Could the biology that helps us grow and reproduce also influence how we age? Researchers have been investigating that question for decades. It connects some surprising subjects: tiny laboratory worms, historical records of eunuchs, vegetarian diets and the age when children begin puberty.
There is real science behind these connections. But turning them into advice requires care. A longer-lived worm does not provide a meal plan for a retired human.
Does reproduction come at a cost?
Evolution favours traits that help organisms survive long enough to reproduce. Those traits do not necessarily maximise health in old age.
In a landmark experiment, researchers extended the lifespan of the roundworm C. elegans by removing cells that would otherwise produce eggs or sperm. Their work implicated hormonal signalling, including an insulin/IGF-1 pathway. This was more complicated than simply saving the energy normally spent on reproduction: signals from different reproductive tissues mattered. [1]
The experiment helps explain how reproduction and ageing can share biological controls. It does not show that avoiding sex, having fewer children or becoming infertile makes humans live longer.
Historical research offers intriguing clues. A study of 81 Korean eunuchs reported longer lifespans than comparison groups. However, historical comparisons cannot fully separate hormone effects from differences in living conditions, selection and record keeping. They cannot establish a safe treatment for longevity. [2]
Do vegetarians sacrifice fertility?
One study discussed in the supplied transcript compared semen samples from 474 men: 443 non-vegetarians, 26 vegetarians who ate dairy or eggs, and just five vegans.
Researchers found lower sperm concentration in the vegetarian group and differences in sperm movement between groups. However, this was an observational study, with very small vegetarian and vegan samples. It did not establish that the diet caused these differences or demonstrate lower pregnancy or live-birth rates. [3]
Sperm concentration, total sperm count, sperm movement and the ability to achieve a pregnancy are related, but they are not interchangeable measurements.
The reasonable conclusion is that this study raised a question worth investigating. It did not prove that a plant-based diet trades fertility for extra years of life.
What about soy?
Soy contains isoflavones, plant compounds that can interact with oestrogen receptors. That does not mean eating tofu has the same effects as taking human oestrogen.
A 2021 meta-analysis covering 41 clinical studies found no significant effects of soy or isoflavones on the male reproductive hormones assessed, including testosterone and oestrogens. A smaller randomised crossover trial also found no adverse effects on semen quality from the soy interventions tested. [4,5]
Hormone results alone cannot prove fertility is unaffected in every circumstance. Nevertheless, these findings do not support the claim that ordinary soy foods undermine masculinity or must be avoided to protect fertility.
Is puberty happening earlier?
Yes, some measures show a clear trend. A systematic review found that the onset of breast development moved earlier by approximately three months per decade between 1977 and 2013. The timing varied across populations. [6]
Breast development and the first menstrual period are different milestones. Findings about one should not automatically be applied to the other.
Puberty normally begins between ages eight and 13 in girls and nine and 14 in boys. Pubertal development before eight in girls or nine in boys warrants medical assessment. Genetics, nutrition and environmental exposures can influence timing; in many cases of central precocious puberty, no specific cause is identified. [7]
An earlier population average does not make unusually early development something to ignore.
Can food influence the timing?
Observational research has associated higher childhood animal-protein intake with earlier first menstruation. A 2020 review reported an average association equivalent to roughly two months earlier per additional gram of daily animal protein. [8]
That striking figure needs context. It is a pooled statistical estimate from observational evidence, not a reliable formula for predicting an individual child's development. It should not be multiplied across a menu to calculate when a girl will start her periods.
Dietary patterns overlap with energy intake, body size, family circumstances and other influences. These studies cannot establish that meat alone causes early puberty, or that removing it will prevent the condition.
Children need sufficient energy and nutrients for healthy growth. Restricting food to delay puberty is not an appropriate home experiment.
Does later puberty mean a longer life?
The relationship is not simply “the later, the better.”
A large UK Biobank study found a U-shaped association between age at first menstruation and mortality: both early and late menarche were associated with higher mortality than the reference age of 15. [9]
This does not establish 15 as an age families should try to achieve. Nor does it mean that someone who began menstruating earlier has a predetermined lifespan. Such findings describe patterns across populations, not an individual's destiny.
For older readers, puberty history may provide background for a medical discussion. It cannot be changed, and it should not become a source of blame or anxiety.
What should senior readers take from this?
Be cautious when laboratory longevity research becomes a recommendation to eat very little protein or suppress hormones.
Older adults need to preserve muscle, strength and independence. The PROT-AGE expert group recommends approximately 1.0–1.2 grams of protein per kilogram of body weight daily for many healthy adults over 65, with needs adjusted for illness and individual circumstances. Severe kidney disease can require a different approach. [10]
Beans, lentils, tofu and tempeh can contribute protein to a plant-based diet. Resistance exercise helps put that protein to work. The goal is adequate nourishment and maintained function, rather than chasing the lowest possible growth signal.
Reproduction and ageing share fascinating biology. For now, the evidence does not justify sacrificing sexual health, adequate nutrition or normal childhood development in pursuit of a longer life.
This article provides general education. Consult a qualified health practitioner about fertility concerns, unusually early puberty, hormone treatment or major dietary changes.
Sources
- Hsin H, Kenyon C. Signals from the reproductive system regulate the lifespan of C. elegans. Nature, 1999. https://doi.org/10.1038/20694
- Min KJ and colleagues. The lifespan of Korean eunuchs. Current Biology, 2012. https://pubmed.ncbi.nlm.nih.gov/23017989/
- Orzylowska EM and colleagues. Food intake diet and sperm characteristics in a blue zone: A Loma Linda Study. European Journal of Obstetrics & Gynecology and Reproductive Biology, 2016. https://pubmed.ncbi.nlm.nih.gov/27280539/
- Reed KE and colleagues. Neither soy nor isoflavone intake affects male reproductive hormones: An expanded and updated meta-analysis of clinical studies. Reproductive Toxicology, 2021. https://pubmed.ncbi.nlm.nih.gov/33383165/
- Beaton LK and colleagues. Soy protein isolates of varying isoflavone content do not adversely affect semen quality in healthy young men. Fertility and Sterility, 2010. https://pubmed.ncbi.nlm.nih.gov/19819436/
- Eckert-Lind C and colleagues. Worldwide secular trends in age at pubertal onset assessed by breast development among girls. JAMA Pediatrics, 2020. https://pubmed.ncbi.nlm.nih.gov/32040143/
- MedlinePlus Genetics. Central precocious puberty. https://medlineplus.gov/genetics/condition/central-precocious-puberty/
- Nguyen NTK and colleagues. Nutrient intake through childhood and early menarche onset in girls: Systematic review and meta-analysis. Nutrients, 2020. https://www.mdpi.com/2072-6643/12/9/2544
- Joint associations of actual age and genetically determined age at menarche with risk of mortality. JAMA Network Open, 2021. https://pubmed.ncbi.nlm.nih.gov/34190994/
- Bauer J and colleagues. Evidence-based recommendations for optimal dietary protein intake in older people: A position paper from the PROT-AGE Study Group. JAMDA, 2013. https://pubmed.ncbi.nlm.nih.gov/23867520/
Editorial note: Prepared after reviewing the supplied Friday Favorites transcript and checking its central claims against the sources above. This is an independent article, not a reproduction of the transcript. Evidence checked 24 October 2026.