Protein: an energy source for your muscles during training
Protein is a building block for muscle, but its role goes well beyond that. Whether you train at the gym, run or simply want to recover better, your total protein intake throughout the day matters far more than the occasional post-workout shake.
The simple truth is that your body needs amino acids every day. They keep your muscles, enzymes, immune system defenses, hemoglobin and hormones such as insulin and IGF-1 functioning.
Why does protein matter?
Excluding water, protein makes up about ¾ of our body mass. It is found in muscles, internal organs, bones, nails and hair. That makes protein an everyday necessity for everyone, rather than a niche interest for bodybuilders.
Protein from food is broken down into amino acids. These move into the muscles, liver and free amino acid pool, which you can think of as a small reserve. Depending on your body mass, this pool contains around 100-150 grams of amino acids. Your muscles and liver contain far more, often 100 times as much: 10-15 kg of amino acids bound into proteins.
A small amount, around 2-5 g, circulates in the blood. That may sound like very little, but the flow is constant. Amino acids arrive from food, move into tissues, take part in protein synthesis and, when needed, are also used for energy.
So what actually happens? When protein synthesis exceeds protein breakdown, your body can build and maintain muscle mass. When breakdown takes over, muscle mass starts to decline. Training aims to tip the balance toward anabolism, but that requires enough protein and energy in your diet.
How do protein and amino acids work?
Your body uses 20 different amino acids to build proteins. Of these, 11 are nonessential and 8 are essential for adults. The ninth, histidine, is essential mainly for young children. Your body can produce nonessential amino acids itself, but essential amino acids must come from food.
Your muscles use a lot of amino acids. Insulin also plays a role in helping muscle cells use them effectively. Amino acids themselves can stimulate insulin production. You do not always need to consume carbohydrates alongside protein, but doing so after a hard workout can support the process.
Animal and plant-based protein
Protein sources are usually divided into two groups: animal and plant-based proteins. Animal sources include meat, eggs and dairy products. Plant sources include beans, grains, asparagus, nuts and soy.
Animal protein contains all the amino acids your body needs, which is why it is called a complete protein. Plant-based proteins may contain smaller amounts of certain essential amino acids or lack them altogether. This does not mean a plant-based diet is poor. It simply means your diet needs variety.
If you are vegetarian, you can improve the amino acid profile of your diet by eating foods such as beans and rice, peanut butter and whole-grain bread, or tofu and rice over the course of the day. You do not necessarily have to eat them together on the same plate, but you should aim for variety within the same day. Soy protein is an exception, as it is already a complete protein on its own.
Different protein sources in your diet
Casein is a milk protein found in dairy products. It accounts for 80% of milk protein. It is absorbed slowly and is a good option when you expect a longer gap between meals, such as before bed. You can get casein from cottage cheese, cream cheese and cheese. Another benefit is calcium, which supports your bones.
Whey also comes from milk, but it behaves differently. It is a byproduct of cheesemaking and accounts for 20% of milk protein. It is absorbed faster than casein and is rich in BCAA. Whey was once considered almost essential after a workout, but the picture is now more measured: in terms of protein synthesis, there is not always much difference between using casein and whey.
Eggs are an excellent source of protein. Egg protein is high quality, but using only the egg white means missing out on some of the nutrients in the yolk. This is why egg-based protein powders are not always better than whey or casein.
Soy protein is suitable if you do not consume dairy products or animal protein. It is used in soups, as a meat substitute, and in cheese, bread, pasta products and some breakfast cereals. Soy has been the subject of much debate, particularly because of its phytoestrogens. The practical advice is simple: use soy in moderation and do not make it your only daily protein source.
BCAA, glutamine and protein in training
BCAA stands for branched-chain amino acids. These are valine, L-leucine and isoleucine. They have been heavily marketed to bodybuilders and athletes, but their effects are not as magical as the label sometimes suggests.
During training that relies on glycogen, such as running or strength exercises in the 8-15 rep range, amino acid use increases as muscle glycogen levels fall. This has led to the idea that supplementing with BCAA might help. However, the evidence shows that athletes and bodybuilders often manage without separate BCAA supplements.
If your daily protein intake is adequate and your protein sources are high quality, BCAA levels in your muscles are usually sufficient. The range of 1.6-1.8 g/kg given in the original article is relevant here. For many people who do strength training, this protein intake meets their needs without separate amino acid supplements.
The picture is similar for glutamine. One study used 45 g/day per person during six weeks of strength training. That amount would cost around 500-1000 ¤ a year, yet no clear benefit for muscle development was observed. Glutamine also already accounts for 60% of free amino acids, so supplementation may not change the amino acid pool as hoped.
During a diet, BCAA or glutamine may help in some cases, especially when carbohydrate intake is low and glycogen stores are depleted. Even then, though, they are not the first thing to address. Start by reviewing your total daily protein intake, calories and training load.
Protein requirements: how much is enough?
Your protein requirements depend on your age, body weight, training and goals. The figures below are useful guidelines, not rigid rules.
| Age group | Protein requirement per kg | Essential amino acids % |
| 1-3 years | 1.8 | 43 |
| 3-5 years | 1.2 | 32 |
| 6-18 years | 1.0 | 22 |
| Adults | 0.6 | 11 (33) |
| Bodybuilder | 1.6-1.8 | Not established |
| Recreational athlete | 1.2-1.4 | Not established |
Studies have found benefits for strength athletes at intakes of 1.4-1.8 g per kilogram of body weight. Someone who does not exercise needs around 0.6-0.8 g/kg of body weight. Kevin Tipton has said that even 2 g of protein per kilogram is generally not harmful to a healthy person. Peter Lemon has recommended 1.6-1.7 g per kilogram of body weight for people who take part in strength sports and 1.2-1.4 g per kilogram of body weight for recreational athletes.
An intake above 2 g/kg does not necessarily offer any additional benefit for your muscles. Instead, the extra protein may affect metabolism or be stored as fat, especially if energy intake is already high. The situation is slightly different during a diet. Then, more than 2 g/kg may make sense because protein helps you feel full and reduces the risk of losing muscle mass.
How should you spread your protein intake throughout the day?
An old piece of gym wisdom says that your body can only absorb 30 g of protein at a time and that you should eat it every two or three hours. That is an oversimplification. Your body takes a long time to digest food and does not simply throw the remaining protein in the trash.
One study found that the body took eight hours to digest and use 80 g of casein. So there is no need to set an alarm for every three hours. Your total protein intake over the whole day matters much more.
In practice, including a good source of protein in each main meal works well. Eggs or quark at breakfast, meat, fish or legumes at lunch, and cottage cheese, tofu or another suitable option at dinner. It does not have to be complicated.
The risks of excess protein and a sensible limit
You sometimes hear that protein damages your kidneys. For a healthy person, that fear is usually exaggerated. If your kidneys function normally and you are in good health, a sensible protein intake is not a problem. If you have kidney disease or a disorder of protein metabolism, however, you need to discuss your diet with a doctor.
Calcium is another consideration. A high proportion of animal protein in your diet may increase calcium loss through urine, but a balanced diet helps replace it. Milk, cottage cheese and cheese provide both protein and calcium. If you do not eat dairy products, you need to pay more attention to your sources of calcium.
Honestly, the bigger problem is usually inconsistent protein intake rather than too much protein. Plenty one day, almost none the next. Your muscles like consistency.
FAQ: protein and muscle development
Do you need protein immediately after a workout?
No, provided your daily protein intake is adequate. Eating after a workout is convenient and often makes sense, but for your muscles, what you eat over the whole day matters more than any one precise minute.
Can you get enough protein as a vegetarian?
Yes, but you need to plan your diet more carefully. Legumes, grains, tofu, nuts and soy help you cover the range of amino acids you need.
Do you need BCAA if you eat enough protein?
Usually not. If your protein intake is adequate and your food is high quality, your body gets enough BCAA from everyday foods.
Translated from Body magazine
Author: Greta
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