Steaming hot vs raw cuts? Black pepper with turmeric? Let’s discuss food absorption.

A carrot is not only a carrot; it is a locked treasure of micronutrients, hidden in its skin and flesh. Such can be said about all vegetables, as their intricate and complex structure of micronutrients drives their diverstiy. If properly cooked and prepared, vegetables can become incredibly powerful players in our health. As an example, let´s return to the carrot. Best advertised for its beta-carotene, a pigment and precursor of Vitamin A, a 2012 study stated that a cooked carrot provides 6.5x more beta-carotene compared to raw carrots. The study did not explain why. In the following article, I aim to introduce which vegetables are best consumed cooked and with which method, which vegetables are best consumed raw and which combination of vegetables and spices enhance absorption of micronutrients. You may be surprised to learn that many of these you already know. 

The Cooking Method

Boiling vegetables leaks any water-soluble vitamins, such as Vitamin B, and C, as well as magnesium and potassium into the water it is boiled in, hence it is a great method to prepare soup, but less ideal when cooking vegetables and discarding the used water. Thereby, steaming broccoli, carrots, spinach and kale help retain more of their nutrients than boiling would. When cooked, broccoli preserves Vitamin A, C, and K, kale preserves vitamins A, K, calcium and iron, and cooked spinach reduces oxalic acid, a compound which inhibits calcium and iron absorption while increasing the availability, not content, of vitamins A and E. Also, cooked broccoli tastes far better than raw. 

Simmering tomatoes increases the availability of lycopene, an antioxident beneficial for the heart. Roasting asparagus, eggplant, bell peppers and courgette increases the availability of vitamins, and antioxidents, while maintaining vitamin C. Sauteeing mushrooms breaks down agaritine, a  harmful carginogen found in raw mushrooms and not only enhances flavour but availability of potassium. In general, sauteing or stir-frying are great method of cooking food, as long as the cooking oil is well chosen (avocado oil, olive oil) and not overdome. Grilling and roasting require an oven or grill, which are often unavailable to the average student or urban household. Microwaving is also a good alternative to heat and cook food.

Chopped and ready

On the other hand, Vitamin C is often lost during any cooking method and thereby best provided in raw vegetables such as bell peppers, cabbage, carrots, onions, and spinach. Very long cooking can degrade heat-sensitive vitamins B, A, K,  and E, hence avoid overcooking. Otherwise, raw lettuce and cucumbers best maintain vitamin  K, the former also maintaining vitamin A and the latter potassium. Raw vegetables are also very water dense, as spinach , bell peppers, tomatoes, courgette, celery, lettuce and cucumbers are all 91-95% water, providing excellent hydration. Some of this water turns into steam during the cooking progress, hence your mushrooms and spinach shrivel when cooked. Furthermore, 20-30% of our hydration comes from food, with the most coming from vegetables and fruits (85-95%), dairy products (80-90%), cooked grains (60-70%) and lastly 60-70% of meat, fish and eggs is water. 

Soak, skin, fats and frozen

1. Soaking for a few hours or milling grains and beans before cooking removes phytic acid, which inhibits absorption of iron, zinc calcium, magnesium and manganese. Soaked oats, or better known as overnight oats, are thereby recommended over instantly mixed oats with milk for breakfast. 

2. Do not peel, but do rinse dirt off the vegetables. Most nutrients are underneath the skin of the vegetables such as courgettes, aubergines, potatoes, carrots and cucumbers and are often physically removed. If the vegetable is eaten raw, then removing the peel does protect from bacteria, but if the vegetable is cooked, all the harmful bacteria will die in the cooking process, hence peeling makes little sense unless it is to improve texture of taste. 

3. Fats mix well with Vitamins K, A, D and E (KADE) hence adding olive oil, avocado, nuts, eggs or fish with your broccoli or carotte helps extract a little bit more of its nutrients. 

4. Frozen food is just as good as fresh food, and should not be slept on as a source of cheap and long-lasting nutrition. Fresh produce can get damaged during transport, as its exposed to humidity, heat and light, however frozen produce is protected, and thereby often maintains more nutrients than fresh ripe produce.

Mix and match

Lastly, some foods act as a lock-and-key system, where one ingredient helps absorb micronutrients of the other. Piperine in black pepper helps absorb the curcumin in turmeric by up to 20x, olive oil helps absorb lycopene in tomatoes, vitamin C in citrus fruits works to absorb iron in spinach or chickpeas and antioxidants in green tea, garlic helps absorb omega-3 fatty acids in fish and zinc and iron in whole grains. Myrosinase in mustard  seeds converts glucosinolates in broccoli into sulforaphane, a plant compound known to be antioxidant, anti-inflamatory and antimicrobial, and the fiber in oatmeal helps absorb antioxidants in berries. For those who love to put bananas in their yoghurts, the probiotics in the yoghurt help digest the prebiotic fiber in the bananas, promoting gut health. Lastly, beans and rice provide all nine essential amino acids and form a complete protein meal. The healthy fats in almonds help absorb the flaonoids in dark chocolate, and enhance the intake of antioxidants. The fat in eggs absorb the fat-soluble vitamin K in spinach, while the fat in avocados improves the absorption of the same vitamins in leafy green vegetables. Finally, but not the last combination, vitamin D in salmon and mushrooms help absorb calcium from kale and sesame seeds, respectively. 

Surprisingly, many of the combinations listed above are already consumed and sold in grocery stores. Chocolate covered almonds are a delicacy,  yoghurt bowls are most often sold with a sliced banana curving the rim, and oatmeal is most commonly served with a side of berries, not any other fruit. A slice of lemon in meals helps with enhance  taste and iron-absorption and spinach in an omelette is not unheard of. Rice and beans are staple dishes, and avocado in a green leafy salad does more than add taste and color. 

Chewing, chewing, chewing

In the short-term, the best intervention for absorption which we, as consumers, can control is how we eat our food. The mechanical breakdown of our food and the chemical mixing of saliva with such food prepares the stomach acid and pancreatic juices in our stomach. The same saliva produced while chewing contains epithelial growth factor (EGF) which stimulates the growth and repair of epithelial tissues, nourishing your gut once the saliva-food combination reaches your intestine. 

The recommend number of chews is 32, however in reality, nobody will count how many times they chew per bite, hence its best to avoid chowing down food. Unchewed or badly broken down food particles can overgrow bacteria or increase fermentation in the gut, resulting in bloating, gas, constipation or indigestion.