The 15 Studies from 2013 that Matter to Your Health MostThere’s nothing we’re more psyched about than awesome, trustworthy research that illuminates the world around us and helps us learn more about the choices we’re making about our health. We’ve rounded up the year’s most important health studies and given you the quick and dirty on what they all mean. Read on for need-to-know information on everything from penis size, sugar, and sleep to booze, breakfast, and body fat.

Milkshake1. Sugar, not fat, causes us to overeat.

It turns out that sugar might be the on-switch that activates compulsive eating. Researchers tracked the brain activity of 106 high school students as they consumed milkshakes and found that those who were drinking sweeter milkshakes experienced greater activation of their brain’s pleasure centers Relative ability of fat and sugar tastes to activate reward, gustatory, and somatosensory regions. Stice E, Burger KS, and Yokum S. American Journal of Clinical Nutrition, 2013 Dec;98(6):1377-84. Although high-fat, low-sugar milkshakes also lit up these areas, the impact was not as great as that of the lower-fat, higher-sugar treats. These pleasure centers are where the magic happens when it comes to our internal reward systems, meaning that the more stimulated these regions are, the more we want to eat.

2. Using Facebook predicts a decline in wellbeing.

For the more than one billion people who use it, Facebook makes staying in touch with friends (and up-to-date on their lives) as easy as opening a new browser tab. But a recent study found that Facebook might actually be undermining our happiness. Researchers surveyed college-aged adults, asking questions about loneliness, anxiety, and general satisfaction with their lives, and found that the more the study participants used Facebook, the more their satisfaction declined Facebook Use Predicts Declines in Subjective Well-Being in Young Adults. Ethan Kross E., Verduyn P., Ybarra, O., et al. PLoS One. 2013; 8(8): e69841.. (But note that this study used a sample of just 82 people who were self-reporting. So, although it raises fascinating questions, this study should be considered more of a jumping-off point for further research about our relationships with social media.)

3. Breakfast isn’t the most important meal of the day (for weight loss).

Studies have tied skipping meals with gaining weight, but no direct relationship between eating breakfast and successful weight loss has ever been proven. This year a study showed that the proposed effect of breakfast on obesity (namely that eating it helps us lose weight) isn’t borne out by existing scientific evidence Belief beyond the evidence: using the proposed effect of breakfast on obesity to show 2 practices that distort scientific evidence. Brown AW, Bohan Brown MM, Allison DB. American Journal of Clinical Nutrition, 2013 Nov;98(5):1298-308.. So far, there is no proof that foregoing breakfast sabotages weight loss.

4. Overthinking and overeating go hand in hand.

While we know that there is a relationship between impulse eating and weight gain, a new study suggests that there’s such a thing as too much mindfulness before meals. Psychologists found that those who think and reflect before eating might stumble upon justifications for indulging that make them just as likely to then overeat "Because I Am Worth It": A Theoretical Framework and Empirical Review of a Justification-Based Account of Self-Regulation Failure. De Witt Huberts, JC, Evers, C, De Ridder, DT. Personality and Social Psychology Review, 2013 Nov 8..

Mixed Nuts5. Eating nuts can make you live longer.

Nut-lovers rejoice! A study of 120,000 people over a 30-year span found that those who ate nuts daily were less likely to die of cancer, heart disease, and respiratory disease. In fact, people who ate nuts seven or more times per week were 20 percent less likely to die during the study Association of nut consumption with total and cause-specific mortality. Bao Y, Han J, Hu FB, Giovannucci EL, et al. New England Journal of Medicine, 2013 Nov 21;369(21):2001-11.. No matter what your nut of choice is, you’re in luck — tree nuts such as almonds and cashews were found to be just as beneficial at peanuts (technically a legume, but included in the study). Whether study participants lived longer because of the nuts themselves or because of a related factor (perhaps, for example, snacking on nuts made them less likely to snack on processed snacks) is not yet clear. Either way, increased nut consumption means less disease and longer life. Start spreading the nut butter!

6. A steady sleep schedule is linked to lower body fat.

Though everyone has different needs when it comes to the amount of slumber they need to feel like a boss the next day, a study this year found that maintaining a regular sleep schedule — that is, going to sleep and waking up at the same time every day — was strongly linked to lower body fat Objectively Measured Sleep Patterns in Young Adult Women and the Relationship to Adiposity. Bailey, BW, Allen, MD, Lecheminant, JD,, et al. merican Journal of Health Promotion, 2013 Nov 7.. for the 330 women in the study sample. Though we know there is a relationship between adequate sleep, appetite, and weight gain, more research will need to be done to further understand the relationship between a regular sleep schedule and less body fat Acute sleep deprivation enhances the brain's response to hedonic food stimuli: an fMRI study. Benedict, C., Brooks, S.J., O'Daly, O.G., et al. The Journal of Clinical Endocrinology & Metabolism, 2012 Mar;97(3):E443-7..

7. Honeybees could be the secret to preventing HIV transmission.

Researchers have shown that honeybee venom can “sting” HIV the way bees sting humans Cytolytic nanoparticles attenuate HIV-1 infectivity. Hood JL, Jallouk AP, Campbell N, et al. Antiviral Therapy, 2013;18(1):95-103.. The venom is capable of poking holes in the protective membrane of HIV cells, killing the virus before it has the chance to infect the carrier (all without damaging other healthy cells). The venom could become a key ingredient in a low-cost vaginal gel that could be used to prevent the spread of HIV.

8. The “right-brained and “left-brained” theory is crap.
Although it’s been a widely-held and popular theory that some people are left-brained (logical, analytical, objective) and others are right-brained (creative, emotional, intuitive), a new study found no evidence to support this idea. Using MRIs to scan participants’ brains, researchers found that while certain activities activated one side or the other, individuals were not preferentially relying on a particular side An evaluation of the left-brain vs. right-brain hypothesis with resting state functional connectivity magnetic resonance imaging. Nielsen JA, Zielinski BA, Ferguson MA, et al. PLoS One, 2013 Aug 14;8(8):e71275..

Grocery Shopping9. Healthy eating costs more, but only by $1.50 per day.

An analysis of 27 studies from ten different countries shows that diets richer in healthier foods like fruits, vegetables, nuts, and fish cost an additional $1.50 per day Do healthier foods and diet patterns cost more than less healthy options? A systematic review and meta-analysis. Rao M, Afshin A, Singh G, et al. BMJ Open, 2013 Dec 5;3(12):e004277.. The study’s authors urged food policy that supports the availability and affordability of whole, healthy foods, rather than cheap, processed items that can be mass produced. Though the public health costs of poor nutrition are significant, shelling out even a bit of extra cash for healthier food could be burdensome, making eating well on the cheap out of reach, especially for those in lower income communities.

10. “Fat but fit” is a myth.

A comprehensive analysis of studies from the last 60 years has produced evidence that it is not possible to be fit and overweight at the same time Are Metabolically Healthy Overweight and Obesity Benign Conditions?: A Systematic Review and Meta-analysis. Kramer CK, Zinman B, Retnakaran R. Annals of Internal Medicine, 2013 Dec 3;159(11):758-69.. Researchers found that individuals with higher-than-recommended BMIs but normal blood pressure and cholesterol were still at higher risk for dying of heart disease than non-overweight people. The researchers believe that their analysis corrects for previous studies that failed to consider all aspects of participants’ metabolic health.

11. “The Pill” for men could be on its way.

If researchers can replicate what they accomplished with mice, a reversible form of male contraception could be on the horizon sometime in the near-ish future. Researchers in Australia were able to genetically modify mice so that they did not produce sperm during intercourse Male contraception via simultaneous knockout of α1A-adrenoceptors and P2X1-purinoceptors in mice. White CW, Choong YT, Short JL, et al. Proceedings of the National Academy of Sciences, 2013 Dec 17;110(51):20825-30.. Knowing which proteins must be manipulated to prevent sperm during ejaculation could mean that birth control pill for men could be produced sometime in the next decade.

Eggs12. One egg per day is a-OK.

After reviewing studies that took place between 1966 and 2012, researchers found that there was no link between eating one egg per day and increased risk of coronary heart disease or stroke Egg consumption and risk of coronary heart disease and stroke: dose-response meta-analysis of prospective cohort studies. Rong Y, Chen L, Zhu T, et al. British Medical Journal, 2013 Jan 7;346:e8539.. The study also pointed out that eating eggs facilitates the formation of LDL and HDL cholesterol, which could help prevent hardening of the arteries. Take note, however, that the study did not investigate the effects of eggs on those with diabetes or already at risk for heart disease.

13. Omega-3 fatty acids are great, but you can overdo it.

Omega-3 fatty acids are delicious (chia pudding, anyone?) and good for you, but research this year showed that there is such a thing overdoing it. Omega-3 fatty acids are essential nutrients linked to a variety health benefits, but excessive amounts can wreak havoc on our immune system, leaving us compromised when it comes to fighting off a virus or bacterial infection Immunomodulation by dietary long chain omega-3 fatty acids and the potential for adverse health outcomes. Fenton JI, Hord NG, Ghosh S, et al. Prostaglandins, Leukotrienes and Essential Fatty Acids, 2013 Nov-Dec;89(6):379-90.. The researchers suggest the establishment of dietary standards that outline the recommended amount of omega-3 fatty acids in our daily diet.

14. It might actually be easier to lose weight in groups.

Seems like we humans always want what we can’t have, and the science backs that up. According to a study, as soon as an item is forbidden to us, we can’t get our minds off it. Researchers also found that when it comes to resisting temptation, doing so in the company of others who are also trying to abstain is easier than flying solo An unforgettable apple: Memory and attention for forbidden objects. Truong G, Turk DJ, Handy TC. Cognitive, Affective, & Behavioral Neuroscience, 2013 Dec;13(4):803-13.. For some reason, when something is off-limits to others, too, it’s easier to resist. This may begin to explain some of the success of Weight Watchers and other group-based addiction solutions.

15. Size does matter.

Turns out it’s not just the motion of the ocean after all. In an Australian study, women were asked to rank computer-generated images of men with varying body shapes, heights, and penis sizes. The study found that women preferred the largest penis size the study offered Penis size interacts with body shape and height to influence male attractiveness. Mautz BS, Wong BB, Peters RA, Proceedings of the National Academy of Sciences, 2013 Apr 23;110(17):6925-30.. They also reported that women found taller men more appealing and that penis size was crucial to sexual attractiveness.

Which scientific studies did you find most impressive this year? Let us know in the comments below or get in touch with us on Twitter.