The fat of the land

Most of the trans fats New Zealanders injest come from the diets of our dairy cows - lush pasture supplemented with palm kernel expeller. Photo / Sarah Ivey

First the good news. New Zealanders don't eat a lot of harmful trans fats and food manufacturers have reduced trans fat levels in the food made in New Zealand.

Now the not so good. Unlike the rest of the world, most of the trans fats we eat come from dairy foods and red meat and that's related to what we feed our sheep and cows - lush pasture with clover, with palm kernel expeller supplement for our cows.

Here's the kicker. Two naturally occurring trans fatty acids in our milk and meat have just been shown to be associated with polyvascular disease and stroke in high risk patients.

Click here for more information on trans fats.

The startling finding comes from an observational study led by Dr Jocelyne Benatar at the Cardiovascular Research Unit of Auckland City Hospital, now published in the peer-reviewed European Journal of Cardiovascular Prevention and Rehabilitation.

"It came out of left field. It was a study looking at lots of other things," says Benatar who is quick to point out it is not a causal finding. "You can't overplay this study. It's just the first time we've shown it."

Fair enough - more studies are needed. But the hypothesis generated by this study has the potential to change how we farm and what we eat.

The startling aspect of the research, which Benatar presented to the Cardiac Society of Australia and New Zealand's June annual scientific meeting, is the presence of palmitelaidic acid, a trans fat derived from palm kernel.

The fact that it turns up in the analysis of blood samples taken from 390 patients with severe coronary disease is evidence that what we're feeding our cows wends its way through the food chain to us. We are what we eat.

Benatar's research shows the palm kernel-based trans fat does not originate from processed food.

"In New Zealand the palmitelaidic acid comes from our dairy foods which means what our cows are being fed is coming up through the food chain," she says. "The ruminant bacteria in the cows' stomachs are making it into trans fat and that's the trans fat we get."

It's long been known that naturally occurring trans fats are present in the milk and the meat of ruminant animals such as sheep and cows, the most common being vaccenic acid.

What most probably don't know is that grazing cows produce more of it than grain-fed cows. So it wasn't terribly surprising that vaccenic trans fat showed up in the lipid analysis of the patients' blood, along with other trans fats found in processed foods.

But the presence of the palmitelaidic trans fat hadn't been seen before.

"I wondered how it was getting into our cows." It was only when Benatar noticed a news item on Greenpeace concerns about the amount of palm kernel animal feed imported into New Zealand that she made the connection. The use of palm kernel expeller - the leftovers from when kernel oil is pressed out from the nut in the palm fruit - to supplement dairy cows' largely grass diet is increasing in New Zealand.

In 2004 when the study began, palm kernel cake imports were just 95,920 tonnes. In 2008 they swelled to just over a million tonnes, falling back to 665,382 tonnes in 2009. Greenpeace's concern was the destructive effect that the palm oil industry was having on the last remaining rainforests in Indonesia.

Trans fat intake is very low in New Zealand - around half a per cent of total dietary energy compared to between 2-4 per cent for other Western countries. New Zealanders' intake of trans fats is predominantly from dairy sources (60-75 per cent), whereas in most Western countries the trans fats ingested come from processed foods (about 85 per cent).

All of which seems to indicate New Zealanders are less at risk from the health hazards of too much trans fat consumption, especially the adverse effect on cardiovascular health.

Studies all tended to show that artificially produced trans fats are the problem, rather than the naturally occurring trans fats in our milk and meat. Until now.

While Benatar's research isn't conclusive, it does raise some intriguing questions. The statistical association between the "natural" trans fats and vascular disease including stroke, like the presence of palmitelaidic acid, is something not seen before.

Polyvascular disease involves atherosclerosis, the thickening of artery walls through a build-up of fatty materials such as cholesterol. The possibility that natural trans fats may play a part in that disease is something Benatar wants to investigate further.

While the World Health Organisation recommends people should consume no more than 1 per cent of their daily kilojoules from trans fatty acids, the Auckland hospital study indicates for high risk patients the safe threshold may be much lower.

"The study is saying if you are a high risk patient, 1 per cent is probably not safe," say Benatar.

"Maybe having a lot of trans fats, regardless of where they come from, affects atherosclerosis throughout your body and not just heart disease on its own."

For at risk patients with cardiovascular disease the conventional wisdom is to reduce the dietary intake of saturated fats - hence no butter, limited red meat and so on.

But Benatar's research indicates a more complex interrelation may be at play, with naturally occurring tans fats - even at very low levels - having a larger role than previously thought. "It may be the combination of trans fats as well as the saturated fats in red meat and dairy that affect the disease."

So does this mean at risk coronary patients should stop drinking milk? Not all says Benatar. If the naturally occurring trans fats are found to be a key factor in cardiovascular disease, rather than the problematic business of trying to alter dietary habits, it should be possible to correct the problem at the source.

First stop feeding cows palm kernel and then investigate how changing our pasture grasses might reduce trans fat production. "You could also look at the bacteria in the gut of cows and see whether changing that has an effect on vaccenic acid in the milk." As Benatar points out, dairy product are not inherently bad. "Things like yoghurt and milk are very good for you."

The huge opportunity for New Zealand, she says, is that we are one of the few countries where researchers can look at dairy trans fats without being overwhelmed by industrial trans fats.

Benatar is about to begin a new a dietary intervention study with subjects who will either increase their dairy intake, reduce it, or leave it the same for a month - because it takes three weeks for trans fats to wash out of a person's system.

"That will prove where these trans fats are coming from." If her research proves correct, it could write a new chapter in the book on cardiovascular disease.