Obesity-related disorders constitute a major global health burden(Reference Haslem and James1). Weight reduction deserves first priority in individuals with obesity and metabolic syndrome(Reference Grundy, Cleeman and Daniels2), and certain eating behaviours may increase metabolic risk(Reference Stunkard and Kaplan3). However, people living in today's fast-paced society tend to do many things, including eating, in a hurried manner. While eating is one of life's simple pleasures, some people tend to overeat when opportunities permit. Traditional Japanese maxims concerning eating include ‘Eat only until you are eighty per cent full’ and ‘Eat slowly’. Although little data exist on eating behaviours in the general population at large and the extent of metabolic risks, the Japanese government and companies encourage periodic health examinations, providing an opportunity to investigate eating behaviours and the associated metabolic risks for a large population.
Materials and methods
Participants and data collection
Participants comprised 8240 men (mean age 51·6 (sd 9·4) years) and 2955 women (mean age 52·9 (sd 10·1) years) who underwent health examinations at a medical centre in Tokyo. Most examinees were government employees and office workers whose examination expenses were subsidized by their employers. Before examinations, participants completed a simple questionnaire on eating behaviour, which included the following items: (i) whether they ate until feeling full; and (ii) whether they felt that they ate rapidly compared with other people. Both male and female participants were divided into four groups to investigate potential links between subjective evaluations of eating behaviour and objective metabolic risk factors: those who reported not eating until feeling full and not eating rapidly (G1); those who ate until feeling full but did not eat rapidly (G2); those who ate rapidly but did not eat until feeling full (G3); and those who both ate until feeling full and ate rapidly (G4).
Measurements
Participants were examined after overnight fasting. Body height and weight were measured by an automatic weight scale (Tanita Company, Tokyo, Japan), and BMI was calculated. Blood pressure was measured with the participant in a seated position by an electronic sphygmomanometer. Levels of plasma glucose, serum TAG, HDL cholesterol (HDL-C) and uric acid were measured by an autoanalyser (LABOSPECT; Hitachi High Technologies Company, Ibaraki, Japan) using enzymatic methods. Abdominal ultrasonographic examination was performed using an SAA-250A device (Toshiba, Tokyo, Japan).
Definitions of metabolic risk factors
The following definitions were used in the present study: (i) overweight as BMI ≥ 25 kg/m2; (ii) hypertension as systolic blood pressure ≥130 mmHg and/or diastolic blood pressure ≥85 mmHg(Reference Grundy, Cleeman and Daniels2); (iii) hyperglycaemia as plasma glucose ≥100 mg/dl(Reference Grundy, Cleeman and Daniels2); (iv) hypertriacylglycerolaemia as serum TAG ≥150 mg/dl(Reference Grundy, Cleeman and Daniels2); (v) low HDL-C as serum HDL-C <40 mg/dl for men and <50 mg/dl for women(Reference Grundy, Cleeman and Daniels2); (vi) hyperuricaemia as serum uric acid >7 mg/dl; and (vii) fatty liver as bright liver, increased liver echotexture compared with kidneys, vascular blurring and deep attenuation of liver on ultrasonography(Reference Sanyal4).
Statistical analyses
The ages among the four groups were compared by ANOVA. The prevalence of metabolic risks among the four groups was compared by the χ 2 test. The age-adjusted odds ratios for metabolic risk factors of G1 to G4 were compared by logistic regression, with G1 as the reference category. The JMP statistical software package version 4 (SAS Institute Inc., Cary, NC, USA) was used in analyses.
Results
Distribution of participants, ages and prevalence of metabolic risk factors classified by eating behaviour
Men
G1 constituted just under half the male population (49·8 %), while G3 constituted the second largest sector (26·3 %). There were significant differences in age and prevalence of all metabolic risk factors among the four groups. G4 was slightly younger than the other groups, while G1 had the lowest prevalence of all metabolic risk factors (Table 1).
Distribution of participants, age and prevalence of metabolic risk factors among men classified by eating behaviour, Tokyo, Japan
G1, not eating until feeling full and not eating rapidly; G2, eating until feeling full only; G3, eating rapidly only; G4, eating both rapidly and until feeling full; HDL-C, HDL cholesterol.
Women
For women as well, G1 constituted the largest segment (55·3 %), followed by G3 (19·0 %). There were significant differences in age and prevalence of overweight, hypertriacylglycerolaemia and fatty liver among the four groups. G4 was slightly younger than the other groups, while G1 had the lowest prevalence of the metabolic risk factors that showed significant differences among the groups (Table 2).
Distribution of participants, ages and prevalence of metabolic risk factors among women classified by eating behaviour, Tokyo, Japan
G1, not eating until feeling full and not eating rapidly; G2, eating until feeling full only; G3, eating rapidly only; G4, eating both rapidly and until feeling full; HDL-C, HDL cholesterol.
Age-adjusted OR (95 % CI) of metabolic risk factors classified by eating behaviour
Men
Compared with G1, the age-adjusted OR (95 % CI) for overweight were significantly higher in G2 to G4, being 1·85 (1·58, 2·17), 1·98 (1·76, 2·23) and 3·46 (2·99, 4·01) respectively. In addition to overweight, the age-adjusted OR were also significantly higher for hypertriacylglycerolaemia, hyperuricaemia and fatty liver (OR = 1·26–1·44) in G2, and for all metabolic risks in G3 (OR = 1·25–1·69) and G4 (OR = 1·30–2·31; Table 3).
Age-adjusted odds ratios and 95 % confidence intervals of metabolic risk factors among men classified by eating behaviour, Tokyo, Japan
G1, not eating until feeling full and not eating rapidly; G2, eating until feeling full only; G3, eating rapidly only; G4, eating both rapidly and until feeling full; HDL-C, HDL cholesterol; Ref., referent category.
Significance of OR and 95 % CI: *P < 0·05, **P < 0·005, ***P < 0·0001.
Women
Compared with G1, the age-adjusted OR (95 % CI) for overweight were significantly higher in G2 to G4, being 2·20 (1·62, 2·97), 2·59 (1·97, 3·39) and 3·12 (2·27, 4·26) respectively. In addition to overweight, the age-adjusted OR were also significantly higher for hyperuricaemia (OR = 2·88) in G2, for hyperglycaemia, hypertriacylglycerolaemia and fatty liver (OR = 1·37–1·62) in G3, and for hypertriacylglycerolaemia and fatty liver (OR = 1·57 and 2·34) in G4 (Table 4).
Age-adjusted odds ratios and 95 % confidence intervals of metabolic risk factors among women classified by eating behaviour, Tokyo, Japan
G1, not eating until feeling full and not eating rapidly; G2, eating until feeling full only; G3, eating rapidly only; G4, eating both rapidly and until feeling full; HDL-C, HDL cholesterol; Ref., referent category.
Significance of OR and 95 % CI: *P < 0·05, **P < 0·005, ***P < 0·0001.
Discussion
In the present study, the number of male participants was larger than that of female participants as men account for a higher percentage of government employees and office workers than women. However, the distribution of eating behaviours was similar in both genders, as about half of them reported eating until feeling full and/or eating more rapidly than others. Although our findings relied on simple self-reporting, the reports may be a true reflection of eating behaviours in daily life. Some people might continue eating after feeling full; it is assumed that those who ate beyond satiety also answered ‘yes’ for until eating feeling full in the present study.
The reasons for higher metabolic risk among participants who reported eating until feeling full would appear to be relatively straightforward: excessive food intake and overnutrition. However, as one interesting finding, the metabolic risks faced by participants who ate rapidly but not until feeling full were not lower than those of the participants who ate until feeling full but did not eat rapidly. Reports concerning the metabolic risk of rapid eating are extremely rare(Reference Shigeta, Shigeta and Nakazawa5, Reference Takayama, Akamine and Okabe6). People who eat rapidly may overeat before the signals of fullness are recognized by the satiety centre of the brain(Reference Schwartz, Woods and Porte7–Reference Moran and Schwartz9). Habitual rapid eaters may also be under greater pressure to limit meal time and return to work than slow eaters. These suppositions would explain why the components of metabolic risk in the participants who reported eating rapidly only were high. Further study is required to clarify the mechanism of increased metabolic risk in habitual rapid eaters. Although people may eat more rapidly during breakfast and lunch due to work-related pressures, we think that one's habit does not change greatly at dinner, i.e. those who eat faster than other people at breakfast and lunch may also eat faster at other times. It is worth noting that behaviour modification is reported as necessary in treating obesity effectively(Reference Stuart10).
Although overweight, obesity and diabetes are more common in economically developed countries, the absolute numbers of individuals with these conditions are considerably larger in developing countries. Moreover, the developing regions are also projected to experience much larger increases in population in future years(Reference Kelly, Yang and Chen11, Reference King, Aubert and Herman12). Various individuals and ethnicities may sense ‘feeling full’ and ‘rapid eating’ differently. East and South Asians may have perceptions of eating patterns similar to Japanese, suggesting they may share similar patterns of metabolic risk. On the other hand, in Western countries, where food is abundant, cheap and highly flavoured, people may no longer recognize the signals of hunger and satiety. Further exploration of all these issues is necessary.
In any case, increased awareness of one's eating behaviour is a useful public health message. If you eat faster than the average of surrounding people, eating more slowly (e.g. simply by chewing more thoroughly) may be beneficial to your health. Greater study of this important field is desired, as it has the potential to reduce global metabolic risks.
Acknowledgements
This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. All authors have no conflict of interest. Authors’ contributions were as follows: S.D.H. contributed to study design, data collection, data analysis, results interpretation and manuscript writing; T.M. (Muto), T.M. (Murase), H.T. and Y.A. reviewed the study and manuscript.
