Vegetables – Blanch, Boil, Steam or Fry…Which is Best?
Health and nutrition has certainly become an ‘on trend’ topic over the past few years. It wasn’t until I first started studying nutrition that I realised how many people in my family and social network considered themselves ‘nutrition experts’. Recently, at a small dinner party with family, I was presented with a large bowl of steamed carrots, to accompany a delicious lamb roast. Of course, I couldn’t help myself, and had to ask the chef why they chose that method of cooking for the carrots. The response? ‘Because steaming is the healthiest way to cook veggies…it keeps in all of the nutrients’. Despite my best efforts to detail the chef on the health benefits of cooking vegetables in a high quality Extra Virgin Olive Oil (EVOO), I was confronted with a confused look, and a comment along the lines of ‘…but that would make them full of calories and unhealthy.’
So…what is the healthiest way to cook veggies? There are certainly pros and cons of all the different methods. However, one thing is for sure – there is scientific evidence to support the health benefits of cooking vegetables in EVOO and other oils.
More about the evidence
A research study published in 2015 showed convincing evidence that cooking vegetables in EVOO resulted in higher levels of polyphenols compared with the raw vegetables.1 This study assessed the impact of various cooking methods (deep frying, sautéing, boiling) on the polyphenol content of potato, tomato, eggplant and pumpkin. Findings included that deep frying and sautéing these vegetables in EVOO resulted in an increased fat content and total phenol content compared with the raw food alone (including phenols such as oleuropein, hydroxytyrosol and tyrosol).1
Tomatoes and lycopene
The main carotenoid found in tomatoes (lycopene) may be associated with a reduced risk of some cancers and heart disease.2 A study published in 2005 showed that the addition of a moderate amount of olive oil to diced tomatoes during cooking resulted in a higher plasma lycopene concentration (e.g. demonstrating higher lycopene absorption and bioavailability).2 It is postulated that the higher lycopene absorption is related to its lipophilic nature, which allows for the extraction of lycopene during the lipophilic phase of cooking.2
A research study published in 2012, assessed the antioxidant capacity of Ocimum species of herbs – including holy basil, wild basil, hairy basil and sweet basil, when cooked in a variety of methods (excess water, blanching, boiling, sautéing and steaming).3 Sautéing the herbs in oil was shown to be the best preparation method of those tested, to increase the antioxidant capacity and phenolic content of the herbs overall.3
Brassica vegetables and glucosinolates
Brassica vegetables, such as broccoli, Brussels sprouts, cabbage cauliflower and kale, contain a phytonutrient family known as glucosinolates, which have been shown to be cancer protective.4 Glucosinolates are water soluble, so will be lost if the vegetables are boiled, blanched or steamed with water. When vegetables from the brassica family are cooked in extra virgin olive oil, the glucoslinolate phytonutrients will be retained and the resultant cooked vegetable therefore has superior health benefits.5
View article references
- del Pilar Ramirez-Anaya J, Samaniego-Sanchez C, Castaneda-Saucedo M, et al. Phenols and the antioxidant capacity of Mediterranean vegetables prepared with extra virgin olive oil using different domestic cooking techniques. Food Chem. 2015;188:430–8.
- Fielding J, Rowley K, Cooper P, et al. Increases in plasma lycopene concentration after consumption of tomatoes cooked with olive oil. Asia Pac J Clin Nutr. 2005;14(2):131–6.
- Trakoontivakorn G, Tangkanakul P, Nakahara K, et al. Changes of antioxidant capacity and phenolics in Ocimum herbs after various cooking methods. JARQ;46(4):347–53.
- Kim M, Park J. Conference on "Multidisciplinary approaches to nutritional problems". Symposium on "Nutrition and health". Cruciferous vegetable intake and the risk of human cancer: epidemiological evidence. Proc Nutr Soc 2009;68:103-10.
- Fowke J, Longcope C, Hebert JR. Brassica vegetable consumption shifts estrogen metabolism in healthy postmenopausal women. Cancer Epidemiol Biomarkers Prev 2000;9:773-9.