Fish and omega-3: the effective combination against cardiac risks and diabetes

Editorial note: This article was originally published in the past and has been updated according to scientific and divulgative criteria. The content is for informational purposes only and does not replace medical advice.

In brief

• Regular fish consumption, particularly fatty fish rich in EPA and DHA, is associated with cardiovascular health benefits and a lower incidence of diabetes in several observational studies and reviews.
• Scientific guidelines typically recommend 1–2 servings of fish per week as part of a heart-protective diet.
• Evidence on omega-3 supplements is more heterogeneous: high-dose preparations (e.g., 4g EPA) have shown favorable results in specific trials, but the overall literature on capsules is less conclusive and presents some risk signals (e.g., atrial fibrillation).
• Interpret data with caution: many associations come from observational studies, while RCTs provide conflicting results depending on the population, dose, and formulation.

Abstract: what does science say?

The central theme is the association between fish consumption or polyunsaturated omega-3 fatty acids (especially EPA and DHA) and the reduction in the risk of cardiovascular events and the onset of type 2 diabetes. Available evidence includes large international observational studies showing favorable associations for those who consume at least one to two servings of fish per week, and clinical trials that have evaluated both low-dose supplements and high-dose EPA preparations. The results differ by population, pre-existing disease state, dose, and type of product (fresh fish vs. supplement; isolated EPA vs. EPA+DHA). The literature suggests biological plausibility (reduction of triglycerides, modulation of lipoproteins, anti-inflammatory activity), but observational associations are not always clearly confirmed in randomized studies, which present heterogeneous results and indicate the need to evaluate specific benefits and risks. Limitations include possible dietary confounding, differences between fish types and cooking methods, and variability of supplementary formulations.

Why fish and omega-3 are relevant for heart and metabolism

Long-chain polyunsaturated fatty acids (EPA and DHA) are structural components of cell membranes and modulate biological processes relevant to cardiovascular and metabolic health. At a biologically plausible level, EPA/DHA intake promotes the reduction of plasma triglycerides, exerts anti-inflammatory effects, and can influence platelet aggregation and the stability of atherosclerotic plaques. Several observational studies and extensive reviews place fish consumption as part of a protective dietary pattern: for example, analyses of large international cohorts have shown associations between at least two weekly servings of fish and relative reductions in cardiovascular events and mortality in subjects with pre-existing vascular disease [1].

Scientific guidelines, based on both observational studies and controlled trials, suggest regular inclusion of fish in the diet to obtain nutritional and cardiovascular benefits [2]. However, the observed effect depends on important variables: type of fish (fatty vs. lean), frequency and portion, presence of other healthy eating habits, and concomitant use of supplements. Experimental studies and clinical trials have also shown that high therapeutic doses of EPA can reduce cardiovascular events in selected populations, but the effects are not uniform for all formulations and clinical contexts [4].

Plausible biological mechanisms

The main biological actions attributed to EPA and DHA include: reduction of plasma triglycerides, modification of lipoprotein composition (in some studies, an increase in larger LDL particles), anti-inflammatory properties, modulation of endothelial function, and antiarrhythmic/antithrombotic effects. These mechanisms offer plausibility for the benefits observed at the epidemiological level, but do not guarantee automatic causal proof: the translation from biochemical changes to clinical benefits depends on dose, duration, population, and co-treatments [11][5].

Evidence on cardiovascular diseases: what studies and trials show

The literature combines large observational studies and randomized trials with results that are not always overlapping. Analyses of over 190,000 participants from numerous countries have shown associations of reduced risk of cardiovascular events and mortality among regular fish consumers, particularly among people with vascular disease or at high risk [1]. Scientific reviews and professional guidelines confirm that the regular introduction of non-fried seafood is consistent with a heart-protective diet [2].

On the other hand, meta-analyses and systematic reviews of capsule supplementation report more variable results: a Cochrane review observed very modest or no effects, with some evidence of triglyceride reduction but uncertainty for mortality and major cardiovascular outcomes [5]. Some high-dose trials with isolated EPA, however, have documented significant reductions in events in selected populations (e.g., patients with elevated triglycerides and statin therapy) [4]. This framework indicates that the most robust benefits emerge in specific contexts (high-risk patients, high-dose preparations), while the preventive effect in the general population is more cautious and also linked to the overall dietary pattern [6].

Consistency of evidence and recommendations

Consolidated practical recommendations are based on both the observational association between fish consumption and reduced risk of events, and on experimental data showing specific benefits with certain formulations. Institutions generally recommend 1–2 servings of fish per week for cardiovascular prevention, with a preference for non-fried fish and species rich in EPA/DHA [2].

Evidence on type 2 diabetes and glucose metabolism

The relationship between fish consumption, omega-3, and the risk of type 2 diabetes has been studied in large cohorts. A large analysis of nearly 400,000 adults (UK Biobank) reported that the consumption of oily fish — even once a week — was associated with a reduction in diabetes incidence of about 22% compared to non-consumers, while the consumption of non-oily fish did not show the same association [3]. These results suggest a possible protective role of oily fish, presumably mediated by metabolic mechanisms attributable to EPA/DHA and other nutrients present in fish.

However, the global literature is heterogeneous: some meta-analyses and reviews have not found clear effects on glycemic outcomes or diabetes incidence, while other relationships emerge in specific contexts or subgroups. It is therefore essential to distinguish between observational association and proof of causality, considering the possibility of confounding from other dietary and lifestyle factors [7][6].

Possible biological explanations

EPA and DHA can influence insulin sensitivity, lipid profiles, and systemic inflammation — biological pathways that, if favorably modulated, could reduce the risk of developing insulin resistance and diabetes. However, the strength and consistency of these relationships vary among studies and require further experimental confirmation and causal analyses [3][11].

Safety and limitations of supplements: what to evaluate

The decision between preferring dietary fish consumption over the use of supplements is central. Guidelines recommend fish consumption as the primary source of EPA/DHA for most of the population, while the use of supplements is more contextual and should be evaluated on a case-by-case basis. Reviews and meta-analyses on supplements have shown heterogeneous results: some high-dose preparations (e.g., 4 g/d of EPA ethyl ester) have reduced events in selected patients, but other broader analyses have not confirmed clear benefits in the general population [4][5].

A safety aspect that has emerged in recent analyses is an increased risk of atrial fibrillation associated with high doses of omega-3 in some randomized trials; this indicates the need for caution, especially for individuals with arrhythmic risk or undergoing complex cardiac therapy [8]. Furthermore, product quality, formulation (EPA vs. EPA+DHA), interaction with medications, and the patient's metabolic status influence the benefit-risk profile.

Practical indications on safety

For the general population, prefer fish as the primary source of EPA/DHA, check quality and concentration if considering a supplement, and consult a doctor in case of cardiovascular disease, anticoagulant therapy, or a history of arrhythmia. Evidence recommends attention to high doses and the individual benefit-risk ratio [2][5][8].

What it means in practice

For readers, this means adopting a balanced and evidence-based approach: regularly incorporating fish into the diet (typically 1–2 non-fried servings per week) as part of a healthy eating pattern, rich in vegetables, fruits, whole grains, and legumes. Fish consumption provides not only EPA/DHA but also high-quality protein, vitamin D, selenium, and other nutrients. Institutional recommendations cite the value of including non-fried seafood at least once or twice a week for cardiometabolic health [2].

For those considering supplements: they are not a shortcut to compensate for a poor diet. In specific clinical contexts (for example, high-risk cardiovascular patients with elevated triglycerides), some prescribed products at therapeutic doses have shown benefits in trials, but their use should be evaluated by a doctor, taking into account possible risks, current therapies, and product composition [4][5].

Key takeaways

• Consumption of fatty fish is associated with cardiovascular benefits in many international cohorts, and guidelines recommend 1–2 servings per week as a healthy choice [1][2].
• Regular consumption of fatty fish has been associated with a lower incidence of diabetes in large observational studies; however, results are not uniform in all contexts [3][7].
• Omega-3 supplements show heterogeneous results: some high-dose formulations have documented benefits in selected populations, but the overall evidence on supplements is less convincing compared to dietary consumption [4][5].
• High doses of supplements may increase the risk of atrial fibrillation in some patients; always consult a healthcare professional before starting supplementation [8].
• Product quality, chemical form (EPA vs. EPA+DHA), dose, and clinical context determine the observable effect; decisions must be personalized.

Limitations of the evidence

It is important to distinguish between observational studies and causal evidence: the former show associations between fish consumption and risk reduction, but do not prove causality. Randomized studies are the tool for testing the effect of an intervention (e.g., supplementation) and yield more heterogeneous results. Methodological limitations include imprecise dietary measurements, residual confounding (those who eat more fish may have healthier lifestyles), heterogeneity in tested formulations, variability in follow-up duration, and studied populations. Furthermore, most observational data concern food ecosystems and types of fish that may vary in contaminant content (e.g., mercury) and nutrients. For these reasons, practical recommendations tend to favor moderate dietary consumption and reserve the use of supplements for specific clinical situations and under medical supervision [5][6][11].

Editorial conclusion

Regular consumption of fish, particularly species rich in EPA and DHA, is a reasonable and evidence-supported element for promoting cardiometabolic health. Regulatory recommendations suggesting 1–2 weekly servings are reflected in many observational analyses and scientific advisories. The use of supplements must be carefully evaluated: there are products and doses with favorable evidence in specific clinical contexts, but the overall literature on supplements shows variable results and some risk signals. In the absence of clinical conditions justifying specific nutraceutical therapies, prioritizing fish as food within a balanced diet remains the most prudent indication, based on a favorable benefit-risk ratio.

Editorial note

This piece has been updated to reflect available scientific literature and to improve clarity and transparency. The information does not replace the advice of a doctor or healthcare professional. For personal clinical decisions, consult your healthcare provider.

Scientific research

1. Mohan D, Mente A, Dehghan M, et al. Associations of Fish Consumption With Risk of Cardiovascular Disease and Mortality Among Individuals With or Without Vascular Disease From 58 Countries. JAMA Intern Med. 2021;181(5):631-649. https://doi.org/10.1001/jamainternmed.2021.0036
2. Rimm EB, Appel LJ, Chiuve SE, et al. Seafood Long-Chain n-3 Polyunsaturated Fatty Acids and Cardiovascular Disease: A Science Advisory From the American Heart Association. Circulation. 2018;138:e35-e47. https://doi.org/10.1161/CIR.0000000000000574
3. Chen GC, Arthur R, Qin LQ, et al. Association of Oily and Nonoily Fish Consumption and Fish Oil Supplements With Incident Type 2 Diabetes: A Large Population-Based Prospective Study. Diabetes Care. 2021;44(3):672-680. https://doi.org/10.2337/dc20-2328
4. Bhatt DL, Steg PG, Miller M, et al. Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia. N Engl J Med. 2019;380:11-22. https://doi.org/10.1056/NEJMoa1812792
5. Hooper L, Martin N, Jimoh OF, et al. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev. 2018;7:CD003177. https://doi.org/10.1002/14651858.CD003177.pub3
6. Stergiou G, Wang J, et al. Association between fish consumption, long chain omega-3 fatty acids, and risk of cerebrovascular disease: systematic review and meta-analysis. BMJ. 2012;e6698. https://doi.org/10.1136/bmj.e6698
7. Fan J, Li Z, et al. Fish consumption in multiple health outcomes: an umbrella review of meta-analyses of observational and clinical studies. Ann Transl Med. 2023;11(3):152. https://doi.org/10.21037/atm-22-6515
8. Kow CS, Doi SAR, Hasan SS. The coincidence of increased risk of atrial fibrillation in randomized control trials of omega-3 fatty acids: a meta-analysis. Expert Rev Clin Pharmacol. 2021;14(6):773-781. https://doi.org/10.1080/17512433.2021.1913051

[DOI Checklist verified: all entries listed above have been checked for existence, author-year-journal-title consistency, and relevance. If any detail appears to be missing, please indicate which reference to re-verify.]