The leading diet-adjacent cancer exposure by breadth of sites and strength of evidence (WCRF does not quantify a per-person effect). WCRF grades greater body fatness a convincing or probable cause of many cancers and presents its recommendation first because the evidence is «particularly strong … and has grown stronger over the last decade». (World Cancer Research Fund & American Institute for Cancer Research, 2018) Facet of the Diet Physical Activity and Cancer Prevention nucleus; the weight-management decision lives in the cardiometabolic cluster -> Does Weight Loss Reduce Cardiovascular Events.
The magnitude of the footprint
- «12 of the 17 cancers reviewed by the CUP are linked to greater body fatness». (World Cancer Research Fund & American Institute for Cancer Research, 2018) Convincing/probable sites include oesophagus (adenocarcinoma), pancreas, liver, colorectum, kidney, endometrium, postmenopausal breast, gallbladder, ovary, stomach cardia, advanced prostate, mouth/pharynx/larynx.
- IARC independently «concluded that greater body fatness is a cause of thyroid cancer, multiple myeloma and meningioma» — three more sites beyond WCRF’s set. (World Cancer Research Fund & American Institute for Cancer Research, 2018)
- «Maintaining a healthy weight throughout life is one of the most important ways to protect against cancer.» (World Cancer Research Fund & American Institute for Cancer Research, 2018)
Risk rises inside the “healthy” range. «For some cancers the increase in risk is seen with increasing body fatness even within the so-called ‘healthy’ range. Nevertheless, most benefit is to be gained by avoiding overweight and obesity.» (World Cancer Research Fund & American Institute for Cancer Research, 2018) So the exposure is graded, not a threshold at BMI 25 — but the decision-relevant mass of benefit sits in avoiding overweight/obesity. Body-fatness grades are marked by BMI (± waist circumference / waist-hip ratio) [matrix asset p3, FN62-64].
Layer-1 — the larger cancer lever, and the one discussed least. On WCRF’s own cancer-prevention scale, body fatness spans 12-of-17 sites (IARC adds three) and is «one of the most important ways to protect against cancer», whereas red and processed meat earn only a single-site colorectal limit -> Red and Processed Meat and Cancer. Same grader, same convincing/probable scale, so the breadth is directly comparable rather than a cross-outcome guess: adiposity is the broader and more strongly graded lever, and a meat cut is a small-lever refinement of it. Public discourse runs the opposite way — meat carries the controversy, adiposity the quiet first recommendation — an instance of attention is an anti-signal. (inferred from World Cancer Research Fund & American Institute for Cancer Research, 2018)
Mechanism — why adiposity is plausibly causal (direction, not proof)
Mechanism informs direction; it does not by itself establish causation (the grades above rest on the cohort epidemiology, not the pathways). Body fatness does «not act through single discrete pathways — instead, they may alter the systemic metabolic milieu» conducive to cancer at many sites (World Cancer Research Fund & American Institute for Cancer Research, 2018). Three linked routes onto the hallmarks of cancer (WCRF Table 2):
- Hyperinsulinaemia — elevated fasting insulin signals through mTOR/PI3K/AKT and MAPK -> proliferation, suppressed apoptosis. (WCRF’s Table 2 lists the IGF-I pathway under dairy and height, not body fatness — so IGF is not claimed here for adiposity.)
- Sex hormones — elevated oestradiol via MAPK/ERK/PI3K drives proliferation in oestrogen-receptor- positive tissues (breast, endometrium).
- Chronic inflammation — «obesity is now recognised as a chronic inflammatory state that predisposes to cancer»; C-reactive protein is «an inflammation marker that is elevated with obesity, is related to cancer risk and reduces with weight loss». (World Cancer Research Fund & American Institute for Cancer Research, 2018)
The CRP-reduces-with-weight-loss link is the closest the report comes to a reversibility signal, but it is a surrogate (an inflammation marker), not a cancer-incidence outcome -> Surrogate Outcomes.
The young-adulthood paradox — a protective arm running the opposite way
Body fatness in young adulthood (~18-30 y) «predicts lower risk» of both pre- and postmenopausal breast cancer — the association runs opposite to adult body fatness (a probable-graded protective arm). (World Cancer Research Fund & American Institute for Cancer Research, 2018) Read it as a unit-of-analysis warning — the label “body fatness” hides two timing-dependent quantities, so the adult-adiposity harm is not a claim about body fatness at every age.
But do not upgrade the reversal to an established causal sign-flip. This is exactly the pattern the wiki’s protective-arm skepticism targets: an opposite-direction association, only probable-graded, with no stated mechanism, and obvious confounding candidates (earlier menarche and lifetime oestrogen- exposure proxies track with early-life adiposity). WCRF itself says «more research is required to help further understand the mechanisms». Until it survives a referent-correction or a genetic/objective check it is a candidate artifact, not a lever -> The U-Shaped Association Artifact. (inferred from World Cancer Research Fund & American Institute for Cancer Research, 2018)
Limits — the loop is open on reversal
- Population causal grade, not a per-person weight-loss effect. The grades are on body fatness -> incidence in cohorts. Whether losing weight reduces your cancer risk is not established here; the survivor evidence is explicitly «limited» on whether changing body fatness after diagnosis alters the clinical course. -> Does Weight Loss Reduce Cardiovascular Events holds the analogous open loop on CV events. (inferred from World Cancer Research Fund & American Institute for Cancer Research, 2018)
- Single body. WCRF/AICR only; IARC’s three-site confirmation is a genuine second reviewer for those three sites (thyroid/myeloma/meningioma) but is reported via WCRF, not independently held.
- Coherence, not validity (R1).