As a registered dietitian and health writer, I typically rely on recent research to guide my practice and writing. However, there’s sometimes what’s called a landmark study from many years ago that influences the nutrition field significantly enough to guide clinical practice and be a constant in clinician-to-patient conversations. In the field of eating disorders, that study is the Minnesota Starvation Experiment. The Minnesota Starvation Experiment—initially titled The Biology of Human Starvation—was performed by scientist Ancel Keys and his team, and is considered the landmark study that fundamentally shaped our understanding of the wide-ranging and serious effects of food restriction.

The purpose of the experiment was to gain insight into the physical and psychological effects of semistarvation (or severely undereating) that occurred in World War II and understand how to help renourish civilians that were malnourished during the war. “The goal was to improve how aid was given to people in Europe and Asia who had suffered from famine after the war,” explains Equip lead dietitian Tucker Reiley, MS, RDN. The experiment revealed jaw-dropping truths about the far-reaching consequences of food restriction, and helped illuminate what’s required to restore health and well-being. Today, we’ll delve into the study and its findings, explore the science of food restriction and its effects, unpack what the study tells us about eating disorders, and see how its findings could help you or your loved one in recovery.

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Overview of the experiment and its findings

In 1944, Keys and his colleagues recruited 36 male conscientious objectors (those who opted out of serving in the war) to participate in semistarvation. All participants were physically and mentally healthy at the start of the experiment.

The study included three phases:

Standardization (3 months): The men received a calorically adequate diet, and they reported feeling well-fed, energized, and engaged in their lives and community.

Semistarvation (6 months): Participants ate about half of what they needed, with their diet reflecting that in war-torn parts of Europe: items like potatoes, turnips, rutabagas, macaroni, and dark bread. They were also required to walk a significant amount each week and expend a certain amount of energy. “The researchers wanted the participants to lose around 25% of their body weight before they explored renourishment strategies,” Reiley explains.

The semistarvation period revealed many drastic changes to the participants’ minds and bodies:

• Physical changes, like heart muscle mass reduction, decreased basal metabolic rate, decreased cold tolerance, fatigue, hair loss, dry skin, increased hunger, decreased hormone levels and libido, difficulty sleeping, dizziness, and blacking out.
• Mental side-effects, like decreased alertness and focus, impaired decision-making, increased obsessive thoughts and rigid thinking, and even psychotic episodes.
• Emotional consequences, like increased depression, dysregulation, anxiety, and irritability.
• Social changes, like isolation and withdrawal, social insecurity, decreased sense of humor, strained relationships, and declining personal hygiene.
• Behavioral shifts, like smoking, biting nails, hoarding and stealing food, obsessing over recipes and cookbooks, binge eating, meticulous meal planning, excessive condiment use, and food preoccupation.

Rehabilitation (3 months): Men were provided one of four rehabilitation diets with higher, varying energy levels, and results showed the most calorically dense intake was most effective at reversing malnutrition. “When it came time to renourish the study participants, pre-starvation levels of dietary intake did not support weight restoration and recovery of normal functioning. Instead, participants required substantially more food than they had ever normally eaten to restore weight,” Reiley shares. “The process of weight restoration had its own set of discomforts and side effects, such as GI distress, elevated metabolic rate, and refeeding syndrome.”

The men also noted that after the restriction period ended, they initially experienced a loss of control around food during refeeding. Some described a constant urge to eat, while others reported episodes of binge eating—something they had never experienced prior to the experiment. Over half of the participants said they engaged in overeating. Estimates of full recovery time ranged from two months to two years, and none of the men believed their participation had any lasting negative effects on their health.

The science of restriction: the "why" behind study participants’ drastic mind-body changes

It’s clear that semistarvation caused the men in the study to experience drastic, holistic changes—but you might be wondering why that happened. “Every living cell in the human body requires energy from food to perform its functions, and when the body doesn't get its needs met consistently, the whole system has to make adjustments to prioritize survival,” Reiley explains. “The lack of energy input means that cells responsible for hormone, neurotransmitter, and antibody production cannot do their jobs effectively, which means all sorts of processes in the body and brain are impacted, from immune function to maintenance of bone integrity to emotional regulation and impulse control.”

Here’s a breakdown of why food restriction causes such serious physical, mental, emotional, and behavioral side-effects:

The physical effects of food restriction

Since the heart is primarily composed of muscle, prolonged undernourishment can cause it to weaken, leading to dangerously low blood pressure and heart rate. As the heart's ability to pump blood declines, symptoms like fatigue and shortness of breath may develop. Additionally, malnutrition can interfere with the heart’s electrical system—the force that drives each heartbeat—which, in severe cases, can be life-threatening. Another serious consequence of restriction is nutrient deficiency, which can cause various health problems like anemia (often due to iron deficiency), cold intolerance, hair thinning, skin issues, insomnia, weakened bones, dizziness, persistent fatigue, and a compromised immune system. When the immune system is suppressed, the risk of infections, colds, flu, and other illnesses increases.

Furthermore, a 2022 research review found that low energy availability due to restriction can suppress the entire reproductive hormone system. In females, this leads to a drop in estradiol and progesterone—two key hormones for reproductive health. In males, inadequate energy intake disrupts testosterone production, resulting in fatigue, reduced libido, sexual dysfunction, and decreased bone mineral density. In short, when the body doesn’t receive enough fuel, it conserves energy by prioritizing essential functions (like maintaining heartbeat and breathing) while shutting down less critical systems such as reproduction.

The mental and emotional effects of food restriction

Food restriction—often accompanied by malnutrition and significant weight loss—can contribute to or intensify depression and anxiety by disrupting brain chemistry. Malnutrition may damage brain tissue and result in deficiencies in key nutrients such as vitamin B12, folate, and zinc, which is linked to depression, cognitive decline, and irritability. Malnutrition can also reduce the production of dopamine and serotonin, two hormones critical for mood regulation, potentially worsening symptoms of both anxiety and depression.

In addition to making it difficult to focus in demanding environments such as work or school, food restriction can interfere with managing daily responsibilities and contribute to brain fog. A 2021 meta-analysis found that anorexia—which often involves chronic restriction—is associated with cognitive deficits, including notably reduced memory performance.

The behavioral effects of food restriction

Food obsession and disordered food behaviors are usually a direct result of food restriction, because “there is an instinct to focus on what we need to survive,” says dietitian Katie Gilder, MPH, RD. “Not having a basic biological need like hunger met is of course going to distract someone from being able to focus on other things, and will lead to a hyperfixation on ways that this need could be met until it is,” she explains. Gilder also points out that when people have the types of food (not just the amounts) controlled, scarcity mindset ensues. “No foods that were simply for enjoyment were provided, so not only were their physical needs not being met, but with the variety of foods being limited as well, it makes sense that the men started to be obsessed with recipes and pictures of food,” she says. “There was even one man who was ‘kicked’ out of the study for sneaking out and bingeing on ice cream, and I think it says a lot that he didn't just sneak out and eat anywhere, but specifically a food that was totally absent in the meals they had been provided.” Another man in the study was so tempted by the delicious smell of a bakery as he walked past that he bought a dozen doughnuts, gave them to children, and watched them eat.

Other behavioral issues that may occur because of food restriction include social isolation, decreased engagement in work or school and hobbies, decreased ability for daily functioning, and other disordered food behaviors like hoarding, hiding, or stealing food. “The brain's reward systems become fixated on food and coping with the psychological stress of the threat of starving to death, sometimes through behaviors that further negatively impact the person's health and well-being,” Reiley adds.

What the experiment tells us about eating disorders

While this study isn’t about people with eating disorders, it offers some profound key points that can be applied to eating disorders and recovery.

Restriction is at the root of many disordered behaviors

The cause of an eating disorder is often multi-faceted, however restriction is present across diagnoses and often leads to a number of eating disorder behaviors—many of which are mirrored in the study’s semistarvation side-effects. “The men in the study who had no prior predisposition to an eating disorder fairly quickly showed similar signs to those we see with many restrictive eating disorders, like obsessive thinking about food, talking about food constantly, and looking at recipes for foods they aren't able to eat,” Gilder explains, “so we can think about how this is evidence that no one with an eating disorder chooses to become so entrenched in some of the thoughts and rituals with foods.” Rather, the thoughts are a direct result of the restriction.

Food restriction is a slippery slope

Not only does food restriction lead to disordered behaviors, it can also make it more difficult to see that those behaviors are harmful or undesirable. “The more malnourished the brain gets, the more difficult it can be for the person to recognize the problem or interpret reality accurately and can result in a slippery behavioral slope,” Reiley explains.

Nutrition rehabilitation is hard, to say the least

Although the men in the study didn’t have eating disorders, many of them said the nutrition rehabilitation period was the hardest part of the experiment. It took many of them a long time to return to baseline and feel like themselves again—which suggests that this process would be even harder for a person struggling with an eating disorder. In addition to healing from the side effects of malnourishment, people in recovery from eating disorders often need to heal from trauma, body image distress, and other emotional issues. The study also highlights the necessity of eating an abundance of food (often more than what many may consider “normal”) to fully reverse side-effects of food restriction. “Consider how difficult it would be for someone who deeply fears eating a normal amount of food or gaining weight to need to eat significantly more than their peers and need to gain significant amounts of weight for their brain to start healing, all while the changes they are making physically feel worse due to the GI side effects and heightened anxiety,” says Reiley.

Recovery is entirely possible

Although it took them a while to feel normal afterwards, the men in the study emerged from the haze of semistarvation and returned to themselves, their hobbies, jobs, and families. One man said he knew he was healed once his sense of humor fully returned. One of the most rewarding parts of being an eating disorder dietitian is getting to witness people return to their true selves and their full lives, which they wouldn’t be able to do if they were still malnourished and living in energy deficits.

How the Minnesota Starvation Experiment can help you or your loved one in recovery

In my practice, I’ve shared the Minnesota experiment and its findings with clients and their families to help them understand how profoundly food restriction impacts their minds, bodies, and emotions, and that changes they’re experiencing are not their fault or something they’re choosing. “An eating disorder is an incredibly interwoven tapestry of the body-wide malnutrition injury and its direct physiological side effects, as well as the way the human brain attempts to adapt to scarcity and the chronic stress of starving,” Reiley explains. “When someone no longer recognizes themselves or their loved one with an eating disorder, it's not the fault of the person with the eating disorder—it is the eating disorder and the havoc it has wrought in that person's life.”

Remember, eating disorders are (maladaptive) coping mechanisms, so the food preoccupation that comes with food restriction and living in an energy deficit often “helps” someone with an eating disorder avoid other issues in life that may be stressful and feel outside of their control. This is why developing healthy coping skills in therapy is critical. Also, to an eating disorder sufferer, obsessively thinking about food can feel like it’s all there is to their personality and existence, which can make recovery feel daunting (“Who am I without my eating disorder?”). However, remembering that the food obsessions are born from restriction can be reassuring and help people to understand that recovery is about reconnecting with their true interests and core values.

If you’re a parent with a child or teen, keep in mind that, like the study shows, food restriction causes food obsession and preoccupation with cookbooks or recipes. Gilder cautions against using such thinking patterns and behaviors even if it seems authentic. “We want to have parents take back control over the planning, cooking, and often plating of foods for a period of time, and then if after their child has been re-fed they are still really into cooking, we can be super open to that,” Gilder explains, “but since we know there is a correlation between the underfed brain and the obsession with food, I do want to make sure we interrupt that at first.” Also, keep in mind that your child or teen’s mealtime behaviors (like shredding food, eating very slowly, or becoming very emotional) are in fact results of starvation, not defiant acts.

Learn about FBT treatment at EquipFamily-based treatment is the gold standard for treating eating disorders in young people.

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Another significant point I often share from the experiment is that nutrition rehabilitation and weight restoration are necessary to recover from eating disorders and eventually heal from all their side effects—and it’s impossible to heal mentally and emotionally if you haven’t restored your physical health. “The brain is the slowest organ to heal from the systemic malnutrition injury that restrictive eating disorders wreak on their victims, and being able to get the body out of a weight suppressed state is a critical part of healing the brain to the point that it can effectively engage with the difficult therapeutic work that recovery asks of people,” Reiley says. “My hope is that people are able to recognize that by addressing the restriction, there is a path forward to get back to who they were before the eating disorder took over.”

If you or your loved one is struggling with an eating disorder, know that recovery (while often difficult) is possible, and like the Minnesota experiment shows, the system-wide impacts of restriction are reversible. Reach out for help from a professional team who will guide you to restoring your or your loved one’s physical, mental, and emotional health and well-being.