1. Diet fads may be doing more harm than good. In a bid to clear up the confusion over what is and isn't healthy, researchers examined 25 studies involving tens of thousands of participants. They found that many of the latest nutritional trends involve significant health risks: Coconut oil is high in artery-clogging saturated fat; juicing concentrates sugars and makes it easier to consume too many calories; and many gluten-free foods are high in processed carbohydrates, which are linked to a higher risk for type 2 diabetes. Andrew Freeman, who led the research, says the ideal diet is "mostly plant based," predominantly consisting of "fruits, vegetables, [and] whole grains."

2. Social media is making people lonely. Sites such as Facebook, Twitter, and Instagram were designed to help people connect, but a University of Pittsburgh study found that spending too much time on them could intensify feelings of isolation. When researchers surveyed 1,787 adults, ages 19 to 32, they found that those who used social media for more than two hours a day were twice as likely to report high levels of loneliness than those who did so for less than 30 minutes a day. Study leader Brian Primack describes his findings as a "cautionary tale" for social media users.

3. Football is even more dangerous than previously thought. A Boston University study found that 110 of 111 NFL players who donated their brains to science had chronic traumatic encephalopathy, a disease that causes the brain to waste away over time, and which has been linked to aggression, depression, memory loss, and problems with speech and vision. A separate study found that children who play youth football are twice as likely to have problems with self-control, judgment, and problem solving. "Head impacts can lead to long-term consequences," says co-author Robert Stern. "We should be doing what we can at all levels in all sports to minimize these repeated hits."

4. Tattoo ink contains dangerous contaminants that can potentially affect the body's immune system. In a small study involving six subjects, French researchers found that those with tattoos had elevated levels of various metals — including titanium, aluminum, chromium, iron, nickel, and ­copper — in their skin and lymph nodes. These findings suggest that potentially harmful pigment particles go much deeper than the skin. "When someone wants to get a tattoo, they are often vary careful in choosing a parlor where they use sterile needles," says co-author Hiram Castillo. "No one checks the chemical composition of the colors."

5. Keeping secrets can lead to stress, sleep loss, and other unhealthy consequences. Researchers at Columbia University asked 2,000 people what secrets they kept and how often they thought about them. On average, participants kept 13, including five they never revealed to anyone. The more time they spent ruminating over these secrets, the less healthy they said they were. "When people were thinking about their secrets," says lead author Michael Slepian, "they actually acted as if they were burdened by physical weight."

6. Binge-watching leads to sleep problems. American and Belgian researchers asked 423 young adults about their TV and sleeping habits. They found that those who watched back-to-back episodes of their favorite shows in one sitting had a 98 percent higher risk for poor sleep, and were more likely to suffer from fatigue and insomnia. "Bingeable TV shows have plots that keep the viewer tied to the screen," says lead author Liese Exelmans. "We think they become intensely involved with the content, and may keep thinking about it when they want to go to sleep."

7. Red meat increases the risk of death from eight major diseases. In a National Cancer Institute study of 537,000 adults between ages 50 and 71 over 16 years, researchers found that those who ate the most red meat had a 26 percent greater risk of dying from cancer, heart disease, stroke, diabetes, kidney disease, liver disease, or lung disease. They speculate that heme iron in red meats and nitrates in cured meats trigger oxidative stress, which damages cells. "Mortality is higher with higher meat intake for every major cause of death except Alzheimer's," says researcher John Potter.