麻豆传媒

DIETARY fads come and go, but perhaps the most enduring of them all is the raw-food movement. It dates back to at least the mid-1800s when US Presbyterian minister Sylvester Graham claimed that people would never become ill if they only ate uncooked foods. The idea that cooking degrades the natural nutrition inherent in foods can seem intuitively plausible. But is it true?

Perhaps the first curious thing you notice when delving through academic journals that have covered this topic is that, although there has been plenty of research on raw-food diets, especially in recent years, almost all of the content is about cat and dog food. When it comes to human studies, there are really only a few papers to date, often using different designs and measures, making for quite a patchy evidence base.

One 2005 study found that followers of , which are key risk factors for cardiovascular disease. This is unsurprising, given that diets high in fruit and vegetables are linked to better heart health, and the participants were eating a whopping 20 servings a day on average. On the other hand, the same study also discovered that participants were often deficient in vitamin B12, a nutrient found almost exclusively in animal products in nature.

Another study in the same year found similarly mixed results. While people on a raw-food diet tended to weigh less and be leaner than the general population, they also . Although the authors were keen to point out the small size of their study, they concluded that this low density was probably due to bone loss coinciding with the adoption of the low-calorie, low-protein, raw-food lifestyle.

But what about other health impacts? In one study from 1999, followers of this diet were found to have much higher rates of erosion of tooth enamel, with . The erosion rate was almost six times that of the control group. This was blamed on the large amounts of acid coming from their high fruit consumption. When researchers looked into the levels of carotenes in the blood of followers of this diet, they found that these plant-derived, antioxidant compounds were either only at normal (and sometimes low) levels, despite the high amounts found in this diet. This was attributed to very low fat consumption, which traditionally acts as a delivery mechanism for such oil-soluble antioxidants to be absorbed by our bodies.

鈥淭he advent of cooking could have been what allowed humans to develop larger brains鈥�

This highlights a critical sticking point in answering the question of health benefits associated with raw-food diets. People following them often have several other notable dietary factors that can affect the results. Most proponents of raw-food diets, for example, are also vegetarian or vegan. They additionally often consume very low levels of starchy carbohydrates 鈥� no bread, rice and pasta. In a very real sense, the defining feature of raw-food diets isn鈥檛 so much the rawness of their ingredients, but the substitution of entire food groups for fruit and vegetables.

This isn鈥檛 without good reason either. Consuming many animal foods in an uncooked state carries a high risk of infection with potentially life-threatening parasites and microbes, which cooking renders safe.

Humans also don鈥檛 produce the right digestive enzymes or harbour the necessary gut flora to access the calories in uncooked carbohydrates either, which is why we have spent inordinate amounts of effort for millennia cooking a lot of our food. This can render toxic foods safe and tasty, and allows us to access calories that are off limits to our species without it.

Even when it comes to plants that are perfectly safe to eat raw, such as tomatoes, cooking breaks open their tough cell walls, allowing significantly improved access to the nutrients within. With crops like kale and spinach, cooking reduces their volume and removes difficult-to-digest compounds, allowing us to consume a much larger amount of them. In fact, many evolutionary anthropologists suggest it was the advent of cooking that triggered the reduction in gut size that allowed us to develop larger brains, which distinguishes our species from our ancestors.

While not a science point, a raw-food diet also doesn鈥檛 sound like much fun. Perhaps it is relevant to flag up that Graham believed that the suppression of pleasure in many forms was essential to health, recommending only cold baths and sleeping on hard mattresses among other things.

Raw food can, of course, be a healthy choice, but cooking food isn鈥檛 just an ideal way of getting a varied, balanced diet, it is probably what made us human.