VITAMINS & SUPPLEMENTS · GUIDE
Protein and Amino Acid Frequently Asked Questions: Quick Answers With Links
Short, sourced answers to common protein and amino acid questions, from daily intake levels to powders and safety, each pointing to the page that explains more.
Content last updated . This page has not been medically reviewed.
Back to Amino Acids & ProteinQuick answer
These are short answers to questions people ask most often about protein and amino acids. Each links to the page that covers the topic in full. Answers describe what named sources say; they are not personal advice. If a question involves a medicine, a health condition, pregnancy or a child, ask a clinician, pharmacist or registered dietitian. For word meanings, see the glossary.
The basics
| Question | Short answer | Read more |
|---|---|---|
| What is the difference between protein and amino acids? | Amino acids are molecules that combine to form proteins, and the basic structure of a protein is a chain of amino acids. [1] [2] | More about What is the difference between protein and amino acids? → |
| Which amino acids are essential? | MedlinePlus names nine: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. They cannot be made by the body and must come from food. [1] | More about Which amino acids are essential? → |
| Do I need animal products to get enough protein? | MedlinePlus says you do not need to eat animal products to get all the protein you need. [2] | More about Do I need animal products to get enough protein? → |
| Do plant foods have to be combined at the same meal? | MedlinePlus says we no longer worry about pairing proteins, such as beans with rice, at a single meal; the adequacy of the diet over the day is what counts. [1] | More about Do plant foods have to be combined at the same meal? → |
| What does protein deficiency look like? | Kwashiorkor is a form of malnutrition that occurs when there is not enough protein in the diet. [3] Concern about a person's eating or weight belongs with a clinician. | More about What does protein deficiency look like? → |
Amounts and official figures
| Question | Short answer | Read more |
|---|---|---|
| What do official bodies say adults need? | Canada: a protein RDA/AI of 0.80 g/kg/day for adults 19 and over in Health Canada's 2005-based table (56 g/day for males and 46 g/day for females aged 19 to 30). [4] Europe: EFSA's 2012 PRI is 0.83 g per kg per day for healthy adults. [5] These are group reference values, not personal targets, and the units differ from percent of calories. | More about What do official bodies say adults need? → |
| What share of calories can come from protein? | Health Canada's table lists an AMDR of 10 to 35 percent of energy from protein for people 19 and over. [4] | More about What share of calories can come from protein? → |
| Do older adults need more? | The PROT-AGE Study Group (2013 position paper) recommends average daily intake at least in the range of 1.0 to 1.2 g per kg for people over 65, and notes an exception: people with severe kidney disease not on dialysis may need to limit protein. [6] | More about Do older adults need more? → |
| Does more protein always build more muscle? | One 2018 meta-analysis of resistance-training trials in healthy adults found no further gains in fat-free mass from supplementation beyond total intakes of 1.62 g/kg/day. This is a study result, not advice. [7] | More about Does more protein always build more muscle? → |
| Is there an upper limit for amino acids? | A 2023 narrative review stated that national health agencies had not set tolerable upper intake levels for amino acids because of a lack of well-conducted human dose-response trials. [8] | More about Is there an upper limit for amino acids? → |
| What is the "anabolic window"? | A popular phrase for a claimed short period after exercise when protein matters most. The timing page checks the claim against research. | More about What is the "anabolic window"? → |
Powders and supplements
| Question | Short answer | Read more |
|---|---|---|
| What is the difference between whey concentrate, isolate and hydrolysate? | One review describes concentrate as having fat and lactose with 29 to 89 percent protein, isolate as 90 percent protein, and hydrolysate as partially digested for ease of metabolism and hypo-allergenicity. [9] | More about What is the difference between whey concentrate, isolate and hydrolysate? → |
| Are protein powders checked for heavy metals? | A Consumer Reports analysis of 15 protein powders raised concern, and a 2020 risk assessment of the reported concentrations concluded they did not pose an increased health risk under its assumptions. [10] Results vary by product and test. | More about Are protein powders checked for heavy metals? → |
| Are supplements tested before sale? | NCCIH says the FDA can take action against adulterated or misbranded supplements only after the product is on the market, and that what is on the label may not be what is in the product. [11] | More about Are supplements tested before sale? → |
| Can athletes trust a supplement for banned substances? | USADA says neither USADA nor WADA approves any dietary supplement. [12] | More about Can athletes trust a supplement for banned substances? → |
| What is NAC, and is it a supplement? | The FDA has determined NAC is excluded from the dietary supplement definition, and has described enforcement discretion for certain products. [13] | More about What is NAC, and is it a supplement? → |
Questions we could not answer from our sources
For some questions, such as which individual amino acid supplement is "best", the sources we read did not offer a ranking, and this library does not rank products. Proper evidence not found for a universal best product; ask a clinician or dietitian about your own situation. A list of questions to ask your clinician or dietitian can help.
Frequently asked questions
Are these answers personal advice?
No. They summarize what named sources say. Your health, medicines, age and diet change what is right for you, so check with a clinician, pharmacist or dietitian. [11]
Why do official protein figures differ between countries?
Different bodies set values for their own populations and years: for example, Health Canada lists 0.80 g/kg/day [4] while EFSA's 2012 value is 0.83 g/kg/day. [5] Always check the group, unit and year before comparing.
Is a higher protein figure for older adults official?
It is a position paper recommendation from the PROT-AGE Study Group (2013), not a Health Canada or EFSA value. [6]
Where is the emergency information?
For severe allergic reactions call 911 [17]; for a possible overdose in the US, MedlinePlus lists the Poison Help line at 1-800-222-1222. [18]
Does this site sell or rank products?
No. We do not name brands, list products or rank them. The Amino Acids & Protein hub explains the library.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety questions
| Question | Short answer | Read more |
|---|---|---|
| Is protein safe with kidney disease? | NIDDK says some people with chronic kidney disease may need moderate amounts of protein, but too little can lead to malnutrition, so work with a dietitian or health care professional. [14] | More about Is protein safe with kidney disease? → |
| Can 5-HTP or tryptophan be combined with antidepressants? | Memorial Sloan Kettering says people taking SSRIs, MAOIs, tricyclic antidepressants or other serotonin-affecting drugs should avoid 5-HTP without a physician's supervision. [15] Do not stop a prescribed medicine on your own; ask the prescriber. | More about Can 5-HTP or tryptophan be combined with antidepressants? → |
| Who must avoid phenylalanine and aspartame? | MedlinePlus describes PKU as a condition in which a baby is born unable to properly break down phenylalanine, and says products containing aspartame should be avoided. [16] | More about Who must avoid phenylalanine and aspartame? → |
| What if someone reacts badly to a protein powder? | For signs of anaphylaxis such as trouble breathing or face, tongue or lip swelling, MedlinePlus says call 911. [17] | More about What if someone reacts badly to a protein powder? → |
| Are supplements safe in pregnancy or for children? | NCCIH says many dietary supplements have not been tested in pregnant women, nursing mothers or children. [11] | More about Are supplements safe in pregnancy or for children? → |
| Where is one page that pulls the safety points together? | The Safety Quick Reference and the checklist before you start a supplement. | More about Where is one page that pulls the safety points together? → |
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.