EAT. LIFT. SLEEP. REPEAT.
A COMPARISON OF DIETS TO DETERMINE PROTEIN COMPLEMENTATION IN PLANT PROTEIN
Javier E. Arevalo
ABSTRACT
In the book “Diet for a Small Planet”, Frances Moore Lappe claims that plant protein is comparable in quality to that from animal sources through a process called protein complementation. The purpose of this study is to determine whether the effects of “complimentarity” of plant proteins is observable from the data obtained from feeding young rats four different diets. For 5 days, young rats were fed four different diets with the purpose of determining whether or not “complimentarity” was seen among the samples fed a combination of two plant proteins (Wheat+Pea). Protein Efficiency Ratio depends on the weight a rat has gained over the period of the study, in this case 5 days; hence the correlation between protein intake and weight gain can be postulated in the PER equation. True digestibility according to Professor Aponte takes into account the extra fecal Nitrogen that does not come “form undigested food but from bacteria, cells from the intestinal walls”
INTRODUCTION
In the book “Diet for a Small Planet”, Frances Moore Lappe claims that plant protein is comparable in quality to that from animal sources through a process called protein complementation. The purpose of this study is to determine whether the effects of “complimentarity” of plant proteins is observable from the data obtained from feeding young rats four different diets. Having a pool sample size of 24 samples for a period of 5 days, the rats in the experiment were fed either: A) Wheat, B) Pea, C) Wheat+Pea, or D) Albumin. To determine any differences among diets, Protein Efficiency Ratio (PER) and True Digestibility (TD) parameters were obtained and recorded.
METHODS
For 5 days, young rats were fed four different diets with the purpose of determining whether or not “complimentarity” was seen among the samples fed a combination of two plant proteins (Wheat+Pea).
To determine the data necessary for the determination of complimentarity it was necessary to observe the following methods:
- Bomb Calorimetry
- Kjeldahl Nitrogen Procedure
- Serum TfR Assay
The specific steps of the following methods are described on the attached lab pages
Bomb Calorimetry
This method is used to determine digestible energy value (DE) while obtaining the following endproducts: CO2, H2O, NO2 while also liberating heat categorized as gross energy.
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Kjeldahl Nitrogen Procedure
This procedure determines nitrogen content of biological materials and calculates the amount of crude protein content in foods. Furthermore this procedure mimics digestion in the stomach through the conversion of organic nitrogen of amino acids to ammonium salts along with the oxidation of carbon and hydrogens.
Serum TfR Assay
Measures transport iron bound to protein transferrin to determine quality of the protein by looking at the amount of amino acids available for the synthesis of such rapid turnover protein
RESULTS
Protein Efficiency Ratio (PER)
PER= Weight Gain / Crude Protein Intake
Diet A-Wheat
Diet B-Pea
Diet C-Wheat + Pea
Diet D-Albumim
Differences in diets based on Duncan’s test
A-B: No difference
C-A: No difference
D-C: No difference
D-A: Difference seen
B-D: Difference seen
Albumin is different than Wheat and Pea alone but similar to Wheat+Pea diet combined.
True Digestibility (T.D.)
((Neaten-Nfecal)/(Neaten)) * 100
Differences in diets based on Duncan’s test
A-C: No difference
B-A: No difference
D-B: No difference
D-A: No difference
D-C: Difference visible
Albumin is different than Wheat+Pea in terms of protein digestibility.
DISCUSSION
PER
Protein Efficiency Ratio depends on the weight a rat has gained over the period of the study, in this case 5 days; hence the correlation between protein intake and weight gain can be postulated in the PER equation. By looking at the means obtained on the results, the Pea diet alone has the lowest value where as Albumin has the highest mean. One may assume that because Albumin has the highest mean it would indicate that it has the best protein efficiency however that is incorrect when computing the Analysis of Variance (ANOVA) along with the Duncan’s test. Furthermore, ANOVA shows a P-value is less than .05 showing the data is not due to chance and instead presents a difference somewhere in the PER data obtained from the different diets. When proceeding with Duncan to locate the specific difference, there appears to be a difference among diets such as the diet D (albumin) and diet A (wheat), along with a difference in albumin and pea. The data infers that wheat+pea are similar in protein efficiency with albumin, which correlates with Lappe’s concept of “complementarity” hence showing both plant proteins as well as animal protein (albumin) are equivalent in quality. The concept of complementarity can be expressed through the example that vegetarians do not suffer from malnutrition if they maintain a healthy diet while pea and wheat by themselves have a lower PER, and weight gain values.
The specific calculations for the ANOVA of PER have been attached to this lab report.
T.D.
True digestibility according to Professor Aponte takes into account the extra fecal Nitrogen that does not come “form undigested food but from bacteria, cells from the intestinal walls”1
While observing the true digestibility it was observed that complementation plays a role in affecting the means of diet D (Wheat+pea) making it the lowest while albumin diet is the highest mean. At first the means for diet D does not make sense considering one would consider that any diet containing pea would be lower in digestibility due to trypsin inhibitor. In this case one should consider the issue of bioavailability because “absolute or apparent lack of digestive enzymes can result in decreased digestibility of a protein”2. With the help of ANOVA and Duncan’s test, a difference is found among Diet D and Diet C concluding that Wheat+Pea differs in digestibility with albumin. A factor that may play a role in this difference refers to trypsin which “acts to break peptide linkages on the carboxyl sides of arginine and lysine”1. Considering pea has a trypsin inhibitor it may be playing a role while combined with wheat therefore decreasing bioavailability and digestibility.
CONCLUSION
Protein efficiency and digestibility play an important role in the quality of protein when metabolized by the human body, however complementation of plant proteins as tested in young rats exposes the importance of working together to improve to quality. Furthermore, complementation is a factor in maintaining the health among vegetarians hence supporting Lappe’s claim from there book “Diet for a Small Planet”. In reference to protein quality, PER expresses that albumin is similar in efficiency to that of wheat+pea while differing in digestability observed through T.D.
CITATION
1) Aponte, Greg. ” Nutrition Experiment with Young Rats.” NST 170. Berkeley, Berkeley. 2/2/2011. Address.
2) Kies, Constance. “Bioavailability: A Factor in Protein Quality.” American Chemical Society. 29.3 (1981): 435-439. Print.
