> For the complete documentation index, see [llms.txt](https://4heal.gitbook.io/4heal-1/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://4heal.gitbook.io/4heal-1/introduction/individual-level-health-brain.md).

# Individual-Level Health Brain

#### 1. What is the Digital Twin?

In 4Heal, the Digital Twin is **not** just an “electronic record”.

It is:

* A continuously updated individual health model;
* A dynamic system that fuses physiology, behavior, environment, and intervention responses;
* A long-term intelligent foundation that can be used for reasoning and prediction.

It consists of four layers:

1. **Behavior Layer:**
   1. Sleep, diet, exercise, stress events, habits.
2. **Physiology Layer:**
   1. HRV distribution, temperature rhythms, sleep architecture, etc.
3. **Risk Layer:**
   1. Trends of metabolic, cardiovascular, mental stress, circadian disruption risks.
4. **Intervention Feedback Layer:**
   1. The body’s responses and adaptations to different interventions.

***

#### 2. The Role of the AI Health Agent

The AI Health Agent is the **interface + brain** through which users interact with their Digital Twin:<br>

* Builds an initial understanding of you from Q\&A and data;
* Participates in data fusion and inference to assess your current health state;
* Generates actionable, personalized health plans;
* Observes your execution and bodily responses to update the Digital Twin;
* Explains reports and test results when needed, helping you **clearly understand your own situation**.

It is **not** just a “Q\&A bot”.

It is:

> **A long-term health intelligence agent that has memory, understanding, and predictive capability about you.**


---

# Agent Instructions
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