Preparation advice for eating a plant-centred diet is relatively uncomplicated: raw and lightly cooked vegetables and fruits tend to have the most nutrients. Many of the vitamins and phytochemicals in plant foods are what are known as water soluble, meaning that that are dissolved by water (in the body). These types of nutrients tend to be easily destroyed, lessened or washed away by heat and exposure to air, so fresh is best. We also do not store water-soluble vitamins in the body and therefore need daily sources to meet dietary needs; excess amounts are excreted in urine. Fat-soluble vitamins, as the name suggests, are dissolved and made available to the body by good quality dietary fats; their breakdown and availability for our body’s use is often aided by cooking and heat. Unlike water-soluble vitamins, fat-soluble ones are stored in body fat and the liver. These are the nutrients that can be toxic if we take much more than the recommended amount as the body has difficulty getting rid of excess. Most of our fat-soluble nutrients are found in animal products, including dairy, but some are found in plant foods too.
Many of the plant foods we eat have a combination of water-soluble and fat-soluble nutrients. Using a variety of preparation and cooking methods helps ensure that we get the most out the foods we eat. For example, watercress has mainly water-soluble nutrients such as the B vitamins and vitamin C, but it also is a great source of fat-soluble vitamins K (for blood clotting), beta-carotene (converts into Vitamin A as the body needs it) and some Vitamin E. Although you could always eat it raw and still take in some of the fat-soluble nutrients, occasionally cooking your watercress (such as watercress soup) will help to get the best absorption of vitamins K and E. So, no matter what you eat even if one or more nutrients are ‘destroyed’ in cooking you may be enhancing others.
Grains, legumes and beans for the most part need to be cooked, or sprouted. Porridge oats and other grains that have been ‘flaked’ such as barley, rye, spelt and quinoa can be eaten raw. Although legumes, beans and grains contain heat-sensitive B vitamins they also have nutrients that are not destroyed by cooking. Fruit is nearly always best raw or freshly juiced, but dried fruit can often be a better source of minerals than fresh. Cooked fruits, such as you might find in southeast Asian cooking, can be a great way of adding interest and taste to meals while still retaining many nutrients, especially if lightly cooked. Even homemade jam can be a source of valuable nutrients.
Water-soluble vitamins: Vitamin C; B vitamins: thiamine, riboflavin, niacin, B6, folate, B12, pantothenic acid, biotin; many phytochemicals.Vegetable preparation advice: raw, lightly cooked: steam, stir fry, poach; eat soon after preparing/cutting
Fat-soluble vitamins: A, D, E, K, many phytochemicals. Vegetable preparation advice: boil, steam, stir fry, roast, braise, slow cook; use oil to aid absorption
Overall preparation advice: ‘Box and cox’ with your cooking methods for variety, taste, and to make the most of the array of nutrients in plant foods.
The following combinations and cooking methods have been clinically shown to either enhance the absorption of specific vitamins/minerals/phytochemicals, or to increase their capacity to interfere with cancer initiation, promotion or progression.
Green Tea + Citrus: Citrus fruits help preserve the catechins in green tea (of which the powerful EGCG is one). Catechins are polyphenol phytochemicals that can halt cancer growth by blocking blood vessel formation: no blood supply to bring nutrients and oxygen, no growth. Grapefruit may interfere with certain medications so use limes, lemons and oranges if you need to avoid grapefruit for now. Preparation suggestions: Squirt some fresh lemon in your next mug of green tea; use cold green tea or finely powdered matcha green tea (from specialist retailers) plus lime juice in a fresh fruit juice or smoothie. Japanese leaf green tea tends to have much more catechin content than Chinese green tea and tea bags.
Turmeric + Black pepper: The anti-cancer activity of curcumin – the main phytochemical in the spice turmeric- is increased by a factor of 1000 in the presence of piperine (in black pepper). Olive oil may further enhance the effect. Preparation suggestions: Add ½ tsp turmeric powder per person, with black pepper and olive oil, in your next curry, even if you are using a prepared sauce or mix; add this combination to North African and East Asian dishes such as tagines, couscous and laksas; put in omelettes, soups, pasta dishes, as a marinade for fish, chicken, lamb or tofu.
Turmeric and Green Tea: These two well-studied ingredients have a similar synergy as mentioned above. In this instance small amounts of EGCG and curcumin on their own added to a cancer cell culture had little effect but when the same small amounts were added together they lead to cancer cells self-destructing. The effect is even more significant when cancer cells are exposed to weak Gamma radiation. So far this relationship has only been studied under laboratory conditions. Preparation suggestion: I’m don’t suggest you have them in the same dish (although that may be a nice culinary challenge), but perhaps follow a dish containing turmeric with a mug or two of refreshing brewed green tea – with lemon, of course.
Raspberries + Apples: the anti-cancer actions of both ellagic acid (raspberries) and quercetin (apples) are multiplied when they are together. Other ellagic acid-containing foods are nuts, other berries, citrus, peaches, pears, cherries and even a little in apples. Preparation suggestions: Indulge in a delicious fruit salad topped with toasted nuts; whiz frozen berries with fresh apple and some apple juice for a deliciously zingy smoothie; add fresh berries and grated apple to porridge or muesli.
Tomatoes + Cooking + Olive oil: Cooking tomatoes allows more lycopene to be released from the tomato’s cell walls, and olive oil makes it easier for us to absorb the lycopene. While most plant foods are best when closest to their natural state (raw, sprouted or lightly cooked), when it comes to absorbing lycopene, the more processed the better. In fact, tomato paste has about three times the amount of lycopene per 100 g as a raw tomato. Even tomato ketchup is a good source. Raw tomatoes are of course fantastic for us, so have both raw and cooked tomatoes in your diet. Preparation suggestions: Ditch the creamy pasta sauces and opt for waistline-friendly tomato ones; add tomato paste to bean pates, tinned tomatoes to vegetable-based soups such as minestrone; spread tomato paste mixed with olive oil and dried herbs onto a plain pizza base and cover with thinly sliced vegetables and strips of semi-dried tomatoes – hold the gooey cheese – and shave over fresh parmesan or even add a handful of rocket/arugula when it’s out of the oven.
Chopped Garlic + Time: The anti-cancer compound diallyl disulphide is made when garlic is left to sit for 10 minutes after being crushed or chopped. Because it is fat-soluble, pair it with some olive oil for better absorption. Preparation suggestion: Whisk one crushed garlic clove with 1 tbsp of apple cider vinegar, 3 tbsp olive oil, 1 tsp of your favourite chopped herb, and a pinch each of salt and pepper. Use this classic vinaigrette on salads, steamed vegetables and to liven up cooked grains.
Broccoli + Light Cooking and/or Thorough Chewing: It may sound daft to list ‘thorough chewing’ but I’m highlighting it because chewing kicks off a pretty remarkable chemical process that changes glucosinolates into the potent anti-cancer compound, sulphoraphane. Light cooking has a similar effect and makes broccoli a bit easier to eat for most of us. Preparation suggestion: Stir fry ½ head of freshly cut broccoli with 2 cloves of garlic and some unsalted cashew nuts. Sprinkle on some soy sauce of quality oyster sauce for a deliciously healthy side to go with garlic and ginger poached fish.