I recently read The Expectation Effect, a fascinating book looking at how what you expect influences what actually happens with regard to your body and life.

Below is a fairly detailed summary of chapter 6 (prioritised as being most potentially relevant to my work). I’m sure I’ll be talking a lot more about the rest of this book in future. But for now, the main topic of this chapter was how your beliefs and expectations influence how your body and brain react to what you eat - potentially useful knowledge for anyone interested in healthy eating.

Our brain’s predictive processing means that our expectation of what nutrients a food contains directly affects how our body responds to that food, including our:

  • digestion, i.e. the breaking down and absorption of nutrients in the gut.
  • metabolism, i.e. how we process the food to power our cells.

If we believe we’re eating fewer calories than we really are, our body responds to that belief. The brain induces a deprivation mindset, and we feel less satiated, more hungry and inclined to expend less energy in order to preserve fat stores.

It’s known that appetite is controlled in part by activity in the digestive system - bottom-up information. However the brain also seems to need top-down info e.g. memory and expectation, to make sense of the digestive information input in order to create the appropriate feelings of hunger or satiation.

Altering how we think about food can change the brain’s assessment of what it has eaten.


A patient who had lost the ability to form new memories, was asked to rate how hungry he was on a scale of 0 -100. He rated his hunger similarly both before and after consuming a meal. After two meals in a row he felt only partly satiated.

This suggests that our appetite is not solely governed by “fullness signals” from the stomach. It’s also influenced by our memory of what we ate.

Milder forgetfulness is also associated with over-eating.

In an experiment asking students to taste test cookies, they consumed 45% less if they had first been prompted to remember their lunch by noting down what they’d eaten.

Working, watching TV or using the internet whilst eating may create a distraction that impairs our memory of what we ate, leading to eating larger meals and more snacks afterwards.


The sense of fullness and satisfaction participants had from eating either 300ml or 500ml of soup was largely based on how much soup they thought they’d eaten, rather than how much they actually had.

Participants who believed they’d eaten a 3 egg omelette felt more satiated than those who thought they’d eaten a 1 egg omelette, even though they’d eaten the same amount.

Patients who believed that they’ve undergone obesity-related surgery, e.g. stomach stapling or gastric balloon, experienced 70% of the benefits of the operation (reduced appetite, higher weightloss) even though the actual surgery never took place.


The presentation of manufactured foods can disrupt our brain’s ability to assess its contents:

  • The brain remembers eating a lot less after drinking a small bottled smoothie vs eating the equivalent portions of fruit, giving the expectation of hunger later in the day.
  • Several studies show that the exact same food leads to lower satiety when it is labelled “healthy” as opposed to when it’s labelled “hearty”.
  • The more viscous a drink is the more filling we expect it to be, and the higher our physiological response.
  • Iron absorption from meals that have been pureed were much lower than the same meal presented in its standard form.
  • “Healthy” snacks may be counterproductive - participants given a “healthy” chocolate bar were hungrier afterwards than those given nothing.


When presented with a choice of 2 items such as a McDonald’s hamburger and a 8.5oz grilled ocean code, most people think the burger has more calories even though they’re about equal, over or underestimating the true value by up to 50%. People who have greater mismatches in their estimates are on average heavier.

People who agree more strongly with statements such as “There is usually a trade-off between healthiness and tastiness” tend to have higher BMIs.


Ghrelin is a hormone secreted by the stomach when it’s empty.

High levels induce our body to:

  • lower its metabolic resting rate, burning less energy.
  • store body fat.
  • feel lethargic, so we don’t waste energy on exercise.

Participants who had drank a milkshake marketed as indulgent saw lower ghrelin levels, as expected after a meal. But those who drank the same milkshake presented as healthy and light, saw very little change in ghrelin.

Brain areas associated with energy regulation are also affected. People given a low-calorie drink labelled as a treat had a stronger hypothalamus response when it was labelled as a “treat” as opposed to “healthy”,

Expectations also affect the movement of food in the gut and our insulin responses.

The environment

Our environment reinforces the idea that healthy foods are less satisfying. An analysis of 26 American chain restaurants that offer “healthy eating” options saw that they were less likely to have descriptions relating to enjoyment, vice, decadence, texture and taste. They were more likely to be described in terms evoking simplicity, thinness, or deprivation.

In one study where these healthy options were described with words evoking enjoyment and indulgent, consumption of them increased 29% and were likely to lead to lower snacking afterwards. Adding the words “fuller for longer” to a yoghurt pot increased people’s satiety for 3 hours.

Low socioeconomic status is a risk factor for obesity. There are many potential explanations. One study showed that when people are primed to feel poorer and less secure they tend to choose sweeter snacks and have bigger portion sizes, corresponding to observable changes in the body and brain. People’s feelings of social and financial insecurity induced a sense of deprivation which influenced their hormonal response. For people living with this sense of vulnerability long-term, it’s possible that this response could increase your likelihood of obesity even if your food choices were healthy.

The belief that healthy foods are unsatisfying isn’t universal.

That belief is strongly held in the US and to a lesser extent the UK and Australia - but the opposite view is more common in France. It’s been shown that labelling a food as healthy in France doesn’t reduce the satisfaction and pleasure as much as elsewhere.

French people also have fewer negative sentiments associated with treats. When asked to describe which word is more associated with ice-cream, more US people pick “fattening” whereas French people more commonly pick “delicious”.

This attitude seems to affect their eating choice and body responses. French people tend to choose smaller servings and spend more time eating them.

The average BMI in France (25.3) is lower than other countries like Germany (26.3), Australia (27.2), the UK (27.3) and especially the US (28.8).

The typical French diet contains higher proportion of saturated fat from butter, cheese, eggs and cream than the UK/US equivalent, yet French people are less likely to suffer from coronary heart disease. There are many possible reasons but expectation could be one. People who believe that they are more at risk of a heart attack are 4x as likely to suffer from heart disease even controlling for other factors.

Eating is not a simple chemical process.

…exactly the same item can be nourishing and satiating, or unfulfilling and nutritionally empty – in large part because of our memories of what we have eaten, our impressions of what it contains and the meanings that we ascribe to it.

Some ways to apply these findings

  • Avoid the liquid calories in sweetened drinks.
    • The satiety of most drinks is low
    • If you must drink juices and smoothies, make them yourself so you are more aware of the food that went into them - research suggests doing this may increase your satiation.
  • Maximise the pleasure in the food you eat. Flavour and texture are important during weight loss as the resulting sense of indulgence increases satiety and hormonal response to food. The lack of later snacking due to greater satiety will outweigh the small number of extra calories this my require.
    • Spicy foods or intensely umami ingredients are good options.
    • Avoid food that gives a sense of deprivation.
    • Thoroughly enjoy any treats - feeling guilt won’t help. One study showed that dieters who associated treats such as cake with guilt gained weight vs those who associated them with celebration progressed towards their goals.
    • Do not label foods as sinful, toxic etc.
  • Visualise and anticipate what you’re going to eat in advance.
    • Participants who were asked to imagine the taste, smell and texture of sweet treats first opted to have a smaller slice of cake when one was offered.
  • Avoid distractions when eating.
  • Eat slowly, savoring each mouthful. The greater sensory experience of eating will trigger a stronger hormonal reaction to the food.
  • Remember what you have eaten.
    • If you feel tempted to snack then first recall what it was like to eat your last meal. Your brain may update its predictions of energy balance, making you feel less hungry.