The Pitfalls of 'Chewing Research': A Checklist for Eliminating Typical Biases in Mastication Studies and Identifying True Evidence

“People who chew well are thin.” “If you chew many times, you are less likely to get dementia.” — It is not uncommon to see such highly attractive headlines in health and diet news. However, to correctly decipher cutting-edge academic information, it is necessary to pay attention to the “quality of research data” behind it.

When unraveling the medical effects of chewing, we are releasing a checklist summarizing the “typical biases” hidden in many observational studies and experiments, and how to eliminate (or account for) them to evaluate the evidence.

1. Reverse Causality Bias: “Do they gain weight because they cannot chew, or can they not chew because they are gaining weight?”

The most important thing to watch out for when evaluating the relationship between chewing and obesity (such as in systematic reviews related to E06) is the “possibility of reverse causality.”

• Misinterpretation: When surveying obese people, they were all fast eaters and had a low chewing count. Therefore, “a low chewing count is the cause of obesity.”
• Real Bias: Could it be that insulin resistance or leptin resistance (a state where appetite-suppressing hormones do not work) associated with obesity existed first, and that “uncontrollable appetite” resulted in fast eating (a decrease in chewing count)?

[Checkpoint] Is the research a questionnaire survey (cross-sectional study) at a single point in time? Or is it a cohort study (longitudinal study) or intervention experiment (RCT) that tracked people over several years and proved that “those who did not chew at the beginning gained weight later”?

2. Elimination of Confounding Factors (Social Background)

Data claiming that “elderly people who chew firmly and eat their meals are less likely to develop dementia (or live longer)” often hides a strong “confounding factor (a third factor affecting the result).”

• Magic by Confounding: “Elderly people who keep many of their own teeth and can chew hard foods firmly” are likely to be people who have been enthusiastic about oral care since their youth, have the financial means to visit the dentist regularly (= can invest in health), and have high health awareness.
• Therefore, the “reason cognitive function is preserved” might not just be the “direct brain-stimulating effect of chewing,” but the “comprehensively privileged lifestyle” itself could be the true cause.

[Checkpoint] Is the research data calculated by properly adjusting (eliminating) confounding factors statistically, such as the subjects’ “income,” “education level,” “smoking history,” and “other dietary habits”?

3. Accuracy of the Chewing “Measurement Method (Measurement Bias)”

The act of “chewing” is one of the most extremely difficult subjects to measure accurately in a laboratory setting (related to the difficulty of measuring chewing and digestion in E05).

• Limitations of Self-Reporting: Many questionnaire studies rely on “subjective self-reporting,” asking, “Do you normally chew your food well? (Chew well / Normal / Do not chew).” Because humans tend to underestimate their bad habits, this does not reflect an accurate chewing count or chewing force (occlusal force).
• The Gap Between the Lab and Daily Life: In artificial experiments where wearable electromyography sensors for research are attached and people “chew specified foods in front of a camera,” they unconsciously chew more than usual (Hawthorne effect).

[Checkpoint] Is “chewing power” or “chewing count” a subjective score based on a questionnaire? Or is it measured using objective numerical indicators (objective indices) such as the degree of crushing of a “color tester (gum or gummy that changes color)” or using sensors?

To decipher scientific articles and judge “will this really work for me?”, passing them through this bias checklist is indispensable. While “chewing” is an extremely low-cost and powerful health intervention, the wise attitude is not to carelessly overtrust its effects, but to practice Evidence-Based Medicine (EBM) based on high-quality evidence.