Protein and the Bariatric Patient: Supplemental Protein or Amino Acids

| November 10, 2008

by Laura Frank, PhD, MPH, RD, CD
Part 3 of 3

Calories provided by protein may be more thermogenic and may help the bariatric surgery patient achieve weight loss goals more efficiently than the equal amount of calories provided from either carbohydrates or fats.1 Therefore, protein supplements are often recommended to help the bariatric patient achieve weight loss. Also, during the early postoperative period, supplemental protein can provide an important source of calories and indispensable amino acids (IAAs) that help prevent the loss of lean body mass and aide in wound healing. However, there is controversy regarding the safety and efficacy of protein supplements.2,3 Caution should be used with supplements that also contain high calories.4

It has been reported that the amino acid found in the highest concentration may be absorbed, but other amino acids in lesser concentration may not be absorbed.3 Therefore, amino acid supplements may result in impaired or imbalanced amino acid absorption. Furthermore, absorption of peptides (obtained from foods) may be absorbed more rapidly than the absorption of an equivalent mixture of free amino acids from dietary supplements.

Nitrogen assimilation following the ingestion of protein-containing foods has also been shown to be superior to that of the ingestion of free amino acids from dietary supplements. Moreover, the necessity of protein supplementation after bariatric surgery has not been established.5

There are several factors that should determine the type of protein supplement used by an individual, including convenience, taste, texture, and price. However, the product’s amino acid profile should be the first priority. A protein supplement that provides all of the indispensable amino acids (IAAs) is of the utmost importance.6 If protein supplements are to be used, the patient should choose complete, good quality proteins such as that provided by milk (whey and casein), egg, and soy. Reputable manufacturers should be able to provide accurate nutrition facts substantiating claims made about the amino acid profiles of their products.

Collagen-based supplements should not be used as a means of complete protein because collagen is missing tryptophan, one of the IAAs.6  In the presence of IAA deficiency, loss of lean body mass can occur despite meeting a daily oral intake protein goal. Collagen-based supplements, however, contain a high level of nitrogen within a small volume. These supplements may therefore be useful for the patient who is able to consume enough good-quality dietary protein to supply the needed IAAs, yet is not consuming enough total nitrogen to meet the nonspecific nitrogen requirement, or the patient who is not achieving nitrogen balance to support muscle protein synthesis.

Digestion Rate  
Protein digestion rate is unequivocally an independent regulating factor of post-prandial protein retention.7 Whey protein and casein, two milk-based proteins, have very different absorption kinetics.2 Whey protein is soluble, allowing for faster gastric emptying; whereas casein clots in the acid environment of the stomach delay gastric emptying, resulting in a slower release of amino acids. It has been reported that slowly digested protein, by inhibiting proteolysis, induces a higher post-prandial protein gain than rapidly digested protein, which stimulates protein synthesis but also oxidation.7, 8

Post-prandial leucine balance over seven days was higher after slow (casein) versus rapid (whey) protein meals.8 These results were confirmed by others9 concluding that digestion of milk soluble proteins (e.g., whey) is too rapid to sustain the anabolic post-prandial amino acid requirement. However, protein digestibility may also be modified by age. In young adults, slowly digested protein resulted in a better protein gain than rapidly digested protein; however, the opposite was found true among older individuals.10 Whether rapid versus slow uptake of amino acids are better for protein gain among bariatric patients have not been explored.

Whey protein typically comes in the following three forms: isolates, concentrates, and hydrolysates. There is greater processing involved in the isolate form, in which most of the fat and lactose are removed. Therefore, whey protein isolates generally contain greater percentages of protein (90–98% protein by weight) but are also generally more expensive. Whey protein concentrates naturally contain varying amounts of lactose, minerals, and fat.5 These products are generally 29- to 89-percent protein by weight, but are also generally less expensive and have greater palatability. Hydrolysates are predigested, partially hydrolyzed whey proteins that consequently are more easily absorbed, but their cost is generally higher. However, both whey protein isolates and whey protein concentrates have been characterized as rapidly and easily digestible sources of dietary protein. Boirie et al7 and Dangin et al8 determined that whey protein produced a large but transient rise in postprandial plasma amino acid levels and subsequent increased protein synthesis. Peak amino acid levels were reported in approximately 90 minutes and returned to baseline within five hours.

Numerous types of whey protein products have been produced commercially, all having various percentages of protein, molecular weights, lactose, and mineral content. Manufacturing process, product composition, and protein source can affect their digestibility, and therefore the effectiveness of the product.11 Furthermore, processing techniques, such as spray-drying, pressurized microfiltration, ultrafiltration, hydrolysis, and ion exchange, are used to produce whey protein products with different physicochemical and functional properties. For example, increasing the degree of hydrolysis concomitantly increases the solubility of the product, thereby making the protein more accessible to proteolytic enzymes and promoting better absorption.12 The source of the whey protein, whether from cheese or milk, as well as the type of milk, can also make a difference in the properties of the final product.13 Animal studies have shown that protein can be denatured or damaged during processing, making these products less soluble and digestible.14 In an in-vitro study of six different milk protein ingredients, Patel and Kilara13 reported that as much as 37 percent of the lysine found in whey protein concentrate products was chemically altered from overprocessing or inadequate storage conditions. It was reported that whey protein from cheese made with whole milk, skim milk, or a skim and buttermilk blend varied considerably in their solubility and other physicochemical properties.

How Much Can We Absorb?
One popular myth is that only 30g of protein can be absorbed and utilized at one time.15 While this is commonly found in both lay and some professional literature, no scientific studies to date have tested this claim, especially in the bariatric community. Arnal et al16 studied the effect of protein-pulse feeding (7% [~5g] dietary protein given at 800, 79% [~55g] given at 1200, and 14% [~10g] given at 2000) versus protein spread-feeding (25% [~17.5g] dietary protein at each meal given at 800, 1200, 1600, and 2000) on protein retention in elderly patients (mean age 68±1 year). Nitrogen balance was more positive with the pulse versus spread diet. Protein turnover rates were also higher with the pulse versus spread diet, due to higher protein synthesis. These authors concluded that a protein pulse-feeding pattern was more efficient than a protein-spread pattern in whole-body nitrogen retention. However, in young women (mean age 26±1 year), these protein feeding patterns did not have significantly different effects on protein retention.17 These data refute the “30g myth.” These authors conclude that protein source, time of consumption, quantity, and composition are factors determining the effect of protein on short-term satiety and food intake in young men. However, more studies are needed to determine how ingested protein load predicts nitrogen balance outcomes, especially among those with varying types of weight loss surgery.

Metabolic Rate
Understanding the body’s metabolic state is also important when supporting or refuting the “30g myth.” Protein, whether from food or supplements, provides amino acids. An important concept in protein metabolism is the amino acid pool(s) that contain amino acids of dietary origin (food and supplemental), plus those contributed by the breakdown of body tissue. The amino acids comprising the pool(s) are used for synthesis of new proteins for growth and/or replacement of existing body protein, for production of important non-protein, nitrogen-containing components in the body; for oxidation as a source of energy; and/or for glucose, ketones, or fatty acid synthesis.3

What Supplement Type Is Best?
Another myth commonly shared by bariatric surgeons is the claim that a powdered protein supplement is nutritionally superior or “works better” compared to liquid, ready-to-feed protein supplements. Again, there are no data to support this claim. A comprehensive review of modular protein supplements6 references all liquid, ready-to-feed products; however, there are no studies that compare the nutritional quality of liquid, ready-to-feed versus powdered protein supplements. Patients should be encouraged to utilize ready-to-feed protein supplements if these products improve compliance with ingestion of good-quality protein and can improve protein nutriture.

The Patient’s Role
It is the consumer’s responsibility to contact protein supplement manufacturers or raw material suppliers to identify the quality assessment and quality control factors associated with the product. Additional issues not explored within this article series are issues of added ingredients, including artificial sweeteners, vitamins, minerals, and botanicals. For the lactose-intolerant patient, casein has the lowest lactose content of the dairy proteins; however, due to the manufacturing process of hydrolysis, whey protein isolates are lactose free and therefore may be the product of choice for those who wish to use a supplemental versus food form of good quality protein.5 Continued follow-up with healthcare providers can shed light on whether the patient’s chosen supplement provides the needed nutrition to prevent or treat protein deficiencies.

Protein is an important macronutrient that provides energy and aids in wound healing, weight loss, and muscle protein accretion. Further research studies are needed in several areas with regard to protein needs in the bariatric patient in order to establish best-practice guidelines. The dietitian should work closely with the patient to help identify good quality proteins and recommend appropriate dietary protein intakes. A thorough nutrition assessment, including blood work and body composition measures, should be completed at regular follow-up intervals. It is important for the multidisciplinary team to work together to optimize patients’ care and outcomes.

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3.    Groff JL, Gropper SS. Advanced Nutrition and Human Metabolism, Third Edition. Belmont CA, Wadsworth;2000.
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9.    Lacroix M, Bos C, Léonil J, et al. Compared with casein or total milk protein, digestion of milk soluble proteins is too rapid to sustain the anabolic post-prandial amino acid requirement. Am J Clin Nutr. 2006;84(5):1070–1079.
10.    Dangin M, Boirie Y, Guillet C, Beaufrère B. Influence of the protein digestion rate on protein turnover in young and elderly subjects. J Nutr. 2002;132(10):3228S–3233S.
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13.    Patel MT, Kilara A. Studies on whey protein concentrates. Foaming and emulsifying properties and their relationships with physicochemical properties. J Dairy Sci. 1990;73:2731–2740.
14.    Sarwar G, Peace RW, Botting HG. Differences in protein digestibility and quality of liquid concentrate and powder forms of milk-based infant formulas fed to rats. Am J Clin Nutr. 1989;49:806–813.
15.    Venuto T. Available at: AUT: Need more info; what is this website?
16.    Arnal MA, Mosoni L, Boirie Y, et al. Protein pulse feeding improves protein retention in elderly women. Am J Clin Nutr. 1999;69(6):1202–1208.
17.    Arnal MA, Mosoni L, Boirie Y, et al. Protein feeding pattern does not affect protein retention in young women. J Nutr. 2000;130(7):1700–1704.

Category: Nutritional Considerations in the Bariatric Patient, Past Articles

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