Do you spend a lot of time in the kitchen cooking? Do you love shish kebabs off a hot skewer or well-done roast beef? Scientists believe there are several dangers to your health – from exposure to toxic chemicals released during cooking to an increased risk of developing lung cancer. How can you avoid it all?
“The only reason we evolved as humans is because we started cooking our food [over fire],” says Jenna Maccchioki, an immunologist at the University of Sussex, England. “When we only ate raw food, we had to eat all the time because our bodies were constantly lacking nutrients.” This is a popular view among biologists. There is a solid catalogue of evidence that confirms that human evolution is directly linked to the use of fire. When our distant ancestors started cooking food over fire, they made it easier to digest and extract nutrients from food, which ultimately helped increase the gap between the amount of energy expended to digest food and the amount of energy derived from the products consumed. And, of course, they had to chew less. It is believed that culinary skills not only reduced the size of our jaws, but also increased the size of our brains – we were able to afford energy-consuming neural activity. In addition, cooking over a fire kills many potentially dangerous bacteria in food, protecting us from food poisoning.
And yet, for all the obvious benefits of this type of cooking, we wonder: Is it possible that high-temperature food processing poses hidden health risks? As raw food diets become more popular around the world, we are seeing a tendency to invent and apply new cooking methods. Meanwhile, scientists are increasingly exploring all aspects of hot dishes with growing skepticism. Not all cooking methods are suitable for all foods. For starchy products, the main risk is from acrylamide – a chemical used in polymer production that is naturally formed when potatoes, for example, are fried – generally any time food is cooked at high temperatures for long periods of time. Carbohydrate-rich foods (potatoes, cereals, cakes and pastries, coffee, etc.) are particularly susceptible – the reaction of these products to temperature is easily recognized by the formation of an appetizing crust that darkens as if burned. Acrylamide has long been suspected of being a carcinogen – although most of the evidence has come from animal studies. Anyway, Jenna McCarthy (and nutritionists) advise to avoid frequent consumption of foods with high acrylamide content, paying special attention to processed industrial products, just in case.
It is believed that humans began cooking food over a fire a million years ago. In particular, the British Food Standards Agency recommends that you stop cooking potatoes at the golden crust stage, and that you do not store potatoes in the fridge if you plan to cook them at high temperatures (cooling potatoes releases sugars that combine with amino acids to form acrylamide when heated). In general, the main idea is not to overcook. But the risks do not end there. “Things like acrylamide in products are just one of many risks of modern diets,” warns Machchioki, who studies how diet and lifestyle affect the human immune system. “By itself, it is unlikely to cause cancer, but if a person has an unhealthy diet in general, that is what we need to address to reduce risks.” The number of offerings should remain. Cooking at high temperatures affects not only what we end up eating, but also what we inhale. Let’s start with the fact that kitchen stoves themselves are the number one cause of disease in developing countries, where cooking with wood, charcoal, and agricultural waste is common. According to the WHO, indoor smoke is responsible for up to 3.8 million deaths each year.
There is some evidence that cooking at home in a poorly ventilated kitchen may increase the risk of developing lung cancer. However, air pollution in the home is also caused by the use of certain food ingredients in cooking. A 2017 study published in the Journal of Cancer Research and Clinical Oncology found evidence that inhaling combustion products from cooking with vegetable oil increases the risk of developing lung cancer. Scientists analyzed 23 studies of 9411 cancer cases in China and concluded that the risk of developing oncology is increased not only by the lack of good ventilation in the kitchen, but also by different cooking methods, each of which has its own consequences for the human body. For example, frying in a pan with stirring increases the risk of lung cancer, while frying at high temperatures does not. Other studies suggest that inhaling the combustion products of vegetable oil during pregnancy may affect weight loss in newborns. In 2017, Taiwanese scientists compared the levels of aldehydes (many of which are toxic to humans) emitted by different cooking methods. The study authors believe that the combustion products of sunflower oil and methods such as frying and sautéing pose a higher risk of aldehyde emissions, while vegetable oils low in unsaturated fats (such as palm or rapeseed oil) combined with gentler cooking methods do not produce such high levels of aldehydes (and harmful aldehydes).
Meat lovers should think about how they cook it and, in general, how often they eat it. Several studies have found that cooking red meat over an open fire and at high temperatures in the oven may lead to an increased risk of diabetes among meat-eating women in the U.S. (although it was unclear why only women, and not men, were susceptible to these risks).
Although cooking over a fire involves certain risks, such foods help us obtain the energy we need to live much more easily than raw foods. Another study found an association between cooking at high temperatures or over an open flame and type 2 diabetes in people who eat red meat, chicken, and fish, regardless of gender or amount consumed. It is important to note that none of these studies took into account the components of lifestyle – for example, regularity of exercise or aspects of a person’s diet, such as sugar consumption. So it is possible that all of this could have played a role. However, scientists have suggested using alternative methods (such as steaming) that do not appear to be associated with the risk of developing diabetes.
Over the past century, cooking technology has evolved and diversified, moving away from old primitive methods. Microwaves, electric stoves, and toasters are now found in almost every household – the need for an open fire has disappeared. More and more scientists are recommending the use of microwaves, depending on what you want to cook. For example, a recent study in Spain showed that one of the safest ways to cook mushrooms is in the microwave. This method significantly increases the amount of antioxidants in the product, which helps protect cells from damage. However, when mushrooms are boiled or fried, the amount of antioxidants decreases. Scientific data shows that the best way to preserve vitamins and nutrients when cooking vegetables is to cook them for a short time and use as little liquid as possible. In this sense, microwaving is a good method because it preserves less of the useful contents than, for example, boiling, where all the useful contents are transferred to the water.
Some types of vegetable oil, such as canola or palm oil, appear to be more beneficial and safe for cooking. “Steaming vegetables instead of cooking them in boiling water is also much better. Problems always arise when you cook something for a long time at high temperatures – it reduces the nutritional properties or produces some undesirable compounds such as acrylamide,” Machchioki points out. Another problem with frying or other cooking methods that use vegetable oil is what happens to certain fats after heating. It turns out that under the influence of the high temperature in the oil, a whole series of chemical reactions occur, and in the end you risk getting a completely different ingredient than the one you started cooking with. But not all oils experience this. For example, olive oil (unlike, say, coconut oil) quickly reaches a point where a rapid loss of nutritional and beneficial properties begins, and the production of harmful compounds such as aldehydes occurs. Nevertheless, Machchioki recommends using olive oil in most cases, as it is very beneficial. Just avoid using it for long cooking.
And yet, while some cooking methods pose certain risks to our health, avoiding cooked foods altogether in favor of raw foods can be much more harmful. According to a German study, people who followed a raw food diet for several years experienced a weight loss of about 9 kg (for men) and 12 kg (for women). By the end of the study, a significant proportion of these people had a body mass deficit, and about one-third of the women had stopped menstruating. The authors came to the scientifically cautious conclusion that “a very strict raw food diet cannot be recommended for long-term use. “Ultimately, cooking meat and carbohydrate-rich foods is a good way to increase the availability of nutrients, as opposed to raw foods,” says Jenna Macchioki. “Think about raw potatoes. It is very difficult to extract nutrients from them, not to mention that the process is unlikely to be enjoyable.” Obviously, our ancestors knew what they were doing when they switched from raw to cooked foods.
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