The biology of aging: epigenetics, fasting, and longevity levers

Executive overview

Aging is not inevitable background noise — it is the primary driver of heart disease, Alzheimer's, and most chronic illness. The root cause is loss of epigenetic information: the system that tells each cell which genes to switch on or off degrades over time, like a scratched CD playing the wrong songs.

80% of longevity is determined by epigenetics, not genetics. That means behaviour — what you eat, when you eat, how you move — has more leverage than your DNA.

The core insight: cells kept under mild, recurring adversity activate ancient longevity genes (sirtuins) that slow epigenetic degradation; cells kept comfortable age faster.

What aging actually is

• Aging is a deterioration in health that kills most people — functionally a disease, just arbitrarily excluded because it affects more than 50% of the population.
• The epigenome controls which genes are active in each cell type; DNA methylation and chromatin structure are the key mechanisms.
• Over time, genes that should be silent turn on in the wrong cells; genes that should stay active get shut off — cells lose their identity.
• This epigenetic drift is measurable: biological clocks (e.g., the Horvath Clock) can predict mortality from chemical changes in DNA.
• The other hallmarks of aging (mitochondrial dysfunction, inflammation, etc.) are largely downstream consequences of this epigenetic loss.

What causes the scratches

• DNA breaks — from X-rays, cosmic rays, UV exposure — physically unwind the carefully organised DNA loops, disrupting gene expression patterns.
• Massive cell stress or nerve damage also accelerates epigenetic aging.
• Aging is fastest early in life (the Horvath Clock rises steeply from birth), then proceeds linearly.
• Early developmental genes are disproportionately vulnerable to these scratches and tend to re-activate inappropriately late in life.
• Slower development and lower growth hormone are associated with longer lifespan; animals bred for low growth hormone are among the longest-lived.

Fasting and the longevity gene pathways

• Animals that eat less — dogs, mice, monkeys — consistently live 30% longer; caloric restriction has been replicated since the 1930s.
• Being constantly fed keeps insulin and insulin-like growth factor (IGF-1) high, which suppresses sirtuin longevity genes — epigenetic maintenance degrades faster.
• Fasting activates sirtuins (responding to low sugar/insulin) and downregulates mTOR (responding to low amino acids, especially leucine, isoleucine, valine).
• Up-sirtuin + down-mTOR together trigger the body's full defensive suite: autophagy, improved insulin sensitivity, cellular repair.
• Autophagy (macro-autophagy) begins during any fast; chaperone-mediated autophagy — a deeper protein cleanse — kicks in around day two or three.
• Triggering chaperone-mediated autophagy extended lifespan by 35% in old mice.

Practical fasting approach

• Skip one meal per day — the minimum effective dose; add it to the overnight sleep window so the fasting period is continuous.
• First two to three weeks involve real hunger and habit disruption; push through rather than quit.
• Skipping breakfast or dinner both work; the goal is an extended daily gap, not a specific meal.
• Occasional two- to three-day fasts add greater benefit, particularly for autophagy.
• Small additions (coffee with a little milk, a spoonful of yoghurt, olive oil) are unlikely to meaningfully activate insulin or mTOR — don't let perfectionism prevent starting.
• Gradual reduction works better than cold turkey; strict overnight overhauls almost always fail.

Leucine, mTOR, and the growth trade-off

• Leucine (and other branched-chain amino acids) directly activates mTOR, promoting muscle growth but also accelerating cellular aging.
• Growth hormone and testosterone supplementation produce short-term gains at the cost of long-term healthspan — burning the candle at both ends.
• The practical resolution: pulse — alternate periods of fasting with periods of eating and supplementing, rather than optimising for one state continuously.
• Exercise enough to maintain muscle and hormone levels without chasing maximum size.

NMN and NAD

• Sirtuins require NAD as fuel; NAD levels decline with age, reducing sirtuin activity.
• NMN (nicotinamide mononucleotide) is a direct precursor: the body converts it to NAD in one step.
• Taking 1–2 g of NMN daily for approximately two weeks roughly doubles blood NAD levels (observed across dozens of individuals).
• Sirt6 activation alone extended mouse lifespan substantially in controlled studies.

Iron load and senescent cells

• Excess iron increases accumulation of senescent cells — non-dividing "zombie" cells that drive chronic inflammation and raise cancer risk.
• Senescent cell burden rises with age; clearing them keeps tissues younger in animal models.
• Individuals eating a primarily plant-based diet often have slightly low ferritin and haemoglobin but maintain high energy — their levels may be optimal rather than deficient.
• Standard reference ranges reflect population averages, not longevity-optimal targets; longitudinal personal data matters more than a single reading.

Key biomarkers to track

• HbA1c — average glucose over the prior month; reflects metabolic health and aging rate.
• hs-CRP (high-sensitivity C-reactive protein) — best marker for cardiovascular inflammation; elevated levels predict heart attack risk even when fasting glucose is normal.
• Track trends over years, not single readings; a decade of data is far more informative than any snapshot.
• High CRP responds to dietary change (more vegetables, less food overall) and anti-inflammatories; address it promptly.

Exercise and hormones

• Aerobic exercise raises sirtuin 1 and sirtuin 3 activity in animals.
• Resistance training maintains muscle mass and endogenous hormone levels — particularly important as testosterone declines with age in men.
• The same fasting/caloric restriction pathways that slow somatic aging also delay reproductive aging: old female mice given NMN resumed fertility months after the normal infertility threshold.