Did you know we assign a "health halo" to some foods? It's a fascinating phenomenon.
Studies have found when a food has a health claim on its label, people tend to assign extra health-giving properties to it.
And when we perceive food to be healthy - a famously studied example is the fare from Subway - we reward ourselves with extras on top of the healthy item.
This has come up again in a recently released study on protein supplements. The Swiss study found exercisers who take protein supplements say they do so to build muscle, control weight and to promote recovery after exercise.
The same people also believed the supplements had further benefits. Their beliefs were influenced by a "halo effect".
The study reported: "People who believe in the benefits related to muscle modulation are also more likely to believe that protein supplements promote health and well-being." In other words, they extrapolate one benefit to another for which there's no real evidence.
Another fascinating effect evident in this study is what's known as the "licensing effect". This is described as "the tendency for positive choices to license subsequent self-indulgent choices".
In the protein study, people who used protein powder didn't necessarily exercise more than other groups, leading the researchers to suggest that some might consume supplements to compensate for exercising less. This makes sense, the study also found some consumers with low levels of physical activity believed protein supplements have a fitness-promoting effect.
Similar behaviour has been seen in other studies. We tend to think taking these things makes us inherently healthier, so can probably get away with exercising less and eating more treats.
I'm sure you will recognise this quirk of human nature. It is especially common in our relationships with food. We treat ourselves with a beer after going for a run. We have been "good" all week so have a blowout at the weekend. We choose a "healthy" cafe and eat a cake.
This is food messing with our heads. When we assign foods "good" and "bad" labels, we give them power over us, and over how we feel about ourselves. But if food is just food, the power is gone.
Food is neither punishment nor reward. It's just food. It can be delicious and it can be sensual pleasure. It can be intensely nourishing or simply what fills us up until the next meal.
But when food is just food, it doesn't have any more power over us than it should have, and the health halo disappears like the illusion it is.
Niki Bezzant is editor in chief of Healthy Food Guide.