Study Design and Limitations of the Two Studies
A validated semi-quantitative food frequency questionnaire (SQFFQ) was used for retrieving dietary information from the participants. This questionnaire encompassed 106 food items. Use of this SQFFQ was an accurate step as these are regarded as the primary method for the measurement of dietary intake, while conducting epidemiological studies (Vioque et al., 2013). The SQFFQ is by far one of the most common food frequency instruments that are in use. The questionnaires were used during the time period from 2001-2002, and 2005-2006. Exhaustive information was provided on the nine response options that were available for each food frequency. Failure of the questionnaire to determine the pattern in which the eggs were cooked, might have added to bias in the results. Some strengths of the assessment can be attributed to the fact that they are intended for individuals, in place of household use, which in turn facilitated the process of calculating the weighted food frequencies of each adult. Moreover, the authors also paid consideration to the potential confounding factors, according to the preliminary results and previous findings.
The main finding of the research was that, 570 new cases of cardiovascular abnormalities were diagnosed among the Korean adults during the average follow-up period of 7.3 years. Following an adjustment for the major confounding variables and risk factors, no significant association was found between consumption levels of egg and incidence of cardiovascular diseases e (HR: 1.14, 95% CI: 0.87–1.49, P for trend: 0.7). However, the authors also found type 2 diabetes to exert an effect on the association. Egg intake was significantly related to an increased risk of the disease among diabetic participants. Furthermore, participants with highest egg intake e (4.2 ± 0.04 eggs/week) showed a 2.8 times increased risk of developing cardiovascular disease (HR: 2.81, 95% CI: 1.25–6.30, P for trend: 0.02), upon comparison to those with low levels of egg consumption (0.1 ± 0.02 eggs/week). In addition, the authors failed to demonstrate any significant association among participants without type 2 diabetes mellitus (HR: 1.03, 95% CI: 0.77–1.38, P for trend: 0.8). The authors suggested that the hazards ratio and confidence interval were calculated by cox proportional hazard regression. They also provided information on the odds ratio, to demonstrate the association between egg intake and cardiovascular disease.
The study design was an appropriate one. The authors conducted a cohort study, the primary aim of which is to follow a group of individuals over a period of time for determining the rate of incidence of certain health abnormalities or risk factors that contribute to major diseases (Woodward, 2013). The study design can be cited appropriate since the researchers conducted a study based on prospective cohort data from previously conducted surveys, and determined their dietary patterns to find an association between egg intake and risks of cardiovascular disease.
Results of the Semi-Quantitative Food Frequency Questionnaire Study
Size of the study was appropriate as the researchers included 9248 Korean adults. Presence of this large sample size provide more accurate values and smaller margin of errors. Large number of participants also made it easier for the researchers to detect differences between the groups. Thus, it can be stated that the large number of participants were representative of the population.
Selection of the participants was done in an accurate way since the researchers used data obtained from the Ansung–Ansan cohort, which were obtained from the Korean Genome and Epidemiology Study (Shin et al., 2013). Participant selection was done in an accurate way since the researchers collected data from the baseline and follow-up study.
However, one major limitation was related to presence of residual confounding due to the presence of unmeasured or unknown factors in the study, in addition to the lifestyle and dietary factor adjustments that were related with risks of cardiovascular disease. Failure to adjust such confounding variables might have exerted an extraneous influence in the design, thereby contributing to bias (Smith, Ventura & Prince, 2013).
Further limitations can be associated with recall bias. This systematic error might have occurred due to differences in the completeness and accuracy of the recollections of the participants regarding their dietary intakes (Sedgwick, 2014). In addition, failure to collect information on the pattern of egg preparation might have also produced incorrect results.
However, the overall study was a first prospective cohort analysis of the association between egg consumption and incidence of cardiovascular disease. 95% CI indicates that similar results are expected to be obtained on repeating the research.
What was the research question addressed in this article?
The researchers aimed to evaluate the impact of a high- and low-egg diet, on circulating lipid profiles (HDL cholesterol), among obese people with type 2 diabetes.
The researchers recruited 140 adult participants, diagnosed with T2D or pre-diabetes, with BMI ≥25, followed by their randomisation to high and low egg based diets. All participants were advised about their diet allocation and prescription for maintaining weight. Those in the high-egg diet were asked to eat 2 eggs/day at breakfast, for 6 days/week. On the other hand, the diet allocation in the low diet group focused on consumption of <2 eggs/week, in addition to other sources of high protein. They were advised to maintain their activity levels. Prescribed quota of eggs were given to the participants under the high-egg diet. On the other hand, participants with low egg-diet were given grocery voucher of equivalent amount. Primary and secondary assessments comprised of anthropometric measures, pathology and vital signs, 3mo and baseline measurements. Primary outcome was related to measurement of HDL cholesterol levels. Five questionnaires were distributed to the participants namely, the Three-Factor Eating Questionnaire-R21, the International Physical Activity Questionnaire–short version, the Impact of Weight on Quality of Life Questionnaire-Lite Version, The Food Acceptability Questionnaire, and a visual analog scale.
Results of the Randomized Controlled Trial Study
The use of these questionnaires can be regarded as an appropriate step as they measured several domains of eating behaviour that encompass uncontrolled eating, emotional eating and cognitive restraint. The International Physical Activity Questionnaire helps in determining the health related physical activity of the individuals. Furthermore, its shorter version has been extensively tested in several international studies (Bermúdez et al., 2013). Thus, it can be stated that these two questionnaires were accurately employed for the study. Owing to the fact that the research specifically focused on overweight people with T2D, the Impact of Weight on Quality of Life Questionnaire helped in assessing impacts of their obesity on the overall HRQoL (Hinz et al., 2014). The Food Acceptability Questionnaire was an appropriate measure to determine the ease of preparation, palatability, perceived benefits, satisfaction, and adverse effects of the selected diet (King, Meiselman & Carr, 2013). The researchers used the SPSS 19.0 software for performing a statistical analysis of the assessment. Use of multiple imputation, in addition to linear regression helped in computing the missing values from the baseline and screening data. Treatment effects between the groups were compared on the basis of ANCOVA, which determined whether means of dependent variables were equal across all levels of the independent variables.
No significant differences were found in the levels of HDL cholesterol, from screening to the 3mo, between the randomised groups. Mean differences between the high-egg and low-egg diet groups were comparatively small +0.02 mmol/L (−0.03, 0.08 mmol/L; P = 0.38, 95% CI). No differences were found between the groups for LDL cholesterol, total cholesterol, glycemic control and triglycerides. Individuals in the high-egg diet group demonstrated increased satiety and less hunger, following breakfast. Significant increase in the levels of MUFA (monounsaturated fatty acids) and PUFA (polyunsaturated fatty acids) were found at baseline in both the groups. Upon analysis of participants with only T2D, no significant statistical difference was observed between the groups (+0.02 mmol/L; 95% CI: −0.05, 0.08 mmol/L; P = 0.65). Similar results were also observed upon analysis of the participants maintaining stable usage of lipid medications during the study (+0.03 mmol/L; 95% CI: −0.02, 0.08 mmol/L; P = 0.26). No differences were found the HbA1c or fasting glucose levels from screening to the 3 mo, between the two groups. Consistency was shown with results obtained upon analysis of participants maintaining stable anti-diabetic medications, or those who showed compliance to their diets. The researchers also failed to find any difference in weight change, waist circumference, fat-free mass, total body fat, heart rate and blood pressure. Small difference was observed between the two groups in relation to intake of total fat, fiber and carbohydrates.
Selection of Participants and Use of Questionnaires in the RCT Study
The authors selected an appropriate study design. They conducted a randomised controlled trial that has often been cited as one of the most feasible ways of determining the presence of a cause and effect relationship between a treatment/intervention and its direct outcome (De Serres et al., 2013). The study design can be cited appropriate since it helped the researchers to compare between the groups subjected to the experimental treatment (high egg diet) to that of those a low egg diet.
The study sample cannot be regarded adequate since small sample size might have resulted in problems in answering the research question. Recruitment of a larger sample size and use of a crossover design where each participant would be subjected to different treatments during separate time period would have helped in showing significant differences in primary HDL cholesterol outcomes (Button et al., 2013). Low dropout or withdrawal of the participants was one major strength that helped the researches to account for most participants at the end of the trial.
Selection of the participants was done properly since it followed the International Conference on Harmonization–Good Clinical Practice guidelines, the primary aim of which is to protect rights of the human subjects who participate in clinical trials, thereby ensuring credibility and validity of the collected data (Tinto et al., 2013).
However, one major limitation was associated with the fact that the researchers failed to blind the intervention group, while obtaining the scale ratings for their appetite. Blinding or concealment are imperative for clinical trials where one or more groups are kept unaware of the intervention arm to which the participants are subjected to (Hróbjartsson et al., 2013). Failure to blind them might have resulted in conscious or unconscious bias in the results.
Furthermore, the RCT was also associated with recall bias, which can be attributed to the presence of a systematic error, caused due to differences in the completeness or accuracy of the recollections made by the participants, during the use of the questionnaires (Vrijsen et al., 2014).
However, the overall study suggested that individuals with T2D or prediabetes can be given a high-egg diet, while reducing their saturated fat intake and maintaining body weight, with no adverse health effects.
Thus, it can be deduced from the evidences presented above that daily egg consumption is not associated with increased risks of cardiovascular abnormalities among individuals. However, no more than three eggs should be consumed by people suffering from diabetes. This can be attributed to the fact that diabetes increases the likelihood of an individual to suffer from chronic health problems such as, heart diseases. Considering the fact that eggs act as rich sources of dietary cholesterol, there is need to keep a check on consumption of saturated fats and maintain body weight, while feeding on a high-egg diet. In other words, efforts must be taken to recommend dietary patterns that focus more on consumption of low-fat dairy products, vegetables, fruits, whole grains, fish, poultry, nuts and fish, in addition to eggs, to keep the blood lipid levels in check. Hence, the evidences discussed above can be put to practice by restricting the cholesterol intake to no more than 300mgs, for individuals suffering from T2D, or who are overweight. Adherence to these recommendations will lower their risks of suffering from cardiovascular disorders.
References
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