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The Science
Fasting & metabolic health
Most foods end a fast. Here's the science behind the bar that doesn't.
Fasting research has a precise answer for what ends a fast, and calories are only part of it, because the body responds to the signals food sends. This article explains how 25+ years of fasting mimicking research produced a nut-based bar formulated to stay under the body's nutrient-sensing thresholds.
By the Prolon Science Team
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August 2026
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7 min read
The Prolon Fasting Bar: formulated to deliver nourishment without triggering the biological pathways that break a fast.
The hunger usually hits somewhere past hour 12. The fast started easily enough the night before, but by late morning energy dips and a small snack starts to look harmless: a handful of granola, or a protein bar. Something that small seems like it shouldn't count — but it does. And it breaks your fast.
Most fasters take that last part on faith. Nothing visible changes when a fast ends, and there is nothing you can feel. So it's worth asking the question precisely: what actually breaks a fast? The answer is specific enough that a research team spent years formulating a bar around it.
What actually breaks a fast
The body doesn't respond to food based on calories alone. It responds to signals. When you eat, cellular nutrient-sensing pathways switch on. The research behind the Prolon Fasting Bar names three of them: RAS, PKA, and mTOR.1 When those pathways activate, they tell the body that nutrients are abundant, and the body shifts into a "fed" state focused on growth and storage.
During fasting, those same pathways quiet down. The body shifts into a different mode, prioritizing fat utilization, cellular cleanup processes, and metabolic reset. 1 That fasting, fat-burning state is the reason people fast in the first place. It's also what a typical snack, even a small one, interrupts.
For comparison · Illustrative only
What a typical snack does to a fast
A conceptual illustration for visual comparison only, not plotted study data: a typical snack sends glucose up and the fed-state response follows, while ketones fall out of the fasting range. The Fasting Bar's measured curves are in Figure 1 below.
The mechanism in one sentence
Snack bars trigger the body's "fed" response; the Fasting Bar stays below nutrient-sensing pathways so the body still thinks it's fasting.
A fasting state is preserved not by the absence of calories but by staying below the thresholds at which the body's nutrient sensing flips from fasting to fed. The bar, even though it has calories, is formulated to stay under them.
The test: put the bar up against water
There's a direct way to test whether a food breaks a fast, and it's the one the researchers used: compare it with the strictest control available, drinking only water. In a randomized controlled study, the Fasting Bar had comparable effects on blood glucose and ketone levels as a water-only fast, meaning it didn't disrupt the fasting state. 1
The study tracked two curves. Glucose stays stable, with no glucose spike. And ketones, the marker of a fasting, fat-burning state, keep climbing the way they do when nothing is eaten at all.
Figure 1 · Randomized controlled study
The Fasting Bar against a water-only fast, over four hours
Redrawn from Prolon's summary graphic of the randomized controlled study comparing the Fasting Bar with a water-only fast. Curve shapes are illustrative of the reported result; see sources below.1
That study is the main evidence behind the product. The bar is low glycemic index and clinically shown to not increase blood sugar, and it was tested in a randomized controlled study and patented to keep the body in a physiological fasting state. 1
The bar from that study is the Fasting Bar. The flavors and where to get it are at the end of this article.
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The research lineage behind the formulation
The Fasting Bar did not begin as a snack product. It comes out of the fasting mimicking research: 25+ years of work on fasting biology, grounded in the research of Dr. Valter Longo and developed by L-Nutra in collaboration with the USC Longevity Institute. 3 It uses the same fasting mimicking technology as the Prolon 5-Day FMD, applied to a single bar.
Longevity scientists studied the biology of how cells sense macronutrients, then researched how much nourishment, and what type, a food could deliver while staying below the activation thresholds of those nutrient-sensing pathways. 1 The bar is the result of that research.
25+
Years of research
Fasting mimicking science behind the formulation
47
Clinical trials
Across the broader fasting mimicking research
18
Research institutions
Leading institutions involved in the research
200+
Patents
Pending or issued, for longevity and healthspan
Research context: the USC Longevity Institute. The fasting mimicking research behind the bar's formulation was developed by L-Nutra in collaboration with the Longevity Institute at the USC Leonard Davis School of Gerontology. 3
What is actually in it
The formulation is nut-based. Almonds, macadamias, and pecans, or “longevity nuts,” form the foundation of the bar: healthy fats, fiber, vitamins, and minerals. 1 Around them sit complex carbohydrates chosen for steady absorption, 6g of plant-based protein for lasting satiety, plus antioxidants and omega-3 fatty acids. Every bar is plant-based, gluten-free, non-GMO, and dairy-free.
The nut choice follows the evidence. Research published in the New England Journal of Medicine found that frequent nut consumption, seven or more times per week, is associated with roughly 20% lower mortality from any cause. 2 The bar's headline ingredients come from the foods longevity research keeps pointing back to.
Cross sections of the Fasting Bar: a nut-based formulation built for steady absorption.
What the bar is not
A product like this is easy to overread, so a few boundaries are worth stating.
The bar has calories. It's real food and real nourishment. What it avoids is the glucose spike and the fed-state signaling that a typical snack produces.
It doesn't put a non-faster into a fat-burning state. If you're fasting, the bar is formulated to let that fasting, fat-burning state continue. If you're not fasting, eating a bar doesn't start one. For non-fasters it's a smarter, low-glycemic alternative to processed, high-sugar snacks.
It supports a fast rather than replacing one. The fasting window is still yours to keep. The bar's job is narrower: to make the window livable, and to nourish you through it, without ending it.
Nut-based nourishment, individually wrapped. Twelve bars per box.
Where it fits in a real day
The product's own guidance is specific: in a 16-hour fasting window, a common approach is to use the bar around hour 12, when energy dips and the fast still has hours to run. 1 Four other uses are common.
Morning nourishment
Skipping breakfast has been associated with poor health outcomes; morning nourishment supports vital organ function, including the brain, heart, and muscles, and a healthy metabolism and weight. The bar delivers that nourishment without ending an overnight fast.
Busy mornings, on the go
Each bar is individually wrapped, with nothing to prepare. It's an on-the-go option for the commute or a rushed morning.
The late-night swap
Late-night snacking is linked to weight gain and higher blood sugar. Swapping the bar in for dessert satisfies the craving without the glucose spike.
Blood-sugar-aware snacking
Low glycemic index and clinically shown to not increase blood sugar. A great option for people managing blood sugar, including diabetics.
Morning nourishment that leaves the overnight fast intact: the use case the bar was formulated for first.
The claim behind the Fasting Bar is narrow, and it was tested: a bar formulated to nourish while staying below the body's nutrient-sensing thresholds, so the body still thinks it's fasting. For anyone who has watched a fast end over a small snack, that is what the bar is for.
Pick your flavor
Three flavors. One way to fast with food.
This is the bar from the research above. Twelve individually wrapped bars per box.
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Available in 3 flavors + Variety Pack · 12 bars per box
The only bar clinically proven to keep you in a fasting, fat-burning state
It uses the same patented fasting mimicking technology as the 5-Day FMD, and comes in three flavors. Get the Variety Pack to try them all, or pick a single flavor on the product page.
Variety Pack
Chocolate Chip
Coconut Macadamia
Nuts & Honey
Plant-Based
Gluten-Free
Non-GMO
Dairy-Free
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Sources & notes
1.
Prolon Fasting Bar materials, including the RAS, PKA, and mTOR nutrient-sensing pathway mechanism, the formulation and ingredient facts, and usage guidance. The study cited: a randomized, controlled study in 105 adults after a 15-hour overnight fast, comparing glucose and ketone results every hour for 4 hours across the Fasting Bar, breakfast, and water-fast groups. Data on file with Prolon.
2.
Bao et al., New England Journal of Medicine, on the association of frequent nut consumption (seven or more times per week) with roughly 20% lower all-cause mortality. Note for review: Prolon's Fasting Bar Info Sheet cites this figure as lower cardiovascular mortality; the approved Round 5 page carries the all-cause form used here. Prolon team to confirm the preferred form.
3.
Fasting mimicking research figures (25+ years of research, 47 clinical trials, 18 research institutions, 200+ patents) per Prolon brand materials. Research grounded in the work of Dr. Valter Longo and conducted with the USC Longevity Institute at the USC Leonard Davis School of Gerontology.
This article is provided for educational purposes and reflects results reported in research on the Prolon Fasting Bar and the fasting mimicking research. Individual results vary. These statements have not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease. Consult your physician before beginning any fasting practice, particularly if you are pregnant, nursing, underweight, or managing a medical condition such as diabetes.
© Prolon · L-Nutra. Patented fasting mimicking technology developed with the USC Longevity Institute.
These statements have not been evaluated by the FDA. Not intended to diagnose, treat, cure, or prevent any disease.