Three Things You Probably Don’t Know About Protein

In this follow-up to The Protein Pendulum, we dive into a few little known facts about how protein works and why you need more of it at midlife.

Last week in The Protein Pendulum, we saw the crucial macronutrient go from Victorian obsession to wartime ration to low-fat-era afterthought. Now the science has caught up, and unsurprisingly, it turns out the truth is more nuanced than any of those swings suggested.

Three things in particular matter more than most people realize:

• Not all protein is the same,

• Our muscles get more difficult to feed as we age, and

• Scientific debate over protein took a detour through longevity research that nearly led us off another cliff.

Understanding all three will change how you think about what’s on your plate.

You Can’t Just Go By What’s on the Label

Not all protein is created equal. Let’s ignore the tribalism that surrounds this topic and talk solely about the science:

Plant proteins are significantly less bioavailable than animal proteins.

Bioavailability basically means, “How much of this protein can your body actually use?” In short, animal proteins — meat, eggs, dairy, seafood — are about 93% digestible, meaning your body can break them down and use nearly all of the protein in them. Plant proteins in their whole-food form are around 80% digestible, and that’s being generous, because grains and nuts are often closer to 70%.

Why the discrepancy?

There are 20 amino acids your body requires and only 11 that it makes itself. The remaining nine are called essential amino acids (EAAs), and they’re called essential because you must get them through your diet.

Your body needs all nine EAAs in adequate amounts to build muscle. If you’re short on even one, the whole assembly line stalls. Plant proteins often lack or are low in certain EAAs. For instance, grains are typically low in lysine, legumes in methionine and cysteine.

And plants also contain what scientists politely call “antinutritional factors,” compounds like lectins, trypsin inhibitors, and phytates that actively interfere with protein digestion and absorption. These are the plant’s natural defense mechanisms. Animals run from predators; plants deploy biochemistry.

Effective for their survival, less great for you.

Humans have traditionally worked around this through soaking, cooking, and fermenting. Modern protein isolation also helps: this is why soy protein isolate is more bioavailable than whole soybeans, and why pea or rice protein powders can approach the digestibility of animal proteins.

But your handful of trail mix or smear of almond butter? Not even close to what the nutrition label suggests you’re getting.

The Leucine Factor

Here’s where we need to talk about an important subset of EAAs called branched-chain amino acids (BCAAs). Of the nine essential amino acids, three have a branched molecular structure: leucine, isoleucine, and valine. And leucine is the prime ignition switch for muscle protein synthesis.

Leucine activates something called the mTOR (short for “mechanistic target of rapamycin”) pathway — think of it as your body’s muscle-building control switch. When leucine levels hit a certain threshold in your bloodstream, mTOR fires up and signals your muscles to start synthesizing new protein. The simple equation is mTOR on = muscles building.

Without sufficient leucine, it doesn’t matter how much total protein you eat; you’re not effectively triggering the cascade that builds and maintains muscle.

Animal proteins are leucine-rich and protein-dense. A four-ounce serving of chicken delivers about 2.5 grams of leucine and clears the mTOR trigger at around 185 calories.

Plant proteins tell a different story. A cup of lentils, already a substantial serving at 230 calories, gets you to only 1.3 grams of leucine, roughly half the threshold. To actually hit 2.5 grams from lentils alone, you’d need close to two cups at nearly 460 calories. Peanut butter is worse: At 0.5 grams of leucine per two tablespoons, you’d need nearly ten tablespoons — about 950 calories — in one meal.

So Why Not Just Supplement It?

This is why the supplement industry has built a multi-million-dollar empire around BCAA powders. People figured out that leucine matters, so why not just take leucine?

I’ll tell you why.

Because taking BCAAs or leucine by itself is useless for building muscle. You need all nine essential amino acids present together, in the right ratios, for muscle protein synthesis to actually happen. Leucine may be the ignition key, but you still need all the other amino acids to fuel the car.

Taking isolated BCAAs doesn’t do that. In fact, some research suggests it might actually make things worse — triggering muscle protein breakdown to scavenge the other amino acids needed for synthesis.

The Protein Tax

One more thing the label doesn’t tell you: Protein is the most metabolically expensive macronutrient to process. Your body burns 20–30% of protein’s calories just digesting, absorbing, and converting it, compared to 5–10% for carbohydrates and a mere 0–3% for fat. Eat 100 calories of protein, and your body immediately spends 25 of those calories just dealing with it.

This is called the thermic effect of food. Your body resists burning protein for energy because protein is primarily a building material, not fuel. Think enzymes, hormones, antibodies, muscle tissue, collagen. These are jobs only amino acids can do. The metabolic inefficiency is your body’s way of protecting a precious resource.

And, bonus!, it also means higher-protein diets carry a built-in caloric discount — which is one reason they consistently outperform lower-protein diets for body composition, even when total calories are matched.

Why Older Muscles Get “Hard of Hearing”

If you’re over 40, we need to have a conversation about what’s happening behind the scenes with your muscles. It’s called anabolic resistance, and it’s one of the primary reasons we lose muscle mass as we age — a phenomenon so common it has a name: age-related sarcopenia.

Here’s how muscle protein synthesis normally works: You eat protein. Your blood amino acid levels rise. This triggers the mTOR pathway we talked about earlier. Your muscles receive that signal and ramp up protein synthesis for a few hours.

Young, healthy muscles are exquisitely sensitive to this signal. Feed them even modest amounts of protein — say, 20 grams — and they respond robustly. You remember those days, right?

But somewhere around your 40s, this system (like everything else, it seems) starts to break down. Your muscles become resistant to the anabolic (muscle-building) signals from protein intake. It’s not that they can’t respond; it’s that they require a much stronger signal to get the same response.

And just how much might shock you. Research shows that to achieve the same muscle protein synthesis response, older adults need about 68% more protein per meal than younger adults.

Where a 25-year-old might max out their muscle-building response with 20–25 grams of high-quality protein, a 65-year-old needs closer to 40 grams to hit the same peak. And even then, the peak might not be quite as high, and it doesn’t last as long.

What Causes Anabolic Resistance?

Researchers aren’t entirely sure, but several factors seem to play a role:

• Chronic low-grade inflammation, which increases with age (researchers call it “inflammaging”), interferes with the signaling pathways that control protein synthesis. Your muscles are trying to build, but inflammatory signals are jamming the communication.

• Your gut and liver start hoarding amino acids as you age, extracting more of them before they can reach your muscles — like your digestive system has become a greedy toll collector.

• Insulin resistance means your muscles become less responsive to insulin, which doesn’t just affect blood sugar. It also affects how well amino acids are delivered to muscle tissue.

• Inactivity. Studies show that even young adults develop anabolic resistance after just 10 days of muscle disuse. Each bout of inactivity makes the problem worse — which might explain a lot about the aging trajectory for most people.

Muscle: The Organ of Longevity

Failure to give both the signal and the fuel to grow is what causes muscle loss. And the loss is insidious. You don’t wake up one day and notice you’ve lost 20 pounds of muscle.

Instead, you lose about 8% of your muscle mass per decade after 40, accelerating to 15% per decade after 70. It’s so gradual that you adjust to it, compensate for it, until one day you realize you can’t open the pickle jar.

Muscle loss isn’t just cosmetic or even only about strength. Muscle is metabolically active tissue — your body’s largest site for glucose disposal, crucial for metabolic health. Less muscle means worse blood sugar control, more insulin resistance, and a higher risk of diabetes.

Muscle also serves as a protein reserve during illness; when you’re sick or injured, your body cannibalizes muscle to get amino acids for healing and immune function. Less muscle means less reserve capacity to handle health crises.

And the mortality data are unambiguous: Muscle mass predicts longevity. Low muscle mass in older adults is associated with higher all-cause mortality. Stated another way, the muscle mass you have in your 60s and 70s is directly related to how long you’ll live and how well you’ll live those years.

Can You Fight Back?

The good news is that anabolic resistance isn’t completely inevitable. Two things can fight it:

Higher protein intake. You can overcome your muscles’ resistance by hitting them with a stronger signal: 30–40 gram servings instead of the 15–20 grams that might have sufficed when you were younger. And it needs to be a high-quality, leucine-rich protein to maximally trigger the mTOR pathway.

Resistance training. Nothing (and I mean nothing) overcomes anabolic resistance like lifting heavy things. Resistance exercise doesn’t just build muscle through mechanical stress; it also makes your muscles more sensitive to the anabolic signal from protein for at least 24–48 hours afterward. It’s like turning up the volume on your muscles’ ability to hear the protein signal.

The combination is synergistic. Resistance training plus adequate protein intake can maintain, and even build, muscle mass in older adults at rates that approach what younger people achieve. But muscle growth only happens when your body has both a reason to build and the materials to do it. That’s why training and sufficient protein intake go hand in hand.

Even the Smartest People in the Room Got It Wrong

For the past decade or so, a faction of the wellness world has been quietly terrified of protein. The reasoning centered on mTOR. If mTOR drives cellular growth, and uncontrolled growth is associated with cancer and accelerated aging, and protein is one of the most potent mTOR activators… then the conclusion seemed obvious: Eat less protein, suppress mTOR, live longer.

Harvard’s David Sinclair became one of the most visible advocates of this approach. He went vegetarian. He restricted protein. In interviews, he’d point to mouse studies showing that chronically suppressing mTOR extended lifespan and applied the same logic to humans. The biohacking podcosphere amplified that viewpoint enthusiastically.

The problem was that those mice lived in highly controlled lab environments. They weren’t cold, they weren’t running from predators, they weren’t having sex, and they weren’t doing anything that required muscle. Later studies in primates showed mixed results at best.

And in humans? There is zero evidence that chronically suppressing mTOR through protein restriction extends lifespan. Zero.

There’s also a rather glaring flaw in the anti-protein mTOR logic that metabolic researcher Dr. Ben Bikman has pointed out: Insulin activates mTOR at least as much as leucine does, and possibly more. So if you’re worried about mTOR and you’re cutting protein, what are you eating instead?

Unless you’re going full dietary fat, you’re eating carbohydrates. And carbohydrates spike insulin. Amino acids from a protein-rich meal clear your bloodstream in about 45 minutes. Insulin from a high-carb meal can stay elevated for hours. If mTOR suppression is actually your goal, a bagel is objectively worse than a ribeye.

Even Sinclair has since acknowledged the nuance: His 80-year-old father eats protein and lifts weights three days a week. Sinclair now talks about “cycling” mTOR — on after meals and training, off during fasting and sleep — rather than keeping it suppressed around the clock. Which is, conveniently, exactly what happens when you eat adequate protein, do resistance training, and don’t graze constantly.

The mTOR panic was a classic case of extrapolating too far from animal models and forgetting to ask the most important question: Longevity for what? To sit still and barely eat?

The goal isn’t to be a frail, protein-deprived centenarian who made it to 100 but spent the last 20 years unable to get out of a chair. The goal is healthspan, which means living independently, functionally, and vigorously for as long as possible.

And for that, you need muscle.

This Isn’t Hype Train 2.0

If the OG protein hype train crashed and burned, and we’ve been undereating protein for 80 years, how do we know we’re not just overcorrecting again? Is the current protein craze just the new version of putting “fat-free” on gummy bears in the ’90s?

Look, I’m as skeptical as you are. We grew up watching corporations turn every nutritional factoid into a marketing bonanza. Remember when Sunny D pretended to be orange juice? When we were told Snackwell’s cookies were healthy because they were low-fat?

You might have noticed that the global wellness-industrial complex has absolutely jumped on the protein bandwagon. Walk through any grocery store, and you’ll find protein chips, protein ice cream, protein pasta, and protein coffee creamer. There’s even protein water and protein Pop-Tarts.

Let that last one sink in.

Here’s what makes this current trend different: The underlying science is actually solid. It isn’t based on one cherry-picked study or a diet messiah’s podcast. Multiple independent research teams using different methodologies across different populations all arrive at the same conclusion: We need more protein than the 1940s wartime rations suggested, and we need even more as we age.

That doesn’t mean every protein-fortified product is worth your money. Most of it is overpriced nonsense designed to separate you from your cash while you feel virtuous about “optimizing your nutrition.”

The difference between good science and marketing? Good science gives you actionable information about actual food. Marketing tries to sell you $8 protein water when you could just eat an egg.

But the core message that says protein intake matters more than we thought, particularly for maintaining muscle mass as we age, is legit. Eighty years of getting it wrong is long enough.

So here’s the TL;DR for last week and today:

• The RDA is way too low: 0.8 g/kg was designed in 1941 to prevent wartime malnutrition, but middle-aged you is not trying to barely survive. You’re trying to thrive, dammit! by maintaining muscle, metabolic health, and independence as you age.

• How much do we need: The Goldilocks range is 1.2–1.6 grams per kilogram (0.54–0.73 g/lb) of ideal body weight daily. Over 50 or very active? Aim for the high end. That’s roughly 80–110 grams for a 150-pound person, 100–130 grams for 180 pounds.

• When do we need it: Spread it across three meals, about 30–40 grams each. This keeps muscle protein synthesis running throughout the day and works against anabolic resistance as you age.

• What kind: Get your MEDS: meat, eggs, dairy, seafood. Each meal should hit roughly 2.5–3 grams of leucine to trigger mTOR (about 4 ounces of meat, 3 large eggs, or 1.5 cups Greek yogurt). Eat the protein first in each meal for maximum satiety. Plant-based? Aim for 1.6–2.0 g/kg, combine sources for bioavailability, prioritize soy and legumes, and consider a protein powder to close the gap.

• What to skip: Protein water. Protein chips. Protein-fortified cereal. Any overpriced wellness product with “protein” on the label. Just eat actual food whenever you can.

• One more thing: Lift heavy things 2–3 times per week. Protein without resistance training is like buying lumber and never building the house.

Keep going-

Samantha (and Brian)

further: flashback

🎶 Prince and the Revolution - Mountains, Parade, 1986 🎶

Everyone loves Kiss from Prince’s final album with The Revolution, but second single Mountains is brilliant as well. Yes, that’s Jerome from The Time in the video, who was Prince’s sidekick in Under the Cherry Moon. (YouTube)

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