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Today’s Health Upgrade

• Beyond the headline: Why does intermittent fasting appear to work so well for some people?

• Two popular supplements went head-to-head

• Dead wrong: coffee and dehydration

Beyond The Headline 
Why Does Time-Restricted Eating Appear To Work For Fat Loss?

Millions of people have tried intermittent fasting with one core assumption baked in: the eating window itself is the active ingredient. Compress your hours, the thinking goes, and your metabolism responds, independent of how much you eat. 

But the real magic isn’t in how much time you spend eating. It’s that shrinking the hours you eat reduces your likelihood of overeating.

Researchers randomly assigned women to two different 8-hour eating windows for two weeks each: one early (8 am to 4 pm) and one late (1 pm to 9 pm). Calories were kept nearly identical across both conditions, isolating meal timing as the only real variable. And adherence was strong, with participants following their protocols more than 96% of the time. 

Despite that, there wasn’t much of a difference in the health metrics that matter most, as those who practiced time-restricted eating saw no additional improvements in insulin sensitivity, blood sugar, blood lipids, or inflammation. 

The fasting group lost slightly more weight (about 1 additional pound), but this appeared to result from an unintended calorie deficit. The people who were intermittent fasting ended up eating about 200 fewer calories per day, which led to the slight improvement in weight loss, not the window itself.

The lead researchers' conclusion is fairly direct: when people follow a time-restricted eating (TRE) protocol in real life, they tend to naturally eat less. Not because of circadian biology per se, but because fewer eating hours create fewer opportunities to add calories. 

The eating window functions less like a metabolic switch and more like a structural cap on intake.

That's not a knock on the method. In fact, it's one of the better arguments for it. For many people, stopping eating at a specific time each day is easier than tracking macros or white-knuckling portion control. If the structure helps you manage intake without feeling like you're on a diet, it's working exactly as intended.

But if it doesn’t work for you, there’s good news: you don’t need to fast to lose weight or improve your health. You just need to find an effective, consistent way to cut calories.

If you’re tired of counting calories or diets that push extreme restrictions, maybe it’s time for a new approach. We can help. 

Together With Momentous
Two Popular Gym Supplements Went Head-to-Head. Here's What Researchers Found

If you've ever stood in a supplement aisle wondering whether any of this stuff actually works — and, if so, which one is worth your money — you're asking the right question. A new study put two of the more-researched options, creatine and beetroot juice, directly against each other in the gym. What they found wasn't really a winner. It was more like a division of labor.

A new head-to-head comparison found that creatine may help you perform more reps at high intensities, while beetroot juice appears to support faster bar speed, better muscle oxygenation, and improved cardiovascular efficiency during the same workout.

Researchers had participants who regularly lifted weights perform bench press and back squat sets to failure at 60%, 70%, and 80% of their one-rep max under three conditions: creatine, beetroot juice, and placebo. They measured repetitions, bar velocity, heart rate, intramuscular oxygen levels, heart rate variability, blood lactate, and perceived effort.

Creatine outperformed both beetroot juice and placebo for total repetitions at 80% of max in bench press, a meaningful advantage if grinding out quality volume at high intensities is your primary goal.

Beetroot juice showed advantages in bar speed across multiple intensities, higher muscle oxygen saturation throughout the workout, and lower heart rates during the same workload.

Both supplements outperformed the placebo in heart rate variability, a marker of how recovered your nervous system feels heading into each set.

This was a small study, so that doesn’t mean the outcomes will be the same for everyone. But with so many supplements lacking evidence of effectiveness, creatine and beetroot remain two options that consistently show positive benefits. 

These two supplements appear to work through different pathways, which means your goal should drive the choice. Prioritizing strength volume? The creatine case is well-established, and this study extends it. Care more about training efficiency and recovery quality between sessions? Beetroot juice has growing evidence supporting its use. 

And neither supplement has shown much of a risk profile or danger. 

We've been following both of these ingredients closely, and the sourcing question — which most people skip entirely — matters more than the supplement aisle suggests.

For creatine, Momentous uses a pharmaceutical-grade creatine that's been the gold standard in peer-reviewed research for over 30 years. It's the specific form used in the trials you actually want to cite, not the generic powder filling most budget tubs. Same molecule, meaningfully different standard. 

It’s also NSF Certified for Sport® — the same certification required by professional leagues — which means what's on the label is verified to be what's in the product.

APC readers get 35% off their first subscription order or 14% off a one-time purchase if you'd rather try before you commit. Just use the code “PUMPCLUB” at checkout. 

If you want a beetroot product, don’t just accept anything. If your beetroot supplement just says "500mg beetroot extract," you have no idea what you're actually getting. 

Studies testing dozens of beetroot supplements found that most deliver far less nitrate than fresh beetroot, and nearly two-thirds failed basic labeling requirements. 

The active ingredient driving beetroot's cardiovascular benefits is nitrate, and research suggests you need at least 400 mg per serving to meaningfully improve blood vessel function, so look for products that list nitrate content in milligrams and carry third-party testing verification like NSF or Informed Sport.

Dead Wrong 
You Don't Need to Chase Your Coffee With Water

We bust myths. But sometimes, you don’t even realize when you’ve bought into something that’s not true. In “Dead Wrong,” we take the things you think are accurate and provide an updated perspective on what the latest science has found.

From our readers: Is the guidance on coffee and hydration wrong? My diet guru tells me coffee always has such a strong negative effect on hydration that I need to drink a cup of water for every cup of coffee just to stay even. What does the science say?

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The idea that coffee dehydrates you is one of the stickiest myths in nutrition, and the actual research tells a more interesting story.

Coffee counts toward your daily fluid intake, and unless you're drinking more than 300 mg of caffeine in one sitting (roughly three 8-ounce cups of brewed coffee or two large coffeehouse drinks), it won't meaningfully increase how often you visit the bathroom.

A meta-analysis of 16 studies found that even when caffeine nudged urine output up, the average difference was so slight that it wasn’t a risk for dehydration. Not to mention, the effect disappeared completely during exercise.

A separate trial used total body water measurement, the gold standard, to examine how habitual coffee drinkers respond to four cups of coffee compared to four cups of water.

Despite what you might think, there was no difference in hydration status in coffee drinkers consuming four cups a day compared to the same volume of water for three days. 

Your body adapts to caffeine's diuretic effect within days, which is why people who drink coffee daily rarely notice anything. If you've been off caffeine for a week or more and then return to it, your response will be stronger for a few days before fading back. 

Sex differences also play a smaller role: women tend to metabolize caffeine more slowly than men. The effect isn’t significant, but it is real, and helps explain why two people can drink the same coffee and feel different things.

For your sake, unless you’re taking down 4 to 5 cups in one sitting, your morning cup is hydrating you, not depleting you. 

There might be other reasons to drink less coffee, such as headaches, stomach issues, or dependency. But hydration does not appear to be much of a concern. 

Drink water when you're thirsty, drink coffee because you like it, and stop counting them as opposites. If you're new to caffeine or regularly going past three cups in one sitting, expect a few extra trips to the bathroom, but not dehydration

The Positive Corner of The Internet
About Arnold’s Pump Club Editorial Standards

We do things a bit differently here, starting with transparency.

1. 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).

2. 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.

3. 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