After decades of a growing appetite for meat, U.S. consumption is finally dropping after hitting “peak meat” a decade ago. But while many people are eating less meat, giving it up totally is much harder. Few people stick with their decision to become vegetarian or vegan.

In an attempt to move animal-free diets “from the margins more towards the center,” the Humane Research Council just put out the first study to put numbers to the lapsed vegetarian phenomenon. Their main takeaway is essentially what people have said for years: getting people to reduce their meat and dairy intake will be more effective overall than demanding “purity,” or complete elimination of animal products from their diet.

According to their research, drawn from a representative sample of more than 11,000 adults over age 17 in the U.S., while only 2% of the U.S. population is currently vegetarian or vegan, another 10% used to be. Put another way, they found that only 1 in 5 vegetarians and vegans maintains their diet; a full 84% eventually revert back to eating meat or other animal products.

Related link: Eating Meat Is Bad For The Planet: But What About Just Eating Less Meat?

The study also shows how and why many people lapse. Most former vegetarians and vegans (65%) said they first transitioned to their veg diet in just a few days or weeks, while fewer current vegetarians (53%) transitioned that quickly, suggesting that perhaps a slower approach leads to longer-lasting results. They also found that the “window of opportunity is limited,” when it comes to getting people to stick to their diets: A third-of people abandoned their animal-free diets in three months or less, and more than half abandoned it within the first year.

Reasons for quitting varied, but perhaps intuitively, a lot comes down to relationships. A third of all former vegetarians lived with a non-vegetarians or non-vegan partner when they went back to eating meat. The study also found that current vegetarians were more likely to cite multiple reasons for being vegetarian–such as animal welfare, environmentalism, and personal health–while many former vegetarians (58%) cited health as the main motivator. In other words, from the advocacy group’s perspective, health can be an effective “foot in the door” approach to increasing the number of vegetarians and vegans, but often not enough to keep people animal-free for the long-term.

The Humane Research Council also says advocates need to change the culture around being vegetarian or vegan and acknowledge its challenges. More than 60% of former vegetarians/vegans disliked sticking out from the crowd because of their diet, and 58% did not see their diet as part of their identity. Nearly 50% said they found it too difficult to maintain a “pure diet.”