Gaining weight can often bring up feelings of confusion, fear, or even resistance. This is a very normal response, especially since we live in a society that demonizes weight gain and sends messaging related to the need to shrink our bodies.

In eating disorder treatment, your dietitian may recommend that you gain weight, even if you're not considered traditionally "underweight".

At KCPN, our dietitians use an evidence-based and individualized appraoch in determining appropriate weight gain goals.

Meet The Starved Brain

Eating disorders are not simply about food, they're illnesses of a malnourished brain. When the brain is starved, it shifts into a survival state, which disrupts how multiple brain systems communicate and function together.

One of the most affected areas is the prefrontal cortex, which is responsible for planning, self-reflection, emotional regulation, and flexible thinking. In a well-nourished brain, this region supports nuance, perspective, and the ability to adapt. But under conditions of starvation, its functioning declines. This is why individuals with eating disorders may seem rigid, stuck in rules, or unable to “just think differently.” This isn’t defiance - it’s the result of a brain operating without the energy it needs.

Many people describe a frustrating internal split: “I know this doesn’t make sense, but I still can’t eat.” This experience highlights an important truth - insight alone is not enough. The ability to challenge fears, tolerate uncertainty, regulate emotions, and shift thinking all depend on adequate nourishment. These are precisely the capacities that are compromised when the brain is under-fueled. In other words, eating behavior often has to change before thinking can meaningfully shift.

From a neurobiological perspective, food is not just fuel - it's a core component of treatment. Expecting the brain to “reason its way” into recovery without sufficient energy is biologically unrealistic. Recovery depends on neuroplasticity, the brain’s ability to adapt, form new connections, and unlearn entrenched patterns. But neuroplasticity requires significant energy and biological resources.

When the brain is functioning in an under-nourished state:

• Learning becomes slower
• Therapy is ineffective
• Fear responses become more dominant
• New habits struggle to take hold

Most psychological therapies for eating disorders rely on skills like reflection, emotional processing, memory integration, and cognitive flexibility. All of these processes are impaired by starvation. Expecting meaningful psychological progress without restoring adequate nutrition places unrealistic demands on an already compromised brain.

Nutrition is not secondary to recovery - it is the foundation that makes all other aspects of healing possible.

Introducing the Minnesota Starvation Experiment

Let’s look at the well-known Minnesota Starvation Experiment from the 1940s. It’s one of the clearest demonstrations of what happens when the body is underfed and, often as a result, loses weight over time. It also sheds light on why dieting so often backfires, while negatively impacting body image and overall relationship with food.

In this study, a group of young men volunteered to participate in a yearlong project that included a period of significant calorie restriction followed by refeeding. During the restriction phase, they were given 1,500 calories per day (which by today's standards may not even sound that low) and were required to stay physically active to mirror the conditions of wartime deprivation.

Over the course of the restriction period, they each lost around 25% of their total body weight. Researchers documented the physical changes, many of which looked very similar to what we now see in people experiencing eating disorders. But the psychological shifts were just as striking - if not more so.

As their intake stayed low, the men became increasingly anxious, low in mood, and irritable. Food began to dominate their thoughts. They developed rituals and behaviors around eating - like cutting food into tiny pieces, eating very slowly, or trying to stretch out meals for as long as possible. Some chewed gum constantly. A number of participants struggled enough that they needed inpatient psychiatric care.

What’s especially notable is how their perceptions changed. Even as their bodies became smaller, they didn’t necessarily see themselves that way. At the same time, they became more critical of others’ body sizes. Their thoughts and behaviors started to mirror what we now recognize as eating disorder symptoms.

The takeaway here is important: when the body is underfed, the brain responds. These men never had issues with their relationship with their body or food before the restriction period. However, that restriction, and ultimately weight loss, induced eating disorders in them. Changes in how someone thinks about food, eating, and their body can be a direct result of not getting enough nourishment.

Signs You Might Need To Gain Weight

Malnutrition can affect people of all body types - not just those who appear thin. Some people may lose a noticeable amount of weight and fall below what’s typical for their body, while others may not lose weight at all, or might even gain weight, despite ongoing restrictive eating habits. Because of this, many people who don’t fit the stereotypical image of being “underweight” may not realize they’re struggling. But the need to restore weight isn’t determined by appearance alone.

1. Low bone density (with or without losing a period in females)

When the body isn’t getting enough fuel, bone strength can slowly decline. While nutrients like calcium and vitamin D are important, they aren’t enough on their own to rebuild bone density. The gold standard of treatment for bone density loss is weight gain. For females who have lost their period, this may also lead to the return of a regular menstrual period. Research consistently shows that gaining weight can help improve bone density over time.

2. Low bone density paired with low testosterone in males

In males, low testosterone combined with undernourishment can speed up bone loss. In fact, bone density may decline earlier and more quickly compared to females, even at higher body weights, increasing the risk of fractures. As with females, restoring adequate nutrition and weight is the most effective way to address this.

3. Slowed or delayed growth in children and teens

For kids and adolescents, not getting enough nutrition can interfere with normal growth. This might show up as falling behind on growth charts. Growth hormone continues to be produced and levels will remain high in the body, however the cells become less responsive to it. When the body is under-fueled, it prioritizes essential functions needed for survival, and growth takes a back seat. This means the issue isn’t a lack of hormones - it’s a lack of nutrition.

4. Loss of menstrual period

Menstrual cycles can vary a lot from person to person, as shown in research:

• About half of people got their period back after reaching the lower end of a "normal" weight range.
  
• A quarter of people either kept having their period or had it return even while still quite underweight.
• 38% of people who were restricting food lost their period despite still being in a "normal" BMI range.
• Interestingly, body fat percentage doesn't seem to predict when periods come back any better than BMI does.
  

While the return of a period is often seen as a sign the body is recovering, it’s not always a clear-cut marker - some people get their period back early, while others may take much longer, even after weight restoration. A commonly cited guideline suggests that about 90% of women will see their period return within 6 months of reaching roughly 90% of their expected body weight. However, what we've learned is that individual differences, including genetics and stress, can play a role.

5. Low estrogen (estradiol) levels in females

Estrogen levels naturally rise and fall during the menstrual cycle, but consistently low levels (< 50 ng/mL) can be a sign that the body is starved of resources. When this happens, the body may essentially “pause” reproductive functions. Over time, this can even cause reproductive organs to shrink toward a pre-puberty state.

Research gives us some helpful context here:

• Nearly 90% of women needed to gain weight to a BMI above 20 before their reproductive system was able to fully mature.
  
• At a BMI of 19, only 40% were able to reach that level of reproductive maturity.

6. Not gaining expected weight during adolescence

Weight gain during puberty is not only normal - it’s necessary. Girls may need to gain 30 pounds or more, and boys around 50 pounds or more during adolescence. This can happen gradually or in spurts, and often includes a phase where the body looks a bit softer or carries more weight around the middle. This is a natural part of development, and not something to worry about.

Growth during this time is not linear, and it’s common for teens to move up percentiles on growth charts as their bodies prepare for adulthood. When expected weight gain doesn’t happen, it can be a sign that the body isn’t getting what it needs to grow and develop properly.

7. The eating disorder is very loud

Sometimes one of the clearest signs is how much space food, weight, or body thoughts are taking up in your mind. If it feels like there’s a constant voice commenting on what you eat, second-guessing your choices, setting rules, or making you feel guilty, that’s important to pay attention to. Even if things look “fine” from the outside, a lot of internal noise and stress around food can be a sign that your body and brain aren’t getting what they need. In most cases, that voice quiets down as your body becomes better nourished and more supported.

A Note On Weight Stigma and Weight-Inclusive Care

Any conversation about weight gain in eating disorder treatment needs to include a discussion of weight stigma.

This has been described as “the social rejection and devaluation that accrues to those who do not comply with prevailing social norms of adequate body weight and shape.” Put simply, people in larger or differently sized bodies are often judged more harshly and treated worse.

Eating disorders are complex conditions with many contributing factors, but weight stigma is often part of the story. In The Body Is Not an Apology, Sonya Renee Taylor describes a kind of “hierarchy of bodies” - the belief that there is a right and wrong way to have a body. In this hierarchy, thinness is often associated with health, discipline, and worth, while larger bodies are unfairly linked to negative traits. These assumptions are both far from the truth and can cause real harm in healthcare, relationships, workplaces, and beyond.

Not all eating disorders are about body image, but many begin with weight loss - whether intentional or not. Weight stigma doesn’t just contribute to the development of eating disorders - it can also make recovery more difficult. In a culture where many people are encouraged to eat less, being asked to eat more during recovery can feel deeply uncomfortable or even unsafe.

Weight stigma is also common in healthcare settings and has been linked to poorer health outcomes and avoidance of medical care. When body size is treated as a problem to fix, it can overshadow the full picture of a person’s health and reinforce unhelpful or unsupported assumptions.

A common example includes the medical treatment of knee pain. A thinner patient might be referred to physical therapy, while a patient in a larger body may simply be advised to lose weight. In some cases, people will restrict their intake significantly in order to qualify for surgery, sometimes arriving at the operating room undernourished - which can complicate recovery.

The goal here is to highlight gaps in current approaches and point toward alternatives that may better support both physical and mental health. This is where weight-inclusive care comes in. It’s the approach that KC Performance Nutrition has embraced since opening. This model is gaining support with the creation of the Association for Weight and Size Inclusive Medicine (AWSIM) in 2024 in addition to the Health at Every Size® (HAES®) framework developed by the Association for Size Diversity and Health.

At KC Performance Nutrition, weight-inclusive care means not assuming that higher body weight is inherently a problem, respecting natural body diversity, and not relying on weight as the primary measure of progress (with some exceptions, such as in children, pregnancy, or during specific phases of medical nutrition therapy). This approach also moves away from diet culture, supporting people in eating consistently and adequately, and engaging in movement in ways that feel supportive and sustainable.

There’s growing evidence that weight-inclusive care can reduce stigma and improve outcomes, particularly for those recovering from eating disorders. Early research in treatment settings is promising, and the approach continues to gain support as a more compassionate and effective way to care for individuals across the body size spectrum.

How An Eating Disorder Dietitian Can Help

At KC Performance Nutrition, our dietitians:

• Analyze growth and weight history
• Monitor lab values and vital signs
• Collaborate with medical providers and therapists
• Implement individualized nutrition planning
• Provide ongoing support through weight restoration

Sara Arnold, founder of KC Performance Nutrition, is a Certified Eating Disorders Specialist (CEDS)  and provides eating disorder nutrition treatment for athletes of all ages and activity levels.

Our dietitians can support all forms of disordered eating and most eating disorders.

Work With A Dietitian That Specializes In Eating Disorders

If you are an athlete, parent, coach, or healthcare provider and have concerns about disordered eating or an eating disorder, early support matters.

KC Performance Nutrition specializes in eating disorders in athletes and provides virtual disordered eating nutrition counseling throughout many states across the country.

Schedule an appointment with a sports dietitian specializing in athlete eating disorders today to support safe and effective recovery.