The use of amino acid infusions to provide nutritional support to individuals incapable of eating a sufficient amount of dietary protein to meet nutritional requirements dates back to the 1960s. An amino acid infusion can either provide partial nutritional support or may be given as part of total parenteral nutrition (TPN). TPN provides all nutrition, including amino acids, carbohydrate, fat, and vitamin and minerals via intravenous infusion, or amino acid injections. But is there a significant advantage to taking amino acids intravenously over taking amino acids orally as a supplement?
Intravenous Amino Acids and TPN
Intravenous amino acids can provide nutritional therapy for protein metabolism (the breaking down and building up of proteins).
An amino acid infusion contains the amino acids with the greatest protein-stimulating effect. These include the essential amino acids leucine, isoleucine, lysine, valine, phenylalanine, histidine, threonine, methionine, and tryptophan, as well as the nonessential amino acids alanine, arginine, glycine, proline, serine, and tyrosine. These amino acids act as protein-building blocks, encouraging protein synthesis in muscle cells and preventing protein breakdown.
An amino acid injection is the administration of amino acids and other nutrients by way of parenteral nutrition. Parenteral administration utilizes routes outside the gastrointestinal (GI tract), such as intravenous routes. Enteral nutrition, on the other hand, is food or drug administered by way of the GI tract, such as with tube feeding.
Intravenous infusion of amino acids is used for patients who cannot take in food or nutrients through the enteral route (GI Tract). For instance, if gastrointestinal absorption is disrupted by inflammatory disease or obstruction, or if tube feeding is not providing adequate nutritional support.
Aminosyn® II is a popular amino acid injection given by way of peripheral vein or central vein infusion and used as a source of nitrogen in the short-term nutritional therapy of patients with adequate body fat who are unable to sustain oral nutrition. This type of amino acid infusion is also administered to help prevent or reverse negative nitrogen balance in patients who cannot take in nutrients via the enteral route.
Individuals who have had large portions of their intestines removed surgically can live indefinitely on total parenteral nutrition (TPN). A 15% amino acid injection can be administered by use of a central venous catheter or by peripheral vein. This amino acid infusion is coupled with vitamins, trace elements, electrolytes, and energy nutrients to provide the necessary nutritional support for weight maintenance or weight gain. In order for the amino acids from TPN to be adequately absorbed and utilized, energy requirements must be met. Energy is typically provided as a combination of dextrose to support carbohydrate metabolism and an intravenous fat emulsion that offers up essential fatty acids to protect against essential fatty acid deficiency and fulfill the dietary balance of fat and carbs.
The primary drawback to amino acid infusion as the sole source of amino acids from the physiological perspective is that the intestine atrophies. This is because some of the amino acid requirements of the gut are satisfied by direct uptake of amino acids from the digestion of orally ingested protein or amino acids. Atrophy makes the intestines more permeable to diffusion of bacteria and bacterial products from the gut into the body. Of course, if TPN is used because of the removal of the gut, this point is moot. If the intravenous infusion of amino acids is used alongside orally ingested protein, gut integrity will be maintained so long as the oral intake is sufficient.
Benefits of Amino Acid Infusion
The clinical benefits of amino acid infusion in patients who are incapable of ingesting adequate nutrition orally are well established. In addition, intravenous infusion of amino acids in individuals fully capable of ingesting amino acids orally is gaining popularity. The “selling point” of this therapy is that the exact concentrations of individual amino acids in the blood can be precisely controlled. This is promoted as particularly important to the relative concentrations of amino acid precursors of specific brain neurotransmitters. This approach is used in recovery from addiction, as well as for general support of protein metabolism in the body.
The premise of intravenous amino acid therapy is that the individual cannot get the full benefit from orally ingested amino acids, or that the intravenous infusion somehow confers special beneficial effects.
Advantages of Oral Ingestion of Amino Acids
The oral ingestion of amino acid solutions has advantages over amino acid infusion. There is no risk associated with oral ingestion, whereas intravenous infusion carries with it the risk of vein irritation. A health care provider is needed to perform the intravenous infusion, whereas free amino acids for oral consumption are relatively cheap and readily available.
It is possible to obtain a mixture of essential amino acids for oral consumption specifically designed for a particular condition, such as reaching your ideal body weight, whereas the options for intravenous infusion are much more limited due to the arduous procedure to obtain approval from the FDA.
There are also physiological advantages to the oral ingestion of amino acids over peripheral infusions. Most important of these is that the uptake and utilization of amino acid solutions by the intestines provides a direct source of essential nutrition.
Orally ingested amino acids are directly absorbed by the intestines and require no digestion. The amount of amino acids provided to the body by the two routes (oral and intravenous) are thus similar. Since orally ingested amino acids pass through the intestines, liver, and other organs before reaching the peripheral circulation, the peripheral plasma concentrations of amino acids reach higher levels when infused intravenously. Conversely, orally ingested amino acids provide more direct support of the internal organs.
Orally ingested and intravenously infused amino acids both stimulate muscle protein synthesis, which is the metabolic basis for muscle growth and strengthening. A clinical study of older individuals showed that muscle protein synthesis was stimulated in response to both intravenously infused as well as orally ingested amino acids. In addition, the profile of amino acid concentrations in the blood reflected the profile of the orally ingested amino acids, so there is no advantage to intravenous infusion in terms of supplying the proper balance of amino acids needed to synthesize neurotransmitters in the brain. Further, a clinical response was observed at dosage levels that are able to be consumed orally without much difficulty.
Side Effects of Amino Acid Injections
Amino acid infusions are now being marketed as a way to boost athletic endurance, protect against muscle loss, and even improve the health of the central nervous system. While amino acid solutions can indeed impart these benefits, amino acid injections were not originally developed for healthy individuals tackling body weight goals. Oral amino acid supplements, however, can help build muscle, sharpen cognitive function, and enhance athletic endurance, and there are no needles or doctors involved. It's as easy as mixing an amino acid powder with water.
One of the biggest advantages of taking an oral amino acid supplement over an amino acid injection is that no special care is needed and there are no side effects to contend with.
Amino acid injections can cause the following adverse reactions:
- Inflammation/redness at the injection site
- Allergic reactions
- Weight gain
- Urine changes
Contraindications for amino acid injections are indicated for individuals in hepatic coma, with hepatic insufficiency, severely impaired kidney function or renal failure, or suffering from metabolic disorders due to compromised nitrogen utilization or hypersensitivity to one or more amino acids.
Amino acids can be delivered either by intravenous infusion or oral ingestion of amino acid solutions. Both routes support protein metabolism in the body, as well as provide amino acids for other purposes.
The intravenous infusion procedure has risks and costs that are avoided by oral ingestion, and the amino acid profiles in available intravenous infusion mixtures are limited. For these reasons, amino acid infusion should be used only in individuals who are incapable of ingesting amino acids or who have a limited capacity for absorption. Oral ingestion is the preferred route of delivery of amino acids in most circumstances.