Food and diet

Olive oil and wholegrains 'lower heart disease risk'

"Butter isn't better than margarine after all," declares the Mail Online, after a new study found eating less saturated fat does indeed lower the risk of heart disease.

The study, which followed the dietary habits of nearly 130,000 people over almost 30 years, found those who had a diet high in unsaturated fats, such as olive oil, and wholegrains had a lower risk of heart disease.

The findings, published in the Journal of the American College of Cardiology, showed replacing 5% of saturated fats in the diet with unsaturated fats reduced the risk of coronary heart disease (CHD) by 25%.

Recent studies have cast doubt on the link between saturated fat intake and the risk of developing CHD. Researchers did not find a link between eating less saturated fat and a lower death rate.

The authors of the study claim this is because many people who cut down on saturated fats replace it with added sugar and refined carbohydrates, such as white bread, which are also linked with CHD.

Overall, the study suggests consuming higher amounts of unsaturated fats and wholegrains was associated with a lower risk of developing heart disease.

While the study included a large sample size and long follow-up period, it cannot prove causality. There is the possibility people didn't accurately recall their diet, and other health and lifestyle factors could be influencing any observed link.

And the results of this study cannot apply to the whole population – it only included health professionals, who may have distinct health and lifestyle characteristics.

Nevertheless, it is advisable to follow a healthy lifestyle, taking regular exercise and eating a balanced diet that includes complex carbohydrates like wholegrains, and is low in saturated fat, salt and sugar.

While the study does not show saturated fats should be avoided altogether, it perhaps supports the well-known adage "everything in moderation". 

Where did the story come from?

The study was carried out by researchers from Harvard Medical School and the Wellness Institute at Cleveland Clinic, and was funded by the US National Institutes of Health.

It was published in the peer-reviewed Journal of the American College of Cardiology.

The UK media reported the findings of the study accurately, but some of the strengths and weaknesses were not explicitly mentioned.

The Mail reports a quote from one of the lead authors of the study, Professor Frank Hu, who said: "Our research does not exonerate saturated fat. In terms of heart disease risk, saturated fat and refined carbohydrates appear to be similarly unhealthy."

He adds: "Our findings suggest that when patients are making lifestyle changes to their diets, cardiologists should encourage the consumption of unsaturated fats like vegetable oils, nuts, and seeds, as well as healthy carbohydrates such as wholegrains". 

What kind of research was this?

This was an observational study that investigated the associations between saturated fat (such as butter, cheese and whipped cream) compared with the intake of unsaturated fat (such as vegetable oil, sunflower oil and walnuts) and different sources of carbohydrates, and the risk of developing heart disease.

Recent studies have cast doubt on the link between saturated fat intake and the risk of developing CHD. But researchers say these studies did not consider that when cutting down on saturated fat, people tended to replace it with carbohydrates from added sugars and refined starches, such as potatoes, white bread and pasta, which did not reduce their CHD risk.

This type of study, involving many people over many years, can show an association between eating less saturated fat and a reduced CHD risk. But it cannot show causality, as many other factors may be involved, including the participants' ability to accurately remember their diet.

What did the research involve?

This study included 84,628 women from the Nurses' Health Study (aged 30 to 55 at enrolment) and 42,908 men from the Health Professionals Follow-up Study (aged 40 to 75 at enrolment). These individuals were free from diabetes, cardiovascular disease and cancer at the start of the study.

Participants completed a food frequency questionnaire once every four years throughout the study period. They were asked what type of fat oil they used for frying and baking, and if they used any margarine during the past year. The questionnaire had nine possible responses, ranging from "never" to "less than once per month", to "more than six times per day".

Daily fat intake by type was calculated by multiplying the frequency of the food consumption with its nutrient content using US Department of Agriculture food composition data.

In the study, carbohydrates were classed as either wholegrains or refined starches, added sugars, refined grains, and sugary foods and drinks.

The outcomes of interest were non-fatal heart attack, heart disease overall, and deaths as a result of heart disease, which were identified through a review of medical records.

What were the basic results?

Over a follow-up period of 24 to 30 years, there were 7,667 cases of heart disease (4,931 non-fatal heart attacks and 2,736 deaths from heart disease).

Some of the main findings of the study are listed below:

  • Highest intake of unsaturated fats was associated with a 20% significantly lower risk of heart disease compared with individuals with the lowest unsaturated fats intake (hazard ratio [HR]: 0.80, 95% confidence interval [CI]: 0.73 to 0.88).
  • Highest intake of carbohydrates from wholegrains was associated with a 10% significantly lower risk of heart disease compared with individuals with the lowest wholegrain intake (HR 0.90, 95% CI 0.83 to 0.98).
  • There was a borderline significant trend for high intake of carbohydrates from refined or added sugars to be associated with increased risk of heart disease (HR 1.10, 95% CI 1.00 to 1.21).
  • Replacing 5% of energy intake from saturated fats with equivalent energy intake from unsaturated fats, monounsaturated fatty acids, or carbohydrates from wholegrains was calculated to reduce the risk of heart disease by 25%, 15% and 9% respectively. 

How did the researchers interpret the results?

The researchers concluded unsaturated fats and high-quality carbohydrates, such as wholegrains, can be used to replace saturated fats to reduce CHD risk.

They said: "Unsaturated fats, such as those from vegetable oils, nuts, and seeds, should have an expanded role as a replacement for [saturated fats].

"However, our data from national surveys suggest that, when decreasing [saturated fats] intake, most people appear to increase the intake of low-quality carbohydrates, such as refined starches and/or added sugars, rather than increase the intake of unsaturated fats." 


This observational study looked for an association between saturated fat intake compared with unsaturated fat intake and complex carbohydrate intake, and the risk of developing heart diseases.

Overall, the study suggested consuming higher amounts of unsaturated fats and complex carbohydrates such as wholegrains was associated with a lower risk of developing heart disease.

This study has several strengths, such as the inclusion of a large sample size of both men and women, and a long follow-up period. But because of the observational study design, it cannot prove causality.

The researchers have adjusted their analyses for various health and lifestyle factors that could be influencing the link, such as body mass index (BMI), smoking status, physical activity and alcohol intake.

However, it is difficult to fully account for the influence of all of these factors – or others that were unmeasured – that could be involved in the diet and heart disease link.

Another important limitation is the possibility of recall bias. People were asked to specify by quantity the types of fat they used in baking and frying in the previous year, and the amount and types of carbohydrates they had eaten. It's possible some of this information may have been inaccurate, and some people could have been put into the wrong intake groups.

As the participants were all health professionals, they may have distinct health and lifestyle characteristics, meaning their results cannot be applied to the population as a whole.

NHS Attribution