#171 - Steve Austad, Ph.D.: The landscape of longevity science: making sense of caloric restriction, biomarkers of aging, and possible geroprotective molecules

Episode Summary

Executive Summary: Peter Attia interviews aging biologist Steve Austad about his unconventional path into gerontology and the science of longevity. They examine why lab mice can mislead, how caloric restriction differs across species and study designs, what the Wisconsin and NIA monkey studies really showed, why sex differences in lifespan may reflect biology beyond behavior, and which geroprotective drugs and biomarkers are most promising.

Main Topics: Steve Austad’s unconventional path into aging biology (Priority: 5/5): Austad recounts a childhood of constant travel, early math/English interests, taxi driving in 1970s New York, lion training in Hollywood, and how field biology and opossum research eventually led him to aging. Why laboratory mice are a limited model for human aging (Priority: 5/5): Austad explains how lab mice were shaped by inbreeding, selection for reproduction, and artificial housing, making them genetically and physiologically unlike wild mice and humans. Caloric restriction history and interpretation (Priority: 5/5): The discussion traces Clive McKay’s early work, later rodent studies, and the idea that caloric restriction’s benefits may depend heavily on diet quality, species, and context rather than calories alone. Wisconsin vs. NIA monkey studies (Priority: 5/5): Attia and Austad compare the two landmark rhesus macaque caloric restriction studies, emphasizing differences in control diets, body weight, housing, and interpretation of outcomes. Wild animals, wild mice, and ecological context (Priority: 4/5): Austad argues that calorie restriction in the wild may not be beneficial because animals face predation, foraging costs, wound risk, and pathogen exposure that are absent in the lab. Sex differences in longevity and possible mechanisms (Priority: 4/5): They explore why women outlive men across ages and conditions, considering sex hormones, X-chromosome effects, mitochondrial compatibility, and behavioral factors. Geroprotective drugs and the biomarker problem (Priority: 5/5): The conversation covers rapamycin, metformin, SGLT2 inhibitors, acarbose, and the need for better biomarkers of aging to run shorter, more informative human trials.

Key Arguments: Lab mice are a poor proxy for humans because they are highly inbred, genetically uniform, and shaped by decades of selection for rapid reproduction and laboratory survival. Wild mice and wild animals differ profoundly from lab animals in behavior, physiology, and lifespan, so results from captive models may not translate cleanly to real-world biology. Caloric restriction is not a single phenomenon; its effects depend on diet composition, baseline body weight, species, and whether the comparison group is already obese or overfed. The Wisconsin and NIA monkey studies were not truly identical experiments: Wisconsin controls were heavier and ate a high-sucrose purified diet, while NIA controls were leaner and fed a more natural diet. The monkey studies suggest that reducing poor-quality food can improve health, but they do not prove that severe caloric restriction is universally beneficial in healthy primates or humans. In the wild, calorie restriction may be harmful because it increases foraging, predation risk, wound-healing problems, and susceptibility to infection. Women appear to survive better than men at every age and under many conditions, implying a robust biological advantage that is not fully explained by behavior alone. Potential explanations for sex differences include X-chromosome redundancy/inactivation patterns, mitochondrial-nuclear compatibility, and hormonal effects, but no single mechanism is established. Rapamycin has the strongest mouse longevity data, while metformin has the strongest human observational/clinical signal, but both need better human trials and biomarkers. Short-term fasting may be more important than total calorie reduction in some contexts, possibly through mTOR suppression and improved stress resistance. The field needs better biomarkers of aging—likely spanning epigenome, proteome, and metabolome—to make human longevity trials feasible and clinically meaningful. Longevity gains may still be possible even when interventions start late in life, as shown by the Intervention Testing Program and related animal studies.

Data Points: Age difference in U.S. lifespan between women and men: about 5 years - Austad says women survive better at every age and in many conditions, contributing to a roughly five-year longevity gap. Opossum lifespan difference on island vs mainland: about 20% - Austad’s early field study found opossums on a predator-free island aged about 20% more slowly than mainland animals. Austad’s size in high school: 105 pounds and about 5 feet 4 inches - He describes being the smallest kid in class and using homework help to avoid being beaten up. Weight during wrestling as a sophomore: 79 pounds in the 98-pound division - He was far below the lowest wrestling weight class and was evaluated for delayed puberty. Wisconsin monkey control diet sucrose: about 28% to 28.5% sucrose - The Wisconsin rhesus macaque diet used purified ingredients and a very high sucrose content. Bethesda/NIA monkey diet sucrose: about 3% sucrose - The NIA study used natural ingredients and much lower sucrose than Wisconsin. Wisconsin monkey control body weight: about 10% heavier than other U.S. research monkeys - Used to argue that Wisconsin controls were relatively overfed/obese. Bethesda/NIA monkey control body weight: about 10% lighter than other U.S. research monkeys - Used to argue that NIA controls were kept at a healthier body weight. Calorie restriction achieved in human trials: about 11% to 12% over two years - Participants aimed for 25% restriction but could not sustain it. Target calorie restriction in human trials: 25% - The human CR studies attempted to reduce energy intake by roughly a quarter. CR society BMI range: about 17 to 20 - Austad describes members of the Calorie Restriction Society as extremely lean. Rapamycin vaccine study dosing: 5 mg and 20 mg once weekly - He cites everolimus/rapalog vaccine-response studies as a model for episodic dosing. Mouse mitochondrial genome size: 16,500 nucleotides - He notes that two mouse mitochondria in a study differed at only five nucleotides across the whole mitochondrial genome. Mitochondrial differences in a rat model: 100 nucleotides - He contrasts rat mitochondrial diversity as more similar to human variation. Human longevity bet: first 150-year-old person likely already born by 2000 - Austad’s long-running bet with Jay Olshansky. Current verified human maximum lifespan: about 122.5 years - He notes no one has exceeded the longest-lived human since the bet was made.

Pivotal Quotes: "I think the culture of evolutionary biology is never really soaked in to the laboratory biology." — Steve Austad: On why lab animal research often ignores evolutionary differences and produces misleading translational results. "I think the worse the diet, the more beneficial the caloric restriction, the better the diet, the less of an impact caloric restriction has." — Peter Atiyah: Summarizing the lesson he draws from the monkey studies: diet quality may matter more than calorie count alone. "We need some biomarkers, which you mentioned before. We need something so we can do an experiment of a few weeks or a few months and have the answer long-term." — Steve Austad: On the central bottleneck in translating longevity science to humans.

Implications: Listeners should view calorie restriction, fasting, and longevity drugs as context-dependent tools, not universal answers. The field’s biggest need is better human biomarkers and better models, so interventions can be tested safely, quickly, and in the right populations.