Here's another reason for taking trans fats out of junk food: Scientists studying herring gull eggs collected from around the Great Lakes have found they are becoming more contaminated with the artery-clogging fat.
The concentrations in the eggs have risen rapidly, doubling or tripling over the past 25 years depending on location.
For birds, the health impact of having trans fats in their eggs is unknown. But the finding, made by Environment Canada and U.S. Geological Survey scientists, highlights the sometimes strange serendipity that occurs when humans mess with Mother Nature.
Scientists attribute the rising amount of fat in the eggs to the well-meaning program governments have orchestrated of stocking the Great Lakes with Pacific salmon. At last count, 745 million salmon have been added, much to the delight of anglers who spend billions each year trying to catch them.
But releasing so many salmon - voracious consumers of small fish - has had the unforeseen consequence of causing herring gulls to go hungry, driving the birds to garbage bins and ultimately to accumulating the junk-food ingredient in their eggs.
The amount of trans fats is "two to three times higher now than it was in the past. Whether that's a problem for the birds, we can't comment," said Craig Hebert, a biologist at Environment Canada's National Wildlife Research Centre in Ottawa and head of the team that analyzed the eggs.
Human diets rich in trans fats are associated with undesirable cholesterol levels and an increased risk of heart disease. The fat, made by modifying edible oils to contain hydrogen, is used in everything from doughnuts to French fries and pastries.
The type of fat the scientists found does not occur much in nature, and the eggs wouldn't contain any if the birds were living in a human-free environment.
Herring gulls, true to their name, don't normally crave doughnuts and other kinds of trashy human fare. If given their druthers they would rather eat small fish, a rich source of omega-3 fatty acids and other beneficial nutrients. (The gulls often found hanging around fast-food parking lots that have developed a hankering for junk food are a different species - ring-billed gulls. Herring gulls are larger and have a red tip on their beaks.)
The problem for the herring gulls is that they now have to compete with the salmon for the smaller prey fish. Both have the same natural diet, pint-sized fish such as alewives, smelt and shiners.
The stocking measures that have pitted bird against fish were undertaken with the best of intentions, starting in the mid-1960s.
At the time, the top natural predators in the lakes were trout, but their numbers had been virtually eliminated by parasitic lamprey eels, which entered the ecosystem from the Atlantic Ocean through canals. As a result, the population of smaller fish on which the trout once fed grew out of control.
So it seemed like a good idea to try to restore some balance to the lakes by adding the salmon to take the place of the trout.
Mr. Hebert says salmon have "done what they were intended to do." But from the standpoint of the birds, the salmon have done too good a job. The abundance of prey fish has declined precipitously in all five Great Lakes since the 1980s, according to a scientific paper that outlined the trans fat finding.
With fewer small fish available, the herring gulls have had to supplement their diets with items they can scavenge, typically from landfills.
Another consequence of the food shortage is a decline in herring gull populations, which have fallen by 9 per cent to 30 per cent since the mid-1970s depending on the lake. The biggest declines were around Lake Huron and Lake Superior.
"It's likely that these dietary changes have contributed to some of the population declines that we've seen," Mr. Hebert said.
Scientists have been able to track trans fats because Environment Canada has been keeping eggs from herring gull colonies in cold storage since the mid-1970s in one of the longest-running wildlife surveillance programs in the world.
Eggs were first collected to track concentrations of dangerous pollutants, such as the pesticide DDT and the industrial transformer oil known as PCBs, both now banned chemicals.
When the egg collection started, trans fats weren't a problem and no one thought to check their levels. Mr. Hebert's team found low levels in eggs from the 1980s, indicating that there was a small amount of garbage feeding then.
"This is a benefit of this long-term program," Mr. Hebert said. "Samples can be used for things that were never envisioned before."
Now researchers will have to study whether a high-trans-fat diet is as bad for birds as it is for humans.
