Brian Wansink, of Cornell University, is a bit of a legend in the area of eating and behaviour.
He's responsible for the findings above, and for other experiments such as the famous "soup bowl", in which subjects were served soup from bowls that never emptied.
That showed we tend to mindlessly eat until the food is gone, rather than tuning into cues from our bodies telling us we are full.
In recent research, Wansink and his team wanted to know what sort of nutrition messages work best to change people's behaviour for the better. They reviewed a range of studies involving positive and negative messages about healthy eating.
The unsurprising result: most people hate being told what not to eat. Although professionals such as dietitians and doctors responded well to messages about why certain foods were unhealthy, most regular folk would rather be told what they should eat and why it is good for them.
"If you're a parent, it's better to focus on the benefits of broccoli and not the harms of hamburgers," said Wansink. In other words, "do eat this, it's great" works better than "don't eat that, it's bad".
This will ring bells for anyone who has ever been on a diet. The psychology of dieting is all too often about the negative. From quitting sugar to going low-carb, the emphasis is on what we should be cutting out or restricting.
Unfortunately, as we know from research and our own bitter experience, restriction messes with our heads. When we deny ourselves to follow the "rules" of a diet, we set ourselves up for failure.
If we know this, you may ask, why do we still have a multi-billion-dollar diet industry that shows no signs of going anywhere?
It's a good question. I think it's because there are always people who - despite what they know - are drawn to the idea of rules.
For some, the only way to make a change is to do something drastic. We all know these people; they're the ones who go on detox diets in January and give up all alcohol, red meat, coffee and sugar for a month, then celebrate with a big champagne breakfast at the end.
Or they sign up for "bikini body challenge" online programmes in the quest for the perfect "before and after" selfies.
For some, the idea of short-term denial is easier than the idea of making positive permanent change.
Unfortunately, there are always others who are happy to exploit that quirk of human nature by promising the holy grail of diets. It should surprise no one that these rarely deliver sustainable weight loss, much less better health.
The old "eat less rubbish, move more" is an unsexy message, even if it is effective.
But, if we take Wansink's message on board, we could reframe that message. Eat more fresh, whole, plant-based food, add more vegetables; eat more colours - these are all positive messages for health and weight management and sticking to them makes for long-term benefits.
It can really make a difference when we accentuate the positive and think carrot (or lots of carrots, actually) rather than stick.
Niki Bezzant is editor-in-chief of Healthy Food Guide magazine. She is the author of two cookbooks and has a lifelong interest in health.
