Endometriosis is tissue similar to the lining of the womb growing outside the uterus, most often on the ovaries, the fallopian tubes and the ligaments. These lesions respond to hormones just as the womb lining does. With every cycle they grow, bleed and keep up an inflammation that has nowhere to go. They also make their own oestrogen and respond less well to progesterone.
This inflammation does not stay in the pelvis. It affects the gut, sleep and energy, and many women notice they have put on weight since their diagnosis or since starting a treatment. To know what to do, you first need to understand where that weight comes from, because several causes are often at play in the same woman.
What the studies say about weight
A meta-analysis pooled eleven studies carried out in Europe, North America and Asia (Liu and Zhang, 2017). The higher the body mass index, the less common endometriosis was. For every 5 extra points of BMI, the risk fell by about a third.
These studies observe a link without explaining it. They do not say that extra weight protects against the disease, and researchers are still looking for the mechanism. What they do show is that women with endometriosis are not, on average, heavier than other women. If anything, it is the reverse.
When the scales go up after a diagnosis, the answer lies elsewhere. Four causes come up most often.
The belly that swells
Many women with endometriosis have a belly that swells dramatically, sometimes called "endo belly". It changes from one day to the next, which fat does not do. Clothes feel tight, you feel heavier, and you conclude that you have gained weight.
This swollen belly comes mainly from the gut, which the disease affects in many women. Before talking about kilos, it is worth separating what swells from what settles.
Hormone treatment
Hormone treatments put the lesions to rest by stopping or spacing out periods. The pill taken continuously, the progestogen-only pill, the hormonal coil or medicines that put the ovaries on pause are among the options. They bring relief to many women and can give back the energy needed to work on everything else.
Weight gain is a known side effect of some progestogens. For dienogest, a progestogen widely prescribed for endometriosis, an analysis of four European trials involving 332 women followed weight closely (Strowitzki et al., 2015). Weight rose slightly over the first 24 weeks in every group, including the women on placebo, then stayed level in those who carried on with the treatment. Most of the authors work for the company that markets this medicine.
On average the effect is small, and an average always hides women who react more than others. If you feel your treatment is making you gain weight, talk to your doctor. Do not stop a treatment on your own. Other options exist, and the choice depends on your symptoms, your plans for pregnancy and whether you have a cyst.
Pain that keeps you from moving
On painful days, moving feels impossible. When those days come back every month, walking and strength training take a back seat, sometimes for years. Yet a working muscle releases anti-inflammatory substances into the blood, improves insulin sensitivity and helps clear excess oestrogen.
The less you move, the less muscle you maintain, and muscle is what supports your metabolism. Strength training still adapts very well to difficult days.
Inflammation, stress and sleep
Ongoing pain keeps the body on alert, with cortisol raised all the time. Sleep suffers too, and after bad nights, immune cells switch to a more inflammatory mode.
Appetite also shifts across the cycle. It is often bigger before a period, and that is normal. Blood sugar spikes, on the other hand, keep inflammation going around the lesions, which is why stable blood sugar matters.
Where to start
The first step is to untangle these causes. A swollen belly, a treatment that has just started, months without moving because of pain and short nights are not tackled in the same way. The scales alone cannot tell them apart. Your waist measurement and the way your belly changes from day to day say more.
The foundation is the same in every case, with a plate that calms inflammation, a gut that is looked after, movement adapted to your days, a nervous system that can settle and enough sleep.
This article is for information only and does not replace medical advice.