Introduce the background: 最近按照Charles的建议使用MacronutrientCalculator计算了一下自己所每日所需的营养，发现自己一天需要190g蛋白质。本来对于190g蛋白质没什么概念，仔细一查，才发现自己每天吃的鲷鱼饺子，一碟推算一下也就25g…也就是说，我每天摄入的蛋白质顶多也就60g而已。突然觉得很惊慌。但是上网一查，有人认为每顿饭能摄入的蛋白质最多也就20-30g，这么说的话我也似乎无能为力；但同时也有另外一个声音认为我们吃的每一克蛋白都会被吸收。到底真相如何，今天就来研究一下蛋白质的文献吧！
Formulate the question: 到底如何才能补充足够的蛋白质来保证肌肉的增长呢？
"Some people claim that the body can't absorb more than 20-30 grams of protein at a time. Others insist that your body utilizes all the protein you take in. Who is right? Is a post-workout shake with 50 grams of protein a waste?"
This idea that the body can only utilize a certain amount of protein at one sitting has become widely accepted nutrition lore. But is there any validity to the claim?It all comes down to what exactly you mean by "utilizing" protein..
This notion about protein seems to have gotten started on body-building forums - and this may be the main source of some of the confusion. Body-builders are particularly interested inprotein's ability to build and repair muscles. And there does seem to bea limit to how much protein the body can use for muscle synthesis at a given time.
If building muscles is your goal, you'll get more benefit by spreading your protein intake out among all of your meals.
In one study, researchers found that a meal containing 30 grams of protein boosted muscle-building activity by about 50%. That's the amount of protein you'd get in a 3-ounce serving of chicken breast or a quarter-pound of lean beef. It turned out, however, that increasing the amount of protein in the meal didn't create a bigger boost in muscle synthesis. On average, subjects who ate 90 grams of protein at a meal got exactly the same benefit as subjects who ate 30 grams.
The precise amount of protein at which the muscle-building effects peak will vary from person to person, of course. Someone with a very large or muscular body, or someone who is engaged in heavy workouts might be able to use a little more protein than someone who is smaller or not as athletic. But, in general, if building muscles is your goal, you're probably better of spreading your protein intake out among all of your meals than by eating the entire day's allowance atone meal.
However, thosewho claim that all of the protein you eat is utilized are also right - because building muscle is only one of the things that our bodies use protein for.
Protein: The Body's Tinker Toy Set
Remember Tinker Toys? It's a collection of sticks and wheels that you can put together to build anything you want. You could build a Tinker Toy house, for example. Then, you could take apart the house and reconfigure the same pieces into an airplane.
Protein is sort of like the body's Tinker Toy set. Every protein is made up of special molecules called amino acids, which are like the individual Tinker Toy pieces. When you digest protein, your body breaks it down into the individual amino acids and then uses them to build enzymes, hormones, immune factors, transport and storage molecules, and all kinds of other useful things, including bigger biceps.
Protein is an essential nutrient because you can't get amino acids from fats or carbohydrates. No amino acids, no enzymes. No enzymes, no life.
When the stakesare that high, it's not surprising that the body prioritizes its use of amino acids. Survival first; six-pack abs second. But when the body has all the amino acids it needs, protein can also be used as an alternative source of energy or calories. In other words, if you have some Tinker Toy pieces left over after building your house, you can burn the extras for heat!
And this is the sense in which all of the protein you take in does get utilized. Protein beyond what your body needs to replenish its amino acid pool (or can put to use for muscle building) is metabolized into glucose and used for energy. And whenever you have more food energy than you need, the surplus is stored as fat. Nothing is wasted.
Advantages of Protein as an Energy Source
As long as you're not taking in more calories than you're burning each day, there's no harm in using protein as a source of energy.
So, is your post-workout shake with 50 grams of protein a waste? In terms of repairing and building up your muscles, a shake with 30 grams of protein might be just as effective. But as long as you're not taking in more calories than you're burning each day, there's no harm in using protein as a source of energy. In fact, there may be some advantages - all of which I've discussed in previous episodes.
1. Protein takes longer to digest than carbohydrates, which means that calories from protein tend to keep you full longer than calories from carbohydrates. This can be very helpful in controlling calorie intake and managing your weight.
See also: 3 Tips on How to Eat Less Without Feeling Hungry
2. Protein doesn't cause sharp spikes in blood sugar, which reduces your risk of diabetes.
See also: What Is High Glucose?
3. Protein can modestly boost your metabolism, or the rate at which your body burns calories.
How Much Protein Should You Eat?
There's a big range in the amount of protein that's considered to be acceptable - and it depends on what your goals are.
It doesn't take a whole lot of protein to keep the body's amino acid Tinker Toy set stocked -about 10% of calories or around 50 grams a day will do it for an average-sized person. Even vegetarians should have no trouble getting that amount.
The muscle building benefits of protein seem to max out around 20% of calories. And if you want to take advantage of protein's appetite-taming and metabolism-boosting abilities, it's OK to go as high as 30%-35% of calories from protein - as long as you don't have any medical issues (such as reduced kidney function).
One last tip: Your body does use extra water to digest protein. So, if you're increasing your protein intake, be sure to increase your fluid intake as well to avoid dehydration.