Eating nuts and olive oil can reduce the risk of a heart attack

reposted from: http://www.nhs.uk/news/2013/February/Pages/Mediterranean-diet-cuts-heart-disease-and-stroke-risk.aspx

crabsallover highlights, key points, comments / links.

Mediterranean diet cuts heart and stroke risk

Tue Feb 26, 2013 09:59

"Mediterranean diet 'cuts strokes and heart attacks in at-risk groups'," The Guardian advises. Along with much of the global media, The Guardian reports on a study that found that eating a diet rich in fruit, vegetables, fish, olive oil and nuts cuts the risk of heart disease and stroke by 30%.

The story is based on an impressive trial looking at the effects of a Mediterranean diet on people at risk of heart disease and stroke, compared with a standard low-fat diet.

Researchers found that after nearly five years people who followed a Mediterranean diet supplemented with either extra-virgin olive oil or mixed nuts were around 30% less likely to have had a heart attack or stroke, or to have died from one.

It should be noted that the number of strokes, heart attacks and deaths that occurred in the study was fairly small. Nevertheless, this large and well-conducted study supports previous research on the benefits of a Mediterranean-style diet for the heart and circulation. 

Where did the story come from?

The study was carried out by researchers from academic institutions across Spain, including the Universities of Barcelona, Valencia, Malaga and Navarra. It was funded by the Spanish government and other public sources.

Olive oil and nuts used in the trial were donated by commercial sources of these foods. Many of the researchers disclosed grants and fees for work done with agricultural and food industry firms and groups, as is common for research in this field.

It was published in the peer-reviewed New England Journal of Medicine.

The study did not compare the Mediterranean diet with statins, as The Daily Telegraph and Daily Mail's headlines imply. The claim that this diet is better than a drug appears to be an opinion of one of the researchers, rather than a statement of fact.

The current study cannot be used as a way of assessing the effectiveness of statins, not least because some of the people in the Mediterranean diet intervention group were also taking statins.

What kind of research was this?

This was a randomised controlled trial (RCT) involving people at risk of cardiovascular disease. It compared the effects of two variations of the 'Mediterranean diet' – one with extra-virgin olive oil and one with nuts – with a standard low-fat diet.

As the authors point out, previous research has suggested the Mediterranean diet may protect against heart disease and stroke. Helpfully, in this study the researchers have defined what they consider a Mediterranean diet to be and, as the paper is open access, you can view their Mediterranean dietary recommendations for free online.

A well-conducted RCT is the best way of examining the effects of a particular intervention (in this case a Mediterranean diet) compared with a control condition (in this case a standard low-fat diet) on a health outcome.

Randomisation helps iron out other factors that may affect cardiovascular risk, balancing them out between groups. For example, many observational studies of specific diets have been conducted. However, observational studies cannot necessarily prove that the particular diet was responsible for the outcomes seen. This is because people who choose to eat a healthier diet may also choose other healthier lifestyle options, such as exercising more or drinking less alcohol.

What did the research involve?

The trial began in October 2003. Eligible participants included men aged 55-80 and women aged 60-80. Participants did not have a history of heart attack or stroke, but were considered to be at future risk of having cardiovascular disease.

This was because they either had type 2 diabetes or at least three of the following major risk factors for cardiovascular disease:

• smoking
• high blood pressure
• high cholesterol
• being overweight or obese
• having a family member who developed heart disease at a young age

Participants were randomly assigned to one of three groups:

• one group was advised to follow a Mediterranean diet supplemented with extra-virgin olive oil
• a second group was advised to follow a Mediterranean diet supplemented with mixed nuts (walnuts, almonds and hazelnuts)
• the third control group were advised to follow a low-fat diet

Participants in the two Mediterranean diet groups received extra olive oil or nuts at no cost, while those in the control group received free non-food gifts.

All of the groups received a dietary training session at baseline (study start). The Mediterranean groups received further sessions every three months afterwards. This included an assessment of their adherence to the diet, while the low-fat group received a leaflet each year for the first three years explaining the low fat diet. In October 2006, this protocol was amended and the control group got the same intensity of diet advice and assessment as the other two groups.

Participants also filled in a general medical questionnaire, a food frequency questionnaire and a physical activity questionnaire every year. Their weight, height and waist circumference was measured. The researchers also measured certain biomarkers (chemicals in the blood or urine) in random subgroups of participants in the Mediterranean diet groups at one, three and five years to see if they were sticking to the advice to supplement their diet with extra-virgin olive oil or nuts.

Over the period of the study, they looked at the main (primary) outcome of interest, which was the number of participants who had suffered either a heart attack or stroke or who had died from any cardiovascular cause. Other (secondary) outcomes the researchers examined were the number of people who had suffered these individual events and those who had died from any cause. They obtained this information from:

• repeated contact with participants
• contact with family doctors
• yearly review of medical records
• the national death index

The researchers initially estimated they would need a sample of 9,000 participants to detect any significant differences in outcomes between the groups. However, this figure was recalculated in April 2008 to 7,400 participants.

What were the basic results?

A total of 7,447 people were enrolled in the trial. The researchers report that the people in the two Mediterranean diet groups said they adhered to their diets, which was confirmed by biomarkers in the blood or urine.

After an average follow-up of 4.8 years, they found that in total 288 people either had a heart attack, stroke or died from a cardiovascular event. Of these:

• 96 (3.8%) events occurred in the Mediterranean diet group with extra olive oil
• 83 (3.4%) occurred in the Mediterranean diet group with extra nuts
• 109 (4.4%) occurred in the control group on a standard low-fat diet

After adjusting for baseline risk factors (such as diabetes), the researchers calculated that, compared with those who followed the standard low-fat diet, those assigned to a Mediterranean diet with extra-virgin olive oil had a 30% reduced risk of suffering a heart attack, stroke or dying from a cardiovascular event (hazard ratio 0.70, 95% confidence interval (CI), 0.54 to 0.92).

Similarly, those assigned a Mediterranean diet with nuts had a 28% reduced risk of suffering a heart attack, stroke or dying from a cardiovascular event (hazard ratio 0.72, 95% CI 0.54 to 0.96).

No diet-related adverse effects were reported.

How did the researchers interpret the results?

The researchers say that among people at high cardiovascular risk, a Mediterranean diet supplemented with olive oil or nuts reduced the number of cardiovascular events over the study period.

They suggest there is a "synergy" in the diet's nutrient-rich foods that fosters favourable changes to some risk factors, including blood fats, insulin sensitivity and inflammation. However, they say that in this trial olive oil and nuts were probably responsible for most of the benefits.

Conclusion

The results of this randomised controlled trial appear to confirm previous studies that there are benefits to following a Mediterranean diet. The trial has many strengths, including its large size, long period of follow-up, thorough assessment of medical outcomes (including reviewing medical records and having contact with the family doctor), and careful attempts to assess whether the diets were being followed.

As this is a randomised controlled trial, it should also balance out other health and lifestyle differences between the groups that may influence cardiovascular risk. This avoids the limitations of many previous diet observational studies, where participants choose which diet to follow.

However, there are still several limitations to bear in mind:

• The protocol for the control groups was changed halfway through the trial. This group did not receive the same intensity of dietary advice as the other two groups, a factor which could have affected their compliance with the diet.
• Despite careful attempts at screening and measuring biomarkers, it is still difficult to know how far participants stuck to their assigned diets.
• The control group had a higher dropout rate (11.3%) compared with the Mediterranean diet groups (4.9%).
• The participants were at high risk of cardiovascular disease at study start, but had not yet suffered any cardiovascular events. It is not certain if the results are generalisable to other groups, including those with no risk factors for cardiovascular disease and those who have already suffered from a heart attack or stroke.

The 30% reduction in risk may sound impressive but, as the authors point out, these results mean that following a Mediterranean diet would mean that about three major cardiovascular events would be avoided per 1,000 person-years. This means that if 1,000 people at high risk of cardiovascular disease ate a Mediterranean diet for one year, there would be three fewer 'events' (such as stroke) than there would be if they ate a standard low-fat diet.

Despite these limitations, this large and well-conducted study adds to the body of previous research on the benefits of a Mediterranean style diet for the heart and circulation.

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.

Links To The Headlines

Mediterranean diet 'cuts strokes and heart attacks in at-risk groups'. The Guardian, February 25 2013

Mediterranean diet 'as good as statins'. The Daily Telegraph, February 25 2013

Eating nuts and olive oil can reduce the risk of a heart attack as much as statins. Daily Mail, February 26 2013

Links To Science

Estruch R, Ros E, Salas-Salvadó J, et al. Primary Prevention of Cardiovascular Disease with a Mediterranean Diet. The New England Journal of Medicine. Published online February 25 2013

Mediterranean diet - high in fruit & veg & olive oil, low in meat

reposted from: http://www.nhs.uk/news/2011/03March/Pages/mediterranean-diet-obesity-blood-pressure-diabetes.aspx

crabsallover highlights, key points, comments / links.

Eating a Mediterranean diet “can reduce the risk of developing conditions such as diabetes, obesity and high blood pressure”, The Daily Telegraphhas today reported. Mediterranean diets are typically high in fruit and vegetables, low in meat and use olive oil in place of dairy fats.

The news comes from a new review of research on the Mediterranean diet that combined and analysed the results of 50 studies in more than 500,000 people. Among the most notable findings were that those eating the diet had lower blood pressure, lower blood sugar and higher levels of ‘good’ cholesterol. The study also found an overall reduction in symptoms of metabolic syndrome, which is a combination of risk factors that increase the likelihood of cardiovascular disease.

This new review did not assess the development of heart disease and diabetes, but it has demonstrated that the Mediterranean diet reduces the development of metabolic syndrome and its components, which are often precursors to the development of these conditions. There were some differences between the gathered studies that suggest that the results should be interpreted somewhat cautiously, although the trends seen do support other research about this dietary pattern.

Where did the story come from?

The study was carried out by researchers from universities in Athens and Ioannina in Greece and in Naples, Italy. The authors do not specify whether they received external funding. The study was published in the peer-reviewed Journal of the American College of Cardiology.

The press has covered this study well, although headlines stating that the Mediterranean diet “cuts risk of heart disease” may incorrectly imply that the study directly measured outcomes of heart disease. The study was concerned with a range of risk factors that are likely to precede heart disease, such as high blood pressure.

What kind of research was this?

This is certainly not the first time that research on the Mediterranean diet has made headlines, with numerous individual studies on the diet having received press coverage. However, this systematic review and meta-analysis provides the most up-to-date assessment of the evidence for the diet as a way to reduce the risk of developing cardiovascular disease in adults.

Specifically, the authors combined the results from 50 previous studies that had measured the effects of the diet on metabolic syndrome, a cluster of risk factors in adults that together can considerably raise the likelihood that a person will develop diabetes or heart disease. Metabolic syndrome is defined formally as the presence of any three of the following:

• high blood pressure (greater than 130/85mmHg or active treatment for hypertension)
• high blood sugar (fasting plasma glucose >5.6mmol/L or active treatment for hyperglycaemia)
• high blood fat (triglycerides ≥1.7mmol/L)
• low levels of ‘good cholesterol’ (<1.03mmol/L for men or <1.29mmol/L for women)
• a large waist circumference (≥102cm in men and ≥88cm in women or ≥90cm in Asian men and ≥80cm in Asian women)

Lifestyle interventions, particularly changes in diet and increases in physical activity, are established ways to prevent metabolic syndrome and, consequently, to reduce the likelihood of cardiovascular disease and diabetes. The Mediterranean diet is generally considered to consist of a high concentration of good oils (monosaturated fatty acids), usually from olives and olive oil; daily consumption of fruit, vegetables, wholegrains and low-fat dairy; weekly fish, poultry, nuts and legumes; low red meat consumption and moderate alcohol consumption. It has been linked to reduced risk of cardiovascular disease, cancer and diabetes.

This study takes a new angle by specifically looking at the effects diet has on the risk factors that often precede the development of cardiovascular diseases.

What did the research involve?

The researchers set out to identify all English language research studies published up to April 30 2010, that assessed the effects of a Mediterranean diet on the development of metabolic syndrome or its components. They searched well known medical databases including PubMed, Embase and the Cochrane Central Register of Controlled Trials. They did not exclude studies on the basis of study design at this stage.

Their search initially identified 474 studies, but after excluding those that did not meet specific inclusion criteria (such as those that failed to be randomised if they were trials, those that failed to compare the Mediterranean diet against another diet or those that missed some of the key components of the Mediterranean diet) they were left with 50 studies that were eligible for analysis. There were 2 cohort studies, 35 randomised controlled trials and 13 cross-sectional studies. They provided a total study population of 534,906 individuals.

The researchers extracted the results data from each study, specifically the reports of changes in or progression of metabolic syndrome or any of the main components (waist circumference, blood pressure, blood cholesterol, blood fat or blood glucose). The results were then pooled using the statistical techniques of meta-analysis. The researchers differed the techniques according to whether they were combining the results from the randomised controlled trials, the cohort studies or the cross-sectional studies. The researchers also rated the quality of each study to help provide a measure of their confidence in the results obtained from the pooling.

From their analyses, the researchers then reported how a Mediterranean diet affects the risk of metabolic syndrome and some of its separate components. Although 50 studies were included overall, the different outcomes they each addressed meant that fewer studies could be included in the meta-analyses relating to each specific outcome. For example, in total, only eight studies assessed the effect of Mediterranean diet on the development or progression of the entire set of metabolic syndrome risk factors. Only two of these were randomised controlled trials, two were cohort studies and four were cross-sectional studies.

What were the basic results?

The Mediterranean diet was found to protect against the development or progression of metabolic syndrome, reducing the risk by about 50%. The Mediterranean diet was also protective against some of the individual components of the syndrome, with people who consumed it having, on average, a 42cm smaller waist circumference, higher levels of good cholesterol (1.17mg more), lower blood triglycerides (-6.14mg lower), lower blood pressure and lower blood glucose.

How did the researchers interpret the results?

The researchers conclude that their results “are of considerable public health importance” because the dietary pattern can be easily adopted by all population groups and is a cost-effective approach to the primary and secondary prevention of metabolic syndrome and its individual components.

Conclusion

This was a well conducted systematic review and meta-analysis, although the interpretation of some of its extensive results is not straightforward. The researchers have performed different sub-analyses, each separately pooling all cross-sectional studies, all cohort studies and all controlled trials. They then reported the results of these groups separately and also combined the results from cohort studies and trials in some cases.

The most noteworthy results are probably those obtained from pooling randomised controlled trials. Randomised controlled trials have the most appropriate study design for assessing the effects of receiving an intervention compared with not receiving it. Pooling just those results from randomised controlled trials showed Mediterranean diet reduced the risk of developing or progressing metabolic syndrome overall, as well as all of the individual components that make up the syndrome. These are the important results of the study, as combining the results of cohort studies and cross-sectional studies has limitations. Neither cohort studies nor cross-sectional studies can prove cause and effect.

There are some other points to keep in mind when interpreting the results:

• Although the researchers excluded studies that did not describe the full Mediterranean diet, the precise pattern of food was likely to vary across the included studies as was the way it was administered and the recommendations given. There were also differences in the diets consumed by the control groups and in whether dietary change was being recommended as part of wider lifestyle changes or not.
• Importantly, some of the analyses combined studies that were very different from one another in terms of the sample size, study duration, trial quality and context of intervention. These analyses had a high ‘statistical heterogeneity’, which is a way of measuring whether it is appropriate to pool them or not (higher heterogeneity means pooling is less appropriate). The researchers say that this “introduces a warning about the generalisation of the present results”.
• The outcomes were related to risk factors for cardiovascular disease, not the disease itself. It is, therefore, an extrapolation, although perhaps not an unrealistic one, to claim that this study proves that the Mediterranean diet has an effect on cardiovascular disease outcomes.

Overall, this research provides further evidence of the benefits of eating a Mediterranean-style diet and quantifies the benefit in terms of the individual risk components of metabolic syndrome.

Links to the headlines

Mediterranean diet 'cuts risk of heart disease'. The Daily Telegraph, March 8 2011

Links to the science

Kastorini CM, Milionis HJ, Esposito K et al. The Effect of Mediterranean Diet on Metabolic Syndrome and its Components: A Meta-Analysis of 50 Studies and 534,906 Individuals. Journal of the American College of Cardiology, 2011; 57:1299-1313