Why the female body calls for its own reading
Training draws resources from the body. In the female body, some of those resources leave faster than they come in, for two reasons that add up: blood loss in the menstrual cycle and the cost of training itself. The result is that four nutritional pillars deserve a closer look in women who exercise: iron, calcium with vitamin D, energy availability and protein. None of them is exclusive to women, but all four have particularities worth a conversation with a dietitian.
This text estimates and explains. It does not prescribe diet or supplement doses. In Brazil, nutrition prescription is an act reserved to dietitians (Lei 8.234/91), and tests and diagnoses belong to physicians. What follows helps you understand the signals and arrive better informed at the appointment.
Iron: the mineral most lacking in the female athlete
Iron carries oxygen in the blood. Lack of iron means less oxygen reaching the muscle, and that shows up as unusual fatigue, dropping performance, shortness of breath in efforts that used to be easy and slower recovery. The daily iron recommendation for adult women of childbearing age is 18 mg, more than double that of men (8 mg), according to the United States Institute of Medicine (the NIH reference). Menstruation explains a good part of that difference.
For those who train, the math gets tighter. Exercise increases small iron losses through several routes (repeated impact, sweat, micro-injuries, inflammatory response), and reviews estimate that endurance athletes may need more iron than the general population. Not surprisingly, iron deficiency is common: reviews indicate that somewhere between 15% and 35% of female endurance athletes have low stores, against 3% to 11% of men.
A point that confuses many people: you can be short on iron and still have a "normal" complete blood count. Anemia (low hemoglobin) is the final stage. Before it comes the drop in stores, measured by ferritin. Several studies show that ferritin below about 30 ng/mL can already impair training and recovery even with normal hemoglobin. That is why the test that matters here usually goes beyond the complete blood count. Only a physician orders and interprets it, but knowing that ferritin exists already changes the conversation.
Calcium and vitamin D: the foundation of bone
Bone is not dead structure. It remodels all the time, and it depends on calcium and vitamin D (which helps absorb calcium) to stay strong. For women aged 19 to 50, the recommendation is 1,000 mg of calcium per day, rising to 1,200 mg from age 51, with 600 IU of vitamin D as the general reference (NIH). For the female athlete, sports science materials suggest a slightly higher range, on the order of 1,000 to 1,500 mg of calcium and 1,000 to 2,000 IU of vitamin D per day, precisely to protect bone under load.
Why does this matter more in women who train? Because weak bone gives no warning. Density loss (osteopenia, and at the limit osteoporosis) is silent until it becomes a stress fracture. And bone health is tied to the next pillar: when energy is short, the hormones that protect bone fall. Calcium and vitamin D are necessary, but they are not enough on their own if the body is underfed.
Energy availability: eating enough for the load
This is the most underestimated pillar. Energy availability is what is left of food after training takes its share, the energy remaining for the body to function: menstruating, repairing tissue, maintaining bone, immunity and mood. When this balance stays chronically low, a condition called RED-S (Relative Energy Deficiency in Sport) sets in, described in the International Olympic Committee consensus.
Science works with a reference threshold of about 30 kcal per kg of fat-free mass per day: below that, hormonal changes begin to appear that suppress reproduction and weaken bone. That threshold is a guide, not a magic number, and it varies from person to person. The most visible warning sign is usually irregular or absent menstruation. If your cycle has disappeared, that is not a "perk of training hard". It is the body warning that the energy account is not balancing, and it is a reason to see a physician. Eating enough for the load is not the opposite of performance. It is its foundation.
We go deeper into the relationship between energy, iron and bone in the text women's health, RED-S, iron and bones.
Protein: the 1.6 g/kg target also applies to you
An old myth is that women need less protein. They need less in absolute terms, because they generally weigh less, but the target per kilo of body weight is similar. Science indicates that muscle mass gain with strength training benefits from intakes around 1.6 g of protein per kg of body weight per day, with little additional benefit above that for most people (the meta-analysis by Morton and colleagues, 2018). Athletes in phases of intense training or a deficit usually work in the 1.4 to 2.0 g/kg range.
As important as the total is the distribution. Spreading protein across the day, something like 0.3 to 0.4 g/kg per meal every three or four hours, makes better use of the stimulus than concentrating everything at dinner. A 60 kg woman, by this logic, aims for close to 96 g per day, split across three or four meals. That is an estimate to give an order of magnitude, not a diet. The final plan is set by a dietitian, looking at your context, your intolerances and your goals.
The honest summary
The four pillars talk to each other. Low energy brings hormones down and worsens bone. Low iron drains the energy of training. Protein and calcium build on a base that only exists if you eat enough. Darwin's role is to estimate your load, track your signals and help you arrive prepared to the right professional. Iron and ferritin, bone health and the menstrual cycle are medical territory. Diet and supplements are the dietitian's territory. See both.
