Scientific papers and research data cited in our articles
E01 🧠 Brain & Mental 2015
Chewing Maintains Hippocampus-Dependent Cognitive Function
Chen H, Iinuma M, Onozuka M, Kubo KY.
PMC / International Journal of Medical Sciences
📝 Summary
A review article, not new experimental work by the authors. It summarises mainly rodent studies showing that sensory input from chewing projects via the trigeminal nerve to the reticular formation, thalamus, cortex and hippocampus; that molar extraction or a soft diet was associated with lower CA1/CA3 neuron density and poorer spatial memory; and that chewing under restraint stress prevented suppression of dentate gyrus cell proliferation and lowered plasma corticosterone. All of these are animal findings and do not demonstrate an effect in humans.
🔑 Key Findings
▸A review, not the authors' own experiments
▸In animals, reduced chewing was linked to hippocampal neuron loss and poorer spatial memory
▸In animals, chewing under stress lowered corticosterone (unverified in humans)
Effects of Mastication Dynamics on GLP-1 Secretion in Mice
菅 悠希（北海道医療大学大学院歯学研究科）
北海道医療大学学術リポジトリ（学位論文）
📝 Summary
A doctoral thesis (not a peer-reviewed journal article) using 190 male C57BL/6J mice. Active GLP-1 30 minutes after intake was significantly higher in the solid-feed (chewing) group than the liquid-feed group (n=10 each, p<0.05). The difference disappeared under pharmacological vagal blockade and with calorie-free feed. In the acute experiment, insulin secretion showed no significant difference under any condition. In the 12-week feeding experiment, however, fasting active GLP-1 and fasting insulin were both significantly higher in the long-term chewing group (MWU, p<0.05), and pancreatic β-cell area was also significantly larger. Body weight, blood glucose, and the oral glucose tolerance test showed no significant difference between groups. The author states that chewing itself did not affect insulin secretion, but a chewing habit did. These are mouse findings, not human evidence.
🔑 Key Findings
▸Mouse study: active GLP-1 significantly higher 30 min after intake (p<0.05)
▸The difference disappeared under vagal blockade
▸No acute difference in insulin, but fasting insulin was significantly higher after 12 weeks of chewing
A randomized crossover trial in 11 healthy young men comparing a 200 kcal liquid meal swallowed directly, held in the mouth for 30 seconds, or chewed for 30 seconds per sip. Diet-induced thermogenesis over 90 minutes rose from 3.4 to 5.6 to 7.4 kcal (p < 0.05). The difference is about 4 kcal, and more than half of the increase is explained by the tasting condition alone. Celiac artery blood flow rose significantly with both tasting and chewing, but chewing did not exceed tasting (5.5 vs 5.9 L), and the superior mesenteric artery showed no difference. Brown adipose tissue was not measured, and there were no significant differences in hunger, fullness, or respiratory exchange ratio.
🔑 Key Findings
▸Postprandial DIT increased significantly (about 4 kcal)
▸More than half of the increase came from tasting alone
▸Celiac artery blood flow rose, but chewing did not exceed tasting
▸Body weight and fat were not measured; the authors only speculate
A Suita Study follow-up of 599 middle-aged men. Low masticatory ability was independently associated with metabolic syndrome, hypertension, high triglycerides and fasting hyperglycaemia. This is an observational study: it does not establish that poor chewing causes these conditions, and the sample is limited to middle-aged men.
🔑 Key Findings
▸Low masticatory ability independently associated with metabolic syndrome
▸Correlated with hypertension and high triglycerides
Mastication of Nuts under Realistic Eating Conditions: Energy Balance
McArthur BM, Considine RV, Mattes RD.
Nutrients (MDPI)
📝 Summary
A within-subject crossover trial in 50 healthy adults (25 men, 25 women) comparing 28 g of whole walnuts with the same amount as walnut butter. Fullness was higher and hunger lower with whole nuts (p < 0.05), but glucose, insulin, and active GLP-1 showed no significant differences, so hormones do not explain the satiety difference. The authors raise a neural pathway as a possibility without testing it. Faecal energy loss was not measured in this study.
🔑 Key Findings
▸Whole nuts produced higher fullness and lower hunger (p < 0.05)
▸No significant differences in glucose, insulin, or active GLP-1
▸Desire for sweets was lower with the butter, the opposite direction
▸The mechanism behind the satiety difference remains unidentified
Chewing and Its Influence on Swallowing, GI, and Nutrition: A Systematic Review
Kumar A, Almotairy N, Merzo JJ, et al.
Critical Reviews in Food Science and Nutrition
📝 Summary
A systematic review by Kumar et al., not new experimental work. It surveys existing research on how chewing affects swallowing, gastrointestinal physiology and nutrition-related factors: poorly chewed boluses may influence behaviour in the gut and glycaemic response, and reduced masticatory function may be associated with narrower food choices and shifts in gut microbiota. Most of the individual studies included are small intervention or observational studies.
🔑 Key Findings
▸A systematic review, not the authors' own experiments
▸An association between insufficient chewing and postprandial glucose response is reported
Masticatory Function and Hypertension: A Cross-Sectional NHANES Study
Guo H, Yang H, Li J, Lv T.
Medicine (Baltimore)
📝 Summary
A cross-sectional observational study using NHANES 2005-2018 data on 25,638 non-institutionalised adults. Masticatory function was assessed by functional tooth units (FTU); the optimal group (FTU 10-12) had an adjusted odds ratio for hypertension of 0.82 (95% CI 0.72-0.92) compared with the impaired group (FTU below 3). Mediation analysis attributed 18.0% (95% CI 14.8-21.1) of the association to HbA1c. The authors state explicitly that the cross-sectional design does not permit causal inference.
🔑 Key Findings
▸Cross-sectional study (n=25,638): inverse association with hypertension (adjusted OR 0.82)
▸HbA1c statistically accounted for 18.0% of the association
▸The authors state that causal inference is not possible
Autonomic Nervous System Balance and Erectile Dysfunction
Xu J, Chen Y, Gu L, et al.
Frontiers in Endocrinology
📝 Summary
A cross-sectional comparison of 75 men with psychogenic erectile dysfunction and 75 healthy men (150 total, mean age 31.9 years). Patients had significantly higher perceived stress, a significantly higher LF/HF ratio (p=0.014), and significantly lower HF and pNN50 (both p<0.001). Despite the HPA axis in the title, none of the cortisol measures differed significantly between groups (CAR AUCi p=0.744, CAR AUCg p=0.972, diurnal AUCg p=0.970, DCS p=0.784); the authors conclude that the stress response in these patients is characterised by autonomic imbalance rather than HPA dysregulation. This paper does not mention chewing at all. A previous version of this entry claimed that rhythmic chewing suppresses HPA axis overactivity; that sentence does not appear in the source and has been removed.
🔑 Key Findings
▸Cross-sectional (n=150): higher LF/HF, lower HF and pNN50 in patients
▸Cross-sectional design does not establish direction of causation
▸Cortisol measures did not differ; the authors attribute this to autonomic imbalance, not HPA dysregulation
Erectile Dysfunction: Definition and Pathophysiology
Johns Hopkins Medicine（患者向け解説ページ）
Johns Hopkins Medicine（査読論文ではない）
📝 Summary
A patient-education page published by Johns Hopkins Medicine, not a peer-reviewed article. It presents erectile dysfunction as a sentinel marker for cardiovascular and metabolic disease and lists the main risk factors for organic ED (obesity, insulin resistance, diabetes, atherosclerosis, hypertension). It makes no mention of chewing.
🔑 Key Findings
▸A hospital patient-education page, not a peer-reviewed article
▸ED is presented as an early marker of cardiovascular disease
Irwin Goldstein（Boston University Sexual Medicine）
BU Sexual Medicine（査読論文ではない）
📝 Summary
An explanatory page published by Boston University Sexual Medicine, not a peer-reviewed article. It explains that initiating and maintaining an erection requires parasympathetic dominance and nitric-oxide-mediated smooth muscle relaxation, that sympathetic activation works against erection, and that nocturnal erections during REM sleep occur when sympathetic activity switches off. It makes no mention of chewing.
🔑 Key Findings
▸A university explanatory page, not a peer-reviewed article
An explanatory article written for a public-relations magazine of the Agriculture & Livestock Industries Corporation by an employee of the Kamukoto research division of Lotte, a gum manufacturer. It is not a peer-reviewed paper and carries a conflict of interest. Reported effects (raised salivary S-IgA, increased scalp blood flow, changes in jawline angle) are drawn mainly from small, open-label studies by the author or the same company. Note that improvements in bite force and sprint start in female junior-high students over one month (Kanno et al. 2020) and improvements in maths scores over 14 weeks (Johnston et al. 2012) come from two separate studies; an earlier version of this entry described them as a single intervention.
🔑 Key Findings
▸Not peer-reviewed: an explanatory article by a gum manufacturer's employee (conflict of interest)
▸The bite-force/sprint result and the maths-score result come from two different studies
▸Most cited work consists of small open-label studies by the author or the same company
Koyama T, Kobayashi K, Hama T, Murakami K, Ogawa R.
PMC / ePlasty
📝 Summary
A massage device (170rpm) applied to one side of the temporal scalp for 4 min/day over 24 weeks increased hair thickness from 0.085 to 0.092mm in 9 healthy men. There was no independent control group; the untreated contralateral scalp of the same participant served as the control. Separately, mechanically stretched cultured human dermal papilla cells showed changes in hair growth-related gene expression and reduced IL6 (an in vitro result, not measured in the participants).
🔑 Key Findings
▸24 weeks of device massage on the temporal scalp significantly increased hair diameter
▸Control was the contralateral scalp of the same person, not an independent group
▸Gene expression and IL6 findings come from cultured cells
Integrative Approach to Hair Growth Cycle and Hair Loss
Natarelli N, Gahoonia N, Sivamani RK.
Journal of Clinical Medicine (MDPI)
📝 Summary
A review article summarizing the hair growth cycle and mechanisms of hair loss; the authors did not conduct new experiments. Blood supply to the deep dermis is involved in angiogenesis and cell division during the growth phase. Androgenetic alopecia involves DHT and other hormonal factors. This source does not address chewing or the temporalis muscle.
🔑 Key Findings
▸Scalp blood flow is involved in hair matrix cell division
▸Androgenetic alopecia involves DHT and other hormonal factors
Mastication and Obesity in Adults: A Systematic Review
Tada A, Miura H.
BMC Oral Health
📝 Summary
A systematic review of 18 studies published between 2007 and 2016 (16 cross-sectional, 1 cohort, 1 RCT). Twelve of the 16 cross-sectional studies reported an association between reduced masticatory function and obesity, and the single RCT (an 8-week gum-chewing intervention) found a significant reduction in waist circumference. The authors conclude that because most included studies are cross-sectional, causality has not been established and further RCTs are needed.
🔑 Key Findings
▸Systematic review of 18 studies, mostly cross-sectional, linking reduced chewing to obesity
▸The single RCT (8-week gum chewing) significantly reduced waist circumference
▸The authors state that causality is unproven and further RCTs are needed
A large cohort study of 31,742 men aged over 50 (Health Professionals Follow-up Study). Higher physical activity and a healthy BMI were strongly associated with maintained erectile function. The paper does not discuss GLP-1, HbA1c or chewing. A previous version of this entry claimed that improved masticatory function indirectly strengthens these protective factors; that sentence does not appear in the source and has been removed.
🔑 Key Findings
▸A large cohort study of 31,742 men
▸Physical activity and healthy BMI were associated with maintained erectile function
▸The source makes no mention of GLP-1, HbA1c or chewing
Cerebral Blood Flow During Chewing and Cognition in Prognathism Patients
Inagawa Y, Kanzaki H, Kariya C, et al.
Scientific Reports（パイロット研究）
📝 Summary
A pilot study (so described in the paper title) comparing patients with mandibular prognathism to healthy controls. Cerebral blood flow during chewing (fNIRS) in the inferior frontal gyrus was significantly lower in patients than in controls (n=17); median values fell from 57% to 23% on the right and from 50% to 33% on the left. Overall cognitive scores (eye-tracking; 59 controls vs 44 patients, mean age around 25) did not differ significantly (p=0.48). Within the patient group, chewing-related blood flow correlated positively with cognitive scores. The figure of a 30-50% drop in chewing efficiency is quoted from earlier work, not measured here, and the authors make no claim about future dementia risk.
🔑 Key Findings
▸A pilot study: chewing-related blood flow was significantly lower in patients (roughly 40-66% of controls, depending on side)
▸Overall cognitive scores did not differ significantly (p=0.48)
▸Participants averaged about 25 years old; the authors make no claim about dementia risk