Anyone who’s heard of the raw food diet will have debated whether it’s better to cook veg or whether the nutrient content is higher when raw. Cooking food can improve its taste, texture and appeal and make it safer for us to consume, so which is better? We asked Registered Nutritionist Kerry Torrens to explain why some foods are better for us raw, and some benefit from a little heat.
What are raw foods?
Raw foods are those that have not been heated or warmed above 48C and have not been refined, pasteurised, canned, treated with chemicals and in some cases frozen either. Following a predominantly raw food diet is not new, these eating patterns have been around since the mid-19th century, and typically include fruit, vegetables, nuts, seeds as well as fermented and sprouted grains and beans.
Does cooking food affect its nutrient content?
You’d be forgiven for thinking that eating all fruit and vegetables raw was the healthier option. After all, some vitamins are sensitive to heat, take vitamin C – just two minutes of cooking decreases the vitamin C content of tomatoes by 10%, similarly the B group of vitamins are water-soluble and at risk of being lost in cooking liquid. However, eating only raw produce ignores the fact that other foods actually benefit from cooking – serving carrots, cooked and puréed with a little oil or butter, allows us to access the carotenoid, beta-carotene much more effectively – this is because cooking breaks down cell walls and being a fat-soluble nutrient, combining beta-carotene-rich vegetables with oil, makes it more accessible to us. Similar effects are seen with lycopene in cooked and processed tomatoes.
Cooking is also a useful means of making more foods available to us, but it is important to choose the right cooking method for the job. Take potatoes: they can’t be eaten raw because they contain solanine and lectins, two compounds that have the potential to make us sick. But when we steam or microwave potatoes we increase their phenolic content and as a result improve their antioxidant activity.
Many raw food advocates claim that cooking destroys important enzymes in food, making our job digesting them harder. However, there's no scientific evidence to support this view.
Our bodies produce the enzymes we need to digest food and re-absorb and secrete those enzymes as needed. So, for a normal, healthy, individual with a balanced diet, the act of digesting cooked food is unlikely to lead to an enzyme deficiency or place our bodies under undue stress. In fact, eating cooked food can actually make the job of digestion easier.
That's because cooked foods are easier to mechanically break down through the action of chewing, and heating food like vegetables breaks down their cell walls, making digestion in the gut easier. Starches and proteins especially benefit from cooking, changing to a form which is easier for us to manage.
That said, cooking may result in some undesired consequences beyond the loss of nutrients. Heat may both positively and negatively affect the flavour and change the colour of the food on your plate, and the formation of toxic compounds, like acrylamide, is also possible.
Foods which are healthier cooked
These include carrots, asparagus and even tomatoes, because cooking makes it easier for our bodies to benefit from some of their protective antioxidants, specifically ferulic acid from asparagus, and beta-carotene, which we convert to vitamin A, from carrots. Similarly, when you cook tomatoes – whether you roast them slowly or make a cooked sauce – it helps to break down the plant cell walls, allowing us to better absorb the lycopene they contain. All these nutrients help to safeguard our cells from damage, may protect us from certain cancers and are heart-friendly. Discover our how to cook asparagus guide.
It’s also worth remembering that even vegetables like beansprouts may be an Escherichia Coli or Salmonella risk; for this reason sprouted beans should be cooked so they are steaming hot throughout, or check labels and ensure the beansprouts are labelled “ready to eat”.
Foods that are healthier raw
There are certainly other vegetables, which benefit from being eaten raw – these include broccoli and watercress (both members of the cruciferous family). When these greens are heated an important enzyme is damaged, this means the potency of helpful anti-cancer compounds called glucosinolates, are reduced. Similarly, cooking makes garlic less potent because heat reduces the amount of health-promoting allicin, so it's best to prepare garlic before you need it and add late in the cooking process to minimise loss. Stir-frying these vegetables may be a more appropriate means of cooking them, if you prefer them cooked.
For those watching their weight, eating some fruit and vegetables raw may help fill you up because raw produce tends to be bulkier and has a higher water content.
Overall, are raw foods healthier than cooked?
A balanced, healthy diet is one that contains a wide variety of different foods – limiting your intake to those that can only be eaten raw reduces the variety you can achieve.
While cooking may cause the loss of some valuable nutrients like vitamin C, there are some fruit and vegetables which offer useful health benefits when they're cooked. Optimising your nutrient intake depends on the fruit and vegetable in question, how you choose to prepare them and what cooking method, if any, you use. It’s also worth remembering that cooking helps extend shelf life and makes food safer by killing possible pathogens. This is especially important for vulnerable groups such as pregnant women, the elderly and very young children, all of whom are more susceptible to food poisoning.
Recipes to try
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If you are considering any form of diet please consult your GP first to ensure you can do so without risk to health.
Kerry Torrens is a qualified Nutritionist (MBANT) with a post graduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the last two decades she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food.
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