Can fish oil reverse insulin resistance? A new study reveals surprising benefits

Many of the wonders of fish oil from improving heart health to reducing cholesterol, are attributed to its abundance of omega-3 fatty acid. Now a groundbreaking study finds the benefits of fish oil supplementation in reversing insulin resistance even in non-obese people.
Published in Nutrients, the highlights how omega-3 fatty acids from fish oil can shift the body’s immune response from pro-inflammatory to anti-inflammatory, improving blood sugar control and reducing diabetes risk.
The research has been mixed about fish oil's role in diabetes prevention or control. A on 10 subjects with mild non-insulin-dependent diabetes mellitus (NIDDM) found that fish oil supplementation raised fasting blood glucose levels by 14%, without improving insulin sensitivity or significantly benefiting plasma lipids. Researchers warned that fish oil supplementation may negatively affect glycemic control in people with diabetes.
A published in The BMJ reviewed 83 trials with over 120,000 participants to examine whether increasing omega-3, omega-6, or total polyunsaturated fats could lower blood sugar or reduce diabetes risk. After nearly three years, researchers found no significant effect on glucose metabolism or diabetes risk, regardless of whether the fats came from supplements, enriched foods, or naturally rich sources.

The new study published in Nutrients conducted on mice suggests that fish oil could reduce insulin resistance in non-obese individuals and also showed improved levels of blood sugar, inflammatory markers and lipid features like cholesterol.
The non-obese mice involved in the study resembled type 2 diabetes, a disorder marked by high blood sugar levels.
The study authors aimed to understand the effects of omega-3 fatty acids on the blood glucose levels of non-obese individuals.
In this study, researchers found that giving non-obese rats 2 grams of fish oil per kilogram of body weight, three times a week for eight weeks, led to a reduction in insulin resistance. The rats also showed improvements in blood sugar levels, inflammation markers, and lipid profiles, including lower total cholesterol, LDL ("bad" cholesterol), and triglycerides.

“Our experiments involved Goto-Kakizaki [GK] rats, an animal model for non-obese type 2 diabetes. We found that insulin resistance can be reduced in these animals by modulating the inflammatory response so as to change the profile of defense cells [lymphocytes] from a pro-inflammatory state to an anti-inflammatory state. This process parallels the response of obese individuals with insulin resistance to omega-3 fatty acid supplementation,” said Rui Curi, Director of Butantan Institute’s Education Center, Professor of Interdisciplinary Graduate Studies in Health Sciences at Cruzeiro do Sul University (UNICSUL), and coordinator of the study.
“In previous studies, we observed alterations in both lymphocytes and macrophages [large white blood cells that often reside in adipose tissue and are part of the innate immune system, engulfing and destroying pathogens] in non-obese rats with insulin resistance. In such cases, these cells produce more pro-inflammatory cytokines, as is central in obese people with diabetes,” Curi explained.

“The main aim of the study, therefore, was to find out whether supplementation with fish oil [rich in omega-3] could reverse specific alterations in lymphocytes that had been observed in previous research. Our findings increased our knowledge of the link between inflammation and insulin resistance in non-obese animals, confirming that this is a key factor in diabetes even in the absence of obesity,” said Renata Gorjão, last author of the article, and Co-Director of UNICSUL’s Program of Graduate Studies in Health Sciences.
The study proved that obesity, although a major risk factor for diabetes isn't the only one. Usually in the case of non obese people developing diabetes, genetics have a major role to play. However, in an article published in the journal Cells, a study discussed how insulin resistance in non-obese individuals may be linked to delayed intestinal transit - the journey of the food from digestion to bowel movement.
“Most obese people have chronic low-level inflammation, which is known to affect the insulin signaling pathways. Adipose tissue, which is augmented in obesity, releases pro-inflammatory cytokines that affect the insulin signaling pathways, promoting insulin resistance. In the non-obese model, this impactful characteristic of adipose tissue is absent, but systemic inflammation is present,” Curi said.
Another study published in the International Journal of Molecular Sciences discusses systemic inflammation in non-obese GK rats with insulin resistance.

“Fish oil supplementation reversed this pro-inflammatory profile, displaying a significant anti-inflammatory effect and reducing polarization of Th1 and Th17 cells, followed by a rise in the percentage of Tregs, which can inhibit the activation of pro-inflammatory lymphocytes. Thus the action of omega-3 fatty acids on lymphocytes, modulating them from a pro-inflammatory state to an anti-inflammatory state, may have triggered the reduction in insulin resistance in these animals,” Lobato said.
However, researchers said more human trials are needed to estimate the ideal dose and the most indicated types of omega-3 fatty acid for non-obese individuals with insulin resistance.

Top sources of omega-3 fatty acids include fatty fish such as salmon, mackerel, sardines, tuna, and herring, along with fish oil, krill oil, and cod liver oil. Shellfish like oysters and mussels also provide omega-3s. For plant-based sources, options include flaxseeds, chia seeds, walnuts, hemp seeds, and soybeans, along with oils derived from them. Algal oil, made from algae, is another excellent vegan source of DHA. Canola oil also contributes to omega-3 intake, though in smaller amounts compared to other sources.
Fish oil is rich in omega-3 fatty acids, which support heart health by lowering triglycerides, reducing blood pressure, and improving cholesterol levels. It also helps reduce inflammation, supports brain health, and may ease symptoms of arthritis. Some research suggests fish oil could benefit eye health and support healthy skin.