If there’s no caramel cheesecake, you’re not likely to eat any. But plop one down on a table among a group of friends and the forks come out.

That’s a simple scene that embodies some of the complex mechanisms that make it so hard for people to lose weight and keep it off.

Researchers in England who were trying to sort out what tempts dieters and what makes them give into temptation looked at a group of 80 people, mostly women, over seven days, giving them phones and apps to record instances of temptation: how they felt, what was happening and whether they took a bite or a sip.

Over the week, they recorded 898 instances of temptation.

As every dieter knows, keeping weight off for good is extremely difficult. And some of the factors the researchers reported last week were no surprise: Being around friends, late-night cravings and alcohol have a major effect.

Other factors, as the makers of desserts and snacks surely know, include being tired.

But while some of those might seem obvious, the researchers are looking at exactly what’s going on in an effort to develop ways to empower people to resist temptation.

Would it help, for example, if you had a phone app to record your feelings every time you happened upon a bowl of chips or an ad for ice cream?

“The findings help piece together the complex jigsaw surrounding the daily predictions of dietary temptations and help us to better understand how dietary temptations and lapses operate,” the researchers wrote in the journal Annals of Behavioral Medicine.

The 80 participants were part of a weight-loss group or were dieting on their own.

For a week, they were asked to fill out a phone diary each time they were tempted. The researchers said previous studies of willpower had been done in lab conditions; this one was done in “real” life.

The participants gave into temptation a little more than half the time, according to their diaries.

They were particularly vulnerable at night and more likely to have an alcoholic drink than to eat a sugary snack.

British dietitians have ranked lack of willpower as more important to the development of obesity than genetics, the researchers said.

“In the fight against obesity, we need to help people become more aware of the various personal, situational and environmental factors that expose them to dietary temptations,” the researchers wrote.

And then, they said, they need to develop skills to cope.

One thing that appeared to help the dieters was an ability to focus on their long-term goals.

No surprise, they reported they were more aware of their eating because they were carrying around the phones.

And one of the limits of the work will surely ring true with dieters: The study was just seven days long. What happened on the eighth day?