How the Brain Recovers in Anorexia: Why the Hippocampus and BDNF Matter

Review on new research.

Link to research

First — what is the hippocampus, and why does it matter?

The hippocampus is a small but critically important structure deep in the brain. It plays a central role in:

• Memory and learning – forming new memories and linking information together

• Emotional regulation – helping modulate fear, anxiety, and emotional intensity

• Stress regulation – working closely with cortisol and the stress response system

• Cognitive flexibility – the ability to adapt, shift perspective, and think less rigidly

The hippocampus is one of the most energy-hungry parts of the brain and one of the few areas that can grow new neurons throughout life. Because of this, it is particularly vulnerable to starvation and chronic stress.

In anorexia nervosa, the hippocampus commonly shrinks in size, which helps explain:

• poor concentration and memory

• rigid, repetitive thinking

• emotional volatility or numbness

• difficulty benefiting from therapy

This study focuses on how and why the hippocampus recovers during nutritional rehabilitation — and what biology supports that recovery.

What this study looked at (in simple terms)

People with anorexia nervosa often experience shrinkage of parts of the brain, especially the hippocampus.

This study followed adolescents and young adults with anorexia over time and used brain scans to see what helps the hippocampus recover during nutritional rehabilitation.

The researchers asked an important question:

Is brain recovery just about gaining weight — or are there biological brain-growth signals involved as well?

To answer this, they measured:

• Hippocampal volume on MRI

• BDNF (brain-derived neurotrophic factor)

• Inflammatory markers (IL-6 and TNF-α)

• BMI changes

They then tracked how these changed during refeeding.

The key finding (this is the headline)

Increases in BDNF were associated with hippocampal recovery even after accounting for weight gain.

In other words:

• Weight restoration helped the brain

• But BDNF added something extra

• Brain recovery was not explained by BMI alone

Inflammatory markers did not explain brain recovery in this study.

This tells us something critical:

The brain doesn’t just need calories — it needs the biological capacity to rebuild itself.

What is BDNF (in human language)?

BDNF = Brain-Derived Neurotrophic Factor

Think of BDNF as:

• Fertiliser for brain cells

• A growth and repair signal

• A neuroplasticity switch

BDNF helps:

• Brain cells survive

• New connections form

• Learning and memory improve

• Emotional regulation stabilise

• The hippocampus physically grow

Without enough BDNF:

• The brain becomes rigid

• Learning is impaired

• Recovery stalls

• Therapy is harder to engage with

Why BDNF is especially important in anorexia

The hippocampus:

• Has a very high energy demand

• Is one of the few brain regions that continues making new neurons

• Is highly sensitive to starvation and stress hormones

In anorexia:

• The brain is under-fuelled

• Stress hormones (like cortisol) are high

• Neuroplasticity is reduced

This study shows that as nutrition improves, BDNF rises, and that rise is linked to actual brain regrowth — not just symptom improvement.

How is BDNF made in the body?

BDNF production depends on several things working together:

1. Adequate energy intake

The brain cannot make BDNF in a starved state.

• Energy availability matters

• Chronic restriction suppresses BDNF production

2. Protein and amino acids

BDNF is a protein molecule.That means it requires:

• Adequate total protein

• Essential amino acids

• Ongoing intake (not intermittent)

3. Micronutrients that support brain signalling

BDNF synthesis and function rely on:

• B vitamins (especially B6, B9, B12)

• Zinc

• Magnesium

• Iron (indirectly, via oxygen delivery)

• Omega-3 fats (especially DHA)

Deficiencies common in anorexia interfere with this process.

4. Reduced chronic stress

High cortisol suppresses BDNF.As nutritional status improves:

• Stress chemistry shifts

• BDNF production becomes more possible

How does BDNF become “functional” in the brain?

BDNF is not useful just because it’s present in the blood.

To work, it must:

1. Be converted into its mature form

2. Bind to specific brain receptors (TrkB receptors)

3. Activate pathways that allow:

   • New synapses to form

   • Neurons to grow and survive

   • Learning circuits to strengthen

This process depends on:

• Ongoing nutrition

• Stable glucose availability

• Reduced physiological stress

That’s why intermittent eating, under-fueling, or partial refeeding can limit brain recovery, even if weight increases slightly.

What the study did NOT find (important)

This study did not find:

• That BDNF explained brain shrinkage in the acute phase

• That inflammation drove hippocampal changes

• That BMI alone predicted full brain recovery

This matters because it challenges a common oversimplification:

“Once weight is restored, the brain is fine.”

This paper shows that biological brain repair signals matter, and they don’t automatically normalize just because the scale changes.

Why this matters clinically

This research supports several clinically important ideas:

• Nutritional rehabilitation is brain rehabilitation

• Eating enough supports learning capacity, not just weight

• Recovery requires consistency, not just calorie targets

• Cognitive rigidity in anorexia is partly biological, not just psychological

• Therapy works better when the brain has regained plasticity

It also explains why people often say:

“My thinking only started to change after I’d been eating properly for a while.”

Take-home message

This study shows that:

BDNF is a key biological bridge between nutrition and brain recovery in anorexia.

Weight gain matters — but brain repair is an active process, not a passive one.

Feeding the brain:

• Requires enough food

• Over enough time

• With the nutrients needed for repair

• In a body that is no longer in survival mode

That’s not a failure of willpower.That’s neuroscience.