Skip the Politics. Argue about Protein.

If you want to avoid political disputes this 4th of July weekend, here’s a conversation starter: What’s the healthiest source of protein?

For instance, if you eat 50 grams of protein tomorrow, should it come from animal products (meat, fish, dairy, etc.), plants (vegetables, grains, nuts, etc.), or supplements (powders, bars, shakes, etc.)?

This is not exactly the hottest question of the day. We’re in the midst of a protein craze, and many Americans are asking instead: How can I get more?

Really, how can you not get more? Protein is being crammed into all sorts of edible products, including the very poster children of ultraprocessed foods.

Our obsession with protein shows no signs of diminishing. According to an April analysis, the U.S. is projected to drive nearly one third of the growth in the global high protein food market over the next four years. But do we really need to be eating more?

Experts agree that most Americans get enough protein, though older adults, dieters, and other groups may be deficient to some extent.

In other words, for most of us, quality rather than quantity should be the main concern.

So, what are the “healthiest” sources of protein?

The answer depends on your priorities. If you care most about reducing disease risk, eggs, for instance, are healthier than bacon. (One large egg or two strips of bacon provide roughly 6 grams of protein, but bacon has more saturated fat and sodium per calorie, and cooking it releases compounds that may be carcinogenic.)

My focus this week is on a different aspect of healthiness: Muscle building. This process, known as muscle protein synthesis, is critical for maintaining strength and physical functioning throughout life. The topic is important for everyone, not just athletes.

I’ll be discussing a new study on which source of protein best promotes MPS. It’s an intriguing study, even though financial conflicts of interest seem to have biased the conclusions.

The new study

This study will appear in the August issue of The American Journal of Clinical Nutrition but is available online now.

First author Žan Zupančič, senior author Nicholas Burd, and colleagues at University of Illinois Urbana-Champaign examined muscle protein synthesis following the consumption of 20 grams of protein. The protein sources were plants (black beans and rice) and a supplement (a protein drink). Separate analyses included an animal source (ground pork) for comparison.

Here’s a key detail: The amino acid composition of the protein sources was identical. So were the calories (548), carbs, fats, and fibers. This allowed the researchers to isolate the effects of source.

(Amino acids are the molecules in protein that your body uses to build muscle. Each protein source in this study was “complete”, in the sense of providing all nine essential amino acids that can only be obtained from food.)

The participants were 11 healthy adults (mostly males in their 20s) who came to the lab, exercised, and then consumed protein. If you’re curious, my Appendix includes details on the exercise protocol, the measurement of muscle protein synthesis and other variables, and the crossover design that was used.

Key findings

1. The extent of muscle protein synthesis (MPS) did not differ across the plant vs. supplement conditions.

You might be tempted to say that the protein drink built muscle just as well as the beans and rice did. Actually, neither source was very effective.

The researchers imported comparison data from a 2025 experiment of theirs, run under the same conditions, and found that neither the beans and rice nor the protein drink spurred more MPS than carb-only drinks did.

In other words, MPS gains in this study probably resulted from the exercise, not the protein.

2. Muscle protein synthesis was greater for meat than for the plant and supplement conditions.

Data from the 2025 experiment showed nearly twice the amount of MPS for 20 grams of ground pork.

For many nutritionists and other experts, the main findings may seem like bad or at least puzzling news. The implication is that for a given amount of protein, (a) meat builds muscle better than plant sources do, (b) plant sources are no better than protein supplements, and (c) neither plant sources nor supplements outperform pure carbs.

Don’t add another hot dog to the grill just yet. We need a closer look at the data.

Porcine bias

Meat may have been the winner in this experiment, but it wasn’t a fair competition.

1. As the researchers themselves note, whole plant foods can create as much MPS as animal proteins do. But this is found for larger amounts of protein (e.g., 30 to 40 grams).

The implication is that this study’s 20-gram comparison is misleading, as it makes plants (and supplements) look like inferior protein sources. Folks who eat little or no meat would just need to consume more protein with their meals to obtain the same extent of MPS.

2. The data on meat (i.e., ground pork) came from a separate study. Although the methods were identical, the samples were not, nor were the amino acid profiles of the pork the same as for the other two protein sources (though 20 grams was consumed in each case). The pork also had about one-quarter the calories, and zero carbs.

Why import the pork data when it doesn’t provide a good basis for comparison?

Here’s a clue: Senior author Nicholas Burd (NAB) receives funding from the National Pork Board, a USDA-sponsored organization that promotes pork as a food product, among other things. (As you might guess, their website is https://pork.org.) The study was also funded by the Pork Board’s Pork Checkoff program.

To be fair, a similar research team, also led by Dr. Burd, published a 2025 study showing no difference in MPS between meat- and vegan-sourced protein. This is an important nuance. Although the new study seems to reflect conflict of interest, the researchers haven’t favored meat in everything they publish.

Takeaway and practical implications

Burd and colleagues created a narrow set of conditions under which animal protein built muscle more effectively than protein from plants or supplements did.

This would matter a lot if your meal choices were exclusively pork, exclusively beans and rice, or a single protein drink. Fortunately, most us rarely if ever eat that way.

My original question was whether your protein should come from animal, plant, or supplement sources.

From the perspective of muscle-building – an admittedly narrow take on the question – let’s assume your next meal provides a complete protein (i.e., it contains all nine amino acids). To trigger muscle protein synthesis, the meal would just need to include 2 to 3 grams of one particular amino acid called leucine.

To give you a concrete sense of what that means, here, from a USDA database, are examples of foods that, by themselves, provide roughly that much leucine:

The tofu, animal sources, and whey and soy supplements provide complete proteins. Others would require additional food for “completeness”. (This isn’t difficult. I don’t know anyone whose entire dinner would consist of a plate of beans.)

Long story short, MPS can be sustained by a variety of protein sources. If your diet is heavily or exclusively reliant on plants, you just need a bit more protein compared to more carnivorous types.

Choosing a protein source should reflect other considerations as well, including nutrient content, chronic disease risk, environmental sustainability, affordability, and personal needs.

For instance, Protein Pop-Tarts, washed down with a protein soda, would be an unhealthy meal, regardless of amino acid content. Per calorie you’d be getting too much sugar and other additives. Plus the Pop-Tarts are fairly high in saturated fat and low in fiber.

More broadly, red and processed meats, as well as most ultraprocessed foods, should be avoided or minimally consumed in order to reduce the risk of cardiovascular disease and other health problems.

Do I practice what I preach? Sort of. I eat a mostly vegetarian diet, including lots of low-fat yogurt, nuts, legumes, and rice. I aim for fish once per week. I use protein powders, though I assume that whole foods tend to be healthier. I try to avoid ultraprocessed foods but often fail. (It’s 97 degrees in my city right now. How could I say no to ice cream?)

I also try not to stress about food choices. You don’t want the perfect to be the enemy of the good. So, I would add one more sentence to Michael Pollan’s famous nutritional advice: Eat food. Mostly plants. Not too much. And try to relax.

Thanks for reading!

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Appendix: More on methods

Participants in the new study were asked to do exercises (leg presses and leg extensions) using weight machines in the lab. Prior to the experiment, the researchers determined the maximum weight each person could lift 10 times. Once the actual experiment got underway, each participant completed four sets of 10 repetitions at a weight equal to 90% of their maximum.

Each participant was then hooked up to an IV that delivered a specially modified amino acid. This amino acid served as a tracer. After each participant exercised and consumed protein, their bodies incorporated the modified amino into newly synthesized muscle protein. The extent of incorporation indicates how much MPS was occurring.

To measure MPS, tiny biopsies of leg muscle were obtained before exercise and then 5 hours later. Blood samples were also obtained multiple times during that 5-hour period. (Participants experienced a lot of poking!)

Each individual participated in the experiment twice. During one visit to the lab, they consumed one protein source. One week later they returned and consumed the other one. The procedure was otherwise identical on each occasion.

This is called a cross-over design; it makes the experiment stronger because each participant serves as their own comparison group, thereby filtering out some of the individual differences that might influence the results.