Traditional plant-centered diets (such as the Mediterranean diet) are based on affordable local specialties and garden vegetables. To see if traditional ways of getting healthy meals on the table stand up to modern food economics, researchers calculated the cost of a 7-day meal plan for an economical version of the USDA MyPlate guidelines, and compared it to that of a plant-based diet with olive oil. They found that choosing a plant-based diet, instead of the budget MyPlate diet, could save $746.46 per person per year, and provide vastly more servings of vegetables, fruits, and whole grains.
Journal of Hunger & Environmental Nutrition. 2015 Sept 23. [Epub ahead of print] (MM Flynna 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.)

Fish is well known for its place in many of the healthiest diets around the world. To determine the link between eating fish and depression risk, Chinese scientists reviewed 26 studies of over 150,000 people. The researchers concluded that “high fish consumption can reduce the risk of depression.”  
Journal of Epidemiology and Community Health. 2015 Sep 10. pii: jech-2015-206278. [Epub ahead of print.] (Li Fu et al.)

Weight is thought to be managed largely by balancing calories eaten with calories burned, so researchers are studying why some people tend to burn calories more easily than others. In an Italian study, researchers recruited 52 adults (half vegetarian, half not) and matched each group by age, BMI, and gender. All of the vegetarians had been following their diet for at least 3 years. After adjusting for age, BMI, exercise, and other lifestyle factors, the scientists found that the vegetarians had a significantly higher resting energy expenditure, meaning that their bodies burned more calories at rest. Of the different dietary components studied, higher intake of vegetable fats (oils, nuts, seeds) were most closely associated with the significantly higher resting energy expenditure seen in vegetarians. 
Nutrients. 2015 Jul 17;7(7):5933-47. (Montalcini T et al.)

Colorectal cancer is the leading cause of cancer mortality, so learning more about dietary prevention is an important area of research. Scientists at Loma Linda University in California analyzed food patterns and health data from over 77,000 adults for an average of 7 years. After controlling for demographic and lifestyle factors (including age, smoking, physical activity, and family history), the researchers found that those who ate vegetarian diets had an approximately 20% lower risk of colorectal cancer compared with nonvegetarians. Researchers also found that pesco-vegetarians in particular (vegetarians who eat fish) had a much lower risk of colorectal cancer. These results support other studies linking the Mediterranean diet (a plant-based diet that features fish) with a decreased risk for colorectal cancer.
JAMA Internal Medicine. 2015 March 9. [Epub ahead of print] (Orlich MJ et al.)

Plant-based diets have proven effective at reducing heart disease markers in adults, but with a large proportion of overweight and obese children, experts wonder if dietary interventions are effective on kids as well. In a small study in the Midwestern US, twenty-eight overweight and obese children (average age = 15) and their parents were assigned to either a plant-based vegan (no animal products at all), no-added fat diet (with only moderate avocado and nuts) or an American Heart Association diet (high in fruits, vegetables, and whole grains, but also includes low fat dairy, some plant oils, lean meat and fish, and permits some refined grains) for four weeks. The plant-based group significantly improved nine different risk factors of heart disease (including improved blood pressure, cholesterol, and weight), while the American Heart Association Diet significantly improved four risk factors.
The Journal of Pediatrics. 2015 Feb 11. [Epub ahead of print] (Macknin M et al.)

Microbes are important for our digestive health, and researchers still have much to learn about how different foods impact our gut microbiome. In this study, researchers cooked 3 days worth of food from 3 different diets (a typical American diet with lots of convenience foods; a USDA recommended healthy diet with whole grains, fruits, vegetables, dairy, and lean meats; and a vegan diet consisting only of plant foods) and then analyzed the microbes present in the foods. The USDA recommended healthy diet was shown to have the highest total microorganisms. However, it was also the only meal plan that included yogurt, a non-heat-treated fermented food well known for its probiotic content.
PeerJ. 2014 Dec 9;(2):e659. doi:10.7717/peerj.659 (Lang JM et al.)

In a study of 63 overweight and obese adults instructed on various diets, South Carolina researchers examined the differences in nutrient intake and Dietary Inflammatory Index (DII). After two months, those assigned to vegan, vegetarian, and pescatarian diets had significantly lower DII scores and greater improvements in fiber, carbohydrate, fat, saturated fat, and cholesterol. However, after six months, no differences were seen among the diets. Due to these short-term benefits, the researchers concluded that greater consideration should be given to “finding ways to provide support for adoption and maintenance of plant-based dietary approaches.”
Nutrition Research. 2014 Dec 3. Pii:S0271-5317(14)00267-X. (Turner-McGrievy GM et al.)

Think a meat-centric diet is the best way to keep your blood sugar in check? Think again! Researchers in the United States and Japan reviewed studies that investigated the relationship between vegetarian diets and blood sugar control in people with type two diabetes. Analyzing data from the 255 adults included in the studies, scientists reported that a plant-based vegetarian diet helps adults with type 2 diabetes improve glycemic control, lower cholesterol intake by 173mg, and trim about 140 calories from their diets each day.  
Cardiovascular Diagnosis and Therapy. 2014 Oct;4(5):373-382. (Yokoyama et al.)