Nutrition III - Nutrition and Lifestyle - Food Preparation: Cooking and Oils

Question 1

Boiling vs. steaming vegetables

Answer 1

Boiling vs. steaming vegetables:

Boiling:
* Boiling greatly reduces nutrient content, in particular B vitamins, vitamin C, potassium and plant compounds such as chlorophyll (drink the water or use it as a base for soups)
* Flavour, colour and texture are also altered

Steaming:
* Steaming minimizes nutrient losses while taste and colour are retained
* The longer the exposure to air, heat and water, the greater the nutrient losses
* Steaming is the best method of cooking vegetables

Question 2

Food preparation Methods

Answer 2

There is no single cooking or preparation method that is the best (including eating vegetables raw) and it’s advised to use a variety of cooking methods.

• Water-soluble nutrients like B vitamins and vitamin C are decreased with cooking, whereas other nutrients such as vitamins A, D, E, K are released from the tick cell wall and increase in the food when cooked at moderate temperatures
• Lycopene is an antioxidant (with a particular therapeutic benefit in prostate cancer) found in tomatoes that increases in content with cooking. Pureeing tomatoes also increases lycopene content.

Question 3

Avoid high heat

Answer 3

• High temperatures in grilling or frying meat produce carcinogenic compounds (heterocyclic amines) – linked with increased risk for cancer, especially colon cancer
• Muscle meats cooked over an open flame (barbecue, grilling) can be coated with polycyclic aromatic hydrocarbons (carcinogenic) if fat from the meat drips and begins to smoke
• If you do barbecue or grill foods, use smaller pieces (kebabs) as they cook faster at a lower temperature
• Marinating meat and veggies in antioxidant spices such as turmeric and rosemary before cooking lowers carcinogenic compounds

Question 4

Broiling, grilling, roasting and frying

Answer 4

High heats in cooking methods such as broiling, grilling, roasting and frying causes formation of inflammatory compounds called advanced glycation end products (AGEs).
* This is particularly so for animal foods that are high in protein and fat
* AGEs I linked to diabetes, Alzheimer’s, atherosclerosis and kidney disease
* Eating some oils to high temperatures causes the oxidation of fatty acids, which can result in free radical damage in the body

Question 5

Steam sautéing

Answer 5

Steam sautéing: sauté foods in water adding a small amount of oil at the end for taste.
* Works very well for vegetables – uses a lower temperature than sautéing with oil or stir-frying
* Frying foods in oil adds many calories to the meal so using water and small amounts of oil is a better choice
* Steaming, boiling, poaching and making stews are also healthier options
* The key is to keep the temp low & maintain the water content of the foods

Question 6

Use of oils

Answer 6

Use of oils:
* Use cold-pressed oils, stored in dark, glass bottles
* Store sealed, in a cool dark place or in the fridge. Heat, light and air cause oils to slowly go rancid
* When cooking with oils that contain unsaturated fatty acids (and hence have doubled bonds in their chemical structure), they are prone to oxidation which leads to free radical damage and inflammation
* Ingesting or inhaling oxidized oils is associated with atherosclerosis and DNA damage (i.e. cancer)

Question 7

When to add in oils

Answer 7

Add oils after cooking the food, to avoid heating them.
* If you need to heat oils for cooking, use oils that are relatively stable even at high temperatures
* Monounsaturated fats such as olive, macadamia and avocado oils and saturated fats such as coconut oil are stable with heat & don’t oxidize unless they reach very high temperatures. Saturated fats barely oxidize at all.
* Extra virgin olive oil can be heated to 180 - 200°C. Extra virgin olive oil, macadamia and avocado oils remain stable when cooked at higher temperatures due to their high antioxidant content

Question 8

Medium temperature cooking

Answer 8

Medium temperature cooking:
* Steam sautéing
* Sautéing
* Lower temperature roasting (e.g. 150°C)
Oils to use:
* Virgin olive oil
* Coconut oil
* Avocado oil
* Butter (from grass-fed cows)

Question 9

Higher temperature cooking

Answer 9

Higher temperature cooking (180°C+):
* Frying (180°C)
* Roasting
* Grilling
* Baking
Oils to use:
* Avocado oil
* Coconut oil
* Ghee or clarified butter

Question 10

Oils to avoid

Answer 10

Oils to avoid:
* Soya-bean oil: has a short shelf life and is often treated with hydrogen gas so it becomes trans-fats
* Corn oil: generally extensively processed and refined. Care with source – predominantly GM in the US
* Canola, palm and vegetable oils (unless cold-pressed) are highly processed and exposed to high heat to create them
* Avoid cooking with polyunsaturated fats – examples: flaxseed oil, fish oils, hemp oil, sunflower, safflower, grapeseed, most nut oils (macadamia is the exception) as they quickly oxidise with heat (due to their many double bonds that are ‘vulnerable points’).