Fatty acid metabolism could lead to new designer eggs

Research in Penn State's College of Agricultural Sciences aims to fortify foods people frequently eat eggs and chicken with heart-healthy, long-chain omega-3 fatty acids. Image: Pexels

Researchers aim to further enrich eggs and poultry meat with omega-3 fatty acids.

Research has shown that the consumption of long-chain omega-3 polyunsaturated fatty acids provides a myriad of health benefits, including lowering the risk of cardiovascular disease and death, according to an announcement from The Pennsylvania State University. Still, few Americans are consuming enough of this nutrient to reap such benefits.

Researchers in Penn State's College of Agricultural Sciences hope to change this deficiency by fortifying foods people frequently eat eggs and chicken with the heart-healthy long-chain omega-3 fatty acids.

"Production of nutritionally enriched eggs and poultry meat will help consumers meet health goals and help egg and poultry producers increase the value of their products," said Kevin Harvatine, associate professor of nutritional physiology in the Penn State department of animal science.

Harvatine and Robert Elkin, professor of avian nutritional biochemistry, have collaborated in this research area since 2011, conducting numerous studies at the Penn State Poultry Education & Research Center with both laying hens and broiler (meat-type) chickens. Elkin has expertise in poultry nutrition and a long history of work aimed at modifying egg cholesterol content, while Harvatine has expertise in lipid (fat) nutrition and metabolism in dairy cattle.

The researchers explained that alpha-linolenic acid is an 18-carbon omega-3 fatty acid; it is one of two essential fatty acids that the human body cannot produce on its own but is vital for cardiovascular, cognitive and immune system health. It also is touted for its anti-inflammatory properties.

The other essential fatty acid is linoleic acid, an 18-carbon omega-6 fatty acid. While omega-6 fatty acids can be beneficial, consuming too much which many people do is not good because it promotes inflammation, Elkin pointed out.

In addition, linoleic and linolenic acids compete for the same set of enzymes in the liver that convert them into longer-chain derivatives, which have opposing functions in the inflammatory process. As a result, when the ratio of omega-6 to omega-3 fatty acids favors the former, fewer omega-3 fatty acids are produced by the liver and transported to tissues such as the brain and retina, where they have other important physiological functions, the researchers noted.

While over-the-counter supplements are available, the researchers believe it is better to reach omega-3 nutritional targets through food such as enriched poultry meat and eggs.

Eggs find their way onto American plates with frequency. According to the American Egg Board, per capita consumption of eggs is about 267 a year, which works out to about five eggs per person per week. In addition, Americans consumed approximately 91 lb. of chicken per person in 2017, according to the National Chicken Council.

Unlike typical nutritionally enhanced eggs found in grocery stores, Harvatine's and Elkin's goal is to create poultry products that are richer in long-chain omega-3 fatty acids but lower in omega-6 fatty acids. Although the chicken is able to convert the 18-carbon omega-3 fatty acid found in plants to the heart-healthy long-chain omega-3s, the process is very inefficient. Humans also have a very limited ability to convert linolenic acid to the important omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

In a recent study published in Lipids, Elkin and Harvatine hypothesized that reducing the dietary level of omgea-6 linoleic acid would promote greater conversion in the liver of linolenic acid to EPA and DHA, while supplementing the hens' diets with a high-oleic acid soybean oil would simultaneously further enrich eggs with oleic acid without influencing egg EPA and DHA contents.

The researchers found that, compared to controls, supplemental dietary flaxseed oil resulted in an enrichment of egg yolks with EPA and DHA, but simultaneously supplementing the hens’ diet with both flaxseed oil and high-oleic soybean oil maximally reduced the yolk deposition of linolenic acid, long-chain omega-3 fatty acids and total omega-3 fatty acids by 37%, 15% and 32%, respectively.

These results suggested that dietary oleic acid was not neutral with regard to the overall process by which dietary linolenic acid was absorbed, metabolized and deposited into egg yolk, either intact or in the form of longer-chain/more unsaturated omega-3 fatty acid derivatives, the researchers said.

Based on their knowledge of fatty acid metabolism, as well as triglyceride positional analyses of the experimental oils, Elkin and Harvatine hypothesized that oleic acid may simply have out-competed linolenic acid for absorption from the intestines, which ultimately would result in less omega-3 fatty acid enrichment of egg yolks.

In addition to being the first study to report this, according to Elkin, the findings also have implications for human nutrition because the initial steps of intestinal fat digestion and absorption are similar in chickens and people.

"It is possible that oils rich in oleic acid might hinder the body's ability to reap the full nutritional benefits of EPA and DHA if consumed along with fatty fish or omega-3 fatty acid supplements, such as fish oil capsules," Elkin said. "This also could be occurring in people consuming a Mediterranean diet in which oleic acid-rich olive oil is the principal source of fat and moderate to low amounts of fish are eaten."

Studies are underway to confirm this finding in laying hens with other oils that are rich in oleic acid in order to demonstrate that it is an "oleic acid effect" and not an effect specific to only high-oleic soybean oil.

"The importance of this research to the (egg) industry is that we have learned of a potential new hindrance to enriching eggs with omega-3 fatty acids, and that information can be used when trying to develop the next generation of ‘designer’ eggs," Elkin said.