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Today’s Health Upgrade
Let’s talk about “Peakspan”
How to absorb fewer calories
Why last week’s meal could influence this week’s hunger
Ask this question, live a happier life (the 85-year study)
Health
Do You Want To Live Longer Or Live Better?
For most of us, "healthy" means no diagnosis. No prescription. Nothing serious is showing up on a blood panel. But some researchers argue that's a pretty low bar, and that we should change how we approach health.
A new study proposes that meaningful functional decline in strength, cardiovascular fitness, immune response, and cognitive processing begins well before your first medical concern, often while you're still technically healthy by every conventional measure.
The researchers introduce a concept called “Peakspan,” or the window during which a person maintains at least 90% of their peak function in a given physiological or cognitive domain.
Drawing on existing data, the researchers estimate that most of those windows start to close earlier than people expect.
For example, scientists say that data suggests “fluid intelligence” peaks between 20 and 30, and cardiovascular fitness peaks in the early-to-mid 20s.
Their model suggests that Immune function declines even more rapidly, to roughly 20% of adolescent levels by age 25. Not everything declines earlier, though. Crystallized intelligence (wisdom, vocabulary, judgment) continues rising through the mid-50s and can remain near peak levels into your 70s.
More importantly, the declines are not inevitable. When decline starts (and how steep it gets) is shaped less by the number on your birthday cake than by the habits you carry into each decade.
Based on prior research, the interventions that raise your peak and slow the decline aren't complicated.
Resistance training slows the loss of muscle and cardiovascular capacity. Quality sleep protects cognitive function. Consistent movement keeps the immune system more resilient longer.
It’s worth mentioning that this is a conceptual framework paper, not an intervention study. The 90% boundary is not a hard biological line. Draw it at 80%, and Peakspans get longer, but the core insight remains the same.
The goal isn't to reverse time; it's to stay closer to your best for longer.
Together With Momentous
The Food That Helps You Absorb Fewer Calories
If you've ever felt like calorie counting doesn't quite add up, you might be onto something.
Research suggests that eating more fiber can reduce the number of calories your body absorbs.
In a tightly controlled study, researchers fed participants two different diets with identical calories and macronutrient ratios. The only difference? One diet emphasized fiber-rich foods while the other mimicked a typical Western diet.
On the high-fiber diet, participants lost an average of 116 extra calories per day.
But here's what caught our attention: some individuals who ate more fiber showed a difference of nearly 400 calories daily. Same food intake, dramatically different absorption.
That’s because fiber feeds the good bacteria in your gut, and some calories end up fueling them instead of you.
What makes this even more interesting: hunger and satiety scores didn't change between the two diets. The people eating the high-fiber, whole-food diet were absorbing fewer calories without feeling hungrier.
And here’s why you should care: studies show that most people eat only about half of the recommended fiber intake per day. And 95% of people don’t get the recommended amount of fiber. If you can sneak more fiber into your diet, then you can experience the benefits.
To get started, prioritize high-fiber foods such as vegetables, fruits (especially berries), legumes, nuts, seeds, and whole grains.
If you struggle to eat enough of the foods listed above and need help getting more fiber, that’s why we developed Fiber+ with Momentous.
We invested two years developing a formula that makes a real difference in gut health: 3 sources of fiber, 6 grams per serving, a mix of soluble, insoluble, and resistant starch. Everything you need to feed your healthy bacteria without bloating or stomach discomfort. It’s the first product ever developed by the Pump Club, and has Arnold’s seal of approval.
As an APC reader, get 35% off your first purchase subscription or 14% off a one-time order. Unlike many supplements, Fiber+ is backed by research, and you will notice a difference within the first week.
If you’re keeping score, aim for at least 25 grams of fiber per day and work up to about 35 to 40 grams daily.
Instant Health Boost
Can Five Days of Junk Food Change Your Brain?
You tell yourself a long weekend of indulgence won't matter. The scale doesn't move, your energy seems fine, and by Monday, you're back to eating normally. No harm done, right?
But researchers discovered that just five days of overeating ultra-processed food may alter how your brain responds to hunger and food cues, even after your diet returns to normal. And the changes can linger even after you stop.
Researchers had one group of participants eat roughly 1,200 extra calories per day for five days, mostly from sugary, fatty, ultra-processed snacks. On the other hand, a control group followed their usual diet. On the surface, the overeating group looked fine. No meaningful weight gain. No changes in cravings, blood sugar, or inflammatory markers. But underneath, something had shifted.
Seven days after both groups returned to their regular diets, brain imaging in the overeating group revealed significantly lower insulin responsiveness in two brain regions tied to memory, learning, and how your brain processes food cues.
The high-calorie group also showed increased liver fat accumulation, another early warning sign that tends to precede more significant metabolic disruption.
The researchers believe the brain adapts to short-term overeating faster than the body does. It’s possible that when you flood your system with ultra-processed food, the reward and learning circuits shift, making it harder for your brain to accurately read satiety signals and respond to food-related feedback.
Think of it like recalibrating a thermostat: the settings change even when the room temperature looks the same from the outside.
Because these are the regions involved in food-seeking behavior and habit formation, the concern isn't just about one bad week. It's about what that week makes the next one look like, and how it affects your hunger and appetite.
As with most studies on ultra-processed food, it’s important not to think in black and white. The research doesn't mean that all ultra-processed food is bad, or that enjoying a few days of vacation eating will permanently derail your health.
But it does reframe what consistent overeating and overconsumption of ultra-processed foods can do to your brain and your eating habits.
Mindset
The Question That Can Help You Live A Happier Life
Somewhere around 40 or 45, many people hit a wall that has nothing to do with their knees. Everything looks fine on paper — career, family, health — but something feels flat. Research from Harvard might explain why.
The happiest people in their 40s, 50s, and 60s weren't the most successful or wealthy. They were the ones who shifted from asking "What can I get?" to "Who can I help grow?"
Researchers tracked participants from adolescence through old age, and a clear pattern emerged at midlife. Those who turned their energy toward contribution (mentoring, parenting, teaching, investing in community) reported higher life satisfaction, stronger relationships, and better health outcomes that persisted into their 80s.
The contrast in the data shows how much mindset can influence happiness. One participant, a Harvard-educated lawyer with wealth and connections, was identified as one of the unhappiest men in the study's 85-year history. Another, a high school art teacher with modest income but deep relationships and community investment, was among the happiest and stayed healthy well into old age.
When participants in their 80s looked back on their lives, the workaholics who'd ignored relationships were, in the study director's words, "Some of the saddest folks in our study, and were filled with regret."
Once basic financial needs are met, additional income doesn't meaningfully increase happiness. But real engagement — putting energy into something beyond yourself — does.
If you want to activate more happiness in your life, ask yourself: Who am I helping grow? (Editor’s note: It’s honestly why the APC newsletter and The Pump Club app are the most fulfilling work of our lives.)
It could be a coworker two steps behind you, a kid learning something new, or a neighbor who could use 10 minutes of your attention. The study says that investment pays compound interest on your own health for decades.
Better Today
Take any of these tips from today’s email and put them into action:
1. Science Suggests Your Body Starts Declining in Your 20s. New Research Shows Exactly How to Slow It.
A new research framework called "Peakspan" defines the window in which a person maintains at least 90% of their peak function. It estimates that immune function drops to roughly 20% of adolescent levels by age 25, while cardiovascular fitness and fluid intelligence peak in the early-to-mid 20s. That sounds like a fixed sentence, but the researchers are clear: it isn't. The timeline of decline is shaped less by age than by the habits carried into each decade — resistance training, quality sleep, and consistent movement all demonstrably raise the peak and slow the rate of fall. The 90% threshold is a definitional choice; the behaviors that push it further out are not arbitrary at all.
2. A Controlled Study Found High-Fiber Diets Helped Some People Absorb 400 Fewer Calories Daily
In a tightly controlled study where participants ate diets with identical calories and macronutrient ratios — differing only in fiber content — those on the high-fiber diet lost an average of 116 calories per day through stool, with some individuals showing a difference of nearly 400 calories daily on the same total food intake. The mechanism is direct: fiber feeds gut bacteria, and some of the calories end up fueling the microbiome rather than being absorbed by the body. What makes this practically significant is that hunger and satiety scores didn't change between the two diets — meaning the calorie reduction happened passively, without the compensation that typically undermines dietary interventions. Most people currently eat roughly half the recommended daily fiber intake; closing that gap with vegetables, legumes, berries, nuts, and whole grains is one of the few nutrition moves where the research, the mechanism, and the real-world experience all point in the same direction. If you struggle to eat fiber-loaded foods, Fiber+ is a research-based supplement to help close your fiber gap.
3. Brain Scans Found Metabolic Changes After Five Days of Overeating (Even Though the Scale Didn't Move)
A study in which participants ate roughly 1,200 extra calories per day for five days — primarily from ultra-processed foods — found significantly lower insulin responsiveness in two brain regions tied to memory, learning, and hunger signaling. Interestingly, the changes were detectable by brain imaging a full week after participants returned to normal eating. On the surface, the overeating group looked fine: no meaningful weight gain, no changes in reported cravings, blood sugar, or inflammatory markers. But the researchers believe the brain's reward and learning circuits adapt to short-term junk food exposure faster than the body does — meaning a long weekend of overeating may be quietly reshaping how your brain reads hunger signals before anything shows up where you'd think to look.
4. Harvard's 85-Year Study Found the Midlife Mindset Shift That Predicts Happiness and Health Into Your 80s
Harvard's Study of Adult Development tracked participants for 85 years from adolescence through old age. It found that people who reached midlife and turned their energy toward contribution (mentoring, parenting, teaching, community investment) reported higher life satisfaction, stronger relationships, and better health outcomes that held into their 80s. The data produced a striking contrast: a Harvard-educated lawyer with wealth and connections was identified as one of the unhappiest men in the study's history, while a high school art teacher with modest income but deep relationships ranked among the happiest and stayed healthy well into old age. Once basic financial needs are met, more income doesn't meaningfully increase happiness — but actively investing in someone else's growth does, and the health returns on that investment compound for decades.
The Positive Corner of The Internet
About Arnold’s Pump Club Editorial Standards
We do things a bit differently here, starting with transparency.
The Content: All APC emails are researched, written, and fact-checked by the APC editors (see bottom of the email), with written contributions from Arnold (noted with “Arnold’s Corner”). Links take you to original studies (not second-hand sources).
Does AI play a role? Not for the primary content, but it is used in two ways. The main items are original content written by the APC team. The summaries at the end are AI-generated based on the human-written content above. We also use an AI tool to review our interpretations of the research and ensure scientific accuracy. We don’t assume AI is right, but we use technology to hold ourselves accountable.
Yes, we have partners (all clearly noted). Why? Because it allows us to keep the APC emails free. We first test products, and then reach out to potential partners who offer ways to help you improve every day. The bar is set high, and to date, we have turned down millions in ad deals. (Example: we will not partner with any non-certified supplements or those without evidence in human trials). If we won’t buy the product, we won’t recommend it to you. And if there’s no evidence it works, then there’s no place for it here.
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Publisher: Arnold Schwarzenegger
Editors-in-chief: Adam Bornstein and Daniel Ketchell
