Researchers tested whether a special compound found in herring oil could help lower cholesterol levels in obese rats. They fed three groups of rats different diets for five weeks: one with herring oil, one with a concentrated form of the compound, and one with regular soybean oil as a control. The rats eating herring oil or the concentrated compound had significantly lower cholesterol levels—about 17-20% lower than the control group. The findings suggest this compound works by reducing how much fat the liver produces and packages for release into the bloodstream, which could potentially help people with high cholesterol, though more research in humans is needed.

The Quick Take

  • What they studied: Whether a special fat compound called cetoleic acid found in herring oil could lower cholesterol levels in obese rats with high cholesterol
  • Who participated: 30 male obese rats that naturally develop high cholesterol (a special laboratory breed called Zucker rats), divided into three groups receiving different diets for 5 weeks
  • Key finding: Rats eating herring oil had 17% lower cholesterol, and rats eating a concentrated form of the compound had 20% lower cholesterol, compared to rats eating regular soybean oil
  • What it means for you: This suggests that herring oil or its active compound might help lower cholesterol in humans with similar conditions, but this is early-stage research in animals—human studies are needed before making any dietary changes. Talk to your doctor before adding herring oil supplements to your routine.

The Research Details

Scientists divided 30 obese rats into three equal groups. One group ate food containing herring oil (which naturally has the cholesterol-lowering compound), another group ate food with a concentrated version of just that compound, and a third group ate food with regular soybean oil as a comparison. All groups ate their assigned diet for five weeks. The researchers then measured cholesterol levels in the rats’ blood and examined their livers to understand how the compound affected cholesterol production and processing.

This type of study is called a controlled experiment because the researchers carefully controlled what each group ate and compared the results. They used a statistical method called one-way ANOVA to determine whether the differences between groups were real or just due to chance.

The study focused on understanding not just whether cholesterol went down, but also how the compound worked in the body—specifically looking at liver enzymes and processes involved in making and packaging cholesterol for transport in the blood.

This research design is important because it allows scientists to test a potential treatment in a controlled setting before trying it in humans. Rats have similar cholesterol metabolism to humans, making them useful for this type of preliminary research. By examining both blood cholesterol levels and liver function, the researchers could understand the mechanism—how the compound actually works—rather than just observing that it works.

This study was published in a reputable peer-reviewed journal (The British Journal of Nutrition), which means other experts reviewed the work before publication. The study used a clear control group for comparison and analyzed results with appropriate statistical methods. However, this is animal research, so results may not directly apply to humans. The sample size of 30 rats is reasonable for this type of preliminary study. The researchers were transparent about what they measured and how they analyzed the data.

What the Results Show

The main finding was that both herring oil and the concentrated compound significantly lowered total cholesterol in the rats’ blood. The herring oil group showed a 17% reduction in cholesterol, while the concentrated compound group showed a 20% reduction—both compared to the control group eating soybean oil.

When researchers examined the rats’ livers, they discovered how this worked: the compound reduced the liver’s production of new fats (a process called lipogenesis) and reduced how much cholesterol the liver packaged into particles for transport in the blood (called VLDL). This is important because VLDL particles carry cholesterol from the liver to other parts of the body, so reducing their production naturally lowers blood cholesterol.

Interestingly, the compound didn’t work by increasing cholesterol excretion (getting rid of cholesterol through waste) or by affecting how much cholesterol the liver made from scratch. Instead, it worked by reducing how much the liver processed and packaged cholesterol for transport.

The researchers also measured several liver enzymes and proteins involved in cholesterol metabolism. They found that the herring oil and concentrated compound diets reduced the activity of enzymes involved in making new fats and in packaging cholesterol for transport. However, the diets did not affect the liver’s ability to make cholesterol from basic building blocks, nor did they affect LDL receptors (the structures that help remove cholesterol from the blood). The amount of cholesterol and bile acids excreted in feces was similar across all groups.

This research builds on earlier studies in rodents that suggested cetoleic acid (the active compound) could lower cholesterol. This study is valuable because it tested both natural herring oil and a concentrated form of the compound, and it investigated the specific mechanisms involved. The findings align with previous research showing that certain fatty acids can influence cholesterol metabolism, though this is one of the first studies to examine this particular compound in detail.

This study was conducted in rats, not humans, so the results may not directly apply to people. Rats with this genetic condition have naturally high cholesterol, which may not perfectly mirror human high cholesterol caused by diet and lifestyle. The study lasted only five weeks, so we don’t know if the effects would continue long-term or if rats would adapt over time. The study didn’t examine whether the compound affects other important health markers like triglycerides or HDL (good cholesterol) in detail. Finally, the study didn’t test whether eating herring oil would be as effective as the concentrated compound in real-world conditions.

The Bottom Line

Based on this animal research, herring oil or its active compound shows promise for potentially lowering cholesterol. However, this is preliminary evidence from rats, not humans. If you have high cholesterol, the strongest evidence-based recommendations remain: eat a heart-healthy diet rich in vegetables and whole grains, exercise regularly, maintain a healthy weight, and follow your doctor’s advice. If you’re interested in adding herring oil supplements, discuss this with your healthcare provider first, especially if you take blood-thinning medications. Confidence level: Low to Moderate (this is animal research; human studies are needed).

People with high cholesterol or those at risk for heart disease should be aware of this research, as it suggests a potential dietary approach. However, this is not yet proven in humans. People taking blood thinners should be cautious about herring oil supplements without medical guidance. This research is most relevant for researchers developing new cholesterol-lowering treatments and for people interested in dietary approaches to cholesterol management. Those with fish allergies should obviously avoid herring oil.

In this rat study, cholesterol reduction was observed after five weeks of consistent consumption. If similar effects occur in humans, you might expect to see changes in blood cholesterol levels within 4-8 weeks of regular herring oil consumption, though individual results would vary. However, remember this timeline is based on animal research and may not apply to humans.

Want to Apply This Research?

  • If you decide to try herring oil supplements (with doctor approval), track your daily intake in grams and log your cholesterol levels every 4-6 weeks through blood tests. Note any changes in energy, digestion, or other health markers.
  • Start by adding herring oil supplements to your daily routine at a consistent time (such as with breakfast). Pair this with tracking your weekly fish consumption and heart-healthy meals to create a comprehensive cholesterol management approach. Set a reminder to take supplements at the same time each day.
  • Establish a baseline cholesterol level before starting herring oil, then retest every 6-8 weeks for the first three months, then every 3 months thereafter. Track consistency of supplement use (aim for 90%+ adherence) and note any side effects. Compare your cholesterol trends over time and discuss results with your doctor to determine if the supplement is working for you personally.

This research was conducted in laboratory rats, not humans. While the findings are interesting, they do not yet prove that herring oil will lower cholesterol in people. Before starting any herring oil supplements or making significant dietary changes to manage cholesterol, consult with your healthcare provider or registered dietitian. This is especially important if you take blood-thinning medications, have fish allergies, or have other health conditions. High cholesterol should be managed under medical supervision. This article is for educational purposes and should not replace professional medical advice.