Most people know that children who grow up eating a processed, nutrient-poor diet are at increased risk of a wide range of medical problems, including obesity, type-2 diabetes, and hypertension. What is less known is that diet – particularly the diet you eat when you grow up – can have a major impact on the development of the bones, jaws, and face. There’s solid evidence to show that the “soft” modern diet, in conjunction with other factors associated with Western lifestyles, can promote abnormal development of the skull and face, and cause malocclusion, impacted wisdom teeth, and narrow dental arches.
The importance of chewing
In the ancestral health community, a lot of focus is placed on how the nutritional value of the human diet has changed since our days as hunter-gatherers, and how we can adjust our modern diet so it has a composition, macronutrient distribution, and micronutrient profile that more closely resemble that of ancestral human diets. Less attention is given to how the “hardness” of our diet has changed since the preagricultural era, and in which ways this might impact human health, growth, and development.
That’s not to say that nobody has been paying attention to this issue, as there has been some blog posts, presentations at conferences, and articles on this topic. However, in general, it’s safe to say that it’s definitely a subject that deserves more attention. Dr. Mike Mew, a London-based Orthodontist, estimates that modern humans use the masticatory system about 3-5% of what Paleolithic humans did, and that’s before you consider non-nutritional exercise of the jaws (i.e., using teeth as tools to make clothes and weapons) (1). 3-5%! That’s a big decline...
A common belief is that teeth alignment and development of the jaws are purely genetically determined. However, what we have to remember is that our genetic heritage isn’t the end all be all for how we are going to grow and develop. There’s a constant interaction between our genome and the environment, and the forces applied to structures during growth will affect how genes are expressed and the development of the size and shape of each structure.
In the same way that you won’t develop healthy and strong limbs if you’re not adequately stressing them through walking, running, and other physical activities during childhood, your jaws won’t grow correctly if you don’t stress them sufficiently from chewing. Chewing on hard, tough food is important because it activates bone cells in the tooth socket and promotes the growth of big and strong jaws in which there is adequate room for the third molars. There’s no doubt that our time spent running, walking, and otherwise moving our bodies has gone done dramatically since our days as hunter-gatherers. However, this reduction fades in comparison to the decline in masticatory effort and usage.
Soft diets cause dental arch abnormalities
Studies in many different animal species show that animals who are put on a diet of soft, processed food when they are young develop many of the same dental arch abnormalities as contemporary humans, such as malocclusion, narrowed dental arches, and crowded teeth (2, 3). One example is a study of hyraxes (relatives of elephants that chew like humans) fed nutritionally identical hard and soft diets. This study found that hyraxes raised on hard food developed jaws that were significantly longer, thicker, and wider than the ones who chewed softer food (4).
There is strong evidence to suggest that many of the same principles apply to our species as well. Studies – such as those carried out by researchers like Dr. Robert S. Corrucini, who campaigned the idea that malocclusion is a disease of civilization, and Dr. Weston A. Price, who documented the health condition of isolated, traditional populations before and after westernization – show that people who transition from a traditional lifestyle and nutrient-rich, whole foods diet to a western lifestyle and nutrient-poor, processed diet experience a rapid decline in health (5, 6). Moreover, there’s a high incidence of malocclusion, crowded teeth, and tooth decay among the children who are born and raised in the “westernized environment” (5, 6).
A study of younger Australian Aborigines whose families recently started eating processed, modern foods is one of the many examples of cases where these effects are seen. This study found that the younger family members had smaller jaws and serious tooth crowding problems compared to elder members of their families who grew up eating traditional food (5).
As for intervention trials, one small study that investigated the effect of masticatory muscle training on facial growth in long-face children found that children who chewed on hard resinous gum for two hours each day for one year grew larger jaws and developed straighter teeth (7).
Besides reduced use of the masticatory system, other factors, in particular pacifier sucking, bottle-feeding, incorrect oral posture, and poor maternal and childhood nutritional status may also be important contributors to the high prevalence of malocclusion, crowded teeth, and narrow dental arches in westernized societies.
Hunter-gatherers and traditional, isolated people generally have broad dental arches, well-aligned teeth, and ample room for third molars (2, 6, 8). Moreover, examinations of fossils indicate that prior to the Agricultural Revolution, malocclusion and impacted wisdom teeth were virtually unheard of (2, 5, 8). This is in stark contrast to modern societies, where these conditions are extremely common.
In industrialized countries such as the U.S., approximately 50% of all wisdom teeth are removed and about 95% has deviations in their dental alignment (1). Of these 95%, some 30% are recommended orthodontics treatment, a treatment that improves the symptoms present, but may actually worsen the underlying problem (1).
Modern faces are “melting down” in the sense that there has been a major change in the human skeleton since the Paleolithic era. Over the last few thousand years – a blink of an eye from an evolutionary perspective – human faces have become approximately 5 to 10 % smaller after correcting for body size (2).
Some would argue that beauty is in the eye of the beholder and/or that culture is the main factor involved in determining what we perceive as aesthetically pleasing. However, we also have to remember that we have evolved an attraction to certain features as a way to distinguish the healthy and virile from the weak.
Physical attractiveness can serve as a biological signal of good health, and we probably find people with well-developed faces, strong jaws, and broad dental arches attractive because these features are indicators of good genetic qualities and health.
Besides being aesthetically unappealing, the change to a longer, thinner craniofacial structure has had important implications for how we breathe, chew, and function.
Processing, cooking, and blending
The introduction of dairy products and cereal grains into the human diet with the Agricultural Revolution marks the beginning of a transition from a hard, tough, and fibrous low-calorie density human diet to a more soft and calorie-dense diet. This change has accelerated in pace and force over the last couple of centuries, as refined grains, vegetable oils, refined sugar, and processed junk food have entered into the human diet in large quantities. Add to that the fact that we now heat, ground, and soften up a lot of the food we eat, have access to blenders, grinders, and other food processing machines, and use knives and forks to cut our meals into nice, easy-to-eat pieces, and you can easily understand that the chewing effort needed to gain calories has declined dramatically since our days as hunter-gatherers.
Since most of the food available to our ancient ancestors in the wild had a relatively low calorie density compared to the food we find at our grocery store today, they had to eat a higher volume of food than we do today to get the same amount of energy. To get 1000 calories from wild meat and fibrous plant foods, you have some chewing to do, whereas to get an equivalent amount of calories from a soda, you barely have to stress your jaw musculature at all. For example, the Hadza spend a lot of time chewing on fibrous tubers to extract as much calories as possible, something that is completely unheard of in the industrialized world.
Cooking and food processing were important innovations in human evolution that allowed our ancient ancestors to broaden the diversity of their diet and extract more calories from the food they were eating. The problem is that we’ve now taken food processing to the extreme, thereby setting the stage for a range of mismatch diseases and disorders, some of which are related to dental health and the development of the jaws.
Toughening up our diet
It’s not just people who eat a processed, Western diet that should be worried that they’re not spending enough time chewing. In comparison to ancestral human diets, modern diets tend to be very soft. Not just because most of us prefer to eat tender meat and relatively soft and easy-to-eat food, but also because domesticated fruits and vegetables are higher in sugar and lower in fiber than uncultivated versions.
So, what can we do about this problem? One obvious solution is to include more tough, hard food into our diet – and especially in the diet of our children. To make a difference it probably has to be a fairly large quantity, not just a fibrous apple here and there. Chewing on gum is another strategy that could help children grow a bigger and stronger jaw.
Besides the importance of chewing on tough, hard foodstuffs, infant feeding practices, maternal nutrition, oral posture, and sucking habits the first few years of life are all important factors that impact dental health and/or the development of the face and jaws.