People who are obese have a worse memory than their thinner friends, a small study shows.
Tests on 150 people showed being overweight was linked to worse "episodic memory" or the ability to remember past experiences.
The study in the Quarterly Journal of Experimental Psychology argues that a less vivid memory of recent meals may lead to overeating.
However, other aspects of memory - such as general knowledge - were unaffected.
Tests on rats have previously shown that with burgeoning waistlines come poorer performances in memory tests, but the evidence in humans has been mixed.
The latest experiments looked at episodic memory - the video tape in your mind - that remembers the smell of a cup of coffee or the feel of holding someone's hand.
Of fifty people with a Body Mass Index (BMI) ranging from 18 (healthy) to 51 (very obese) who took part in a memory test - a bit like doing a treasure hunt on your own.
They had to "hide" objects at different times and on different scenes displayed on a computer screen.
They were later asked to recall what they had hidden, when and where. The results showed obese people's scores were 15% lower than thinner people.
Can't remember what I had for dinner
Dr Lucy Cheke, from the University of Cambridge, said, "The suggestion we're making is that a higher BMI is producing reduction on the vividness of memory, although they're not drawing blanks and having amnesia.
"But if they have a less strong memory of a recent meal, with a less strong impact in the mind, then they may have less ability to regulate how much they eat later on."
Hunger hormones play a huge role in how much we eat, but it is already recognized that our minds have a key role too.
People watching TV while they have their dinner have been shown to eat more or feel hungrier sooner.
And those with amnesia will repeat meals in a short period of time. Dr Cheke concluded: "It is too early to talk in terms of advice, but we are certainly beginning to observe the mechanisms with which obesity perpetuates itself.
"Concentrating on your food intake has been a recommendation for a long time, but that may be a harder if you're overweight."
The other factor to be aware of is that a high carb intake just creates a craving for more carbs. Combine that with a poor memory of what one has already eaten and you have the recipe for obesity.
"Hopefully knowing what's going on will help us to develop ways of helping people."