Yes, the most likely culprits behind extra weight gain include your couch and the snack shelf. But some new studies suggest there are less obvious factors that could lead to mid-section spread. Here are four subtle and weird ways you could be adding pounds—and how to stop it.

1.  Couple trouble
Want a compelling reason to immediately resolve your marital woes? Letting your fights get too hot might make you more susceptible to weight gain. A recent study found that couples whose arguments were tinged with hostility had higher levels of a hunger hormone—and were more likely to make poor food choices—than couples who were kinder to each other.  

Researchers at the University of Delaware tracked hormone levels in 43 couples as they ate a meal and then discussed their differences. Observers rated the discussions—which often boiled into arguments—on the use of hostile language. Couples who ranked high in the use of hostile language also had the highest circulating levels of ghrelin, a hunger-related hormone that encourages eating. When the researchers asked the couples to fill out food surveys, hostile couples were more likely to report eating foods high in sodium and unhealthy fats compared to those whose interactions were more civil.

"The findings suggest marital distress may be an important risk factor for weight gain," said study author Lisa Jaremka, PhD, assistant professor at the University of Delaware, though she is quick to add that the effect was missing in people already overweight. In other words, don't wait too long to get couples counseling. (Lose up to 15 pounds WITHOUT dieting with Eat Clean to Get Lean, a 21-day clean-eating meal plan.)

2.  Overdoing it on iron
If you were thinking about cutting back on red meat to help control calories, here's one more reason that could be a sound plan: A new study suggests the amount of iron in red meat might alter hunger hormones in your body, slowing metabolism and encouraging you to eat more.

Donald McClain, director of the Center on Diabetes, Obesity, and Metabolism at Wake Forest School of Medicine fed mice diets that contained high or low levels of iron while tracking their levels of leptin, an appetite-suppressing hormone. After two months, McClain discovered that leptin levels had dropped by as much as 42 percent in the high-iron mice. To test whether low leptin led to over-eating, he let both groups of mice eat as much as they wanted: Sure enough, the high-iron group downed more calories than mice on the low-iron diet. Finally, McClain checked iron and leptin levels in 76 people and discovered that the higher their iron, the lower their leptin levels were. People with the highest iron had one-third the leptin of those with the lowest amounts of iron. (Everyone's iron levels fell within the normal range.)

McClain's findings suggest iron recommendations—18 mg a day for women 18 to 50 and 8 mg a day for women 51 and older—may be too high, he says. Eating more than a pound of red meat per week could be enough to raise leptin to levels he observed in his research, warned McClain. Unless your doctor says otherwise, you'll want to limit the amount of iron you get from meat and supplements, McClain said. But don't be too concerned about iron sources such as nuts, beans, spinach, tomatoes: You don't absorb as much from these food sources as you do from red meat.

MORE: 15 Teeny Tiny Changes To Lose Weight Faster

3. Blaming your DNA
Some day, science may be able to link certain genes to a tendency to gain weight—but we're not there yet. And a recent study suggests that believing weight problems are genetic practically guarantees you'll pack on the pounds.

Tapping into a survey of nearly 9,000 women and men, Michael C. Parent, PhD, assistant professor in the department of psychological sciences at Texas Tech University and colleagues analyzed the people's beliefs regarding the genetics of being fat. When Parent followed up three years later, he discovered that the more strongly people believed genetics played a significant role in fatness, the more likely they were to have gained weight. This group was also less likely to exercise and eat right.

Mind is definitely influencing matter here, since Parent's findings also revealed that people who believed their weight was under their control were more likely to eat well, exercise regularly, and have a lower BMI.

"There is no direct genetic cause for obesity," Parent said.

He recommends you avoid playing the genetic blame game; instead, embrace the idea that you are in control of your weight.

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4. It's just harder than it used to be
This is truly frustrating news: Recent findings published in Obesity Research & Clinical Practice indicate that we're getting fatter on fewer calories than our parents did. Although we're eating about the same amount of food—and we're equally active—the current generation is gaining more weight than people did 40 years ago.

The researchers analyzed info on more than 36,000 people between 1971 and 2008, comparing diet, activity, and weight. Study author Jennifer Kuk, professor of health and sciences at York University in Toronto found that given the same amount of calories, an adult in 2008 is about 10 percent heavier than she would be in 1971.

"Again, we're finding that weight management is much more complex than just energy in versus energy out," Kuk said.

The solution isn't complex, however: We all have exercise more and be more careful about what we eat. Sigh—see you at the gym.

MORE: 20 Super-Healthy Smoothie Recipes

This article originally appeared on Prevention.com.