Lysine requirements of moderately undernourished school-aged Indian children are reduced by treatment for intestinal parasites as measured by the indicator amino acid oxidation technique

BACKGROUND

Lysine requirements of well-nourished children from developing regions have been found to be similar to those of children from developed regions (33.5 mg · kg⁻¹ · d⁻¹). However, intestinal parasites have been shown to increase lysine requirements in undernourished adults, and it is not known if a similar phenomenon occurs in undernourished children from poor and unsanitary environments.

OBJECTIVE

Our objective was to measure the lysine requirement of moderately undernourished school-aged Indian children by the indicator amino acid oxidation technique before and after successful treatment for intestinal parasites.

METHODS

Twenty-one undernourished school-aged children (∼8 y of age) with z scores between -2 SD and -3 SD for height-for-age or weight-for-age, who tested positive for intestinal parasites, were studied before and after successful antiparasite treatment. Children were fed any 2 of 7 levels of lysine intakes (5, 15, 25, 35, 50, 65, and 80 mg · kg⁻¹ · d⁻¹) in random order. The lysine requirement was determined by applying a 2-phase linear regression crossover analysis on the fractional oxidation rate of the tracer L-[1-¹³C] phenylalanine in response to the graded lysine intakes.

RESULTS

The lysine requirement of undernourished children with intestinal parasite infestations was determined to be 42.8 mg · kg⁻¹ · d⁻¹ (95% CI: 32.6, 53.1 mg · kg⁻¹ · d⁻¹), and after successful antiparasitic treatment it was determined to be 35.5 mg · kg⁻¹ · d⁻¹ (95% CI: 25.5, 45.5 mg · kg⁻¹ · d⁻¹). The results were significantly different (P < 0.05), although the 95% CIs overlapped.

CONCLUSIONS

The lysine requirement in undernourished children is similar to that of well-nourished children, and intestinal parasitic infestation increased the lysine requirement by ∼20%.

Dietary Protein Requirement of Men >65 Years Old Determined by the Indicator Amino Acid Oxidation Technique Is Higher than the Current Estimated Average Requirement

BACKGROUND

The current estimated average requirement (EAR) and RDA for protein of 0.66 and 0.8 g ⋅ kg-1 ⋅ d-1, respectively, for adults, including older men, are based on nitrogen balance data analyzed by monolinear regression. Recent studies in young men and older women that used the indicator amino acid oxidation (IAAO) technique suggest that those values may be too low. This observation is supported by 2-phase linear crossover analysis of the nitrogen balance data.

OBJECTIVE

The main objective of this study was to determine the protein requirement for older men by using the IAAO technique.

METHODS

Six men aged >65 y were studied; each individual was tested 7 times with protein intakes ranging from 0.2 to 2.0 g ⋅ kg-1 ⋅ d-1 in random order for a total of 42 studies. The diets provided energy at 1.5 times the resting energy expenditure and were isocaloric. Protein was consumed hourly for 8 h as an amino acid mixture with the composition of egg protein with L-[1-13C]phenylalanine as the indicator amino acid. The group mean protein requirement was determined by applying a mixed-effects change-point regression analysis to F13CO2 (label tracer oxidation in breath 13CO2), which identified a breakpoint in F13CO2 in response to graded intakes of protein.

RESULTS

The estimated protein requirement and RDA for older men were 0.94 and 1.24 g ⋅ kg-1 ⋅ d-1, respectively, which are not different from values we published using the same method in young men and older women.

CONCLUSIONS

The current intake recommendations for older adults for dietary protein of 0.66 g ⋅ kg-1 ⋅ d-1 for the EAR and 0.8 g ⋅ kg-1 ⋅ d-1 for the RDA appear to be underestimated by ∼30%. Future longer-term studies should be conducted to validate these results. This trial was registered at clinicaltrials.gov as NCT01948492.

Protein requirements of healthy pregnant women during early and late gestation are higher than current recommendations

BACKGROUND

Adequate maternal dietary protein intake is necessary for healthy pregnancy. However, current protein intake recommendations for healthy pregnant women are based on factorial calculations of nitrogen balance data derived from nonpregnant adults. Thus, an estimate of protein requirements based on pregnancy-specific data is needed.

OBJECTIVE

The objective of this study was to determine protein requirements of healthy pregnant women at 11-20 (early) and 31-38 (late) wk of gestation through use of the indicator amino acid oxidation method.

METHODS

Twenty-nine healthy women (24-37 y) each randomly received a different test protein intake (range: 0.22-2.56 g · kg(-1) · d(-1)) during each study day in early (n = 35 observations in 17 women) and late (n = 43 observations in 19 women) gestation; 7 women participated in both early and late gestation studies. The diets were isocaloric and provided energy at 1.7 × resting energy expenditure. Protein was given as a crystalline amino acid mixture based on egg protein composition, except phenylalanine and tyrosine, which were maintained constant across intakes. Protein requirements were determined by measuring the oxidation rate of L-[1-(13)C]phenylalanine to (13)CO2 (F(13)CO2). Breath and urine samples were collected at baseline and isotopic steady state. Linear regression crossover analysis identified a breakpoint (requirement) at minimal F(13)CO2 in response to different protein intakes.

RESULTS

The estimated average requirement (EAR) for protein in early and late gestation was determined to be 1.22 (R(2) = 0.60; 95% CI: 0.79, 1.66 g · kg(-1) · d(-1)) and 1.52 g · kg(-1) · d(-1) (R(2) = 0.63; 95% CI: 1.28, 1.77 g · kg(-1) · d(-1)), respectively.

CONCLUSIONS

These estimates are considerably higher than the EAR of 0.88 g · kg(-1) · d(-1) currently recommended by the Dietary Reference Intakes. To our knowledge, this study is the first to directly estimate gestational stage-specific protein requirements in healthy pregnant women and suggests that current recommendations based on factorial calculations underestimate requirements. This trial was registered at clinicaltrials.gov as NCT01784198.

Dietary protein requirement of female adults >65 years determined by the indicator amino acid oxidation technique is higher than current recommendations

BACKGROUND

Studies on protein requirements in vulnerable groups such as older adults are few, and results are conflicting.

OBJECTIVE

The main objective of this study was to determine the protein requirements of free-living women >65 y by measuring the oxidation of l-[1-(13)C]phenylalanine to (13)CO2 in response to graded intakes of protein.

METHODS

Twelve subjects participated in the study, with protein intakes ranging from 0.2 to 2.0 g · kg(-1) · d(-1) for a total of 82 studies. The diets provided energy at 1.5 times each subject's resting energy expenditure and were isocaloric. Protein was given as an amino acid mixture on the basis of the egg protein pattern, except for phenylalanine and tyrosine, which were maintained constant across the protein intake amounts. All subjects were adapted for 2 d before the study day to a protein intake of 1.0 g · kg(-1) · d(-1). The mean protein requirement was determined by applying a mixed-effects change-point regression analysis to F(13)CO2 (label tracer oxidation in (13)CO2 breath), which identified a breakpoint in the F(13)CO2 in response to graded amounts of protein.

RESULTS

The mean estimated average requirement (EAR) and upper 95% CI (approximating the RDA) protein requirement of women >65 y were 0.96 and 1.29 g · kg(-1) · d(-1), respectively.

CONCLUSION

These estimates of protein requirements for older women are higher than the current EAR and RDA based on nitrogen balance data, which are 0.66 and 0.80 g · kg(-1) · d(-1), respectively. This trial was registered at clinicaltrials.gov as NCT01604980.

Assessment of protein requirement in octogenarian women with use of the indicator amino acid oxidation technique

BACKGROUND

Data on the protein requirements of elderly adults are limited, because it is impractical to conduct repeated nitrogen balance protocols in these vulnerable humans.

OBJECTIVE

This study was designed to determine the dietary protein requirement of elderly women by using the recently developed minimally invasive indicator amino acid oxidation (IAAO) technique.

DESIGN

Six white women aged 80-87 y [mean ± SEM: 82 ± 1 y and body mass index (in kg/m²) 26 ± 2] completed a 3-d protocol 7 times. Each woman consumed an adaptation diet for 2 d and on day 3 consumed a complete test diet with a crystalline amino acid mixture containing 1 of 7 protein intakes (0.1, 0.3, 0.6, 0.9, 1.2, 1.5, or 1.8 g · kg⁻¹ · d⁻¹) tested randomly. A group-based protein requirement was assessed by using a nonlinear mixed model of protein intake and L-[1-¹³C]phenylalanine oxidation. The breakpoint, at which there was no further decline in the rate of appearance of ¹³C in the breath, was used as an index of the mean protein requirement.

RESULTS

The mean protein requirement (95% CI) was 0.85 (0.60, 1.09) g · kg⁻¹ · d⁻¹. This requirement is 29% higher than the current Estimated Average Requirement (EAR) for adults of 0.66 g · kg⁻¹ · d⁻¹ based on the nitrogen balance technique, although the 95% CI includes the current EAR. The corresponding adequate protein allowance of 1.15 (0.77, 1.54) g · kg⁻¹ · d⁻¹ is 44% higher, although the 95% CI includes the Recommended Dietary Allowance (RDA) of 0.80 g · kg⁻¹ · d⁻¹.

CONCLUSIONS

Notwithstanding uncertainty about the validity of the use of the IAAO technique to assess protein requirements, the results of this study with octogenarian women suggest that the current EAR and RDA for elderly women may be underestimated. The limitations of this short-term, noninvasive method underscore the need for new research that uses alternative experimental designs and measuring physiologic, morphologic, and health-related outcomes.

Isoleucine requirement of pregnant sows

The objective of this study was to determine the Ile requirement in early (d 39 to 61) and late (d 89 to 109) pregnancy using the indicator AA oxidation method. The same 7 Large White × Landrace sows in their fourth parity were used in early and late pregnancy. Each sow received 6 diets based on corn, corn starch, and sugar in both early and late pregnancy at constant feed allowances (2.5 kg/d). Diets provided Ile at 20, 40, 60, 80, 100, and 120% of the Ile requirement (6.2 g/d based on the 1998 NRC) in early and 60, 80, 100, 140, 160, and 180% in late pregnancy. After determination of (13)C background in expired CO2 and plasma free Phe for 1.5 h when confined in respiration chambers, sows were fed the tracer, L[1-(13)C]Phe, a rate of 2.0 mg/(kg BW·h) over 4 h divided into eight 30-min meals. Expired CO2 and plasma free Phe were analyzed for (13)C enrichment above background. Requirements were determined as the breakpoint in 2-phase nonlinear models. Sow BW was 246.5 kg in early and 271.6 kg in late pregnancy. Daily gain of the 6 sows was similar in early (344 g/d) and late pregnancy (543 g/d). During pregnancy, sow maternal gain was 19.1 ± 4.4 kg and litters of 17.7 ± 0.8 piglets weighed 22.6 ± 0.9 kg at birth. The Ile requirement was 3.6 ± 1.2 g/d (P = 0.001) in early pregnancy with a Phe retention (-0.59 g/d) and energy retention (-0.31 MJ/d) that were not different from 0. This indicates that the fourth parity sows had requirements close to maintenance in early pregnancy. The Ile requirement in late pregnancy was 9.7 ± 1.9 g/d (P = 0.001) when sows retained 3.30 g/d of Phe and -1.45 MJ/d of energy. The greater Ile requirement in late pregnancy was probably caused by the increased conceptus growth after d 70 of pregnancy. Phenylalanine flux, oxidation, and nonoxidative disposal increased (P < 0.1) from early to late pregnancy, but body protein breakdown did not. Phenylalanine oxidation, nonoxidative disposal, and retention increased (P < 0.01) with increasing Ile intake in early pregnancy but were not affected by Ile intake in late pregnancy. Body protein breakdown did not respond to Ile intake in early or late pregnancy. Although energy retention was similar in early and late pregnancy, the respiratory quotient decreased (P = 0.047) from early (1.05) to late pregnancy (0.98), indicating lipid mobilization in late pregnancy when Ile was at or above the requirement. The results of this study show that the Ile requirement of sows increases from early to late pregnancy.

Splanchnic first pass disappearance of threonine and lysine do not differ in healthy men in the fed state

We previously showed that the splanchnic bed of neonates takes up a significantly higher amount (43%) of threonine in contrast to lysine (12%). We questioned whether this same pattern applied in adult humans and found no information in the literature. Therefore, our objective in the current study was to determine the difference in splanchnic first pass disappearance of threonine and lysine in adult humans during the fed state. During two 5-d study periods, 6 healthy men received l-[1-(13)C]threonine or l-[1-(13)C]lysine enterally or parenterally randomized to either study d 3 or 5, respectively. The diets were in the form of an amino acid mixture providing a protein intake of 1 g · kg(-1) · d(-1) and an energy intake of 1.5 times the resting energy expenditure. Blood and breath samples were collected at baseline and plateau for amino acid and 11CO(2) enrichment. Splanchnic disappearances in adult males were similar for threonine and lysine. The splanchnic disappearance of threonine as a percentage of intake was 17.9% (8.4 mg · kg(-1) · d(-1)) in the healthy men compared with 18.5% (11.2 mg · kg(-1) · d(-1)) for lysine. We conclude that the threonine requirement of the gut of healthy men consuming a liquid formula diet based on free amino acids is similar to the lysine requirement, which is in contrast to our previous findings for neonates.

Lysine from cooked white rice consumed by healthy young men is highly metabolically available when assessed using the indicator amino acid oxidation technique

Cooked white rice (CWR) provides up to 71% of the dietary protein for many people worldwide. The protein digestibility-corrected amino acid (AA) score is the method adopted by FAO/WHO to evaluate protein quality. Our group has proposed the metabolic availability (MA) of AAs as another determinant of protein quality. It measures the percentage of an indispensable AA that is incorporated during protein synthesis. This study is the first to our knowledge to assess the MA of l-lysine (L-Lys) from CWR in humans using the indicator AA oxidation (IAAO) technique. Three amounts of L-Lys, 10, 15, and 19 mg · kg(-1) · d(-1) (= 28.5, 42.8, and 54.3% of the mean L-Lys requirement of 35 mg · kg(-1) · d(-1)), were studied in 5 healthy young men in a repeated-measures design. To test the principle that the Maillard reaction has an effect on the MA of LLys, we also assessed the MA of L-Lys in oven-browned, cooked rice (n = 3) in the amount of 19 mg · kg(-1) · d(-1) L-Lys. The MA of L-Lys was estimated by comparing the IAAO response with varying L-Lys intakes in rice compared with the IAAO response to varying l-Lys intakes in the reference protein (crystalline AA mixture patterned after egg protein) using the slope ratio method. The MA of L-Lys from CWR was high (97%), but the effect of the Maillard reaction reduced it to 70%. The results show that despite its relatively low content in rice, L-Lys has a high MA when the rice is cooked without being browned.

Lessons learned regarding symptoms of tryptophan deficiency and excess from animal requirement studies

Tryptophan is the precursor for several neurotransmitters and metabolic regulators, which, although quantitatively of little importance in determining the dietary requirement, have major importance for interpreting symptoms of dietary tryptophan deficiency and excess. The quantitative dietary tryptophan requirement appears to vary widely across species, so intakes relative to requirements are more appropriate expressions for comparison of adverse effects across species than daily intake or diet concentration. Symptoms of tryptophan deficiency may occur at intakes as little as 25% below the requirement. Symptoms include reduced feed intake and reduced growth rate but also impaired skeletal development and aberrant behavior. Older animals appear less susceptible than younger animals to tryptophan deficiency and females less than males. Symptoms of excess tryptophan intake include reduced food intake and growth rate. In growing animals, it appears that tryptophan intakes of >10 times the requirement are necessary before there are detrimental effects on growth performance. At still greater intakes, fatty liver and fibrotic changes in muscles, lung, and pancreas and the serotonin syndrome may develop. In pigs, tryptophan intake of 60 times the daily requirement did not cause mortality. The maximal tryptophan oxidation rate, measured in vivo using (13)C universally labeled tryptophan, may be a possible marker of the intake above which increasing intake increases the risk of adverse effects. The advantage of the oxidation technique is that it does not necessarily rely on but still allows the identification and measurement of amino acid metabolites and is therefore simpler and more universally applicable.

Determination of the tolerable upper intake level of leucine in adult men

Leucine is purported to improve athletic performance. Therefore, the BCAA, especially leucine, are popular as dietary supplements among strength-training athletes. There are, however, concerns regarding possible adverse effects of excessive leucine intake. The objective of the current study was to determine the metabolic and adverse effects of the acute ingestion of very high intakes of leucine supplements. Five healthy men (20-35 y) each received graded stepwise increases in leucine intakes of 50, 150, 250, 500, 750, 1000, and 1250 mg · kg(-1) · d(-1) corresponding to the Estimated Average Requirement, and Estimated Average Requirement ×3, ×5, ×10, ×15, ×20, and ×25 to a total of 29 studies. The graded stepwise approach was used rather than a randomization of leucine intake to minimize the possibility of severe adverse effects. Participants were given a maintenance diet for 2 d prior to each leucine level containing 1 g · kg(-1) · d(-1) of protein and 1.7× measured the resting metabolic rate. Leucine oxidation was determined using L-[1-13C]-leucine and the appearance of (13)CO(2) (calculated as F(13)CO(2)) in breath. A range of markers was used to monitor for adverse effects, including glucose, insulin, alanine aminotransferase, and ammonia. Plasma leucine concentrations significantly increased beyond an intake of 500 mg · kg(-1) · d(-1). The metabolic limit to oxidize leucine was between 550 and 700 mg · kg(-1) · d(-1). An increase in blood ammonia concentrations was observed at leucine intakes >500 mg · kg(-1) · d(-1). There were no changes in liver alanine aminotransferase. Glucose concentrations fell (P < 0.004) but remained within the normal range and without any change in insulin. This study is the first to our knowledge to directly estimate the safe upper limit of leucine intake in humans and raises concerns that intakes >550 mg · kg(-1) · d(-1) or ~39 g/d may be a risk to health. It is important to note that these are acute studies, where each participant was exposed to graded increases in leucine intake. Longer term adaptation was not studied.

Determination of the tolerable upper intake level of leucine in acute dietary studies in young men

BACKGROUND

Leucine has been suggested to improve athletic performance. Therefore, the branched-chain amino acids (BCAAs), especially leucine, are popular as dietary supplements in strength-training athletes; however, the intake of leucine in excess of requirements raises concerns regarding adverse effects. Currently, the tolerable upper intake level (UL) for leucine is unknown.

OBJECTIVE

The objective of the current study was to determine the UL for leucine in adult men under acute dietary conditions.

DESIGN

Five healthy adults (20-35 y) each received graded stepwise increases in leucine intakes of 50, 150, 250, 500, 750, 1000, and 1250 mg · kg⁻¹ · d⁻¹, which corresponded to the Estimated Average Requirement (EAR) and the EAR ×3, ×5, ×10, ×15, ×20, and ×25 in a total of 29 studies. The UL of leucine was identified by the measurement of plasma and urinary biochemical variables and changes in leucine oxidation by using l-[1-¹³C]-leucine.

RESULTS

A significant increase in blood ammonia concentrations above normal values, plasma leucine concentrations, and urinary leucine excretion were observed with leucine intakes >500 mg · kg⁻¹ · d⁻¹. The oxidation of l-[1-¹³C]-leucine expressed as label tracer oxidation in breath (F¹³CO₂), leucine oxidation, and α-ketoisocaproic acid (KIC) oxidation led to different results: a plateau in F¹³CO₂ observed after 500 mg · kg⁻¹ · d⁻¹, no clear plateau observed in leucine oxidation, and KIC oxidation appearing to plateau after 750 mg · kg⁻¹ · d⁻¹.

CONCLUSION

On the basis of plasma and urinary variables, the UL for leucine in healthy adult men can be suggested at 500 mg · kg⁻¹ · d⁻¹ or ~35 g/d as a cautious estimate under acute dietary conditions.