GLP-1 for Athletes: My Journey to Race Weight

• Weight (kg)
• Body fat (%)
• hollow = estimated, not measured
• shaded = on that drug · bars = dose, scaled within each compound

1. 1 20 Feb First injection — 2.5 mg tirzepatide (Mounjaro)
2. 2 27 Mar End of the 5-week protocol — dose cut to 20 units
3. 3 21 Apr Femur fracture — cycling crash. Stopped tirzepatide; no weigh-ins for two months
4. 4 5 Jun Restarted tirzepatide after the off-drug gap
5. 5 29 Jun Switched to semaglutide (Ozempic) — first full dose, 18 units
6. 6 16 Jul Up to 30 units — 15u never held appetite for a full week
7. 7 28 Jul Up to 35 units — 30u stopped holding around day 6
8. 8 3 Aug Taper begins — back down to 30 units

20 weigh-ins (19 measured) · 19 body-fat readings (12 measured) · 21 injections. Weigh-ins and body-fat readings from my own tracking; injections from my dose log. Body fat is a circumference model, not a DXA — treat the level as indicative and the trend as the signal. Updated 24 Aug 2026.

Protocol Timeline — Key Events

1. Feb 20 First injection
   (2.5 mg tirzepatide)
2. Feb 22 Week 1 weigh-in
   95.8 kg
3. Mar 27 End of 5-week
   protocol
4. Late Mar Dose cut to
   20 units
5. Apr 21 Crash — stopped
   tirzepatide
6. Early Jun Off-GLP peak
   ~96 kg
7. Jun 6 Restarted — now
   just under 94 kg
8. Jun 29 Switched to Ozempic
   first dose, 18 units
9. Jul 3 Dose down to
   15 units
10. Jul 16 Up to 30 units
    (15u didn't hold)
11. Jul 28 Up to 35 units
    (30u didn't hold)
12. Aug 6 Lowest of the whole course
    89.7 kg
13. Aug 10 40 units — highest
    dose so far

Why This Question Is Suddenly Everywhere

GLP-1 medications are on the verge of going mass. Morgan Stanley projects the number of Americans on GLP-1s will quadruple over the next decade — from roughly 13 million at end of 2025 to 55 million by 2035, about 15% of the US population. A KFF survey already found 12% of US adults (~30 million people) saying they were currently taking a GLP-1 drug. The gap between those numbers comes mostly from the booming compounded market — people getting prescriptions through Hims, telehealth clinics, and online pharmacies that don't show up in pharma sales data.

The next wave will be larger. Lower prices from generics and compounders, new pill-based formulations that require no weekly injection, and expanded Medicare coverage are all converging in 2026–2027. This is no longer a niche question for diabetics or the severely obese. It's becoming a mainstream tool — and endurance athletes are ahead of the curve, already asking the practical questions that matter: Can I train on this? Will it ruin my race fueling? Will I lose muscle? That's exactly what I documented.

Why I Started GLP-1

In early 2026 I was deep in Ironman prep for Challenge Roth (July 2026) and running multiple marathons a year. Training weeks regularly hit 15–20 hours, and the hunger that comes with that volume is relentless. The loop was always the same: train hard, get ravenous, overeat, undo the deficit. Ironman training did not solve it. It made it worse.

I also have a lifelong sensitivity to sugar. Childhood sugar binges, emotional eating when stress is high, the kind of pattern that doesn't go away, it just waits. This is not a clinical obesity story. I started around 96 kg and wanted to get to a real race weight, where watts per kilo actually changes what I can do on the bike and what the last 10 km of a marathon feels like. Willpower had failed me for years. Every training block I'd get leaner for a while, then the appetite would win.

The doctor conversation was short. He prescribed tirzepatide (Mounjaro) 5 mg KwikPen at 2.5 mg per week — the starter dose. Not long-term maintenance. A tool to break the hunger loop during the heaviest training block and get me to race weight before the season started. First injection went in on February 20, 2026.

My Protocol

• Medication: Tirzepatide (Mounjaro) 5mg KwikPen
• Dose: 2.5mg per week (30 units) for weeks 1-6, reduced to ~1.67mg (20 units) from week 7
• Injection day: Fridays at 19:30 — evening before bed, to sleep through any potential side effects
• Start date: February 20, 2026
• Initial protocol end: March 27, 2026 (5 weeks)
• Continuation: Reduced to 20 units from late March through mid-April
• Paused: Stopped April 21, 2026 after femur-fracture surgery — deliberately off GLP through recovery to eat enough to heal the bone
• Restarted: Early June 2026, working through the doses left in the pen — maintenance, not another cut
• Switched drug: June 29, 2026 — first injection of semaglutide (Ozempic), 18 units. No clinic in Saigon reliably stocks tirzepatide, so the resumed protocol moved to a single-receptor GLP-1

The plan was always 5 weeks, not indefinite use. Break the hunger loop in the heaviest training block, build habits that would carry after stopping, get into Ironman season at race weight. That was the theory.

Monitoring: weekly circumferences (weight, waist, belly, chest, hips, thighs), body fat and lean mass estimated from those numbers via a linear regression model, blood work before and after the protocol.

Weight Timeline

All measurements taken at the same time of day, tracked in my athlete tracking system. Numbers below are the raw measurement data.

Date	Weight (kg)	Notes
Jan 18, 2026	94.1	Pre-protocol baseline
Feb 16, 2026	96.4	Last measurement before GLP-1 start
Feb 20, 2026	—	First tirzepatide injection (2.5 mg, 30 units)
Feb 22	95.8	Week 1
Mar 1	94.9	Week 2
Mar 7	93.2	Week 3
Mar 16	92.0	Week 4
Mar 22	89.0	Week 5 — excluded as an outlier, see note below
Mar 29	90.2	Week 6 — protocol officially ended Mar 27
Apr 6	93.6	Week 8 — 2 weeks at reduced dose (20 units)
Apr 11	—	Week 9 — lower dose, hunger clearly returning, small binges
Apr 21	—	Femur fracture + surgery — tirzepatide stopped, deliberately off GLP to heal the bone
May 6	94.0	Off GLP — medical check-in, weight rising on a healing surplus
Early Jun	~96	Off-GLP peak (approx.) — eating to heal, non-weight-bearing
Jun 6	—	Restarted — remaining doses from the original pen
Jun 13	<94	One week back on — rebound coming off the top
Jun 29	—	First semaglutide (Ozempic) injection, 18 units — switched off tirzepatide (not stocked in Vietnam); before breakfast, no hunger, no nausea
Jul 3	—	Second Ozempic injection, 15 units — stepped down from 18 after a week that held cravings and a clean deficit; moved to an evening (18:00) dose
Jul 10	95.2	Back up to 20 units — 15 units was not holding appetite
Jul 16	—	30 units — skipped the 25-unit step ahead of travel
Jul 28	91.2	35 units — 30 units failed to hold food noise for a full 7 days
Aug 2	91.1
Aug 3	—	Back to 30 units, a day earlier than planned — 35 units broke at day 6 too
Aug 6	89.7	Lowest reading of the whole course
Aug 9	91.8	Three days later, 2.1 kg higher — travel and refeed noise
Aug 10	—	40 units, the highest dose of the course

Weight swings 2–3 kg day to day with hydration, training load and meal timing, so the trend matters more than any single reading. The 89.0 kg on Mar 22 sits about 3 kg below the weigh-ins either side of it (92.0 kg on Mar 16, 90.2 kg on Mar 29), so I treat it as a bad reading and leave it out of the trend. The lowest weight of the whole course is 89.7 kg on August 6. Two weeks after cutting to 20 units I was back at 93.6 kg on April 6, and this week (week 9) hunger is noticeably sharper than it was at full dose. The suppression is weaker, the window before the next injection feels longer, and for the first time on this protocol I've had a few small binges. Honest bit: alcohol made it worse. Evenings with a drink or two, the brakes came off and portions went sideways in a way that simply did not happen at 30 units. The old childhood pattern — emotional eating, sugar sensitivity — is still there. The lower dose just stopped covering for it. In mid-April I was weighing whether to go back to the full dose or accept slower progress and work on the habits directly. A cycling crash on April 21 settled that question for me — see the update below. More on the appetite-alcohol-binge dynamic in the sugar cravings update.

Update — June 2026: Off GLP to Heal a Femur, Then Back On

On April 21, 2026 I broke my right femur in a cycling crash and had surgery the same day. I stopped tirzepatide that day and stayed off it on purpose. A fracture heals on a surplus, not a deficit. The bone needs calories and protein to rebuild, and appetite suppression is the exact opposite of what that job needs. So I parked the protocol and let myself eat.

It did what you would expect. Over the weeks off the drug my weight drifted from around 93 kg back up to roughly 96 kg. The May 6 check-in had me at 94.0 kg on the way up. I'm fine with that trade. Carrying a couple of extra kilos while non-weight-bearing matters far less than putting enough material into a healing femur, and there was no race to be light for — Da Nang and Challenge Roth 2026 were already gone.

About a week ago, in early June, I restarted — working through the doses left in the original pen. The bone is far enough along that feeding a deficit is no longer the risk it was in late April, and the end-of-week hunger had crept back toward the same patterns I logged at the reduced dose. One week back on and I'm at just under 94 kg. This is not another cut to race weight. It's maintenance — taking the top off the rebound while training volume is still a fraction of normal and the leg is still healing. Race weight is a 2027 problem now.

June 29 update — a drug switch. The early-June restart was the last of the original Mounjaro pen. When it ran out there was nothing to refill it with: no clinic in Saigon reliably stocks tirzepatide, and all five I contacted said the same thing. So after an endocrinology consult at Victoria Healthcare on June 22, the prescription moved to semaglutide (Ozempic) — same GLP-1 class, single receptor instead of tirzepatide's dual GIP/GLP-1 mechanism. I broke down what that change actually costs you as an athlete in Ozempic vs Mounjaro.

I took the first semaglutide injection on the morning of June 29 — 18 units, before breakfast. It landed easy: no hunger through the morning and zero nausea, which is about as gentle as a first dose of a new GLP-1 gets. The suppression didn't last the whole day, though — about five hours in, the appetite was back, hunger around a 5 out of 10. A low starter dose of a single-receptor drug was never going to flatten hunger the way the full tirzepatide dose did; that's expected, and the plan is to titrate up. I'm starting low and titrating slowly on purpose. The goal is the same modest one — shed the kilos that crept on during the non-weight-bearing layoff at roughly half a kilo a week, timed with the light early rebuild block, without starving a femur that's still remodelling. Not a cut to race weight. That's still 2027.

July 3 update — going down, not up. The day-one read on June 29 looked weak: hunger back within about five hours, so the plan then was to titrate up. The full week changed it. Across the seven days, 18 units held the cravings and kept a clean caloric deficit — which is all I need in a light rebuild block. So today's injection went the other way: 15 units, taken in the evening at 18:00 rather than the morning. The point is to find the lowest dose that still does the job and hold there — minimum effective dose, not maximum — which stretches the pen and keeps side effects near zero. If cravings break through over the coming week I step back to 18. Still maintenance, still a 2027 race-weight plan.

Update — August 2026: Four Dose Increases, Same Day-6 Wall

The July 3 entry above ends on a tidy idea: find the lowest dose that still does the job and hold there. That is not what happened. Over the next five weeks the dose went up four times, and the honest summary of it is that none of the increases bought a single extra day of appetite coverage.

Date	Units	Dose	Why
Jun 29	18	0.25 mg	Label starting dose, switching over from tirzepatide
Jul 3	15	0.21 mg	Stepped down, testing the minimum that still works
Jul 10	20	0.28 mg	15 units was not suppressing appetite
Jul 16	30	0.42 mg	Jumped the 25-unit step ahead of travel
Jul 22	30	0.42 mg	Hold
Jul 28	35	0.49 mg	30 units failed to hold food noise for seven days
Aug 3	30	0.42 mg	Step back down, pulled forward a day by strong evening hunger
Aug 10	40	0.56 mg	Highest dose of the course

Read the "why" column downwards and the pattern is hard to miss. At 30 units, hunger came back on day 6. At 35 units, hunger came back on day 6. At 40 units it came back the following day and I ate through the evening. Four increases, one unchanged failure point. If the dose–response curve worked the way the internet says it does, that column would read differently.

I have not found an explanation I trust yet. Tolerance is the obvious guess and I do not think the timeline supports it — the failure point did not drift later and then collapse, it sat on day 6 from the beginning. The more uncomfortable possibility is that the thing breaking through is not physiological hunger at all, in which case no dose fixes it.

What the food log actually shows: variance, not restriction

My first read on this was that I was under-eating during the day and paying for it at night. Then I pulled the whole fortnight instead of the two days that fit the theory, and it did not hold up. Eight logged days between July 28 and August 10 average 3,138 kcal against a 3,100 target. On average I am eating exactly what I should be.

The problem is the spread. Those same days run from 1,340 kcal to 5,360 kcal, and both extremes fall inside the same five-day window. That is a restrict-then-correct cycle, not a deficit — and it is a much better explanation for the night hunger than the dose is. A 1,340-kcal day does not stay a 1,340-kcal day. It gets paid back, usually after dark, usually as something I did not plan to eat.

Caveat, and it is a real one: 6 of those 14 days have no food log at all. Every conclusion in this section rests on partial data, and I would rather say that than present eight days as a fortnight.

Weight: 5 kg down, then flat

The good part first. 96.0 kg on January 7, 95.2 kg on July 10 when the Ozempic phase got going properly, and 89.7 kg on August 6, the lowest reading of the whole course. Roughly 5 kg in four weeks.

The part that matters more: that trend has stalled. 91.1 kg on August 2, 89.7 on the 6th, 91.8 on the 9th. Net for the week, I am up 0.7 kg. The ~1 kg per week figure describes July 10 to August 6. It does not describe the week after it, and quoting it as a current rate would be the sort of thing this log exists to avoid.

Two things to hold alongside those numbers. Daily scale readings swing about 2 kg on travel and refeed days, so the August 6 low and the August 9 high are three days apart and both are real — that is noise, not a reversal. And 1 kg a week is genuinely fast for someone already lean; at this point most of what is left to lose is not fat. On an athlete's body that is a body-composition question, not a weight-loss one, and it is the reason the plan from here is a taper back down — 30, 25, 20, 18 units through early September — rather than another step up.

What is next: back to tirzepatide, on the Japanese label

The taper is the near-term plan. The one after it is a change of molecule, not a change of dose: back to tirzepatide, sourced on the Japanese label.

The reasoning follows directly from the table above. Four semaglutide increases moved the day-6 wall by nothing, which is the clearest signal in this whole log that the limit is not the amount of drug. Tirzepatide is a different mechanism, a dual GIP/GLP-1 agonist rather than GLP-1 alone, and it is the one I was on when the first block actually worked. I did not leave it because it failed. I left it on June 29 because no clinic in Saigon reliably stocked it, which is a supply problem, and supply problems have a different fix than pharmacological ones.

One naming detail worth stating plainly, because getting it wrong would misdescribe a prescription medicine. In Japan, Eli Lilly Japan and Mitsubishi Tanabe market tirzepatide under two labels for two indications: Mounjaro (マンジャロ) is the type 2 diabetes label, and Zepbound (ゼップバウンド) is the obesity label, approved by the MHLW in January 2025. Same molecule, same six dose steps from 2.5 mg to 15 mg. I am not diabetic, so the label that actually matches why I would be taking it is the obesity one, whatever the box ends up saying. That is a conversation for the prescribing physician, not something to sort out by reading a website.

What I will be watching, and what I will log here: whether the day-6 wall moves at all on a different mechanism, and what happens to the rate of loss. Tirzepatide produced roughly 21% mean weight reduction at maximum dose in SURMOUNT-1 against semaglutide's ~15% in STEP 1, so the honest expectation is that it comes off faster. At 8.8% body fat that is not automatically good news. Faster loss from an already-lean starting point is exactly the setup that takes the face with it, which I have written up separately in Ozempic face at 11% body fat. If the rate picks up, the dose comes down.

Body Composition

No DEXA scan access locally, so body-comp tracking is weekly circumference measurements run through a linear regression model for body fat and lean mass. Not perfect. Consistent enough to trend.

Body fat estimates: 13.0% (Feb 22) → 11.3% (Mar 22, low point) → 11.6% (Apr 6, reduced dose).

Lean mass estimates: 83.3 kg (Feb 22) → 78.9 kg (Mar 22). This is the number I keep staring at. About 4 kg of estimated lean mass came off alongside the fat, even with full resistance work and high protein intake. So much for "muscle preservation happens on its own." It's active work, and I was doing all of it, and I still lost lean mass.

Measurement	Start (Feb 22)	Mar 22	Current (Apr 6)	Δ start → Mar 22
Weight (kg)	95.8	89.0*	93.6	−6.8*
Waist (cm)	87.5	85.5	84.5	−2.0
Belly button (cm)	86.0	82.5	83.0	−3.5
Chest (cm)	99.5	100.0	100.0	+0.5
Glutes (cm)	104.0	102.0	103.0	−2.0
Left leg (cm)	63.0	62.0	63.0	−1.0
Right leg (cm)	64.0	62.5	63.5	−1.5
Left arm (cm)	39.5	38.3	39.5	−1.2
Right arm (cm)	40.0	39.0	40.5	−1.0
Body fat (%)	13.0	11.3	11.6	−1.7

* The 89.0 kg weight on Mar 22 is excluded as an outlier. It sits about 3 kg below the weigh-ins either side of it and is not treated as a low point. The lowest weight of the whole course is 89.7 kg on August 6. The tape and body-fat measurements from that date still stand.

Pattern: trunk loss dominates. Waist down 2 cm, belly button down 3.5 cm, chest basically flat. Limbs moved 1–1.5 cm by Mar 22 and most of that came back as weight rebounded, which fits glycogen and water swings better than actual leg-tissue loss. Subjectively I still look and feel leaner, and the waist is still ticking down even as weight goes back up.

Race Results — Baseline & Upcoming

Context: every marathon result below is pre-GLP-1. Baseline performances at various weights. The first races I'll run at the new weight are still ahead.

Race	Date	Time	Weight	Notes
Shanghai Marathon	Nov 2024	3:49:47	95.3 kg
Metropolis Marathon	Feb 2025	3:23:41	92 kg	Personal best
Berlin Marathon	Sep 2025	3:55:07	92 kg	Hot conditions
Valencia Marathon	Dec 2025	3:51:01	95 kg

Race plan at new weight — disrupted April 21, 2026:

• IM 70.3 Da Nang (May 10, 2026) — cancelled. Right femur fracture from a cycling crash on April 21 ended the Da Nang start.
• Challenge Roth 2026 (July 6, 2026) — cancelled. Registration transferred in early May 2026 to Challenge Roth 2027 (Sunday, July 4, 2027).
• Valencia Marathon (December 6, 2026) — TBD pending the 10-12 week follow-up.

The lower-weight race data hypothesis is on hold until I'm cleared to race again. Recovery progress lives on the Road to Ironman log.

GLP-1 protocol — paused for the fracture, resumed in early June. I stopped tirzepatide right after surgery on April 21, 2026 and stayed off it through the early recovery so I could eat enough to heal the bone — weight drifted from about 93 kg back up to roughly 96 kg in that window. I restarted in early June on the doses left in the pen and I'm back to just under 94 kg. The biggest takeaway from the time on it still holds: going well below the prescribed dose stopped working for binges and sugar cravings, while the prescribed dose worked very well. Full detail in the June 2026 update above.

For detailed split analysis and Garmin data from past races, see my full race results breakdown.

What Actually Changed

The number I care about most on the bike is watts per kilogram. Across the 5 weeks my FTP went from 261W to 281W, a 20-watt gain (+7.7%). Combined with the weight loss, my W/kg went from 2.72 to 3.04. A 12% jump. On a hilly Ironman course, that's real.

I want to be careful with attribution here. The FTP gains could easily be down to structured training — I was in a dedicated build phase with intervals and threshold work, and that alone adds 10-15 watts in a 5-week block if you do it right. The weight loss and body-comp changes are clearly the medication. The appetite suppression broke the loop where training hunger would always blow up the deficit.

The clear wins were body comp, power-to-weight, and how I actually feel running. Training volume held (no missed sessions), in-session energy held, sleep and recovery held. The one thing I can't separate cleanly is how much of the FTP gain was the weight loss and how much was a well-structured build phase. Probably both, in some ratio I'll never know exactly, and I'm fine with that.

Side Effects

First injection was during the day (Feb 20). I was nauseous for a couple of hours afterwards. That was the only time. Every injection after that went in Friday at 19:30, right before bed, and the side-effect profile was zero. The trick was simple: inject in the evening, sleep through the window where GI stuff might show up, wake up normal.

No energy dips in training, no GI issues on long rides or runs, no hit to sleep or recovery. The appetite suppression did exactly what it was supposed to do: cravings dropped, hunger was manageable, and the post-big-session urge to eat the kitchen was gone for most of the week.

One pattern stood out. Suppression is strongest days 1–5 post-injection. By days 6–7, hunger starts creeping back before the next dose. Manageable, but noticeable.

I also got lucky. Plenty of athletes report serious GI issues, especially during dose titration. The starter dose (2.5 mg tirzepatide) plus evening timing probably helped a lot. Your experience may look nothing like mine. This is a sample size of one.

For the full protocol on managing side effects around training, see my side effects and dose timing guide.

Deep Dives & Resources

Frequently Asked Questions

Can you train for a marathon or Ironman while on Ozempic or Wegovy?

Yes — I maintained full training volume throughout my GLP-1 protocol (tirzepatide/Mounjaro), including Ironman and marathon preparation. The key adaptations were adjusting fueling strategy (GLP-1 slows gastric emptying), timing injections on Friday evenings to minimize side effects, and prioritizing protein intake to preserve lean mass. I did not miss a single training session due to the medication.

Does semaglutide (Ozempic, Wegovy) affect running performance?

In my experience, the net effect was positive due to improved power-to-weight ratio — my W/kg went from 2.72 to 3.04 over 5 weeks. However, it is hard to isolate GLP-1 from general training progression. The performance benefit comes from the weight loss itself, not from the medication directly affecting athletic capacity. I had to actively manage fueling and muscle preservation throughout.

How do you fuel long runs and races on GLP-1?

GLP-1 slows gastric emptying, which means gels and carbohydrates take longer to absorb. I adjusted by starting fueling earlier in long sessions, using more liquid calories (which absorb faster), and testing every nutrition change during training before race day. I cover this in detail in my race day fueling guide.

Is semaglutide (Ozempic) banned by WADA for competitive athletes?

As of 2026, semaglutide is on WADA's monitoring program but is NOT on the prohibited list. It is legal for use in competition across all sports. However, WADA is actively studying it and could move it to the banned list in future years. I discuss the ethics and regulatory landscape in my WADA analysis.

Does a higher Ozempic dose give you more days of appetite suppression?

Not in my case, and I tested it four times. Between July 3 and August 10, 2026 I went from 15 units to 20, 30, 35 and finally 40 units of semaglutide. Appetite came back around day 6 after the injection at every single dose, and after the 40-unit dose it came back the next day. Four increases produced no additional coverage. My working conclusion is that what breaks through late in the week is not something a larger dose fixes — in my own food log the stronger signal is intake variance (1,340 to 5,360 kcal inside five days) rather than a shortfall the medication should be covering.

How do you prevent muscle loss on Ozempic or Mounjaro as an endurance athlete?

Studies show 25-40% of weight lost on GLP-1 can be lean mass without intervention. My protocol included full body resistance training throughout, high protein intake, and maintaining training volume. Circumference measurements showed fat loss concentrated in the trunk while limb measurements stayed stable, suggesting good muscle preservation. The full protocol is in my muscle preservation guide.