It’s a fair question, and one that more people are starting to ask now that GLP-1 medications have moved from niche diabetes prescriptions into mainstream weight-loss medicine. If a drug works by making you eat less — sometimes a lot less — then it’s worth asking what nutrients are quietly going missing in the calories you no longer consume. Omega-3s are one of the first ones I’d look at.
The short answer: there’s no peer-reviewed study yet that has specifically measured EPA and DHA status in people taking semaglutide or tirzepatide. But the underlying math is hard to argue with. People on GLP-1 medications eat 20–35% fewer calories. They also disproportionately cut back on foods they no longer crave or tolerate well — which, for many Americans, includes the fish that already wasn’t on their plate very often. If your omega-3 intake was marginal before you started Ozempic, there’s a decent chance it’s now genuinely low.
This post walks through what we know, what we don’t, and what the practical answer actually looks like if you’re on one of these drugs and trying to do right by your long-term health.
How GLP-1 Drugs Change What You Actually Eat
GLP-1 receptor agonists — the class that includes semaglutide (Ozempic, Wegovy), tirzepatide (Mounjaro, Zepbound), and liraglutide — work by mimicking a gut hormone that signals fullness to the brain and slows gastric emptying. The result, well documented in trials going back to the original STEP and SURMOUNT studies, is a sustained 15–20% reduction in body weight over 12 to 18 months for most people on a therapeutic dose (NEJM, 2023).
That weight loss comes from a real, measured drop in caloric intake. But it’s not just calories that fall. A 2025 narrative review in the International Journal of Obesity noted that GLP-1 users frequently report changes in food preference — protein-rich foods, fatty foods, and strong-smelling foods often become unappealing — and that early satiety means the meals people do eat are smaller and less varied (Nature, 2025). Clinicians treating this population now routinely watch for shortfalls in protein, iron, vitamin B12, vitamin D, calcium, and thiamine (Mass General Advances, 2025).
Omega-3s aren’t typically on that clinician checklist yet. They probably should be.
Why Omega-3s Get Squeezed Out First
Most Americans get their EPA and DHA from a fairly narrow set of foods: fatty fish (salmon, sardines, mackerel, anchovies), the occasional tuna can, and supplements. That’s about it. Plant-based ALA from flax or walnuts converts to EPA and DHA at a rate of roughly 5–10% and 0.5% respectively, so it doesn’t realistically move the needle.
The average U.S. adult already takes in only about 0.1 grams of combined EPA and DHA per day (American Heart Association, 2023) — roughly a third of the most commonly cited 250–500 mg target, and a small fraction of the 1–2 grams that cardiovascular guidelines often suggest for people with elevated risk. A global 2025 analysis of red blood cell omega-3 status, covered in Science Daily and built on data from dozens of countries, estimated that roughly three-quarters of the world’s population has an omega-3 index below the 8% target associated with lower cardiovascular mortality (Science Daily, 2025; Nutrition Insight, 2025).
So the baseline is already poor. Now layer GLP-1-induced appetite suppression on top. Two things tend to happen:
The fish that was already infrequent gets eaten less often, because the meal is smaller and fish — especially oilier, stronger-smelling fish — is exactly the kind of food that some GLP-1 users start avoiding. And the supplemental fish oil capsule that was already in the cabinet often gets skipped, because nausea and reflux are common GLP-1 side effects, and fish oil is well known for “fish burps” that make those symptoms worse (Ubie Health).
The end result is a population that was already running low on EPA and DHA, eating less of the few foods that contain them, while skipping the supplement that was supposed to fill the gap. It’s not paranoia to think this is creating a quiet deficiency problem.
What the Research Says So Far
To be honest about the state of the evidence: there is not yet a published randomized trial that has measured omega-3 index in semaglutide users before and after a year of treatment. That study is the obvious next thing somebody should run, and I’d guess it’s in the works at one of the obesity research centers. Until it lands, we’re reasoning from adjacent data.
What we do have:
A 2025 PMC review of n-3 PUFAs in obesity and metabolic disease noted that omega-3 supplementation during rapid weight loss helps prevent unfavorable changes in fatty acid tissue composition and “may help prevent essential fatty acid deficiency” — language that’s about as direct as nutrition research usually gets when warning about a deficiency risk (PMC, 2025).
A 2024 Scientific Reports analysis of dietary omega-3 intake and mortality among people with cardiovascular disease found that higher dietary EPA and DHA intake was associated with lower all-cause and cardiovascular-specific mortality (Scientific Reports, 2025). The population on GLP-1 drugs overlaps heavily with the population that has cardiovascular risk, which makes the stakes of any quiet shortfall higher, not lower.
And the lean mass literature is worth flagging: GLP-1 weight loss includes a meaningful share of lean tissue — up to 15–40% of total weight lost can be lean body mass (Mass General Advances, 2025; Healio, 2025). Omega-3s aren’t a magic muscle-preservation tool, but multiple controlled trials have shown they modestly support lean mass retention when paired with adequate protein, particularly in older adults. If you’re losing weight quickly and want to lose less muscle in the process, this is one of the few supplements that has reasonable evidence behind it.
None of this is proof that GLP-1 users are deficient. But the direction of the arrows is consistent: lower intake, higher need, more vulnerable population.
How Much EPA and DHA Do You Actually Need?
For a healthy adult with no cardiovascular risk factors, most guideline bodies converge on 250–500 mg of combined EPA and DHA per day, which works out to about two servings of fatty fish per week (Cambridge Nutrition Research Reviews). The omega-3 index — a measurement of EPA and DHA as a percentage of red blood cell fatty acids — has a target of 8% or higher for cardiovascular protection, with most people sitting at 4–5% (PMC, Omega-3 Index and Cardiovascular Health).
For people with established cardiovascular disease or higher risk, a 2025 dose-response analysis put the suggested intake closer to 2 grams of total omega-3s per day (Scientific Reports, 2025). That’s roughly 4–8 capsules of standard fish oil, or a smaller, more concentrated dose from a higher-potency product.
If you’re on a GLP-1 and eating noticeably less than you used to, the honest framing isn’t “do I need a supplement” — it’s “what’s my actual intake right now, and is it covering the floor.” A week of food logging is usually enough to answer that. If you’re eating salmon twice a week and tolerating it fine, you’re probably okay. If your protein has shifted to lean chicken and Greek yogurt and fish has fallen off the menu, you have a gap.
Why the Form Matters When Appetite Is Low
Here’s where this gets practical, and where the choice of supplement starts to matter more than it usually does. People in normal eating mode can tolerate a 1000 mg fish oil softgel with breakfast and barely notice it. People on GLP-1s often cannot. Nausea, slowed gastric emptying, and reflux are the most common GLP-1 side effects, and oil-based supplements that linger in the stomach are exactly the kind of thing that aggravates them (Inspira Health; Ubie Health).
This is where the phospholipid form of omega-3s — the form that omega-3s naturally take inside krill, and the form they take inside the membranes of your own cells — becomes genuinely interesting rather than just a marketing talking point. A 2024 network meta-analysis of bioavailability studies found that at doses below 2000 mg, krill oil’s phospholipid-bound EPA and DHA delivered superior absorption compared to standard triglyceride fish oil (PMC, 2024 Network Meta-Analysis). A separate 2023 crossover study in healthy adults confirmed that phospholipid-bound omega-3s are more readily incorporated into plasma than ethyl ester forms (PubMed, 2023).
Practically, that means a smaller capsule of phospholipid omega-3s can deliver a comparable amount of usable EPA and DHA to a larger capsule of conventional fish oil. For someone whose stomach is already full at half the meal it used to handle, smaller-and-better-absorbed is a real advantage. The phospholipid form also tends not to repeat the way triglyceride fish oil does, which matters more than it sounds when reflux is already a regular feature of your week.
I’d be cautious about overclaiming this. The bioavailability advantage is real but modest, and a high-quality, well-tolerated triglyceride fish oil taken consistently will absolutely get the job done if that’s what you have. The question is whether you’re actually taking it. For a lot of GLP-1 users, the answer is no, because the tolerability isn’t there.
Practical Takeaways
A few things that follow from all of this:
Track what you’re actually eating for a week. Not what you used to eat — what you ate this week. If fatty fish is showing up twice, you probably don’t need to think about this further. If it’s showing up zero times and you’re three months into a GLP-1, you have a gap worth filling.
Don’t take a fish oil capsule on an empty stomach if you’re on a GLP-1. Take it mid-meal, with the fattiest part of the meal, and stay upright for at least half an hour. This is true for any omega-3 supplement, but it matters more here.
Consider the omega-3 index test if you want to know where you stand. It’s about $50, mail-order, and gives you a real number instead of a guess. Target is 8% or higher.
Mind the protein first. Omega-3s are important, but lean mass loss is the bigger nutritional concern with GLP-1s, and the answer there is 1.6–2.2 grams of protein per kilogram of body weight per day, distributed across meals, paired with resistance training (Mass General Advances, 2025). Omega-3s support that goal but don’t replace it.
Don’t assume your multivitamin is covering it. Most don’t include meaningful EPA and DHA, and the ones that do typically include amounts measured in milligrams that don’t move the needle.
Captains Krill Oil exists in this conversation only as one of several reasonable phospholipid-form options. If you’re on a GLP-1 and you’ve decided you want a smaller, better-tolerated omega-3 supplement, krill oil is a sensible category to look at, and ours is one of the longer-standing products in it. But the more important thing is that you’re getting EPA and DHA from somewhere — fish on your plate, a triglyceride fish oil capsule you actually tolerate, or a phospholipid product if the tolerability is what’s been holding you back. The form is a detail. The intake is the point.
If the science gets clearer in the next year or two — and I expect it will, because this is exactly the kind of question that gets studied once enough patients are on these drugs — I’ll update this post.