Tired, anxious, gaining weight? It could be your hormones | Dr Helen O’Neill

What It Covers

Dr. Helen O'Neill, reproductive genetics lecturer at University College London who has measured hormones in over 100,000 people, and ZOE nutritionist Dr. Federica Amati explain how modern lifestyle disrupts the body's 50-plus hormones, covering PCOS, endometriosis, thyroid dysfunction, fertility, and dietary interventions that can restore hormonal balance.

Key Questions Answered

• •Gut-produced GLP-1: The gut contains specialized L cells that naturally produce GLP-1 and PYY hormones, which regulate appetite and insulin signaling. Feeding gut microbes fermentable fibers like inulin and beta-glucan, found in oats, can improve insulin resistance in PCOS patients as effectively as the pharmaceutical drug metformin, while also producing better weight management outcomes.
• •Iodine deficiency and thyroid function: The thyroid, which acts as the conductor of the hormonal orchestra, cannot produce its hormones without iodine. Iodine deficiency prevalence increases with distance from the sea. Primary dietary sources are seafood and shellfish. The UK does not fortify table salt with iodine, unlike many other countries, making deficiency a widespread and underdiagnosed driver of fatigue, weight gain, and hair loss.
• •Sperm quality resets in three months: Male sperm completes a full production cycle every three months, meaning dietary and lifestyle changes can measurably improve all sperm health parameters within that window. One clinical study found that consuming a daily handful of walnuts improved every measured sperm parameter. Sperm DNA quality also influences placental development, miscarriage risk, and the child's long-term metabolic and mental health.
• •Endometriosis detection via symptom data: Analysis of nearly one million health assessments reveals that painful bowel movements are among the strongest predictors of endometriosis, yet this question is rarely asked during gynecological examinations. Using this symptom data alongside blood and scan results, Dr. O'Neill's team can identify likely endometriosis cases with 98–99% precision, reducing average diagnosis time from nine years to under nine days.
• •Testosterone injections suppress natural production: Men self-administering testosterone without a confirmed hypogonadism diagnosis risk permanent suppression of natural testicular testosterone production. The testes cease their own output when exogenous testosterone is detected, leading to infertility. Hypogonadism requires multiple fasted blood tests to confirm. Zinc, obtainable through nuts, seeds, and seafood, supports natural testosterone synthesis without this suppression risk.