★ Key Takeaways from Three Years of Testing
- ✓ InsideTracker and Function Health are genuinely good at surfacing data. That's the ceiling. Neither one tells you what mechanism is driving your specific pattern of results.
- ✓ After three years of quarterly panels and about $1,800 in testing fees, the symptoms that sent me to these platforms were still there. The numbers improved on paper. Nothing else moved.
- ✓ The gap I found wasn't in the data. It was in the nitric oxide pathway, specifically a compound called ADMA that blocks the standard eNOS route. Standard panels don't test for it.
- ✓ GRN Labs is the only service I've found that builds a protocol around your specific cluster of vascular markers and gives you a 90-day re-test to verify the markers actually moved.
- ✓ At $199 per year, it costs less than a single InsideTracker panel. That math doesn't require much commentary.
- ✓ It's not a replacement for comprehensive bloodwork. If you haven't had a panel recently, start there.
- ✓ If you already have the data and you're trying to figure out what to do with it, GRN Labs is where I'd go next.
This review isn't going to be balanced for the sake of sounding fair. I used InsideTracker and Function Health as a paying customer for three years, I know what they're good at and where they fall short, and I ended up somewhere different because of a specific gap they couldn't close. That's what this is about.
I'll cover what both platforms actually deliver, what three years of quarterly testing showed me, and why I eventually landed on something that cost less than one of their panels and moved markers that years of data collection hadn't.
What these platforms actually deliver
InsideTracker and Function Health are both built around the same core premise: comprehensive bloodwork, visualized clearly, with general recommendations attached to each flagged marker. They do this well. InsideTracker covers 63 to 170 biomarkers depending on your tier. Function Health runs over 100. Both give you longitudinal trend data, both flag what's out of range, and both tie each marker to a lifestyle recommendation you can act on.
Those recommendations are reasonable. Add magnesium. Improve your protein quality. Prioritize sleep. Reduce saturated fat. None of that's wrong. It's also roughly what a well-informed GP with 20 minutes to spare would tell you, which is more or less the category these platforms occupy.
What they don't do is tell you which mechanism is driving your specific pattern of results. They surface numbers and attach general guidance to each one. There's no protocol built around your cluster. That distinction matters more than it sounds like it should.
Why I started tracking in the first place
I started on InsideTracker in early 2022. I was 47. Blood pressure had been drifting upward since around 45, nothing alarming on paper, but it was moving in a direction I didn't like and hadn't moved back despite the usual adjustments. Energy was lower than it used to be in ways that were hard to pin down. Mornings were getting less reliable in ways that men over 40 tend to recognize without much elaboration.
I'd been paying attention to this stuff for a while. I wasn't someone who stumbled onto the topic through a single article. I'd read Attia, followed the r/PeterAttia threads, been on ExcelMale long enough to recognize the regulars. I thought I had a decent sense of what the markers were and what I was looking for.
Three years of panels, no protocol
My first InsideTracker panel flagged a handful of amber items: suboptimal ferritin, slightly elevated hsCRP, testosterone in range but low-normal. The platform recommended magnesium, a protein source adjustment, and better sleep hygiene. I ran that for eight months and retested. Numbers moved. The ferritin came up. Inflammation markers improved slightly. Nothing I actually cared about changed.
I switched to Function Health after a friend made the case for it. More biomarkers, cleaner interface, lower cost per panel than InsideTracker if you're testing quarterly. I stayed on it for about 14 months with tests every three or four months. My vitamin D came up meaningfully. Homocysteine improved. Blood pressure kept doing its own thing, and the other symptoms stayed right where they were.
By year three I had built a pretty detailed tracker, correlating markers across time, cross-referencing changes in sleep quality and training volume with each test, trying to find what was actually driving what. The data was thorough. The picture it was pointing me toward wasn't something either platform was built to surface.
Both platforms are optimized to help you improve individual markers. That's a legitimate goal. The problem is that some patterns of symptoms aren't being driven by any one marker you can tweak in isolation. They're driven by a mechanism that sits upstream of all of it, one that the standard panel isn't designed to measure.
I didn't figure that out from the platforms. I found it on my own, which is sort of the point of this review.
The research that changed how I was thinking about this
I'd been through the standard nitric oxide research before. The forum consensus on ExcelMale and similar communities is roughly: L-arginine feeds the eNOS pathway, citrulline converts more efficiently, stack them with some pycnogenol, see what happens. I'd run that protocol for a few months and noticed modest improvement that didn't hold past the initial response.
What I hadn't read carefully was a 2015 paper by Nathan Bryan published in Future Science OA. It describes something that made three years of inconsistent results suddenly make sense.
Your body has two entirely separate routes for producing nitric oxide. The first runs through an enzyme called eNOS, which converts L-arginine into NO. This is the pathway that nearly every supplement on the market targets. It's also the one that gets blocked by a compound your body produces naturally called ADMA, asymmetric dimethylarginine.
ADMA is an endogenous eNOS inhibitor. In some men, particularly past 40, it accumulates to a level where the first pathway is effectively suppressed regardless of how much L-arginine or citrulline you take. You can keep feeding a route that's locked upstream and get nothing from it.
The second pathway converts dietary nitrates directly to nitric oxide without going through eNOS at all. It's not affected by ADMA. Men whose first pathway is compromised can often get meaningful NO production through this second route when the first one is getting nowhere.
Standard panels don't test ADMA. InsideTracker doesn't test for it. Function Health doesn't test for it. That's not a knock on either platform, they weren't designed with this mechanism in mind. But it means that for a specific subset of men, three years of data collection can tell you almost nothing about what's actually going on with their blood flow.
I rebuilt my protocol around this. Shifted the supplement approach toward compounds targeting the second pathway, adjusted the dietary inputs toward high-nitrate sources that feed the nitrite-to-NO conversion directly, added pycnogenol in a higher dose than I'd been using based on the FMD literature. Ran it for 90 days and retested.
Things that had been declining over two years reversed inside that window. Not all at once, but clearly enough that I wasn't having to talk myself into believing something had changed.
What GRN Labs does and why it's different
GRN Labs isn't a testing service. It doesn't replace InsideTracker or Function Health if you want broad biomarker coverage with longitudinal visualization. What it does is take the lab data you already have, map it to a vascular age estimate, assign you to a cluster based on your specific combination of markers, and build a protocol around the mechanism that's most likely driving your pattern.
The starting point is a four-minute assessment. It pulls in your existing lab values and current symptoms and produces a vascular age estimate. Vascular age is distinct from your calendar age. A 47-year-old man can have a vascular age of 38 or 58. The difference lives in arterial flexibility, endothelial function, and nitric oxide production capacity. None of those things show up on a standard lipid panel or testosterone screen.
Every supplement recommendation in the protocol follows a citation-first structure: mechanism, study, dose, product link. You're not getting a list of things to try. You're getting a specific recommendation with the published research attached to it.
The 90-day re-test is built into the subscription. At 90 days you re-test the same markers. The goal is a number, a before and an after sitting next to each other. If the markers moved in the right direction, the protocol continues. If they didn't, the protocol adjusts. The year continues either way. At $199 per year, both tests and the full protocol are included.
Side-by-side comparison
| Feature | InsideTracker | Function Health | GRN Labs |
|---|---|---|---|
| Annual cost | $699+ | $499 | $199 |
| Runs its own bloodwork | ✓ Yes | ✓ Yes | No (uses your existing labs) |
| Cluster-specific protocol | ✗ | ✗ | ✓ Yes |
| Vascular age assessment | ✗ | ✗ | ✓ Yes |
| 90-day re-test for verification | ✗ | ✗ | ✓ Included |
| Protocol adjusts if markers stall | ✗ | ✗ | ✓ Yes |
| Addresses vascular-sexual health link | ✗ | ✗ | ✓ Yes |
| Supplement recs with published citations | Partial | Partial | ✓ Every recommendation |
What I liked, and where it falls short
I'm going to split this into GRN Labs specifically, since that's probably why you're reading this far.
- Protocol is built around your marker cluster, not a generic action list
- Targets the vascular age gap that standard panels miss entirely
- 90-day re-test produces an actual before and after, not just a feeling
- $199/year is less than a single InsideTracker panel
- Every supplement recommendation has a mechanism, study, and dose attached
- Protocol adjusts based on re-test results, not left static
- Addresses the blood pressure, energy, and sexual function cluster directly
- Doesn't run its own bloodwork, you need to bring lab data
- Less precise if your most recent panel is more than 18 months old
- No physician oversight built into the subscription
- Newer product, less long-term outcome data than the major platforms
- Not the right fit if you want broad metabolic tracking across 100+ markers
The honest pushback worth taking seriously
The strongest version of the counterargument goes like this: InsideTracker and Function Health have been around longer, have processed substantially more data, and their general recommendations are evidence-based. A newer, smaller platform built around a specific mechanism is a bet on that mechanism being the right one for you specifically. That's not guaranteed.
That's fair. If you're starting from zero and you want a comprehensive baseline, both of the major platforms are genuinely useful. I'd probably start with Function Health on price-per-panel grounds, but InsideTracker's tier structure gives you more flexibility if you want to go deep on specific categories.
The problem with the counterargument is that it's most relevant for people who haven't already been through the data collection phase. If you've run the panels, followed the recommendations, and still haven't moved the specific markers that sent you to these services in the first place, you're not in that situation anymore. More data isn't the next step. A protocol built around what you already know is.
GRN Labs doesn't compete with InsideTracker and Function Health in the category those platforms occupy. It picks up where they leave off.
Who this is actually for
- You've had bloodwork in the past 18 months and have the results
- You've tried the standard supplement stack and seen limited response
- Blood pressure, morning erections, or baseline energy are the specific things bothering you
- You want a 90-day protocol with a re-test built in, not an open-ended optimization loop
- You're done guessing at the mechanism and want something specific built around your data
- You're already spending $499 or more per year on tracking and want to know what to do with it
- You've never had comprehensive bloodwork and want a starting baseline
- You want physician oversight included in the service
- You're looking for broad metabolic tracking across 100+ markers with trend visualization
- You want a service that runs its own labs
- You're early in the process and not yet sure what you're trying to fix
A few questions worth asking yourself
These are the questions I wish I'd asked three years ago. If most of them land close to home, the protocol is probably worth testing.
- Has your blood pressure been creeping upward since your mid-40s despite making the changes your lab report recommended?
- Have you tried L-arginine, L-citrulline, or a standard nitric oxide product and noticed little to no lasting response?
- Has your energy floor dropped over the past two to three years in a way that more sleep and better training didn't fully correct?
- Have morning erections become less reliable than they were at 35 or 40, and has your doctor's answer been some version of "that's normal for your age"?
- Do you have lab results from the past 18 months that include inflammation markers, testosterone, and a basic metabolic panel?
- Have you ever looked at a test result that came back "in range" and still felt like something was clearly off?
If you're sitting on lab data you've collected over months or years and you're still not clear on what to do with it, that's the gap. Understanding the mechanism helps. Actually having a protocol built around your specific numbers is what moves the markers.
Find Out Your Vascular Age
Four-minute assessment. Uses your existing lab data. No new bloodwork required.
Assigns a protocol built around your specific cluster. 90-day re-test included to verify the markers moved.