Spinach for people who train: what it actually gives you and when to eat it

Spinach gets dragged around fitness circles as a superfood, mostly because of iron and one old cartoon. The reality is more boring and more useful: it is a cheap vegetable with an excellent volume-to-calorie ratio, a lot of potassium and vitamin K, and one compound that genuinely has a measurable effect on endurance. Here are the numbers and what is actually worth changing on your plate.

What spinach actually contains

These values are for 100 g of raw spinach, which is one well-packed handful and only about 23 kcal:

• Protein: 2.9 g
• Carbohydrates: 3.6 g, of which 2.2 g is fibre
• Potassium: around 558 mg
• Magnesium: around 79 mg
• Iron: around 2.7 mg
• Calcium: around 99 mg
• Vitamin K1: around 480 mcg (daily need is 90 to 120 mcg)
• Folate: around 195 mcg
• Vitamin C: around 28 mg
• Nitrates: 50 to 250 mg, depending on soil and season

One detail matters a lot: 300 g of raw spinach cooks down to roughly 100 g. A plate of cooked spinach therefore carries about three times more of everything than a plate of raw, including the things you do not want in bulk.

What spinach is not

It is not a protein source. 200 g of raw spinach gives about 6 g of protein with a weak amino acid profile. If you weigh 80 kg and target 1.6 to 2.2 g of protein per kilogram of body weight, that is 128 to 176 g per day, and spinach is effectively invisible in that math. Do not log it toward your protein.

It is not a serious iron source either, even though it looks like one on paper. Plant iron is absorbed at only 2 to 10 percent, and the oxalates in spinach block it further. Out of the 5.4 mg in 200 g, maybe 0.1 to 0.4 mg actually reaches your blood. Vitamin C in the same meal, say half a fresh bell pepper (60 to 80 mg) or the juice of half a lemon, roughly doubles or triples that absorption. Coffee or black tea within an hour of the meal cuts it by 40 to 60 percent.

Nitrates: the one place spinach touches performance

Spinach is among the richest dietary nitrate sources there is. The studies that show an effect use 300 to 600 mg of nitrate, and 200 to 300 g of raw spinach lands in that range in a good season. The effect is real but modest: roughly 1 to 3 percent on endurance, plus slightly lower oxygen cost at the same pace.

Practically, that means a 10 km runner or someone riding 40-plus minutes will notice it before someone doing 5 sets of 5 in the squat. Blood levels peak 2 to 3 hours after the meal. One small catch: antibacterial mouthwash inside that window cancels part of the effect, because oral bacteria are what convert nitrate into its active form.

When to eat it around training

• 2 to 3 hours before: the best window. 150 to 250 g raw alongside a normal meal with carbs and protein.
• 30 to 60 minutes before: pointless, because the nitrates will not have kicked in, and 200 g carries 4 to 5 g of fibre plus a lot of water in your stomach. If you are squatting or deadlifting, you will feel it.
• After training: perfectly fine, but as a side dish, not as recovery. It adds potassium and magnesium to a meal you were eating anyway.
• In the evening: the best call if you are in a deficit and need volume without calories. 200 g raw is 46 kcal.

Oxalates and cooking

100 g of raw spinach contains 600 to 970 mg of oxalates. For most people that is not a health problem, but it does decide how much you actually get out of it.

Boiling for 3 to 5 minutes and discarding the water removes 30 to 50 percent of soluble oxalates. Sauteing and steaming remove far less, roughly 5 to 15 percent.

Oxalates also bind calcium, so you absorb only about 5 percent of the 99 mg per 100 g. That is exactly why pairing spinach with yoghurt or cheese makes sense: calcium from that source binds the oxalate in the gut and lowers how much ends up in your urine.

Lutein, vitamin K and vitamin A are fat soluble, so add a tablespoon of olive oil (10 ml, about 90 kcal) or 20 g of walnuts. Frozen spinach is nutritionally very close to fresh, is usually blanched (so lower in oxalates), and is cheaper per gram.

How much and how often

1. 100 to 200 g raw per day, or 3 to 5 times per week, is plenty and safe for a healthy person.
2. Rotate your greens. Spinach, chard and kale are all high in oxalates; rocket, lettuce and broccoli are much lower.
3. If you are cutting, 200 g of raw spinach fills half a plate for 46 kcal. That is the single most useful thing spinach does for a lifter.
4. There is no reason to push past 400 to 500 g raw every single day for months. That is where the benefit stops and the oxalate load starts.

When to see a doctor

• If you take warfarin or a similar blood thinner: vitamin K directly affects your dose. You do not have to cut spinach, but your intake must stay consistent week to week, and that gets agreed with your doctor.
• If you have had a kidney stone, especially a calcium oxalate one: ask before spinach becomes a daily habit.
• If you have chronic kidney disease: 200 g of raw spinach carries around 1,100 mg of potassium, which is exactly the kind of number that gets monitored in that case.
• If you suspect anaemia, meaning unexplained fatigue, breathlessness on stairs, a sudden drop in performance: spinach will not fix it. You need bloodwork, specifically a full blood count and ferritin.
• Flank pain, nausea or blood in your urine after a stretch of eating large amounts of greens: get it checked, do not wait it out.

The short version

• 100 g of raw spinach is 23 kcal, 2.9 g protein, 558 mg potassium and around 480 mcg vitamin K.
• It is not a protein source and, because of oxalates, not a usable iron source either; vitamin C in the same meal helps, coffee right after the meal hurts.
• The one clear performance benefit is nitrate: 200 to 300 g raw, 2 to 3 hours before a long cardio session, worth roughly 1 to 3 percent.
• Boiling 3 to 5 minutes and discarding the water removes up to half the oxalates; a tablespoon of oil improves vitamin uptake.
• Warfarin, kidney stones and kidney disease are the three situations where the amount is decided with a doctor, not estimated on your own.