Your periods depend on your body having enough energy to spare. When weight changes quickly or exercise outpaces what you eat, ovulation can be delayed or stop, and your period with it. The NHS lists sudden weight loss, being overweight and doing too much exercise among the common causes of late or missed periods.
Why weight and energy affect your cycle
Each cycle, your brain sends signals that lead to ovulation. Your period usually starts about two weeks after that. If ovulation is late, so is your period.
The part of the brain that controls these signals also keeps track of your body’s energy. If it senses you’re using more energy than you’re taking in, it can slow down or pause the reproductive system to save resources. That’s why sudden weight loss, strict dieting and very heavy training can all lead to late or missed periods.
Carrying extra weight can affect periods too, in a different way. Body fat produces hormones, and higher levels can disrupt the balance that triggers ovulation.
Sudden weight loss and dieting
Periods can become late or stop after:
- losing a lot of weight quickly
- cutting calories sharply, or cutting out whole food groups
- an illness that stopped you eating normally
- being underweight
If you’ve lost weight on purpose, a late period can be a sign your body needs more fuel than it’s getting. If you’ve lost weight without trying, see a GP. Unexplained weight loss is worth checking whatever is happening with your periods.
Exercise
Regular, moderate exercise is good for your periods and your health. It’s training hard without eating enough to match that tends to cause problems. You’re more likely to notice changes if you:
- suddenly increase how much or how hard you train
- train for endurance events, or a sport where low body weight is valued
- restrict food while training a lot
Missed periods in athletes aren’t a sign of fitness. Low hormone levels over a long time can weaken bones, so it’s worth taking seriously.
Being overweight
Being overweight is also linked to late and irregular periods. It’s often connected with polyendocrine metabolic ovarian syndrome (PMOS, formerly called PCOS), a hormone condition that commonly causes long gaps between periods.
The NHS notes that for people with PMOS who are overweight, losing some weight can help make periods more regular. A GP can help with a plan that’s realistic and safe for you.
Rule out the other common causes
Weight and exercise often aren’t the only thing going on. A late period could also be explained by:
- pregnancy. If there’s any chance, take a test from the first day your period was due
- stress, which often goes alongside dieting or heavy training
- hormonal contraception
- breastfeeding
- perimenopause, usually from your mid-40s
- thyroid problems
The late period checker asks about these and shows which common causes match your answers.
Getting your period back
For most people, periods return once the underlying cause eases. That might mean:
- eating enough to fuel your activity, with regular meals
- easing back on training, or building up more gradually
- aiming for steady, gradual weight change rather than rapid loss
- getting enough rest and sleep
It can take a few months for your cycle to settle. Logging your periods in the period tracker shows when things start to return to normal.
When to see a GP
See a GP if:
- you’ve missed your period three times in a row
- you’ve missed a period and have other symptoms, such as weight gain or loss, tiredness, new facial hair, or dry or oily skin
- you’ve lost weight without trying
- your periods don’t come back after you’ve changed your eating or training
If you’re struggling with food, eating or your body image, you don’t have to deal with it alone. A GP can help, and so can eating disorder charities such as Beat in the UK. Missed periods can be one of the physical signs that your body needs support.