According to the Global Burden of Disease Study 2013, suboptimal diet is the main risk factor for death and disability world-wide. Our knowledge on both beneficial and harmful effects of specific foods has expanded rapidly, but there’s a lot of conflicting information. Our food choices must be backed-up by a strong scientific rationale, but how do we find our way around the overwhelming amount of evidence?

It’s useful to be aware that different types of studies provide different ‘levels of evidence’, based on their “their design, validity, and applicability to patient care”. The top of the hierarchy of evidence includes systematic reviews or meta-analyses of all relevant randomized controlled trials (RCTs) (level I) and large multi-center RCTs (level II). Meta-analyses allow combining the data from a number of individual studies.

In this blog, I summarize recent findings from a large cohort study and three meta-analyses of prospective studies, which provide good-quality evidence on the effects of various nutritional modifications on health outcomes.

Is the Mediterranean diet the best, outside of Mediterranean countries?

Rich in vegetables, fruit, cereals, nuts, regular ‘splash’ of olive oil, and occasional glass of wine, the Mediterranean diet has multiple beneficial health effects, such as decreasing the risk of cardiovascular diseases (CVD), diabetes, cancer, and cognitive disorders. The effect seemed to be clear-cut in Mediterranean populations, but it wasn’t so consistent for the non-Mediterranean regions, probably because of the use of different Mediterranean diet scores.

To tackle this issue, a study in the large UK-based cohort looked at four Mediterranean diet scores and their association with CVD risk. All but one consistently showed that following this diet was associated with decreased CVD incidence and mortality in the UK. More broadly, this study provides evidence that Mediterranean diet can be recommended as a part of CVD prevention programs.

Remember your greens…

“Increasing the consumption of magnesium-rich foods may be beneficial to overall health” Dr. Fudi Wang (read the entire blog here)

Magnesium is an essential mineral involved in a number of vital processes in the body, such as muscle and nerve function, energy production, and bone development. Foods with highest magnesium contents are dark green, leafy vegetables (spinach, Swiss chard, kale). Other magnesium-rich sources include nuts, seeds, beans, lentils, and whole grains.

Dr. Fudi Wang’s group carried out a dose-response meta-analysis looking at magnesium intake and the risk of CVD, type 2 diabetes and all-cause mortality. They compiled the data from 40 prospective studies with over 1 million participants from all over the world. Increasing dietary magnesium intake was linked to decreased risk of stroke, heart failure, diabetes, and all-cause mortality, but not of coronary heart disease or total CVD.

…and a wise amount of nuts

“Just adding a handful of nuts to the diet seems to be wise and might add more years to our life with a better quality of life” Prof. Agneta Åkesson & Dr. Carolina Donat-Vargas (read the entire blog here)

As mentioned above, nuts are rich in magnesium and are important part of the Mediterranean diet. Their consumption clearly has beneficial effect of on cardiovascular health, but the comprehensive scientific evidence on their impact on other health outcomes wasn’t consistent.

To address that, a recent comprehensive meta-analysis by Dr. Dagfinn Aune et al. evaluated nut consumption and the risk of CVD, cancer, and mortality (both all-cause and cause-specific), looking specifically at portion sizes. Data from 20 studies with 819,448 participants showed that adding a serving (28 g) of nuts to your daily nut intake decreases the risk of coronary heart disease, stroke, CVD, cancer and all-cause mortality.

…but don’t go overboard with alcohol!

“The take home message from this study is that for those who drink alcohol, the consumption should be no more than 1–2 drinks per day” Dr. Susanna C. Larsson (read the entire blog here)

Moderate alcohol consumption is linked to potential health benefits, particularly for the heart. On the other hand, binge drinking increases risk of CVD and mortality. As the effect of alcohol intake on stroke and its specific subtypes wasn’t clear, Dr. Susanna C. Larsson et al. conducted a meta-analysis on the topic.

They identified 27 prospective studies with 3,824 cases of ischemic stroke, 555 – intracerebral hemorrhage, and 176 – subarachnoid hemorrhage. Light and moderate alcohol consumption decreased the risk of ischemic stroke only, whereas heavy drinking was linked to increased risk of all stroke types.

It’s important not to take any nutritional recommendations at face value, but try to verify the underlying data. Well-conducted meta-analyses are the best level of evidence, followed by for large, multi-center studies. Another important point is to balance out the recommendations and look for specific information on portion sizes. For example, the Mediterranean diet has potential benefits with regular consumption of nuts and wine, but too many nuts in your diet, or too much wine, will have negative impacts on your health in the long run. So moderation is the key!