19.
  • Jiménez-Monreal AM, García-Diz L, Martínez-Tomé M, Mariscal M, Murcia MA. Influence of cooking methods on antioxidant activity of vegetables. J Food Sci. 2009 Apr;74(3):H97-H103. doi: 10.1111/j.1750-3841.2009.01091.x.
  • Moreno DA, López-Berenguer C, García-Viguera C. Effects of stir-fry cooking with different edible oils on the phytochemical composition of broccoli. J Food Sci. 2007 Jan;72(1):S064-8.h.
  • NPR/Allison Aubrey. Get The Most Nutrition From Your Veggies. July 27, 2009.Accessed at http://www.npr.org/templates/story/story.php?storyId=106968683
  • Pellegrini N, Miglio C, Del Rio D, Salvatore S, Serafini M, Brighenti F. Effect of domestic cooking methods on the total antioxidant capacity of vegetables. Int J Food Sci Nutr. 2009;60 Suppl 2:12-22. doi: 10.1080/09637480802175212. Epub 2009 Mar 2.
  • Ramírez-Anaya Jdel P, Samaniego-Sánchez C, Castañeda-Saucedo MC, Villalón-Mir M, de la Serrana HL. Phenols and the antioxidant capacity of Mediterranean vegetables prepared with extra virgin olive oil using different domestic cooking techniques. Food Chem. 2015 Dec 1;188:430-8. doi: 10.1016/j.foodchem.2015.04.124. Epub 2015 Apr 28.
  • Sacchi R, Paduano A, Savarese M, Vitaglione P, Fogliano V. Extra virgin olive oil: from composition to "molecular gastronomy". Cancer Treat Res. 2014;159:325-38. doi: 10.1007/978-3-642-38007-5_19. Review.
  • Vallverdú-Queralt A, Regueiro J, Rinaldi de Alvarenga JF, Torrado X, Lamuela-Raventos RM. Home Cooking and Phenolics: Effect of Thermal Treatment and Addition of Extra Virgin Olive Oil on the Phenolic Profile of Tomato Sauces. J Agric Food Chem. 2014 Mar 27. [Epub ahead of print]
  • Violi F, Loffredo L, Pignatelli P, Angelico F, Bartimoccia S, Nocella C, Cangemi R, Petruccioli A, Monticolo R, Pastori D, Carnevale R. Extra virgin olive oil use is associated with improved post-prandial blood glucose and LDL cholesterol in healthy subjects. Nutr Diabetes. 2015 Jul 20;5:e172. doi: 10.1038/nutd.2015.23.
Ad