With all the conflicting studies on what you should and shouldn’t eat, you might be getting confused, hungry and cranky.
The saturated fat debate is the most puzzling of all. Could the foods we’ve avoided for decades be the ones to actually lap up? Nutritionists are divided, and then last week came another twist – a dramatic study claiming that 30 years of dietary fat guidelines lacked any solid grounding.
So who can you trust? Does anyone out there have a clue? Stuff readers, we feel your pain!
So here’s our crack at simplifying things – summing up the current perspectives on saturated fats and what it means for existing dietary guidelines.
1. Why is saturated fat such a hot topic?
Because people are getting fatter despite decades of advice to cut down on dietary fat.
It seems we’ve replaced fat with sugar and carb-laden food – so the argument for saturated fat is often also an argument against carbohydrates.
Those in favour of saturated fat say it is not a direct cause of heart disease. They say replacing carbohydrates with fat can actually aid weight loss, reduce the risk of diabetes and improve other health markers. But such claims are shunned by conventional wisdom which tells us saturated fat increases cholesterol and a number of other risk factors for heart disease.
Evidence shows replacing saturated fat with either unsaturated fat, or the right types of carbohydrates, reduces cardiovascular risks.
2. What changed last week?
A new study published in the BMJ’s Open Heart journal found no solid evidence for the national dietary guidelines introduced in 1977 and 1983 by the US and UK governments respectively, which urged millions of people to limit their fat intake in order to reduce their risk of coronary heart disease.
It claims to be the first study to review the randomised controlled trials available at the time the dietary fat guidelines were introduced.
3. What was wrong with the original evidence?
Researchers found holes in the quality and robustness of the original studies and say the evidence did not support the guidelines issued.
While the original studies found that serum cholesterol levels were reduced by dietary interventions (such as lowering fat intake), they did not find any relationship between dietary fat intake and deaths from coronary heart disease (CHD), despite those reductions in cholesterol levels. This finding, researchers said, contravenes the theory that reducing dietary fat reduces the risk of CHD.
4. Did the earth move with this study?
No. Subscribers to conventional wisdom, such as the University of Otago’s Professor Jim Mann, says the “review” was flawed as it looked at “mortality” when the original trials weren’t designed to look at that. The guidelines introduced 30 years ago aimed to reduce coronary heart disease overall, not mortality (though if you reduce CHD, over time you’ll reduce mortality too).
“The evidence available in the 1970s would not pass the test today, but it did pass the test in the ’70s,” Mann says. More importantly, the “totality of the evidence” gathered in the past 30 years backs the existing guidelines.
5. So is there proof of a direct link between dietary saturated fat and coronary heart disease?
Individual studies have argued this point – one review involved more than 347,000 people and found no “significant evidence for concluding that dietary saturated fat is associated with an increased risk of coronary heart disease”. The problem with this study and some others, says Mann, is that the benefit of reducing saturated fat depends on the replacement foods used, which means all variables should be looked at.
Replacing saturated fat with unsaturated fat or appropriate carbs (not rapidly-digested white rice, potatoes and free sugars) would show a benefit to CHD, says Mann. For example, a 2009 review of 344,000 people showed that substituting five per cent of energy from saturated fats with five per cent of energy from polyunsaturated fats resulted in a 26 per cent reduction in risk of coronary death. Substituting saturated fats with carbohydrates or mono-unsaturated fats, however, was not associated with benefit.
He says cherry-picked studies can’t stand up to the “totality of evidence” that backs the status quo. If you put all the studies together and allow for all the variables, it’s clear that saturated fat increases blood cholesterol, and high blood cholesterol is the best marker there is for heart disease.
6. So is cholesterol the major perpetrator of heart disease?
Authors of the latest review claimed their evidence “undermines the role of serum cholesterol levels as an intermediary to the development of CHD”. Others have questioned it too, saying it’s inflammation – not cholesterol per se – that causes heart disease.
Mann can’t believe this debate goes on: “You can show that if you reduce cholesterol, whether by drugs or by diet, the benefit that you get in terms of coronary heart disease risk reduction is directly proportional to the reduction you get in cholesterol.”
7. And there’s no argument that saturated fat raises cholesterol?
Everyone agrees on this one, but some say it depends on the fat.
Hawke’s Bay clinical nutritionist Ben Warren says coconut oil, for example, raises your good cholesterol more than it raises the bad, improving your cholesterol profile overall.
Other pro-fat advocates blame the combination of fat and carbs for increased cholesterol. AUT’s Professor Grant Schofield says in cultures with diets high in saturated fats, but low in carbohydrates, heart disease is uncommon.
Not as much as first thought. Saturated fats and trans fats are thought to contribute more to blood cholesterol levels than dietary cholesterol does.
Last week America’s top nutrition advisory panel decided to drop its caution on eating cholesterol-laden food – this is no surprise to Kiwi nutritionists, they’ve worked on the assumption for a while that dietary cholesterol is no villain.
9. Does that mean carbohydrates are the enemy, not fat?
Pro-fat advocates do believe sugars and refined carbohydrates are worse for you than saturated fat. The trend among nutritionists though, is to talk about “real foods” and “whole foods” rather than various nutrient groups. After all, no-one sits down to eat carbohydrates, fats and protein – instead they eat potatoes with chicken and avocado.
Almost any nutritionist agrees processed foods are the ones to watch.
10. So what is the current dietary advice in New Zealand?
The Ministry of Health recommends between 30-33 per cent of our daily intake should come from fat, of which no more than 12 per cent should be saturated fat.
As for the Heart Foundation, they’re developing a fat policy paper as a priority, and will be looking at the totality of the evidence (there’s that phrase again) to inform their recommendations, says nutrition spokesperson Dave Monro.
For now, their position remains the same: have some fat in the diet, but replace saturated fat with unsaturated fats, such as oily fish, nuts, seeds, plant and vegetable oils.