Your cycle, medication and life stage

Energy balance still rules, but several things change how much energy you spend, how hungry you are and what the scale shows from week to week. Knowing them stops you from "fixing" a plateau that is water, or blaming yourself for a slowdown that is a prescription. None of this replaces your doctor: they interpret your tests and your medication, and the coaching adjusts your nutrition around their findings.

01 · The menstrual cycle

Fat loss is never linear, and for women the cycle adds a monthly loop. Menstruation lasts 2 to 8 days and opens the follicular phase (oestrogen rising; ideally about 14 days); ovulation opens the luteal phase (progesterone rising); if there is no pregnancy both hormones fall and the period comes. Tender breasts, bloating, lethargy and irritability before the period are normal, and dieting plus hard training are stressors on top of it.

Abridged normal daily production rates by phase. Many women feel strongest around ovulation (the testosterone peak) and recover best then; the early follicular phase tolerates volume but not always maximal loads; the days before the period are a reasonable time to keep training easier. These are suggestions to test on yourself, not rules.

02 · Hormonal contraception

About three-quarters of women believe the combined pill causes weight gain. A Cochrane review of combination contraceptives found no evidence of an effect on weight; the WHO's provider handbook does not list weight gain among the side effects. If the scale moves after starting one, treat it like any other change: track, use weekly averages, and look at the intake first.

03 · PCOS

Around one woman in ten of child-bearing age has symptoms of polycystic ovary syndrome: irregular cycles (as short as 14 or longer than 32 days), heavier bleeding, hirsutism, sometimes elevated testosterone and a higher risk of type 2 diabetes. A meta-analysis of lifestyle programmes in PCOS found lower fasting glucose and insulin, with the improvements tied to weight change and lasting only as long as the habits do. PCOS can lower how much you spend, so the intake has to be a little lower for the same result; it does not stop fat loss, and fat loss improves the symptoms. Diagnosis and treatment belong to your doctor.

04 · Thyroid and coeliac disease

Hypothyroidism lowers resting energy: fatigue, poor concentration, heavier periods, and fat loss that is slower than the equation says. Medicated, the difference largely disappears; the equation simply over-predicts for you, so confirm your maintenance by tracking. Hyperthyroidism raises it: you can eat more and still lose, and if you do not eat more you lose lean mass. Coeliac disease (about 1% of the population) is strongly associated with autoimmune thyroid disease; if you have it, a thyroid panel (TSH, T3, T4) belongs in your blood tests, which is why they are part of the blood-test guide.

05 · Medication that changes the maths

06 · Perimenopause and menopause

Visceral fat starts rising three to four years before the last period as oestradiol falls, and the risk of obesity, cardiovascular disease and metabolic syndrome rises with it. Oestrogen helps control fat breakdown and protects bone, so bone density falls too. What the data support: energy balance still governs; lean mass and activity fall with age, so expenditure falls and intake has to follow; protein matters for every tissue, not just muscle; and strength training is the best single tool for bone density. Diets high in fruit and vegetables are associated with a later natural menopause. Men do not get a menopause but testosterone declines steadily with age, with the same consequences for lean mass.

07 · Under-fuelling: the signs

Eating far below your needs for a long time shows up before the blood tests do: a lost or irregular cycle, low libido, feeling cold, getting ill more often, headaches, hair, skin and nails deteriorating, poor sleep, brain fog, a short temper, working harder in the gym while performance falls, "eating less but getting softer", injuries and stress fractures. Men are not immune. If this is you, a slow calorie ramp is not automatically the answer; the rebuild roadmap flags these and recommends an individual review first.

Studies

1. The normal menstrual cycle and the control of ovulation. Endotext.
2. Gallo MF et al. Combination contraceptives: effects on weight. Cochrane Database Syst Rev 2014.
3. WHO. Family Planning: A Global Handbook for Providers.
4. Domecq JP et al. Lifestyle modification programs in polycystic ovary syndrome: systematic review and meta-analysis. JCEM 2013.
5. Sun X et al. Increased incidence of thyroid disease in patients with celiac disease: a systematic review and meta-analysis. 2016.
6. Sharma AM et al. Beta-adrenergic receptor blockers and weight gain: a systematic analysis. Hypertension 2001.
7. Liu D et al. A practical guide to the monitoring and management of the complications of systemic corticosteroid therapy. 2013.
8. Serretti A, Mandelli L. Antidepressants and body weight: a comprehensive review and meta-analysis. J Clin Psychiatry 2010.
9. Davis SR et al. Understanding weight gain at menopause. Climacteric 2012.
10. Randolph JF et al. Change in estradiol and FSH across the early menopausal transition (SWAN). 2004.
11. Guidelines for dietary management of menopausal women. 2015.
12. Estrogen and bone metabolism. 1996.
13. Lifestyle and dietary factors determine age at natural menopause. 2014.
14. Mountjoy M et al. 2023 IOC consensus statement on relative energy deficiency in sport (REDs).

This guide is general information for healthy adults and is not medical advice. Diagnosis, blood-test interpretation and medication decisions belong to your doctor.