A disclosure before we go further: I develop soup cleanse products, which is a reason to read the evidence sections closely rather than take my word for it. Where the research is thin, I’ve said so.
What the cycle does to hunger
Appetite isn’t flat across a cycle. A 2025 meta-analysis in Nutrition Reviews found energy intake higher in the luteal phase, the weeks between ovulation and the next period, than in the follicular phase. A review of studies that confirmed the phase with hormone tests put the difference at roughly 160 to 530 calories a day. Resting energy use rises in the luteal phase too, by about 30 to 120 calories a day in a 2026 systematic review. In the early follicular phase, which covers the bleeding days, rising estrogen goes along with lower appetite and better insulin sensitivity.
Not every study finds a difference, and individuals vary. On average, hunger is lowest during the bleed and highest in the week before it. A cleanse asks you to sit with hunger, as the 3-day guide lays out, so the week before a period is the hardest time to start one.
Iron
The recommended iron intake for women aged 19 to 50 is 18 milligrams a day, against 8 for men, and menstrual blood loss is the reason for the gap. Heavy menstrual bleeding, defined as more than 80 milliliters a period, affects about 10% of women, and many don’t know they have it. It frequently leads to iron-deficiency anemia.
A three-day cleanse adds nothing to the blood lost. The concern is stacking: a few days of lower intake on top of a bleed, in someone whose iron stores are already low. Fatigue and lightheadedness are common on day two for ordinary reasons, and they are also symptoms of low iron, so in the moment the two are hard to tell apart.
Iron from plants is absorbed less readily than iron from meat, and vitamin C in the same meal improves it. A soup built on legumes and greens carries iron, and tomato, lemon, or peppers in the pot help you take it up.
The 3-day guide’s list of people who should skip it covers pregnancy and several medical conditions. Heavy periods and known low iron belong on the same list. If your periods disrupt your days, or a doctor has told you your iron is low, skip the cleanse and ask for a blood test. Iron deficiency is common and treatable.
If you eat no meat
The NIH Office of Dietary Supplements puts the iron requirement 1.8 times higher for people who eat no meat, because iron from plants is absorbed less well. Applied to the 18-milligram RDA for women aged 19 to 50, that is about 32 milligrams a day. Absorption runs 14 to 18 percent on mixed diets and 5 to 12 percent on vegetarian ones. Vitamin C in the same meal raises it, and coffee and many teas lower it.
Keep coffee and tea away from iron-rich meals. Many herbal teas contain polyphenols that inhibit absorption too, so the guide’s herbal additions are best taken between meals. A blood test settles the question: ask for hemoglobin and ferritin, which reflects iron stores.
What a few days of restriction does to the cycle
The laboratory work on this was done in the early follicular phase, the days of a period. In 2003, researchers manipulated the energy available to 29 regularly menstruating women for five days, with a set diet and supervised exercise. Energy availability is calories eaten minus calories spent on exercise, divided by lean body mass. At 30 calories per kilogram of lean mass, the pulse pattern of luteinizing hormone, a reproductive hormone, stayed normal. At 20 and 10 it slowed. For a woman with 45 kilograms of lean mass, 30 calories per kilogram works out to about 1,350 calories a day left over after exercise. That figure is the study’s threshold, and nobody should read it as a calorie recommendation. A later study from the same lab found the response in adolescents and not in adult women.
Those are hormone measurements and not periods, and none of the work tracked a soup cleanse. The cycle problems described in this literature, such as missed periods, come from sustained low energy availability. Whether a given cleanse sits above or below that line depends on its calories and on any exercise added to it.
Reading your cycle
In a 28-day cycle, bleeding covers about days 1 to 5, ovulation falls near day 14, and the luteal phase runs from about day 15 to the next period. The week after bleeding stops is days 6 to 12. Adult cycles run from 21 to 35 days, so count from your own first day of bleeding and your own usual length.
If you want to time it
Ramadan builds the cycle into the fast: women do not fast while menstruating and make up the days afterward. For a cleanse, reasoning from the cycle research, the week after bleeding stops avoids both the iron loss and the late-cycle hunger peak. That is an inference and has not been tested, and cycles vary. If yours is irregular, or you use hormonal contraception, the phases described above can fall out of line with your calendar. If your period is late, rule out pregnancy before you start, since pregnancy is on the guide’s skip list. For what the three days feel like once you begin, see what to expect on a soup cleanse.
Common questions
- Can you do a soup cleanse on your period?
- Many healthy women can, and iron is the main concern. If your periods are heavy or you have been told your iron is low, skip it and ask a doctor for a blood test.
- When in my cycle is the best time to start a soup cleanse?
- No study has tested it. Reasoning from the cycle research, the week after bleeding stops avoids both the iron loss and the late-cycle hunger peak.
- Does a soup cleanse affect your period?
- Nobody has measured it. Sustained low energy intake can disrupt cycles, and in laboratory studies a few days of restriction changed hormone pulses only at very low energy availability.
- Do vegetarians need more iron?
- Yes. The NIH Office of Dietary Supplements puts the requirement 1.8 times higher for people who eat no meat, about 32 milligrams a day for women aged 19 to 50.