EAL

UM: Role of Umami in the Regulation of Energy Intake (2014)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To examine the longitudinal association between MSG consumption and incidence of overweight.

Inclusion Criteria:

Participant in the CHNS survey between 1991 and 2006
Aged 18 to 65 years
MSG data available.

Exclusion Criteria:

Pregnancy
Implausible MSG intake (more than 10g per day).

Description of Study Protocol:

Recruitment

There were a total of 20 randomly selected households from each of 190 sampling units; the cohort included nine provinces of varying geography, economic development and health status. Four counties within each province (one low- , two middle- and one high-income) were randomly selected by using a weighted sampling scheme. In addition, a large higher-income city and a lower-income city were selected. Villages and townships within the counties and urban and suburban neighborhood with the cities were randomly selected for the 190 units.

Design

Prospective open-cohort, ongoing nationwide survey.

Intervention

Comparisons of quintiles of MSG intake.

Statistical Analysis

Chi-square tests and analysis of variance and non-parametric Kruskal-Wallis tests to compare the baseline characteristics of participants according to quintiles of MSG intake. Mixed effects linear regression models (BMI) and logistic regression models (overweight) with measurement occasions nested within individuals, household and community. Cox regression models with a gamma-distributed random effect to examine the association between MSG intake and incidence of overweight. General linear regression model to examine the cross-sectional relation between MSG and serum leptin in a sub-cohort. Spearman's rank correlation coefficient was computed for the MSG intake validation study.

Data Collection Summary:

Timing of Measurements

1991
1993
1997
2000
2004
2006.

Dependent Variables

Overweight: BMI of 25.0 or higher in main analysis and 23.0 or higher in sensitivity analysis
In accordance with recommendations of the World Health Organization (WHO) and the International Association for the Study of Obesity for Asian populations, overweight was defined as a BMI (in kg/m²) 25.0 in the main analysis and as a BMI 23.0 in the sensitivity analyses
Leptin: Fasting blood specimen.

Independent Variables

MSG intake: MSG, soy sauce and all other condiments weighed before and after a 24-hour recall. The difference between the two weights was calculated as the household MSG consumption. MSG for each household member was estimated based on the proportion of each individual's food consumption. Individual dietary intake was assessed by 24-hour recalls collected on three consecutive days (two weekdays and one weekend day). Using digital and kitchen scales, household consumption was determined by changes in inventory from beginning of each day to the end of each day of the three-day recall.

Control Variables

Measured by questionnaire-based interview in the surveys:

Physical activity
Age
Sex
Urban residence
Region
Smoking status
Alcohol consumption
Education level
Individual income.

Description of Actual Data Sample:

Initial N: 10,095
Attrition (final N): 10,095
Age: 18 to 65 years
Ethnicity: Chinese
Location: China.

Summary of Results:

Findings

Mean cumulative MSG intake was 1.8g per day (mean ±SD was 2.2±1.6g per day). Men had a slightly higher MSG intake than women (median: 1.9g vs. 1.7g per day; P<0.01)
In general, participants with a high MSG intake had a higher BMI and individual income, higher intakes of total energy and sodium and lower physical activity levels
MSG intake was significantly, positively associated with BMI in a dose-response manner (P<0.01) after adjustment for potential confounders and control for clustering of data. For participants in the highest compared with the lowest quintile of MSG intake, the prospective odds ratio of overweight was 1.28 (95% CI: 1.12, 1.45; P<0.01) after baseline BMI and other potential confounders were adjusted for.
Of 7,192 normal-weight individuals at baseline, 824 incident cases of overweight were documented 5.5 years later. Compared with those who were in the lowest quintile of MSG intake, those in the highest quintile were 33% more likely to develop overweight [hazard ratio (HR) 1.33; 95% CI: 1.01, 1.75; P<0.01] independent of baseline BMI and other confounders.
In a pilot study of 669 participants, the median leptin concentration was 7.2ng per ml (mean ±SD: 9.92±9.15ng per ml. MSG intake was positively related to serum leptin concentrations. Serum leptin concentration increased by 0.45ng per ml (SE=0.16, P<0.01) with every 1g increment increase in MSG intake.

Author Conclusion:

MSG intake was positively, longitudinally associated with BMI and incidence of overweight independent of baseline BMI, physical activity, total energy intake and other potential confounders among apparently healthy Chinese adults.

Funding Source:

Government:	NIH, Chinese Center for Disease Control and Prevention
University/Hospital:	Global Health Partnership, U North Carolina

Reviewer Comments:

Limitations as cited by authors:

Because of ethical considerations and other methodologic constraints (eg, no proper placebo), we may not be able to conduct a large-scale, randomized, placebo-controlled clinical trial. Thus, data from a large cohort study may be very important to advance our knowledge.
Accuracy of MSG measurement: Household MSG consumption was considered accurate because it
was measured by direct weighing of the MSG container before and after each of three 24-hour recalls. The accuracy of MSG intake for individuals was evaluated using riboflavin as an adherence marker.

Quality Criteria Checklist: Primary Research
Relevance Questions
	1.	Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies)	Yes
	2.	Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about?	Yes
	3.	Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice?	Yes
	4.	Is the intervention or procedure feasible? (NA for some epidemiological studies)	Yes

Validity Questions
1.	Was the research question clearly stated?		Yes
	1.1.	Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?	Yes
	1.2.	Was (were) the outcome(s) [dependent variable(s)] clearly indicated?	Yes
	1.3.	Were the target population and setting specified?	Yes
2.	Was the selection of study subjects/patients free from bias?		Yes
	2.1.	Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study?	Yes
	2.2.	Were criteria applied equally to all study groups?	Yes
	2.3.	Were health, demographics, and other characteristics of subjects described?	Yes
	2.4.	Were the subjects/patients a representative sample of the relevant population?	Yes
3.	Were study groups comparable?		Yes
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	Yes
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	N/A
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	N/A
	3.4.	If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis?	Yes
	3.5.	If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.)	N/A
	3.6.	If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")?	N/A
4.	Was method of handling withdrawals described?		Yes
	4.1.	Were follow-up methods described and the same for all groups?	Yes
	4.2.	Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.)	Yes
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	Yes
	4.4.	Were reasons for withdrawals similar across groups?	N/A
	4.5.	If diagnostic test, was decision to perform reference test not dependent on results of test under study?	N/A
5.	Was blinding used to prevent introduction of bias?		???
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	N/A
	5.2.	Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.)	N/A
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	???
	5.4.	In case control study, was case definition explicit and case ascertainment not influenced by exposure status?	N/A
	5.5.	In diagnostic study, were test results blinded to patient history and other test results?	N/A
6.	Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described?		Yes
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	N/A
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	Yes
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	Yes
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	Yes
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	N/A
	6.6.	Were extra or unplanned treatments described?	N/A
	6.7.	Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?	N/A
	6.8.	In diagnostic study, were details of test administration and replication sufficient?	N/A
7.	Were outcomes clearly defined and the measurements valid and reliable?		Yes
	7.1.	Were primary and secondary endpoints described and relevant to the question?	Yes
	7.2.	Were nutrition measures appropriate to question and outcomes of concern?	Yes
	7.3.	Was the period of follow-up long enough for important outcome(s) to occur?	Yes
	7.4.	Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?	Yes
	7.5.	Was the measurement of effect at an appropriate level of precision?	Yes
	7.6.	Were other factors accounted for (measured) that could affect outcomes?	Yes
	7.7.	Were the measurements conducted consistently across groups?	Yes
8.	Was the statistical analysis appropriate for the study design and type of outcome indicators?		Yes
	8.1.	Were statistical analyses adequately described and the results reported appropriately?	Yes
	8.2.	Were correct statistical tests used and assumptions of test not violated?	Yes
	8.3.	Were statistics reported with levels of significance and/or confidence intervals?	Yes
	8.4.	Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)?	N/A
	8.5.	Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?	Yes
	8.6.	Was clinical significance as well as statistical significance reported?	Yes
	8.7.	If negative findings, was a power calculation reported to address type 2 error?	N/A
9.	Are conclusions supported by results with biases and limitations taken into consideration?		Yes
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	Yes
10.	Is bias due to study's funding or sponsorship unlikely?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes