Did you know you could potentially eat the exact same meal (with the exact same calories) as your best friend, but experience it differently depending on how you think about it – aka, whether you see it as ‘healthy’, ‘naughty’, ‘a treat’ or even ‘a failure’?
That’s what nutritionist Sarah Ann Macklin, author of Healthy Shouldn't Be This Hard, argues in a recent podcast episode of The Doctor’s Kitchen with Dr Rupy Aujla. And while the science is still emerging, a handful of studies back her up, suggesting that our expectations about food may influence certain physiological responses.
‘It's bidirectional – it's not just the food that affects our mind, our mind can also affect our entire physiology,’ says Macklin.
The evidence
One of the studies she discusses on the podcast is the 2011 'Mind Over Milkshakes' study, an experiment conducted by Dr Alia Crum where, on two separate occasions, 46 participants were given the same 380-calorie milkshake to drink.
On one visit, they were told it was an ‘indulgent’ 620-calorie shake; on the other, it was presented as a ‘sensible’ 140-calorie option.
The researchers measured ghrelin levels – the hunger hormone – at three different points: before seeing the shake’s label, after viewing the label but before consumption, and after drinking the shake.
When participants believed they were drinking the ‘indulgent’ version, their ghrelin levels decreased, a response associated with satiety – meaning they felt fuller. But when they believed they were drinking the ‘sensible’ version, their ghrelin levels remained roughly the same, meaning they felt less full in comparison.
Yet the milkshake itself had not changed. The only difference was what participants believed they were drinking, not the calories they had consumed.
‘For years, I've been seeing clients in clinic as a nutritionist saying, “This is really healthy” or “This is more indulgent”,’ Macklin says. ‘How food is described and interpreted should be the baseline of scaffolding when we're talking about health and food.’
It's changed how Macklin works with clients – making her more conscious of the language we use around food.
Of course, it's worth noting that this study was a small experiment – it's not evidence that our thoughts can make food more or less calorific, override biology or change metabolic rate at will.
But the milkshake experiment is not the only study to suggest that expectations may shape our physiological response to food. Macklin goes on to describe a second, small 2020 study, conducted by Ellen Langer, a professor of psychology at Harvard. This study saw 30 people with type 2 diabetes drink the same sugary beverage on two separate occasions, labelled as either ‘high sugar’ or ‘low sugar’.
While both drinks contained 62g of sugar, participants’ blood-glucose responses differed according to the amount of sugar they believed they had consumed.
‘What was fascinating was that participants' blood-glucose levels actually went up when they thought they were consuming a high-sugar drink,’ says Macklin. ‘Even though, again, similar to the milkshake study, all the drinks were the same.’
Again, it is an eye-opening finding, but a small study of just 30 people with type 2 diabetes is not a reason to try to think your way out of a blood-sugar spike.
Can feeling ‘bad’ or guilty about food change how we feel afterwards?
While these studies are interesting, they can't prove that feeling guilty about eating makes you physically hungrier, or that thinking positively about a meal changes its calories.
But they do offer insight about the power of expectation. When we approach food with a sense of restriction or an ‘I shouldn’t be having this’ attitude, it can make eating feel more emotionally charged.
The bottom line
While your thoughts cannot make food more or less calorific, the way we think about food is perhaps more important than we realise – and can shape how we respond to it.
If you choose to have a treat you think of as 'indulgent', try to enjoy it without the side order of guilt. Sometimes, giving yourself permission to enjoy the little things can be way healthier than labelling food as ‘bad’, or letting one decision become a reason to restrict or compensate an otherwise healthy diet.
