Abstract

Lysine is one of the essential amino acids for normal growth and development. However, it is the limiting amino acid in rice which is the staple food of Filipinos. The aim of this study is to evaluate the lysine intakes of selected Filipino populations and determine the vulnerable population groups that are at risk of having inadequacy of lysine intake by locale and wealth quintile. The data is obtained from the 2013 National Nutrition Survey with about 8,592 sample households (response rate: 87.7%) and 35,884 individuals used in the current analysis: 6-11 months old (n=355), 1-3 years old (n=1,450), 4-10 yo (n=6,909), 11-14 yo (n=4,060), 15-18 yo (n=3,204), and 19-49 yo (n=19,906). Food intake was collected on 2 non-consecutive days. The first food recall was collected from all household members. The second day recall was only from a random sub-sample of 50% of those members with a first day recall. Energy and nutrient content of foods were processed using an electronic Individual Dietary Evaluation System containing the updated Philippines Food Composition Table. Mean and usual lysine intake was estimated using the PC Software for Intake Distribution Estimation version 1.02. The mean intake of lysine of Filipinos is adequate across all physiologic age groups. However, the prevalence of lysine inadequacy was highest among 6 to 11 months old children (54%). For other agegroups, prevalence were 14% among 1-3 yo, about 2% among 4-10 yo; 8% among 11-14 yo; 13% among 15-18 yo, and 15% among 19-49 yo. Lysine inadequacy was also most common among females, the poorest sectors, and in the rural areas. Lysine intake of stunted children is lower than normal children. The result of this study is a step forward to design immediate interventions to address the marked inadequate lysine intake of the 6 to 11 months old infants.

1. Introduction

Protein is made up of amino acids which are the building blocks that build and repair worn-out tissues. There eight essential amino acids (EAAs) for human nutrition namely: phenylalanine (Phe), valine (Val), threonine (Thr), tryptophan (Trp), isoleucine (Ile), methionine (Met), leucine (Leu) and lysine (Lys). They are essential because they could not be synthesized by the body, hence, these must be obtained from diet. Insufficient intake of essential amino acids could adversely affect multiple metabolic pathways since they play diverse roles in human health ¹. Animal sources of protein contain all the essential amino acids, on the other hand, plant sources lack one or more-these are called the limiting amino acid ². Protein complementation is the most efficient way to get all amino acids into a vegetarian’s diet. Protein complementation is when you combine two vegetable proteins to get all amino acids that are essential for the body ³.

The biologically active form of lysine is L-lysine. Lysine as one of the essential amino acids plays an active role in the metabolism of protein, carbohydrates, and fatty acids. It builds muscle and rebuilds muscle after periods of illness and inactivity. Lysine is also necessary for normal growth and development because it increases the absorption of calcium and collagen formation which are important for muscle and bone health. Together with methionine, lysine forms carnitine which helps cells utilize fat as energy. Lysine also plays an important role in the immune system, including preventing recurrence of herpes simplex virus ⁴ and reducing morbidity as a result of diarrhea and bronchopneumonia ⁵. Moreover, lysine supplementation can increase levels of C3, Ig G, Ig A, Ig M ⁶, and CD3 & CD4 ⁷. These immunoglobulins are important part of the immune response to fight infections by specifically recognizing and binding to particular antigens, such as bacteria or viruses, and aiding in their destruction. CD3 and CD4 peroxidases, on the other hand, are co-receptors of the T cell receptor which assist the latter in communicating with antigen-presenting cells ⁸.

Determination of lysine requirement has gained attention because of its nutritional importance as the first limiting amino acid in cereals and rice. The amount of lysine in rice is not sufficient to sustain the body’s needs.

Based on the FAO/WHO/UNU Expert Consultation on Protein and Amino acid requirements in Human Nutrition, lysine requirement of infants is higher as compared to adult requirements, and recent recommendations indicated a lysine requirement is highest among infants 6-11.9 months with about 64 mg/kg body weight /day ⁹. Table 2 presents the requirements by age groups. Older populations have lower requirements. Most estimates of a limiting amino acid requirement, including lysine, have been made in Western well-nourished young male adults and their modulation by factors such as sex, dietary, and nutritional factors. Also, the possibility that the limiting amino acid requirements might differ among populations living in other environments is a concern ¹⁰. Recent studies in Indian subjects showed that lysine requirement is not different between well-nourished young adults living in the United States and those in India. However, the same does not hold true for undernourished Indian adults whose lysine requirement is significantly higher (44 mg/kg/day) than that of healthy subjects (30 mg/kg/day). This higher requirement was attributed to intestinal parasite infestation ¹¹.

Persons with inadequate lysine may experience fatigue, nausea, dizziness, loss of appetite, agitation, redness of the eyes, lethargic growth, anemia, and disorders of the reproductive system ¹². On the other hand, those with a high risk of lysine deficiency are the athletes, body builders, burn patients because of high demands; the vegetarians, and vegans because plants are poor sources of lysine. These people can get additional sources of L-lysine from nutritional supplements ¹². Food sources that are high in L-lysine include high protein foods like nuts, red meat, fish and seafood, eggs, milk, cheese, legumes, and sardines. While lysine in the diet is considered safe, excessive doses may cause gallstones. There were also reports of renal dysfunction, including Fanconi syndrome and renal failure. Thus, lysine supplements should still be taken with precaution ¹².

Considering the important role of lysine in growth, and muscle and bone health, estimation of lysine intake of Filipinos is necessary to determine the vulnerable population groups that are at risk of having inadequacy of lysine intake by locale and wealth quintile for policy recommendation.

2. Methodology

This study used the data extracted from the 2013 National Nutrition Survey (NNS). The 2013 NNS is a cross-sectional study conducted nationwide in the Philippines. A multi-staged stratified sampling design was used to represent 17 regions encompassing 80 provinces, covering both urban and rural areas. The first stage of sampling is the selection of Primary Sampling Units, consisting of one barangay or a combination of contiguous barangays with at least 500 households each. From these PSUs, enumeration areas with 150 to 200 households were identified, from which housing units were randomly selected. The third stage was the random selection of the households, which is the ultimate sampling unit ¹³.

The Ethics Committee of Food Nutrition Research Institute (FNRI) approved the survey protocol. All surveyed households provided informed consent prior to participation.

A total of 8,592 sample households with 87.7% response rate were covered in the dietary survey. From the total population of individual respondents, those with data on dietary intake were grouped by age: 6-11 months old (n=355), 1-3 years old (n=1,450), 4-10 years old (n=6,909), 11-14 years old (n=4,060), 15-18 years old (n=3,204), and 19-49 years old (n=19,906), resulting in this study’s analytics sample size of 35,884 individuals ¹³.

Trained dietitians conducted face-to-face 24-h dietary recalls with a parent or caregiver of each child during household visits, wherein the dietitian recorded all food and beverages that the child consumed the previous day. A first 24-h recall was performed on all children and a second 24-h recall was repeated in 50% of randomly selected households, typically two days after the first recall. The amount of each food item or beverage was estimated while using common household measures, such as cups, tablespoons, by size, or number of pieces. The information was then converted to grams while using a portion-to-weight list for common foods compiled by FNRI or through weighing of the food samples ¹³.

The current Food composition table (FCT) of the Philippines does not contain lysine. Hence, lysine values of all food items consumed were barrowed from other FCT. The updated FCT new food items (325) found in the 2013 food consumption survey. With this effort, the new Philippine FCT contains 27 nutrients with a total of 1359 food items from the original FCT with 12 nutrients and 1034 food items. About half of data (47%) were from the USDA National Nutrient Database and 39% data from the original Filipino FCT compiled by FNRI ¹⁴. The rest of the data were sourced from food composition database of Association of Southeast Asian Nations and other Asian countries such as Japan (8%) and information from food labels (6%). All imported data were adapted according to the FAO INFOODS guidelines ¹⁵. The amino acid content of foods was calculated after adjusting for protein content. The Protein Digestibility Corrected Amino Acid Score (PDCAAS) was used in the calculation of the amino acid as it is the method preferred for the routine prediction of the protein quality ⁹. Stated below is the data compilation procedure for Philippine data of Lysine. Food records were entered and estimated energy and nutrient intakes were processed with a computer system called Individual Dietary Evaluation System (IDES). This system contains the data of the updated Filipino Food Composition Tables (FCT) created for this study.

Data Compilation Procedure:

1. Followed the Food Matching Guidelines of INFOODS version 1.2 which include the following criteria:

a. For food identification:

- food name and descriptors;

- taxonomic/ scientific name; and

- water and fat content

b. For food components:

- expression;

- definition;

- analytical methods;

- unit; and

- denominator

2. Adapt to protein contents between foods since amino acid content in foods depend on protein content

3. Adjust lysine data with values for digestibility of protein in humans

Formulas 1-3 were used to compute for the adjusted lysine contents of existing food items in the FCT and new food items included in the 2013 NNS. On the other hand, Table 1 presents the values for true digestibility of protein food sources.

Formula 1. Lysine content from Food Match

Lysine content= Protein content of food (g) x Lysine content of food match

Formula 2. Adjusted Lysine value

Adjusted Lysine value= (Lysine value per 1 g of Protein) x True Digestibility

Formula 3. Adjusted Lysine value with moisture content

A. Existing FCT food items:

Adjusted lysine value _mc = 100- Moisture content (FCT) X Lysine value

B. New FCT food items:

Adjusted lysine value _mc = 100- Moisture content from Food Match.

The Lysine requirements from the 2007 WHO/FAO/UNU Expert Consultation on the “Protein and Amino Acid Requirements in Human Nutrition” ¹⁶ was considered as the EAR for lysine which will be used to assess adequacy of lysine intake of the different age groups.

Socio-demographic variables, extracted from the main database of the survey were: ID code, age, survey weights, recorded day, sex, urbanity or locale. The variables collected for the household information were the following: type of dwelling unit, tenure status of the house, tenure status of the lot, type of roof, type of wall, type of floor, number of bedrooms, type of fuel used, and transport utilities. Wealth index was computed based on principal component analysis (PCA) of household assets, household characteristics, access to utilities, and infrastructure variables. Weights or factor were generated for each household asset/information through PCA. The standardized scores were then used to create the break points that define the wealth quintiles: poorest, poor, middle, rich, and richest.

To investigate food sources of lysine, a list of 85 food groups was created in a similar format from previous dietary intake studies ¹⁴. All foods and beverages reported were assigned to one of the 85 food groups. Fortified milk powder manufactured for toddlers and young children in the Philippines is called toddler/preschooler milk in this study while other milk was the regular powdered/fluid milk. The weighted percentage contribution of each food group for selected key nutrients was calculated by adding the amount of a given nutrient provided by each food group for all individuals and dividing by the total intake of that nutrient consumed by all individuals from all foods and beverages.

Mean ± SE usual intakes, percentile distributions, and prevalence of inadequate intakes of lysine were assessed using the Iowa State University (ISU) method. The ISU uses a statistical adjustment procedure that better explains some of the characteristics of dietary intake data ¹⁴. Briefly, the ISU method estimates distributions of usual nutrient intake by eliminating the effect of the day-to-day variability in consumptions from daily intakes. It uses data provided by ≥2 independent 24hour food recall. A good feature of the method is that it permits incorporation of the study design to generate national representative results ¹⁵. All calculations were carried out using sampling weights to adjust the complex design of the survey.

For the evaluation of lysine intakes, implausible intakes were defined as those that exceed 1.5 times the 99^th percentile of the observed intake distribution in the corresponding age group. Intakes above this upper limit were substituted by a random value generated from a uniform distribution in the interval with lower bound equal to the 95^th percentile of observed intake and an upper bound equal to 1.5 times the 99^th percentile. The prevalence of inadequacy in a group is estimated as the proportion of individuals with usual lysine intakes below the Estimated Average Requirement (EAR) i.e. EAR-cut-point method. The Lysine requirements from the 2007 WHO/FAO/UNU Expert Consultation was considered as the EAR for lysine which was used to assess adequacy of lysine intake of the different age groups with additional 20% of the each requirement for the effect of infections during absorption e.g. parasitic infestation.

3. Results

Table 3 shows the general profile of the respondents according to age groups. Most of the respondents were male among the age groups 1-3 years old (52.1%), 4-10 years (50.5%), 11-14 years (52.3%), 15-18years (53.3%), 19-49 years (50.5%). On the other hand, most respondents were female among the 6-11 months old children (50.8%).

Most of the respondents across all the age groups were from rural areas and from the poorest wealth quintile. In terms of work status among adults, 57.86% of the 19-49 years old age group is working. However, within the younger age groups, some of the 15-18 years old (11.72%) already work for a living. The prevalence of stunting among the different age were 13.83% among 6-11 months old, 30.15% 1-3 years old children, 29.83% among 4-10 years old, 30.79% among 11-14 years old, 31.02% among 15-18 years old, and 30% among 19-49 years old.

Table 4 shows the mean lysine intake among 6-11 months infants was 105.9 mg/kg BW/d. There was no difference in intake between sexes. However, lysine intake was significantly lower in rural areas and in the poorest quintile. The prevalence of lysine inadequacy among infants aged 6 to 11 months was 54%; the prevalence was higher in rural areas (64%) than in urban areas (46%). Comparing the data across wealth index, the poorest (67%) and the poor (64%) wealth quintiles have the highest prevalence of inadequacy than those in the other wealth indexes. Stunted and normal infants have equal mean lysine intake.

Among the young children aged 1-3 years old, the mean lysine intake was 145.2 mg/kg BW/d. (Table 5). There was no difference in lysine intakes between male and female. Lysine intake was significantly lower in rural areas (121 mg/kg BW/d) than in urban areas (165.8mg/kg BW/d). The poorest quintile had the lowest intake across the wealth index. The prevalence of lysine inadequacy among young children was 14%. The inadequacy of intake was higher in rural areas (18%) than in urban areas (10%). There is a declining prevalence of inadequacy as wealth quintile is improved. The poorest and poor wealth quintiles were 25% and 15%, respectively. Lower prevalence was observed in other wealth quintiles. Stunted children have lower mean lysine intake compared to normal children.

Among the 4 -10 year old children, the mean lysine intake was 106.3 mg/kg BW/d (Table 6). However, lysine intake was significantly lower among females (104.5mg/kg BW/d) than males (108.1 mg/kg BW/d). Comparing between localities, those residing in the urban area have significantly higher mean lysine intake (114.6mg/kg BW/d) than those in rural area (97.7 mg/kg BW/d). The prevalence of lysine inadequacy among this age group is at 2%.

Table 7 shows that the average lysine intake of 11-14 years old children was 74.6 mg/kg/d. Lysine intake was significantly lower in rural areas (69.7 mg/kg/d) and in the poorest quintile (62.3 mg/kg/d). Females had lower intake compared to male children. The prevalence of lysine inadequacy among 11-14 years old children was 8%.

For adolescents 15-18 years old, the average lysine intake was 64.3 mg/kg/d. (Table 8). Lysine intake was significantly lower in rural areas (59.3 mg/kg/d) and poorest quintile (53.8 mg/kg/d). Males had higher intake compared to females. The prevalence of lysine inadequacy among adolescents was 13%.

Table 9 shows that the mean lysine intake among adults was 57.5 mg/kg/d. Lysine intake was significantly lower in rural areas (54.9 mg/kg/d) and poorest quintile (51.1 mg/kg/d). Males had higher lysine intake compared to females. The prevalence of lysine inadequacy among adults was 15%. The prevalence of inadequacy of lysine intake decreases as wealth quintile increases.

Almost half (43%) of the total lysine intake was from infant formula for 6-11 months babies. The other top 4 sources of lysine for 6 11 months babies were other milk (powdered and fluid), rice, growing up formula milk, and infant cereals. Other milk (25%) and growing-up formula milk (17%) were the top 1 and 2 food sources of lysine for children age 1-3 years old followed by fish and shellfish, rice, and poultry. For 4-10 years old children, fish and shellfish was the top 1 food sources of their lysine intake while rice was the second contributor with 20% contribution to the total lysine intake. About 20% were from poultry and pork and only 7% was from other milk (Figure 1).

Fish and shellfish, rice, pork, and poultry were the common top four (4) food sources for all age group. Sausages/hotdogs, luncheon meat and cold cuts were the top 5 source of lysine for 11-14 years old and 15-18 years old while eggs and dishes with eggs for 19 years old and above (Figure 2).

4. Discussion

This study evaluated the lysine intakes of selected Filipino population by age groups, locale and wealth quintile. Lysine inadequacy exists in all agegroups in this study but the prevalence is significantly highest among infants 6-11 months old as compared with the other agegroups. The high prevalence might be due to the poor complementary feeding during this age. The top 5 sources of lysine for 6-11 months infants were infant formula (43%), other milk (26%), rice (7%), toddler/preschool milk (6%), and infant cereals (4%). A recent analysis of nutrient intake and food sources of infants revealed that considerable high prevalence of inadequate intakes were found for protein (43%), and other B- vitamins including vitamins vitamin A (84%), iron (76%) and zinc (63%) ¹⁷. On the other hand, the top-5 most consumed food items were refined rice, human milk, infant formula, cookies and cow’s milk. This lack of variety in the diet might have been a factor affecting the prevalence of stunting observed in this study (13.8%). Stunted children in this agegroup had 58% inadequacy of lysine intake. Incorporating high-quality protein source into the diet of the children has shown to have a positive impact on the improvement of nutritional status. Since lysine is the limiting amino acid in rice, the results of this study are important to emphasize the need to develop nutritious complementary foods that will fill the nutrient gap in this agegroup coupled by intensive nutrition education among parents to prevent stunted growth.

Lysine, along with other amino acids such as threonine and methionine, has been associated with the release of growth hormone in young children. Thus, the dietary restriction of these essential amino acids affects the production of plasma insulin-like growth factor. In a study determining the role of protein and amino acids on child growth, protein deficiency was identified to be the principal dietary cause of growth failure in children. Hence, protein quality was a potential determinant of nutritional status and growth in children ¹⁸. The inadequacy level among the other agegroups is also a cause of concern because amino acids are involved in building muscles and repairing worn – out tissues.

Human growth is regulated by the mechanistic target of rapamycin complex C1 (mTORC1), a pathway that is mediated by the availability of amino acids. This might explain the results of this study that stunted children had lower intake of lysine than their normal peers ¹⁹. This is manifested also in the results of the National Nutrition Survey (NNS) of the Department of Science and Technology – Food and Nutrition Research Institute wherein the prevalence of stunting was 30.1% ¹³. However, the amino acid requirements of young children—particularly those at high risk like stunting are not yet established. Advances in metabolomics and mass spectrometry facilitate the rapid quantification of serum metabolites including amino acids, thus, it is timely to investigate their role in the pathogenesis of stunting and its metabolites. Since the negative impact of protein malnutrition on growth was deemphasized in favor of addressing micronutrient deficiencies, elucidating the mechanistic pathways that lead to stunting through application of advances in modern technology is critical for its prevention to improve immediate and long-term health among children ¹⁹.

The place of residence demonstrated that the mean lysine intakes of individuals residing in urban areas are higher as compared to those in rural areas. Although fish and shellfish are the major sources of lysine in the older agegroups aged >4 years old, only 26 to 33 % were consuming. These findings are supported by the data in the 2013 NNS where 16.7 % of Filipino households were severely food insecure and was higher in rural (20%) than in urban areas (13.5%). Similar to these results, intra-country variations in Pakistan were observed and showed significant differences from the country average. The cities and surrounding areas have lower food energy availability than the rural areas. Also, total protein and animal protein consumption were often greater in the urban and city areas ²⁰. Animal protein are much more bioavailable as compared to the plant sources of protein. A study conducted in rural Bangladesh on amino acid intakes also highlighted that protein intake were lower in rural areas. Based on a 1996 report by the United Nations Subcommittee on Nutrition, it was found out that Bangladeshis have low intake of lysine, and overall, lower intakes of amino acids even compared to other developing countries ²¹.

Further analysis also indicates that there is a significant difference between the lysine intake of the rich and the poor. The diets of individuals within the poor wealth quintile are heavily based on cereals. Such diets are likely to be low in a number of micronutrients, including lysine. A study on the food and nutrient intakes of Filipino adults revealed that Filipinos in the poor wealth quintile had higher energy and nutrient inadequacies and the major source of different nutrients is rice wherein lysine is the limiting amino acid. Similarly, food availability data from various countries demonstrated that as wealth decreases, major changes in food patterns were also observed, particularly in the decrease of the consumption of animal protein foods while there is increase in dependency on cereals. This means that lysine intake parallel the changes in food and energy protein ²⁰. It was also found, of the essential amino acids, lysine is the amino acid for which the largest differences occur between the diets of the rich and the poor. Lysine content of most cereals ranges from 26 to 38 mg per gram of protein whereas the lysine content of animal foods is much higher, ranging from 70 to 100 mg per gram of protein. These relationships thus permit the estimation of lysine value from considerations of the amounts of animal protein and cereal protein ²⁰. Also, a further variable is the possible interaction between protein and food energy availability which may affect the protein value of diets when food energy is limiting to a significant degree. Thus, the additional effects of food energy deficiency on protein utilization could well be seen on the very poorest ²².

The analysis of lysine intake by sex reflected that lysine intakes of female respondents are lower as compared to the intake of males. One study measured the lysine requirement in women and reported an influence of the menstrual cycle phase (35 and 37.7 mg·kg⁻¹·d⁻¹ during the follicular and luteal phase, respectively), a difference that was ascribed to hormonal factors. In terms of the difference in the lysine intake between males and females, very limited studies give particular focus on specific amino acids. However, mean intake of amino acids are parallel to the protein intake. The results of the study confirm the data as revealed in the 2013 National Nutrition Survey that protein intake of males were higher compared to females. The human lysine requirement is the one of the essential amino acids focused on as subject of current collaborative international research and future agreement on the actual value is essential for the assessment, on a global basis, of those at risk for deficiency, as well as for the assessment of whether diets meet essential amino acid needs. Thus, reference standards are needed for comparison ²⁰. In the FAO Expert Consultation recommendations in 2011, amino acid requirements in different conditions and circumstances such as in varying population age groups and sex were determined.

5. Conclusion

The lysine intakes of Filipinos revealed that the prevalence of inadequacy is present in all age groups but higher prevalence was observed among the 6 to 11 month old infants. The prevalence of inadequacy was higher among the females, the poorest sectors, and in the rural areas as compared with the richest and urban areas, respectively.

It is crucial to focus future actions in improving diet quality of 6 to 11 month old agegroup to prevent retarded growth.

Limitation of the Study

Lysine intake was calculated based from all food and beverages only, dietary supplements were not included. About 60% of the infants age 6 -11 months were breastfed; however, human milk was also not included in the diet of the infants.

Acknowledgements

The authors would like to extend their gratitude to the International Life Sciences Institute-Center for Health Promotion (ILSI-CHP), Tokyo, Japan and Ajinomoto Corporation, Tokyo, Japan for funding this study.

References