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Illustration of assorted types of protein, including fish, beans, a steak, egg, and drumstick.

When it comes to protein, you really are what you eat.

Aside from water, proteins are the most abundant molecules in our bodies: Our muscles, skin, hair, bones, and organs are made mostly of protein. And it’s one of the three macronutrients (along with fats and carbohydrates) important for providing us with energy and nutrition.

Protein takes center stage, however, because of its role in muscle building, growth, and healing.

It’s also the subject of spirited debate. Some folks worry that most of us get too little, others that we get far too much.

Some point out that it’s not just the quantity, but the quality that matters.

Still others insist that it’s not just how much or what kind of protein you eat that counts, but also when you eat it, and what other foods you combine it with.

What is clear is that protein is a significant and vital part of our diets — for health, fitness, and satisfaction.

The International Society of Sports Nutrition (ISSN) reviewed the available research in 2007 and again in 2014 and stated that, unless you’re completely sedentary, the USDA’s recommended daily allowance (RDA) of 0.36 grams of protein per pound of body weight is likely not enough for optimal health and fitness.

Research from the Harvard School of Public Health also suggests that replacing some of the refined carbohydrates in your diet with protein is good for your heart and your waistline.

But the most pressing questions remain: How much protein do you need for your body size, activity level, and workout goals?

What’s the best way to ensure you’re getting what you need without burdening your body — or driving yourself crazy worrying about unimportant details?

To help you sort out your protein questions once and for all, we scoured the latest studies, spoke to sports-nutrition experts, and developed the following protein primer.

Here’s what you need to know about this essential macronutrient.

1. What Does Protein Do?

You might remember from grade school that proteins are “the building blocks of life.” But what does that really mean?

Every cell in the body contains protein, and protein does a lot of work — providing tissue structure and growth, supporting immune function and metabolism, maintaining healthy weight, and helping performance.

Protein molecules are made up of thousands of smaller units called amino acids. Protein and amino acids are also essential for producing adequate enzymes, hormones, neurotransmitters, and antibodies.

Basically, you need protein (and the various amino acids) in your diet to help your body repair cells and make new ones. You eat protein. Your body digests the protein and releases the amino acids into your system, and the amino acids are absorbed by other tissues or synthesized into new proteins.

2. How Much Protein Should I Eat?

The amount of protein you need varies according to your body size and activity level, and to your weight loss and fitness goals (more on that in a minute). But it’s safe to say the RDA of 0.36 grams of protein per pound of body weight is a bare minimum.

“Active adults have a greater daily protein requirement than their sedentary counterparts,” says Oliver Witard, PhD, exercise-science lecturer at the University of Stirling in Scotland and author of several studies on the body’s response to exercise and protein.

The ISSN and the National Academy of Sports Medicine (NASM) give the following guidelines:

  • Sedentary adults: 0.4 grams of protein per pound of body weight per day. This works out to 60 grams of protein daily for a 150-pound person.
  • Adults seeking to improve their endurance: 0.5 to 0.6 grams of protein per pound of body weight per day. This equates to 75 to 90 grams of protein daily for a 150-pound person.
  • Adults looking to build muscle and strength: 0.6 to 0.9 grams of protein per pound of body weight per day. This works out to 90 to 135 grams of protein daily for a 150-pound person.

3. How Much Protein Should I Eat Daily?

A good goal for most active people is to eat 20 to 30 grams of protein at each meal, and you might add a couple of smaller protein-rich snacks in between. So what does a healthy serving of protein look like? For cooked meat, it would be a piece about the size of a deck of cards (about 3 oz.).

Use the suggestions below as a visual guide for other recommended portions:

Small chicken breast 2 1/2 to 3 1/2 ounces
Small salmon fillet 3 to 4 ounces
Eggs 4 to 5  (or 6 to 8 egg whites)
Hamburger 3 to 4 1/2 ounces
Whole raw almonds 3/4 to 1 cup
Cooked lentils 1 1/4 to 1 3/4 cup
Tuna 4 oz. (2/3 of a standard 6-ounce can)
Greek yogurt 1 to 1 1/2 cups
Dry-roasted soybeans 2/3 to 3/4 cup
Cooked black beans 1 1/2 to 2 cups

(Also see, “Here’s What 30 Grams of Protein Looks Like” for additional protein-rich foods and serving sizes.)

4. How Important Is Protein to Weight Loss?

For weight loss, it’s crucial.

Protein helps satisfy and ward off hunger while it steadies blood sugar and supports the healthy hormone profile essential to optimal metabolism.

Harvard Medical School researchers found that protein exerts an “increased thermic,” or calorie-burning, effect when compared with carbs and fats. This means that our bodies use more energy to digest and burn protein than carbs or fat.

And while there’s no need to count calories to lose weight, the fewer overall calories you consume, the more of them should come from protein as opposed to carbs or fats, says Margriet Westerterp, MS, researcher at Maastricht University in the Netherlands.

Westerterp authored a 2009 study on dietary protein and weight loss and discovered that protein helped subjects feel satiated even when they decreased their overall calories. She calls it the “protein effect.”

Eating protein also helps maintain muscle mass, which in turn supports a faster-burning metabolism.

5. Will Eating More Protein Help Me Build Muscle?

First, recognize that exercising against resistance is really what builds muscle. But you do need to eat adequate protein to support and maintain the new muscle you are building — and that will be more protein than if you weren’t exercising intensely.

If you’re training hard, aim to meet the ISSN and NASM guidelines of 0.6 to 0.9 grams of protein per pound of body weight per day (plus plenty of non-starchy vegetables to ensure you’re getting good nutrition and adequate fiber). And pay attention to how your body feels and responds to what you’re eating. While the conventional weight-room wisdom for powerlifters of eating 1 gram of protein per pound of body weight daily is considered safe by NASM, it’s probably more than most fitness enthusiasts need.

6. Do I Need to Combine Carbs With Protein Postworkout?

It’s not a bad idea, but it’s also not essential. A postworkout snack or smoothie that contains some carbs will deliver quick energy and help restock what your body just used during exercise. But, if your goal is weight or body-fat loss, you may be sabotaging your efforts by consuming additional carbs, which can challenge your body’s glucose and insulin regulation, warns Cindi Lockhart, RD, LD, senior program manager of health and nutrition coaching at Life Time Fitness in Chanhassen, Minn.

Eating protein will support the building and repair of challenged muscle tissue. But it’s not clear that you need to actually ingest the two macronutrients together, or eat them in strict quantities, or even eat them directly after exercise.

Even if there’s less specific muscle-enhancing benefit than previously thought in pairing carbs and protein, there’s certainly no harm in combining the two.

The classic advice has been to eat a 4:1 carbs-to-protein ratio to enhance nutrient uptake immediately postworkout. But the current reality is more nuanced: “There’s no magic ratio,” says John Ivy, an exercise physiologist at the University of Texas at Austin and coauthor of Nutrient Timing. “Anywhere in the range from 2.5:1 to 4:1 works well.”

That range is best if you’re working on improving performance. But many experts suggest eating a 1:1 carbs-to-protein ratio or even fewer carbs if your goals are losing weight or body fat.

Lockhart agrees and advises this strategy for clients who are overweight, insulin resistant, or over age 40.

She also advises individuals who are trying to drop excess weight to wait an hour after exercise before eating.

7. How Soon After Exercise Should I Eat Protein?

For years we’ve been told to consume protein within an hour of a hard workout — the so-called anabolic timing window. But new research says that the timing window could be much larger than previously thought.

Researchers at Lehman College in New York and California State University found that for people doing resistance training, total protein intake throughout the day is more crucial to muscle gain than protein timing alone.

Witard agrees: “I would argue that the importance of eating protein immediately following exercise is not as critical as has been previously proposed.” He notes that muscle remains responsive to protein ingestion for at least 24 hours after exercising.

Still, downing a shake or protein bar immediately after a hard workout isn’t bad for you — and it could be helpful in other ways.

Protein restores your energy and helps you feel full, so you’re less likely to binge on unhealthy food. And a 20-gram dose of protein after a workout has been clinically shown to stimulate protein synthesis by your muscles, helping tissue repair and grow. So, you’ll recover quicker.

Just don’t sweat it if you can’t get that protein snack right away. Some of us like to shower, hydrate, and take our time cooling down before we can think about eating or drinking a shake — and that, new research suggests, is OK.

8. Can I Eat Too Much Protein?

There’s some scary news floating around about high-protein diets causing kidney problems, decreased bone health, and even cancer. But experts say if you’re otherwise healthy and observing sensible limits, there’s little cause for concern.

“There is no scientific data that shows a negative effect of high-protein diets on kidney or bone health in otherwise healthy individuals,” says Witard. If you have preexisting kidney or other health problems, however, you should consult your doctor before embarking on a high-protein diet, he suggests.

“If you get your protein from primarily high-quality, nutritious whole foods like seafood and grassfed meats, it is nearly impossible to consume too much protein. You would become uncomfortably full before you overdid it,” says Jonathan Bailor, New York Times best-selling author of The Calorie Myth.

There are some potential downsides of eating huge amounts of protein, though, namely that if excessive proteins are crowding out other healthy whole foods (like nonstarchy vegetables), you could wind up deficient in phytonutrients, fiber, and healthy fats. You could also wind up with a disrupted microbiome or sluggish elimination, all of which could make you more vulnerable to a variety of chronic health conditions.

9. Are Protein Supplements Necessary, or Even a Good Idea?

If you find yourself reaching for convenience foods or if you rarely have time to cook eggs for breakfast, a protein supplement is a solid alternative.

While you shouldn’t rely solely on supplements to meet your protein needs, a protein shake or bar can be a convenient way to boost your intake and get some essential amino acids. (For more on choosing the protein powder that’s right for you, see “Pick Your Protein Powder“.)

Powders made from whey, eggs, soy, hemp, rice, and peas are the most popular types and can be blended into shakes, sprinkled over fruit or Greek yogurt, or added to recipes for a protein boost. (For a delectable, protein-powder-packed snack, check out the recipe for almond-butter protein balls at “The Hearty Vegetarian“.)

Whey protein isolate is a favorite among many experts because it digests quickly. Within 30 minutes, it delivers amino acids to your muscles, fast-tracking their repair and growth, Bailor says. Many whey powders are low in lactose, but if you need to avoid dairy altogether, consider high-quality pea, egg, or brown rice protein powders instead.

Keep in mind that protein powders, like other nutritional supplements, aren’t regulated like food. So you’ll need to do a little research and read the ingredients label. Whey comes from milk, for example, so you’ll want to be sure the milk comes from grassfed cows not treated with artificial growth hormones. If the protein comes from a plant source, you’ll want to know whether it’s organic or genetically modified. Lastly, avoid powders that contain artificial sweeteners and preservatives or are high in sugar.

Taste, of course, is subjective. So once you’ve narrowed down your choices, have fun experimenting with different powders and shake recipes.

Remember that your shake is only as good as the sum of its parts. For instance, “mixing protein powder with a soft drink is not a good idea,” says Bailor. Mixing protein powder with kale juice, unsweetened almond or coconut milk, or other healthy drinks, however, packs a double punch of protein and healthy phytonutrients.

10. Are Some Protein Sources Better for Me Than Others?

It depends on what you mean by “better.” Certain protein sources are definitely more concentrated than others. Eggs, for example, are 34 percent protein, beans are 20 percent protein, nuts are less than 20 percent protein. But each of these foods have unique nutritional strengths beyond protein — like healthy fats, fiber, and phytonutrients.

Animal sources of protein provide complete amino-acid profiles, meaning they deliver all your essential amino acids in one protein source, while plant-based proteins do not. So if you’re vegetarian or vegan, you will need to be more vigilant in making sure you’re getting enough protein and amino acids, says Heidi Skolnik, MS, CDN, FACSM, owner of Nutrition Conditioning Inc. and coauthor of Nutrient Timing for Peak Performance.

Plants also contain less concentrated protein, so you’ll have to eat more volume to get your daily requirement, and eat a wide variety of whole foods to get all your essential amino acids.

The other thing to consider is the potential toxins lurking in protein-rich foods. Consider buying organic, wild and non-GMO products that are free from artificial hormones and antibiotics (read more on the healthier fat profiles of grassfed meats below). Seek out fish lower in mercury and other heavy metals, such as salmon, tilapia, freshwater trout, catfish, sardines, and sole.

11. Does Eating a Lot of Protein Fuel Cancer?

Recent epidemiological studies do indeed suggest there may be a connection between cancer and high protein intake in midlife. “The key point is that epidemiology can only find associations, but cannot prove cause and effect,” says Dwight McKee, MD, a board-certified oncologist and hematologist who specializes in nutrition and integrative medicine.

McKee suspects the cancer association could be due to toxins that make their way into conventional meat production.

“A lot of factory-produced meats come from animals fed diets high in GMO grain and soy, which is high in omega-6 fats and low in omega-3 fats,” he says. “Omega-6 fats will fuel inflammation, and we do know that chronic inflammation provides a terrain that is permissive to malignant cell growth and spread.”

In other words, eating a large amount of low-quality meat can fuel cancerous cells or inflammation you may already have in your body. Also beware of chemical preservatives in conventional processed meats.

On the other hand, a diet rich in animal protein from free-range, pasture-fed sources (which deliver more omega-3 fats), and other whole and organic foods, is safer, says McKee.

Each individual needs to look at the whole picture — complete diet, family history, lifestyle choices, and preexisting problems.

12. Do I Really Need to Worry This Much About Protein?

Probably not. You’re better off putting your attention on the quality and balance of your eating overall.

“I think it’s very likely that a diet that brings people to a sense of well-being, good blood chemistry and lipid profiles, and optimal physical performance is one that will also keep their risk for cancer and other degenerative diseases low,” notes McKee.

“For one person, this may mean a vegan diet with no sugar or processed foods (which can be a major trap for vegans). For another, it may be a paleo-type diet, high in naturally raised, non-grain-fed, or wild-game animal protein, (which is much closer to what our hunter-gatherer ancestors ate).”

If you have specific performance, weight-loss, or health goals, it’s important to have a basic grasp of nutrition and how protein plays into it. But it’s also important to take a step back and observe how different foods make you feel. Let your body be your guide.

This article has been updated. It was originally published online on September 22, 2014.

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