The body engine

Loads press on parts, and parts lean on each other. Turn loads up, drag parts around, and watch how strain on shared parts adds up. Then ease one load by one notch and watch room come back in more places than that one load touches.

How the model works

Each load pushes on the parts it's linked to: Some counts once, A lot counts twice, times the link's strength (1 to 3).
A part passes part of its strain on to the parts it feeds. A strained part passes on more, the way a struggling part makes the next one work harder.
That's why loads that share parts add up to more together than one at a time. The extra is what shared parts add.
The ring around each part shows how much of its reserve is used. A part can use most of it before it reads as strained.
It runs both ways. With other loads on, easing one load by a notch gives back more than that load's own share, because the parts it shares slide back down the same curve. Room to spare shows it.
No single load, even at A lot, reads as strained on its own. Strain takes loads that meet on shared parts.
Open questions are left out unless you count them.

Every link and its source

Sleep and recovery

The nightly repair shift. When it runs short, the other parts start the day behind.

Poor sleep · Expert consensus: Healthy adults need at least 7 hours; 6 or fewer is too little to sustain health. American Academy of Sleep Medicine and Sleep Research Society, 2015
Long-running stress · Open question: Does long-running stress wear down sleep, sleep wear down stress, or both?
Ultra-processed food · Review of studies: More ultra-processed food went with sleep problems. Lane and colleagues, 2024

Brain and mood

The control room: attention, stress response and mood.

Sleep and recovery · Health agency: Enough sleep eases stress and lifts mood. CDC, 2024
Sitting a lot · Health agency: Activity eases depression and anxiety. WHO, 2024
Ultra-processed food · Review of studies: More ultra-processed food went with anxiety and common mental disorders. Lane and colleagues, 2024
Regular drinking · Health agency: Alcohol is tied to depression and anxiety. WHO, 2024
Chronic inflammation · Review of studies: Chronic inflammation is tied to neurodegenerative conditions. Furman and colleagues, 2019

Immune system

The repair crew and the guards: fights infection and clears damage.

Sleep and recovery · Health agency: Enough sleep helps people get sick less often. CDC, 2024
BPA · Agencies disagree: EFSA's 2023 review pointed to effects on the immune system and cut the safe daily intake; FDA says current levels in food are safe. EFSA, 2026 FDA, 2023

Lungs

The air intake: everything you breathe passes through here first.

Polluted air · Health agency: Fine particles cause lung disease and lung infections. WHO, 2024
Tobacco smoke · Health agency: Children around smoke get more lung infections and more severe asthma. CDC

Heart and vessels

The fuel lines: pump and pipes that reach every other part.

Sleep and recovery · Health agency: Enough sleep lowers the chance of heart disease, high blood pressure and stroke. CDC, 2024
Sitting a lot · Health agency: Activity helps prevent and manage heart disease. WHO, 2024
Ultra-processed food · Review of studies: More ultra-processed food went with death from heart disease. Lane and colleagues, 2024
Regular drinking · Health agency: Alcohol plays a causal part in heart disease. WHO, 2024
Polluted air · Health agency: Most deaths tied to outdoor air pollution are from heart disease and stroke. WHO, 2024
Tobacco smoke · Health agency: Secondhand smoke can cause coronary heart disease and stroke. CDC
Chronic inflammation · Review of studies: Chronic inflammation is tied to heart disease. Furman and colleagues, 2019

Metabolism

Fuel use: how the body handles sugar, fat and weight.

Sleep and recovery · Health agency: Enough sleep lowers the chance of type 2 diabetes and helps keep a healthy weight. CDC, 2024
Sitting a lot · Health agency: Activity helps prevent and manage type 2 diabetes. WHO, 2024
Ultra-processed food · Review of studies: More ultra-processed food went with type 2 diabetes and obesity. Lane and colleagues, 2024
Chronic inflammation · Review of studies: Chronic inflammation is tied to diabetes. Furman and colleagues, 2019
Hormone signals · Open question: Which hormone changes from everyday exposures, if any, shift metabolism?

Hormone signals

The messages that set pace and timing for the other parts.

BPA · Open question: Does everyday BPA exposure change hormone signals in people?

Gut

The intake and the barrier: digests food and keeps what should stay out, out.

Ultra-processed food · Weaker evidence: Gut outcomes were among the links, with weaker evidence. Lane and colleagues, 2024
Glyphosate · Open question: Does glyphosate at everyday doses change gut bacteria in people?
Liver · Review of studies: The axis runs both ways: the liver also sends signals back to the gut. Tripathi and colleagues, 2018

Liver

The filter and the chemical plant: clears and changes most of what comes in.

Regular drinking · Health agency: Alcohol plays a causal part in liver disease. WHO, 2024
Too much acetaminophen · Reference: An overdose can cause sudden serious liver injury; it is the main cause of acute liver failure in the US and Europe. NIDDK LiverTox, 2016
Gut · Review of studies: The gut and liver talk through the gut-liver axis; gut bacteria play a part in fatty liver disease. Tripathi and colleagues, 2018
Chronic inflammation · Review of studies: Chronic inflammation is tied to fatty liver disease. Furman and colleagues, 2019
Metabolism · Health agency: Fatty liver is more likely with obesity, insulin resistance or type 2 diabetes. NIDDK, 2021

Cells and repair

Upkeep at the smallest scale: copying, fixing and replacing cells.

Regular drinking · Health agency: Alcohol is an established carcinogen, tied to several cancers. WHO, 2024
Polluted air · Health agency: Fine particles cause cancers, including lung cancer. WHO, 2024
Tobacco smoke · Health agency: Secondhand smoke can cause lung cancer. CDC
Glyphosate · Agencies disagree: IARC classed glyphosate as probably carcinogenic; EPA concluded it is not likely to cause cancer at expected exposures. US EPA, 2026 The Lancet Oncology, 2015
Chronic inflammation · Review of studies: Chronic inflammation is tied to cancer. Furman and colleagues, 2019
Oxidative stress · Open question: How much does everyday oxidative stress add to wear on cells?

Chronic inflammation

The repair crew stuck on: a low, steady immune response that doesn't switch off.

Poor sleep · Review of studies: Disturbed sleep went with higher inflammation markers; short sleep alone showed only a small link. Irwin and colleagues, 2016
Long-running stress · Review of studies: Psychological stress is one of the things that can keep low-grade inflammation going. Furman and colleagues, 2019
Sitting a lot · Review of studies: Physical inactivity is one of the things that can keep low-grade inflammation going. Furman and colleagues, 2019
Ultra-processed food · Review of studies: A poor diet is one of the things that can keep low-grade inflammation going. Furman and colleagues, 2019
Polluted air · Review of studies: Environmental toxicants are among the things that can keep low-grade inflammation going. Furman and colleagues, 2019
Oxidative stress · Review of studies: Oxidative stress can set off inflammation. Biswas, 2016
Immune system · Open question: When does the immune system's normal response turn into one that doesn't switch off?

Oxidative stress

Reactive oxygen species (ROS) are made by the body itself; oxidative stress is when they outpace its defences.

Polluted air · Open question: How much of polluted air's effect on people runs through oxidative stress?
Chronic inflammation · Review of studies: Inflammation can set off oxidative stress. Biswas, 2016

Connects to

Toxicology basics Mixtures
Mixtures adds up doses that act the same way. The engine shows loads adding up on the parts they share.
Toxicology basics Aggregate exposure
Aggregate exposure counts one substance from every route. The engine counts every load on one part.
Toxicology basics Dose and response
Off, Some and A lot in the engine are dose and response, drawn as a picture.
Seven areas Movement
Sitting a lot is one of the engine's loads. A walk after a meal eases it one notch.
Seven areas Food
Processed food is one of the engine's loads. Vegetables in one meal ease it one notch.
Short reads One small step at a time
Ease one load by one notch in the engine and watch what comes back: one small step, as a picture.
Short reads Small changes, more room
The engine draws this read as a picture: easing one load frees parts it shares with others.

Sources for this page

American Academy of Sleep Medicine and Sleep Research Society (2015). Recommended amount of sleep for a healthy adult: a joint consensus statement.
Expert consensus: what a panel of specialists agreed on.
What we use: Healthy adults should sleep at least 7 hours a night; 6 or fewer is too little to sustain health. No upper limit was set.
Checked Oct 11, 2026 · https://doi.org/10.5665/sleep.4716 · DOI 10.5665/sleep.4716 · PubMed 26039963
Irwin and colleagues (2016). Sleep disturbance, sleep duration, and inflammation: a systematic review and meta-analysis of cohort studies and experimental sleep deprivation.
Pooled analysis of many studies, 72 studies, more than 50,000 people: an average across studies; only as good as the studies inside.
What we use: Disturbed sleep went with higher inflammation markers (CRP and IL-6). Shorter sleep went with a small rise in CRP only, and short spells of sleep loss in the lab showed no change.
Checked Oct 13, 2026 · https://doi.org/10.1016/j.biopsych.2015.05.014 · DOI 10.1016/j.biopsych.2015.05.014 · PubMed 26140821
US Centers for Disease Control and Prevention (2024). About sleep.
Health agency advice: what a public health body recommends; check the page for its own sources.
What we use: Adults 18 to 60: 7 or more hours a night. Habits: steady bed and wake times; devices off 30 minutes before bed; no caffeine late in the day. Enough sleep lowers the chance of type 2 diabetes, heart disease, high blood pressure and stroke, helps people get sick less often and stay at a healthy weight, and eases stress and mood.
Checked Oct 13, 2026 · https://www.cdc.gov/sleep/about/index.html
Furman and colleagues (2019). Chronic inflammation in the etiology of disease across the life span.
Review: experts read and summed up the research.
What we use: Infections, physical inactivity, poor diet, environmental and industrial toxicants and psychological stress can promote low-grade inflammation throughout the body, which in turn is tied to heart disease, cancer, diabetes, kidney disease, fatty liver disease, and autoimmune and neurodegenerative conditions.
Checked Oct 13, 2026 · https://doi.org/10.1038/s41591-019-0675-0 · DOI 10.1038/s41591-019-0675-0 · PubMed 31806905
World Health Organization (2024). Physical activity (fact sheet).
Health agency advice: what a public health body recommends; check the page for its own sources.
What we use: Any amount of physical activity is better than none; all age groups should limit time sitting. Activity helps prevent and manage heart disease, cancer and diabetes, and eases depression and anxiety; insufficiently active people have a 20% to 30% higher chance of death.
Checked Oct 13, 2026 · https://www.who.int/news-room/fact-sheets/detail/physical-activity
Lane and colleagues (2024). Ultra-processed food exposure and adverse health outcomes: umbrella review of epidemiological meta-analyses.
Review of reviews, 45 pooled analyses, about 9.9 million people: pulls together many reviews; only as good as the reviews inside.
What we use: More ultra-processed food went with higher chances of death from heart disease, type 2 diabetes, anxiety and common mental disorders (convincing evidence), and of obesity, sleep problems and depression (highly suggestive). Gut outcomes were among the links, with weaker evidence. These are links from observational studies, not proof of cause.
Checked Oct 13, 2026 · https://doi.org/10.1136/bmj-2023-077310 · DOI 10.1136/bmj-2023-077310 · PubMed 38418082
World Health Organization (2024). Alcohol (fact sheet).
Health agency advice: what a public health body recommends; check the page for its own sources.
What we use: Alcohol plays a causal part in more than 200 diseases and injuries, including liver and heart disease, several cancers (it is an established carcinogen), and mental health conditions such as depression and anxiety.
Checked Oct 13, 2026 · https://www.who.int/news-room/fact-sheets/detail/alcohol
World Health Organization (2024). Ambient (outdoor) air pollution and health (fact sheet).
Health agency advice: what a public health body recommends; check the page for its own sources.
What we use: Fine particulate matter causes heart and lung disease and cancers; most deaths linked to outdoor air pollution are from heart disease and stroke, then lung disease, lung infections and lung cancer.
Checked Oct 13, 2026 · https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health
US Centers for Disease Control and Prevention. About secondhand smoke.
Health agency advice: what a public health body recommends; check the page for its own sources.
What we use: There is no safe level of exposure to secondhand smoke; eliminating smoking is the only way to fully protect people from it. In adults who don't smoke, it can cause coronary heart disease, stroke and lung cancer.
Checked Oct 13, 2026 · https://www.cdc.gov/tobacco/secondhand-smoke/about.html
European Food Safety Authority (2026). Bisphenol (topic page).
Health agency advice: what a public health body recommends; check the page for its own sources.
What we use: In 2023 EFSA re-evaluated BPA in food contact materials and sharply lowered its tolerable daily intake from the 2015 level; earlier data had suggested BPA might affect the immune system in animals. Opinion: doi 10.2903/j.efsa.2023.6857.
Checked Oct 13, 2026 · https://www.efsa.europa.eu/en/topics/topic/bisphenol
US Food and Drug Administration (2023). Bisphenol A (BPA): use in food contact application.
Health agency advice: what a public health body recommends; check the page for its own sources.
What we use: FDA's position is that BPA is safe at the levels found in foods, for its approved uses in food containers and packaging.
Checked Oct 13, 2026 · https://www.fda.gov/food/food-packaging-other-substances-come-contact-food-information-consumers/bisphenol-bpa-use-food-contact-application
US Environmental Protection Agency (2026). Glyphosate.
Health agency advice: what a public health body recommends; check the page for its own sources.
What we use: EPA concluded in 2017 that glyphosate is not likely to cause cancer in people and is updating that evaluation (expected late 2026). IARC classed it as probably carcinogenic; EPA says IARC asks whether something can cause cancer under any conditions, while EPA weighs expected real-world exposure.
Checked Oct 13, 2026 · https://www.epa.gov/ingredients-used-pesticide-products/glyphosate
Guyton and colleagues (IARC) (2015). Carcinogenicity of tetrachlorvinphos, parathion, malathion, diazinon, and glyphosate.
Official announcement: what an organization said about its own decision; not a study.
What we use: The IARC working group's summary of its 2015 evaluation, which classed glyphosate as probably carcinogenic to humans (Group 2A).
Checked Oct 13, 2026 · https://doi.org/10.1016/S1470-2045(15)70134-8 · DOI 10.1016/S1470-2045(15)70134-8 · PubMed 25801782
National Institute of Diabetes and Digestive and Kidney Diseases (LiverTox) (2016). Acetaminophen. In: LiverTox, clinical and research information on drug-induced liver injury (page last updated January 28, 2016).
Reference table: a standard definition or unit conversion; not a finding.
What we use: An overdose of acetaminophen, on purpose or by accident, can cause sudden serious liver injury; it is the main cause of acute liver failure in the US, Europe and Australia.
Checked Oct 14, 2026 · https://www.ncbi.nlm.nih.gov/books/NBK548162/
Tripathi and colleagues (2018). The gut-liver axis and the intersection with the microbiome.
Review: experts read and summed up the research.
What we use: The gut and liver talk to each other through the gut-liver axis; gut bacteria play a part in alcohol-related and non-alcohol fatty liver disease, though much remains to be learned.
Checked Oct 13, 2026 · https://doi.org/10.1038/s41575-018-0011-z · DOI 10.1038/s41575-018-0011-z · PubMed 29748586
Biswas (2016). Does the interdependence between oxidative stress and inflammation explain the antioxidant paradox?
Review: experts read and summed up the research.
What we use: Oxidative stress and inflammation are closely related; one can easily set off the other, and both show up together in many chronic conditions. Antioxidant trials have mostly not worked as prevention.
Checked Oct 13, 2026 · https://doi.org/10.1155/2016/5698931 · DOI 10.1155/2016/5698931 · PubMed 26881031
National Institute of Diabetes and Digestive and Kidney Diseases (2021). Symptoms and causes of NAFLD and NASH.
Health agency advice: what a public health body recommends; check the page for its own sources.
What we use: Fatty liver disease not caused by alcohol is more likely with overweight or obesity, insulin resistance or type 2 diabetes, and abnormal blood fats.
Checked Oct 13, 2026 · https://www.niddk.nih.gov/health-information/liver-disease/nafld-nash/symptoms-causes

Every source on the site