Spanish researchers randomly assigned 239 adults (half with metabolic syndrome, half without) to either a Mediterranean diet, or a low fat, high complex carbohydrate diet (with foods like pasta and cereals) for two years. They found that the Mediterranean diet was able to “restore potentially beneficial members of the gut microbiota,” in patients both with and without metabolic syndrome. The low fat, high complex carbohydrate diet did not result in as many positive changes in gut microbiota as the Mediterranean diet did, although some beneficial changes still occurred.
The Journal of Nutritional Biochemistry. 2016 Jan;27:27-31. (Haro C et al.)

Eating a variety of healthy plant foods is one of the best ways to nurture our friendly gut bacteria, and new research suggests that Mediterranean and vegetarian diets may be useful models. Scientists analyzed the eating patterns and gut bacteria of 153 Italian adults. They found that those most closely following a Mediterranean diet or vegetarian/vegan diet had higher levels of short chain fecal acids, a compound associated with many health benefits. On the other hand, those not following a Mediterranean diet had higher levels of urinary trimethylamine oxide, a potential risk factor for heart disease. The researchers also noted that both vegetarian/vegans and those on a Mediterranean diet scored highly on the Healthy Food Diversity Index, meaning that these eating styles could be a useful blueprint for people wanting to incorporate a variety of nutritious foods into their diet.
Gut. 2015 Sept 28. [Epub ahead of print] (De Filippis F et al.)

Evidence is mounting that the healthiest diets are built around a variety of minimally processed, whole foods, and can’t be reduced to specific nutrients. To determine saturated fat’s role in heart disease risk, researchers from California reviewed the existing literature about saturated fats, polyunsaturated fats, carbohydrates, and heart disease. The scientists found that when saturated fat (found mostly in red meat and milk fat) is replaced with polyunsaturated fat (found mostly in nuts, seeds, and fish), heart disease risk decreases. However, when saturated fat is replaced with sugary refined carbohydrates, heart disease risk remains the same, if not worsens. The researchers also note a small, yet growing body of research that dairy fat (especially in fermented dairy, like yogurt), may be neutral (or even decrease risk) for heart disease. The researchers concluded that “overall dietary patterns emphasizing vegetables, fish, nuts, and whole versus processed grains form the basis of heart-healthy eating, and should supersede a focus on macronutrient composition.”
Annual Review of Nutrition. 2015 July 17;35:517-43. (Siri-Tarino PW et al.) [Epub]

Dairy foods are most often prized for their calcium content, but new research reveals that changes to the gut microbiome, especially from eating fermented dairy products, like cheese, might help explain the “French Paradox,” the phenomenon in which traditional cheeses are linked with low rates of heart disease. In a small study to investigate the protective effect of dairy foods, Danish scientists randomly assigned 15 healthy men to one of three diets for two weeks: a diet with lots of partly skim (1.5%) milk, a diet with lots of semi-hard cow’s cheese, or a control diet with butter, but no other dairy products. Both the milk and cheese diets had the same amount of calcium per day (1.7g). The men rotated through each diet, with a two-week washout period in between each new diet group. Compared to the control diet, both the cheese and milk diets were associated with significantly lower production of TMAO, a compound that is thought to be a marker of heart disease risk. The researchers also found that “dairy consumption, especially cheese, can beneficially modify the gut microbiota to increase SFCA levels.” SFCAs (short chain fatty acids) are compounds produced by gut bacteria that are linked with many health promoting effects, such as lower risk of diabetes, heart disease, and inflammatory diseases.  
Journal of Agricultural and Food Chemistry. 2015 Mar 18;63(10):2830-9 (Zheng H et al).

Researchers have given us yet another reason to fill our plates with fruits, vegetables, whole grains, legumes, olive oil, and nuts! A European study followed more than 2,500 Greek adults for over a decade, tracking their medical records, lifestyle habits, and eating patterns. Those who most closely followed the Mediterranean Diet were 47% less likely to get heart disease, regardless of their smoking habits, age, family history, or other lifestyle factors. The scientists estimate that every one-point increase on the Mediterranean Diet score (a measure of how closely participants followed the Mediterranean Diet, on a scale of 1 to 55) is associated with a 3 percent drop in heart disease risk, so every little bit counts. In fact, the researchers found that the Mediterranean Diet was even more protective against heart disease than physical activity!
Presentation at the American College of Cardiology’s 64th Annual Scientific Session. San Diego CA. March 15, 2015.