FOOD FOR THOUGHT
You know that eating your greens – and reds, oranges and purples – is fundamental for fuelling your body optimally. But could your prepping methods be draining their health benefits?
How to cook your vegetables with nutrients in mind
Sure, they’re not the sexiest topic in nutrition (unless you’re partial to an aubergine or peach emoji), but fruit and vegetables bring some pretty attractive benefits. Evidence shows that, when consumed daily, they can help reduce the risk of diseases, including heart disease and some cancers. There’s also some research to suggest they may protect against type 2 diabetes.
Currently, global recommendations for fruit and vegetable intake (set in 2003 by the World Health Organization) are a minimum of 400g – or, as you and I know it, five 80g portions a day. With the average daily intake in England coming in at under 3.7 portions, there’s room for improvement. But portions aside, the way you prepare your veg affects the benefits, too.
While most fruits come ready to eat, vegetables typically undergo some sort of cooking before they reach your plate. This matters, because cooking affects nutrient levels and how those nutrients are absorbed by the body. So, if you’re going to get your veg prep on, what’s the most nutritious way to do it?
In short, it depends on the vegetable and the nutrients in question. One Chinese study investigated the effects of five cooking methods (five minutes each of steaming, microwaving, boiling, stir-frying, or boiling and stir-frying) on the nutrient levels in broccoli. The researchers found that, except for steaming, all cooking methods led to significant losses of vitamin C and glucosinolates – compounds associated with protective effects against cancer. Steaming: one, boiling: nil.
Other studies have investigated the impact of cooking on a broader range of vegetables. One Spanish study tested the effects of different cooking methods (boiling, microwaving, pressure-cooking, frying, griddling and baking) on the antioxidant activity of 20 types of vegetables, including corn, green beans, Brussels sprouts and courgettes.
While there were variations according to the type of veg, overall, results showed that microwaving and griddling produced the lowest nutrient losses, while pressure-cooking and boiling led to the greatest. This mix of results might seem confusing when considered in isolation, but when taken together, the evidence suggests that submerging your vegetables in water isn’t your best bet if you want to preserve those precious nutrients. Steam to avoid this (a colander over a pan of simmering water works a treat as a DIY steamer), or if you’re boiling (or stir-frying), keep it brief and, if possible, throw the nutrient-filled cooking water into a soup.
As ever, there are a few exceptions. Carotenoids and lycopene (yellow, orange and red pigments with antioxidant effects, found in foods like pumpkin and tomatoes) tend to be more bioavailable when boiled or stewed for a longer period, as cooking softens the cell walls, facilitating their absorption. One study found that cooking tomatoes for 30 minutes increased lycopene levels by 35% – evidence, if you needed it, that pomodoro sauce is a legit health food.
But getting maximal nutritional bang for your buck isn’t just about prep; how you store veg counts, too. A 2017 study found that frozen vegetables retained more nutrients than fresh ones that had been kept in the fridge for five days. So, if you’re not eating them within a couple of days, adding frozen produce to your shopping list could serve you well. Something to chew over.