ave you ever wondered whether it is more nutritious to eat your vegetables raw or cooked, or whether to eat foods on their own or combined with other foods? Many people have asked me about how they can get the most health benefits out of the foods they eat. It is an intriguing topic, since the amount of nutrients in a food does not necessarily reflect the amount of nutrients your body will absorb, but how you eat them can be a determining factor in their nutritional power.

Bioavailability is the term used to describe how much of a nutrient within a food is usefully absorbed and used by the body. Certain nutrients are more bioavailable if they are heated, while other nutrients are destroyed by heat. There are still other nutrients that will not be absorbed without the presence of other nutrients in a meal. Cooking and eating to maximize bioavailability usually depends upon which nutrients we are interested in maximizing.

To cook or not to cook?

That is the question on everyone’s mind. Unfortunately, there are few definitive answers to this quandary. Research indicates that using dry heat methods, such as roasting and microwaving with minimal amounts of water, are better for preserving some heat-sensitive nutrients, since fewer nutrients are leached out into cooking water than from moist heat methods, such as boiling and steaming.

Since plant foods contain an array of nutrients, chances are that some nutrients will be enhanced by cooking. Plants are often made up of tough cell walls that are fibrous and difficult for our bodies to break down on their own. These tough cell walls usually contain phytonutrients (plant nutrients that can act as antioxidants) that are only released through cooking, since the heat can soften and break down these walls to release and activate the nutrients. Nutrients in the carotenoid family, including beta carotene, lutein and lycopene, are made more bioavailable by cooking.

Certain other plant nutrients will be destroyed by heat. This can be a good thing when those nutrients pose health risks, as with raw mushrooms and celery; raw white and button mushroom varieties contain natural toxins and celery contains psoralens (which sensitize the skin to the sun’s harmful ultraviolet radiation) that are each deactivated by cooking.

However, there are other plant nutrients that you should try to avoid destroying by cooking, as their health benefits are most bioavailable when left either raw or slightly cooked. For instance, anthocyanins, vitamin C and the B vitamins thiamin, riboflavin, niacin, biotin, pantothenic acid, vitamin B6, folate and vitamin B12 are nutrients that do not like heat and can be destroyed by high-heat cooking. Foods such as broccoli should be cooked briefly, if at all, in order to avoid destroying their vitamin C and cancer-fighting sulfur-based nutrients like sulforaphane. When it comes to foods rich in vitamins B and C, it is best to eat them cooked sometimes and raw at other times, just to cover your bases. Berries, for example, which are prized for their anthocyanins, are best when eaten raw but also provide certain other health benefits when cooked.

Grinding is great

Other foods need to have their tough cell walls broken down by cutting or grinding instead of by cooking. Flax seeds and garlic are two good examples.

Flax seeds need to be ground or crushed in order to release their lignans (which are weak phytoestrogens that help protect against certain hormone-related cancers) and omega-3 fatty acids; otherwise they are just a source of fiber.

Garlic contains enzymes that form several sulfur compounds called allyl sulfides that are released through chopping and crushing. Allowing chopped or crushed garlic to stand for ten minutes maximizes the formation of these heart-healthy, cancer-protective compounds.

Fat free = nutrient free

Remember the days of fat-free salad dressings? Contrary to popular belief, you may actually be better off with a dressing that contains a fair amount of fat (as long as it is a healthful type of fat). Research shows that when you eat a salad that contains no fat, you don’t absorb any of the wonderful nutrients that the salad has to offer. Certain nutrients—specifically vitamins A, D, E and K, as well as beta carotene, lutein, zeaxanthin and lycopene—are fat-soluble, meaning that they travel in fat. Fats such as olive oil, avocado and nuts are necessary for the absorption and storage of many plant nutrients. Therefore, for many red, orange and green produce items, some healthful fat is a necessary addition if you want to reap their benefits.

Dynamic duos

Some nutrients require that you eat another nutrient with it in order to maximize their benefits. For example, certain plant foods are excellent sources of iron (called non-heme iron), but the iron is not readily absorbed without vitamin C. That means that you can eat lentils, the best source of dietary iron, every day of the week and twice on Sunday, but if you don’t add a chopped tomato or some red bell pepper to your meal then you may not absorb much, if any, of the iron. In fact, vitamin C can boost non-heme iron’s bioavailability by six-fold!

Inulin, a prebiotic fiber that occurs naturally in onion family foods, like leeks and garlic, asparagus, artichokes, bananas, legumes and whole intact grains, like oats and barley, can aid in the absorption of calcium. Studies have shown that increasing your inulin intake can increase bone mineral density by boosting calcium absorption.

Research has also recently shown that in order to get the most benefit out of the catechins in green or black tea, it is best to add a generous amount of acidic citrus juice. It seems that drinking a tea blend that contains 20-50% vitamin C-rich juice can make the cancer-fighting properties of tea up to 13 times more potent than when they are consumed without vitamin C.

Since bioavailability is not set in stone, I’ve prepared a handy chart that lists important foods and their nutrients and if they should be eaten cooked, raw or in combination with other foods in order to maximize their nutrients. I also have a key of important complimentary nutrients and their function.

Food	Major Nutrients	How to Prepare
Beans, tofu, dark leafy greens, dried fruit	Iron	Add vitamin C-rich foods
Berries	Anthocyanins	Raw
Broccoli	Vitamin C, sulforaphane, indoles	Raw and lightly cooked
Carrots	Beta carotene	Add olive oil; cook until slightly tender
Dark leafy greens, canned salmon and sardines with bones, black-eyed peas, nonfat milk	Calcium	Add onion family foods, asparagus, artichokes, bananas, legumes and whole intact grains
Flax seeds	Lignans, omega 3s	Grind or crush; eat raw
Garlic	Allyl sulfides	Chop and let stand 10 minutes before eating raw or cooking
Green and black tea	Catechins	Add lemon, orange, grapefruit or lime juice
Red bell peppers	Beta carotene, vitamin C	Add olive oil, nuts or avocado; cook until slightly tender and eat raw
Spinach, other leafy greens	Beta carotene, lutein	Cook lightly, add olive oil or nuts
Tomatoes	Lycopene, vitamin C	Add olive oil or avocado; cook and eat raw
Zucchini	Vitamin C, beta carotene, lutein	Add olive oil or nuts; cook and eat raw

Nutrient	Nutrient Function
Allyl sulfides	Helps lower cholesterol and blood pressure; antibacterial
Anthocyanins	Antioxidant; protects against heart disease, cancer and aging of the brain
Beta carotene	Antioxidant; maintains health of eyes, skin, lungs, immune system; protects against certain cancers; can be converted into vitamin A in the body
Calcium	Mineral that helps build strong bones and teeth, important for muscle and blood vessel function
Catechins	Antioxidant; helps neutralize free radicals; reduces risk of skin, esophageal, and stomach cancers
Indoles	Antioxidant that helps protect against cancer
Iron	Component of enzymes and proteins in the body; helps form hemoglobin
Lignans	Act as weak phytoestrogens in the body to help protect against certain hormone-related cancers
Lycopene	Protects against heart disease and many types of cancers, especially prostate cancer
Sulforaphane	Antioxidant that helps protect against breast, lung, stomach, esophageal and colon cancers
Vitamin A	Maintains health of eyes, skin, lungs and immune system
Vitamin C	Antioxidant; reduces risk of cancer and cataracts

Now you know the little tricks for boosting your absorption of nutrients from your diet. Don’t let this information overwhelm you, though; just let it guide you in making better choices. As I said before, the safest and most moderate approach is to eat a variety of cooked and raw produce items and, when you do cook, be sure not to overdo it. Cook for the shortest time possible, using no water or the smallest amount of water that you can. Bake, grill, roast, sauté and microwave most often and steam with the smallest amount of water possible; boil only when necessary. Understanding bioavailability means that you can put optimal nutrition into action. Eat your plant foods with these tips in mind and the benefits will add up to more than the sum of their parts!