Chew Your Food More To Be Healthier:Sound Advice or BS?

I spend every day ensuring that people can regain their innate ability to chew or simply maintain their ability to access nutrients. Chewing seems so normal; we take it for granted. Like breathing, it requires little thought or effort. It turns out to be a miraculous combination of coordinated movements regulated by a highly sophisticated network of teeth, nerves, muscles, ligaments, membranes, hormones, sub-conscious and conscious brain activity, and spinal mechanisms. It is so precise, we are barely aware of the entire process.

When we cannot chew efficiently, we may not get all of the nutrients required for health maintenance. (1) There are plenty of studies to back this up. (2,3,4) Inadequate chewing is not what this post is about; instead, I want to focus on people who are perfectly capable of chewing correctly. 

Are there people who just don't chew enough to absorb enough nutrients to be healthy, even though they could if they wanted to? How do we know when we have sufficiently masticated food to safely swallow it? Are all of the recommendations to chew more based on legitimate science? Let's find out.

This is a long post, so if you want the nitty-gritty, you can skip to the conclusion now.

First, let's look at a bit of background information. Chewing is technically called mastication in professional circles. Teeth are a prerequisite. Several sensory nerves in the mouth, pharynx, and larynx bring information to the brain that allows us to know what type of material is in the mouth and throat. Signals are sent to the brain about the size, temperature, and texture of food. (5,6) The oral phase is a fully conscious act, although most of us have little awareness of any conscious effort. When the bolus of food arrives at the pharynx, the unconscious brain takes over.

Even though chewing is a conscious endeavor when was the last time you gave any thought to when you have chewed your food enough to swallow? I can't think of a single incident in my life where I have done so. Can you? Even though chewing is fully conscious, we don't commonly find ourselves wondering when to swallow food.

Many health experts stress the need to chew our food adequately as if each time we chew and swallow, we pause to consider whether it is time. I could find no valid literature on the subject. The literature does indeed have some information on the effects of chewing more versus less. Still, the studies don't indicate what constitutes a normal number of chews. Most of the information I am presenting assumes a healthy functioning set of teeth. 

There are no agreed-upon parameters about the number of chews required, the acceptable size for a bite, the rate we should chew, the consistency food must possess before it can be safely swallowed, etc. Despite the lack of knowledge or consensus, all the advice out there tells us to make sure we chew our food extra well for health benefits. After all, it is good for us. Isn't it? The research is really sparse on the subject. What follows are a few of the better studies I was able to find.

Food preparation has been happening since we gained the ability to use tools. Indeed, there is evidence that our teeth and jaws have become smaller because they are no longer required to do all of the work. Not only does processing make it easier to chew, but it also vastly increases our ability to extract calories and nutrients. Scientific studies have shown that sufficiently grinding vegetable matter will break open the indigestible cell walls to liberate the nutrients inside. (7) Unfortunately, the studies don't actually look at chewing; they break the food down for the subject and consider it a proxy for chewing. The conclusion they draw is that the smaller the particles of food are, the greater the nutrient absorption is. I agree that this sounds plausible. An easy method to study chewing would be to use ileostomy patients as subjects. The food could be removed from colostomy bags for analysis after chewing and digestion. Unfortunately, I could not find any studies that have done this. If you know of any, please let me know about them in the comments.

In a 2010 study on carrot nutrient absorption, the authors found that cooking made β-carotene more accessible. The researchers determined that grinding the carrots into finer particles also helped absorption, but the grinding was not accomplished by chewing. They claim that chewing carrots into finer particles can significantly impact, even though chewing had nothing to do with the study design. (8) They were studying food processing, not mastication.

One Japanese study from 2015 looked at fifteen young Japanese women who were asked to spit the food bolus in a glass dish just before swallowing. They used three different foods: boiled rice, fish sausage, and peanuts. Their significant conclusion was that the less food you put in your mouth, the more it ended up being chewed as a measure of overall volume. (9) 

The next study is out of Singapore from 2015. They measured the amount of blood glucose two hours after eating rice. They used three methods of introducing the rice to the mouth: spoon, chopsticks, and fingers. Since chopsticks and fingers cannot deliver the food as fast as spoons, the subjects needed more mouthfuls to finish their meal of rice with chopsticks. Because it took longer to eat, the rice caused a lower spike in blood sugar. (10) Their conclusion was not about chewing directly; it was about the delivery systems' differences and consumption rate. 

The next study is from 2012, and they studied 113 people, some of whom reported that they considered themselves to be quick eaters. Those who ate quickly did so by chewing less overall and less before they swallowed. They did not chew at a faster rate. (11)The study did not address the health outcomes of speedier eating.

The next study from 2014 is similar to the first study I just cited. Fifty Japanese subjects took three different sized bites of rice. They also concluded that that smaller bite sizes were associated with more chews per volume of food. (12) 

The next paper from 2013 studied the chewing patterns of fifteen subjects as they consumed 35 different foods. They made three observations. The average number of chews for 50 grams of food varied from 27 for mashed potatoes to 488 for tortilla chips. The more they chewed, the longer it took to swallow and ranged from 27 seconds for canned tomatoes to 350 seconds for tortilla chips. They also saw that the chewing rate was relatively constant, with an overall average chewing rate of approximately 1 chew per second. Their significant conclusion once again was that foods consumed in smaller bites were chewed more and longer and expected to impart higher satiation. However, the longer chewing time was contingent on specific foods and flavors; chewing longer was not a conscious decision. (13)

Wehight loss may be a benefit to chewing your food longer. One explanation for greater satiation after chewing more comes from a 2015 paper that determined it caused alterations in gut hormone responses related to satiety. (14)  Many health care practitioners have suggested that the longer food is chewed, the fuller one feels, and less food is ultimately consumed. They command us to consciously chew more. Based on the research I have seen, rather than count our number of chews (which is difficult), we should choose foods that require more chewing. Assuming feeling fuller after smaller meals is our goal.

In 2011, a group of researchers determined that obese subjects had similar bite sizes compared to lean subjects but chewed less. The result was that the obese subjects ate more per meal as a result. Blood glucose and insulin concentrations were not influenced by chewing for either group. They also found that when they forced the participants to chew their food more, less food was eaten. (15) The conclusion drawn by the authors is that faster eating is a "risk factor" for obesity. This is in keeping with most health experts' recommendations to chew more to avoid overeating. 

But hold on, studies also find that BMI has no effect on bite-size, ingestion rate, or meal size. A 1993 study found that the larger the bite size, the more quickly ingestion rate decelerated; by the end of meals, the ingestion rate was not different across conditions. The decrease in the ingestion rate with smaller bites was offset by an increase in meal duration, such that meal size did not differ across conditions. The eating behavior of lean and obese subjects was not different. There were individual differences related to the ingestion rate. Still, these were not associated with bodyweight nor to meal size. These results bring into question the recommendation of behavior therapists that obese people eat more slowly in order to eat less. (16) Wagner and Hewitt came to the same conclusion in 1975. (17)

I must reiterate that I am not talking about populations that cannot chew properly. They may likely develop health problems. You can read my post about that subject here. 

My Verdict

I debunk the idea that people with fully functional sets of teeth need to carefully consider chewing more to achieve adequate health status based on the available research. As far as I can tell, chewing is innate and mainly done to facilitate swallowing.  Have you ever heard of anyone having to teach a healthy baby how to chew? After chewing and swallowing, our digestive systems do the rest. Assuming they are healthy and fully functional.

For instance, cows and other ruminants rechew regurgitated stomach contents several times. Their constant chewing and rechewing are done to break plant matter down into smaller particles so that their gut bacteria can ferment it into nutrients. So yes, cows need to chew more, but this is done as a matter of course. It is not something they need to carefully consider.

On the opposite end of the spectrum, snakes don't chew at all. Their stomach acid is high enough to digest whole animals. Incidentally, our stomach PH is the same as snakes. As a result, animal protein is easily digested in humans early on in the intestines. (18) 

Fiber is not digested at all by humans; it is still vaunted as one of the healthiest parts of any diet despite its lack of nutritive value. 

The experts claim that grinding food into smaller particles makes more of the nutrients available. If the food is plant-based, I agree because we need to physically break down cell walls to get to the nutrients. We can’t chemically digest cell walls. Prior to the advent of farming, humans used to eat all kinds of tough fiberous foods. These foods would have cretainly required more chewing in order to swallow them, but there is no evidence that we had to be instructed to do so. Take improperly prepared asparagus as an example. Most often the tougher end of the asparagus is cut off so that it is easier to chew and swallow. If left on, the tougher end of asparagus spears need to be chewed more than the softer part. You will automatically chew them more.

 More chewing (according to researchers) leads to smaller meals but liberates more nutrients. Bioavailability is the correct term to use when considering how easy or hard a nutrient is to absorb from particular foods. More nutrients in our diets could mean less malnutrition, but more nutrients could also mean more weight gain. Smaller meals seemingly trump the impact of increased nutrient availability, but this would depend on the type of foods and quantity available.

Chewing, digesting, and nutrient bioavailability are all critical, and I believe they all need consideration during research. When it comes to health, food selection, how it is processed, how we chew it, and how well our digestive systems can extract nutrients are all important. Take nuts, for example. If we eat a handful of nuts and barely chew them, remnants will end up passing entirely through our guts without digestion. Churn the nuts into nut butter and swallow a tablespoon without much chewing, and we will extract most of the nutrients. Now compare the nutrient content to an equal portion of ribeye. Whether it is chewed a little or a lot, our digestive system is designed to digest it well, as it does not contain digestive-resistant cell walls. The number of nutrients absorbed will be superior to either preparation of nuts. 

Conclusion

Chew your food. Don't stress over how much. You will automatically know when to swallow it. Spend your brainpower choosing nutrient-dense whole foods, devoid of processed carbohydrates and seed oils, consisting of plant and animal-based foods. If you select a primal/paleo-based diet, you should not have to stress over whether you have overeaten. To ensure you have achieved the correct nutrient levels, you can use a free app like Cronometer or myfittnesspal. Beware, these apps assume higher bioavaiability of certain plant-based nutrients. For a general idea of which foods to choose, click here.