The harbinger of an unhappy marriage may be your gut.

A new study by psychologists found that newlyweds had underlying positive or negative gut feelings about their spouses that many were unaware of and that predicted marital satisfaction years later.

The experiment used a photo of the newlywed spouse and a series of positive and negative words to elicit a so-called automatic attitude.

“Either people are completely unaware of this automatic attitude, or they’re completely aware and just not willing to talk about it,” said psychologist and study author James McNulty of Florida State University. The study was published online Thursday in the journal Science.

Automatic attitudes are unfiltered, knee-jerk reactions that can sometimes oppose the conscious thoughts.

McNulty, who primarily conducts research on romantic relationships, showed a newlywed the photo of his or her spouse for just a third of a second, followed by a word that was positive or negative: “delightful” or “disgusting,” for instance. The newlywed, as fast as possible, had to push a button indicating the word that was good or bad.

Psychologists say that seeing the photo for just long enough to recognize who you’re looking at, but not enough to study the detail of the picture, causes your brain to automatically retrieve from memory any associations you have. This facilitates a speedier response to any words that match those associations.

So, for example, a newlywed who pushed the button for a negative word faster than for a positive word after the photo of the new spouse flashed by, was indicating a negative automatic attitude.

McNulty and his colleagues tested for automatic attitudes in 135 heterosexual couples that had gotten married in the previous six months. They filled out a questionnaire about marital satisfaction. Unsurprisingly, the newlyweds’ marriage evaluations had a decidedly rosy outlook. At six-month intervals for the next four years, each partner reevaluated his or her feelings about the marriage using the same questionnaire.

As time passed and the honeymoon phases waned, the initial automatic attitudes gradually started to match up with their reported happiness or unhappiness.

Twelve of the couples divorced within the four years of the study, McNulty said.

So are some people just in denial about their unhappiness, or are they completely unaware of these feelings to begin with?

McNulty said there is pressure for newlyweds to seem ecstatic: “They just got married, spent thousands of dollars on their wedding, and committed to one another in public. They better be happy.”

But because they were later able to admit their less-than-stellar opinions of the partnership, it suggests that certain people may not realize their deep feelings. But there’s no fooling an automatic attitude test.

“People can’t fake it. They don’t even know what it’s measuring,” he said.

Clinical psychologist Gregory Kuhlman of Brooklyn College thinks the study should have asked more specific questions to find a link between conscious and automatic attitudes.

“He’s only asking them, ‘Partner good or bad?’ ” Kuhlman said. “But if you asked about more specific behaviors, you might get a better correlation.”

He and his wife, Patricia Schell Kuhlman, hold a research-based seminar called Marriage Success Training for couples considering marriage, engaged couples and newlyweds. Having a lukewarm gut reaction or cold feet can be normal, he said.

“People are nervous about getting married, that’s a normal response,” Kuhlman said. “Sometimes gut feelings are misleading because they are just the gut feelings that everybody has.”

Popular belief says that you need to find someone perfectly compatible with you, but he dismisses this as a harmful fallacy that often leads to an uneasy gut. Every couple will have incompatibilities. What matters is how good they are at managing them.

Kim is a freelance science journalist based in Philadelphia.