The Milkshake Delusion: Five studies demonstrating the biological power of belief
The Invisible Force Shaping Your Health
I first came across the mindset research of Harvard University’s Alia Crum and Ellen Langer when I was preparing a health psychology module for undergraduate students in 2007. The findings of their first study made me scratch my head in disbelief. Alia Crum has since moved to Stanford University and continued this work with a series of further mindblowing studies. I find Crum’s mindset research the most fascinating of any other psychological research this century.
We often treat our minds and bodies like two different countries. Our thoughts, beliefs, and expectations exist in one realm, while our physical health, metabolism, blood pressure, and hormones are governed by concrete biological laws in another. However, what if that border is an illusion? What if our thoughts can rewrite the laws of our own biology?
Crum’s research suggest that the separation of mind and body is a myth. Our mindsets, the powerful lenses through which we perceive and interpret the world, don't just colour our subjective experience; they can directly and measurably alter our objective physical reality. These core beliefs are not passive thoughts but active instructions that can change how our bodies function.
The following five scientific findings are all drawn from the pioneering work of Alia Crum and her colleagues. Through a number of rigorous studies, they have scientifically demonstrated the incredible, and often surprising, connection between the mind and the body.
1. Your body's response to a milkshake depends on what you think you're drinking
The way our body metabolises food isn't just about nutrients and calories. It's profoundly influenced by our belief about that food's calorific and indulgent ingredients.
In a famous experiment known as the "Mind Over Milkshakes" study, researchers gave participants the exact same 380-calorie milkshake on two separate occasions. The manipulation wasn't in the milkshake, but in its label.
One time, the shake was presented as a 620-calorie, high-fat "Indulgent" shake.
The other time, it was presented as a 140-calorie, low-fat "Sensible" shake.
Scientists measured the levels of ghrelin, a hormone that regulates hunger, in the participants' blood. Ghrelin rises to signal hunger and should drop significantly after a satisfying meal to signal to the brain that we are full
The results shocked the researchers. When participants believed they were drinking the "Indulgent" shake, their ghrelin levels dropped five times more steeply than when they thought they were drinking the "Sensible" shake. This means the body's hormonal response was psychologically mediated. The indulgent mindset sent a powerful signal of satisfaction, leaving people physiologically satiated. The sensible mindset left the body physically unsatisfied and more likely to seek out food sooner. What's even more fascinating is that while the physiological responses were dramatically different, participants' subjective ratings of their own hunger did not significantly change. Our bodies can be left in a state of scarcity even when our conscious minds don't register the difference.
This reveals a profound irony: the restrictive diet mindset might actually be working against our physiological goals by telling our bodies we haven't received enough. Maybe we can begin to approach even the healthiest foods with a mindset of indulgence, we will experience the physiological satisfaction of having had our cake and eaten it too."
This principle doesn't just apply to food; it can also redefine our relationship with one of life's most common challenges: stress.
2. Believing stress is good for you makes it so
Adopting a ‘stress-is-enhancing’ mindset can fundamentally change its effect on you, turning it from a harmful force into a resource for growth and performance.
The conventional wisdom is that stress is a negative experience to be avoided, but what if that belief is part of what makes it so harmful? As Crum explains, from an evolutionary perspective, "the body's stress response was not designed to kill us... It was designed to help us rise to the occasion." It's a powerful survival tool, not a modern malfunction. Her research contrasts two core mindsets:
Stress-is-debilitating: The common belief that stress drains health, vitality, and performance.
Stress-is-enhancing: The belief that stress can fuel learning, growth, and productivity.
Studies found that people holding a ‘stress-is-enhancing’ mindset report better health and higher life satisfaction. The physiological proof is compelling. When faced with a stressful task, people with a stress-is-enhancing mindset showed more adaptive responses, including a more moderate cortisol response (not too high, not too low) and sharper increases in the anabolic growth hormone DHEAS. Behaviorally, they also showed a greater desire for feedback after the task, indicating an approach-oriented, growth-focused response.
The implication can be empowering. Our "stress about stress" might be a key part of what makes it toxic. We may not be able to eliminate stress, but we can change our relationship with it, transforming it into a resource instead of a threat. The message of this research is ultimately a positive one: eliciting the enhancing aspects of stress (as opposed to merely preventing the debilitating ones) may be, in part, a matter of changing one’s mindset.
This power of belief extends beyond our internal states and can even reshape the benefits we get from our physical actions.
3. You can get the health benefits of exercise just by believing you're active
The physiological benefits of physical activity are not just a result of the activity itself, but are powerfully moderated by the simple belief that you are getting good exercise.
The origin of this study began with a simple conversation. Crum, a former high performing ice hockey player at Harvard, was in a class taught by her professor, the renowned psychologist Ellen Langer. After coming to class from practice, Langer remarked, "Oh, you know, exercise that's just a placebo." That idea stuck with Crum and led to an incredible study of 84 female hotel maids. These women were already doing physically demanding work that easily met the government’s recommendations for an active lifestyle, yet most of the maids didn’t think of it as exercise.
The researchers divided the maids into two groups:
The informed group was told that their daily work was excellent exercise and was shown specific information on how many calories their tasks burned.
The control group was given no such information.
Crucially, neither group changed their behaviour. Managers confirmed that their workload and activity levels at work and outside of work remained the same.
After just four weeks, the results were remarkable. Compared to the control group, the informed group showed significant physiological improvements. They lost an average of 2 pounds, showed a 10-point drop in systolic blood pressure, and had improvements in their body fat percentage, waist-to-hip ratio, and body mass index (BMI). Their bodies responded not just to the physical work, but to the awareness and belief that the work was beneficial. This suggests that millions in physically active jobs may not be reaping the full rewards of their labour because they simply don't count it as exercise.
However, if a belief can change the effects of our actions, could it also change the effects of our biology itself?
4. Your belief about your genes can outweigh the genes themselves
Information about your genetic predispositions can change your body's performance in a way that is independent of your genetic makeup.
Perhaps the most mind-bending finding comes from a 2019 study on the CREB1 gene, which is linked to exercise capacity. Participants first ran on a treadmill to establish a baseline measurement of their respiratory efficiency, specifically, how effectively their lungs exchanged oxygen for carbon dioxide while under physical strain.
A week later, they returned to repeat the test. Before they began, they were given a genetic report. Critically, the information in the report was randomised and did not always match their real genetics. This allowed researchers to separate the effect of a person's genes from the effect of what they believed about their genes. For example, some people who actually had the protective gene were told they had the high-risk gene, and vice versa.
The outcome was remarkable. The results revealed that an individual's physiological performance was shaped by what they were told their genetic risk was, not what it actually was. Those who believed they had the "bad" gene became measurably less efficient in their oxygen-to-CO2 exchange during exercise. The belief created the physiological reality. In an age of direct-to-consumer genetic testing, this is a powerful reminder that information isn't neutral. Our mindset about that information can become a self-fulfilling prophecy, even in the face of our most difficult life challenges.
5. A cancer patient's mindset can improve their quality of life
For cancer patients, their core beliefs about the illness, whether it's a "catastrophe," something "manageable," or an "opportunity", can significantly impact their quality of life, and this mindset can be changed.
In a sensitive but empowering study, researchers found that a cancer patient's mindset about their illness was not correlated with the clinical severity of their disease. A patient with stage I cancer might view it as a catastrophe, while another with stage III cancer might see it as a manageable challenge.
To see if these mindsets could be shifted, researchers developed the Cancer Mindset Intervention (CMI). This was a brief, digital program where newly diagnosed patients watched films of other survivors discussing how their mindsets evolved. The intervention included modules with tangible themes like My Body Is Capable and Opportunities Emerge to help patients reframe their experience.
Patients who went through the CMI showed significant improvements in their overall health-related quality of life (HRQoL), which includes physical, social, emotional, and functional wellbeing, compared to a control group. The intervention also increased their engagement in adaptive coping behaviours and reduced their distress from physical symptoms.
This is not about thinking your way out of cancer. It is about providing an evidence-based tool that can improve the quality of a person's life through one of the most difficult challenges. It shows that even when facing a devastating illness, changing your mindset about the experience is a powerful way to regain a measure of control and improve wellbeing.
Your reality is more malleable than you think
Our mindsets are not just passive thoughts; they are active biological instructions. Whether it's the nutritional value of a milkshake, the impact of stress, the benefits of exercise, or even the expression of our genetic code, the lens of our beliefs shape our physical reality. The body doesn't just listen to the facts, it listens to the story our mind tells it.
If your beliefs can so clearly influence your body, what single mindset would you choose to adopt today to shape a healthier reality for yourself tomorrow?