Benefits
Blood pressure after nitrate-rich spinach meals
In randomized crossover trials in healthy adults, a nitrate-rich spinach meal or soup lowered systolic blood pressure compared with a low-nitrate control; after 7 days of daily spinach soup, brachial systolic pressure was about 3.5 mmHg lower 3 hours after the soup. Diastolic results varied. A 1-week high-nitrate leafy-vegetable diet in adults with high-normal pressure changed no readings.
Arterial stiffness and artery lining function
On the first day of a 7-day spinach soup trial, augmentation index, a measure of arterial stiffness, fell 6.5% versus 0.8% with a low-nitrate asparagus soup, though on day 7 the difference versus control was not significant. A single spinach meal raised large artery elasticity, and in another trial spinach raised flow-mediated dilation of the arm artery versus control.
Lutein intake and macular pigment
Spinach is one of the richest food sources of lutein, the carotenoid that forms macular pigment in the retina. In a study without a control group, adding 60 g of spinach a day raised serum lutein and macular pigment in 8 of 11 adults. In an 8-week randomized trial, spinach powder did not change macular pigment compared with carrot juice.
Appetite and body weight with spinach thylakoid extract
This is a concentrated extract of spinach chloroplast membranes (thylakoids), not whole spinach. In a 12-week placebo-controlled trial in 38 overweight women, 5 g a day before breakfast was followed by 5.0 kg versus 3.5 kg weight loss, but waist size and body fat did not differ between groups. A maker-funded single-dose trial found less hunger over 2 hours.
Muscle strength with training in a spinach extract trial
This was a branded water extract of spinach leaf containing the ecdysteroid 20-hydroxyecdysone, not whole spinach. In 45 adults over 50 on a 12-week training program, 2 g a day gave larger strength gains than placebo on most knee dynamometry tests, while lean mass rose in both groups without a significant difference.
A source of folate, vitamin K and magnesium
Per 100 g raw, spinach supplies about 194 micrograms of folate, 483 micrograms of vitamin K, 79 mg of magnesium and 12,198 micrograms of lutein plus zeaxanthin. Its 99 mg of calcium is poorly absorbed: in a crossover test, about 5% of spinach calcium was absorbed versus about 28% from milk, because oxalate binds it.
Mechanism of action
Nitrate-nitrite-nitric oxide pathway
Dietary nitrate is reduced to nitrite by bacteria on the tongue, and nitrite can then be converted to nitric oxide (NO), which relaxes blood vessel walls. After a spinach meal, salivary nitrite rose about eightfold, and in another trial plasma nitrite and other nitric oxide markers rose compared with a low-nitrate control meal.
Lutein deposition in the retina
Lutein and zeaxanthin collect in the retina as macular pigment, which absorbs blue light. Eating more spinach raised serum lutein in most people studied, but the response varied: some people raised serum lutein without any rise in macular pigment, and one showed no change in either.
Oxalate binds calcium in the gut
In one absorption test, the spinach contained slightly more oxalate than was needed to bind all of its calcium, so little of that calcium was absorbed. Part of the oxalate is absorbed and passes into urine: after about 10 oz of spinach, healthy adults absorbed an estimated 2 to 12% of the oxalate eaten, with peak urinary output about 7 hours later.
Thylakoid membranes and satiety signals (extract only)
Thylakoid extract is proposed to slow fat digestion and so prolong fullness signals. In the 12-week extract trial, the release of the satiety hormone GLP-1 after a standard breakfast was higher than with placebo. This applies to the concentrated extract, not to spinach eaten as a vegetable.
Clinical trials
Randomized, controlled crossover trial: soup made with 250 g of spinach (about 845 mg nitrate a day) or a matched low-nitrate asparagus soup (about 0.6 mg nitrate) for 7 days each, with a 1-week washout. The primary outcome was augmentation index. Two authors declared current or past part ownership of Glycemic Index Laboratories (Toronto). (Jovanovski et al. 2015, Clin Nutr Res)
27 healthy adults.
On day 1, augmentation index fell 6.54% with spinach versus 0.82% with asparagus soup at 180 minutes (p = 0.01). On day 7 it fell 6.93% from baseline, but the difference versus control was not significant (p = 0.35). On day 7 only, spinach soup lowered central systolic (3.39 mmHg) and diastolic (2.60 mmHg) and brachial systolic (3.48 mmHg) pressure at 180 minutes versus control. Compliance was self-reported and plasma nitrate was not measured.
Randomized, controlled crossover trial of two energy-matched meals: high nitrate (220 mg of nitrate from spinach) or low nitrate, with measurements up to 210 minutes. (Liu et al. 2013, Nitric Oxide)
26 healthy men and women aged 38 to 69.
Salivary nitrite rose about eightfold. Compared with control, spinach raised large artery elasticity and lowered pulse pressure and systolic blood pressure (all P < 0.001). Carotid-femoral pulse wave velocity (P = 0.07), augmentation index, small artery elasticity and diastolic pressure did not change significantly. A single meal; whether effects last was not tested.
Randomized, controlled crossover trial comparing four energy-matched treatments in random order: control, apple, spinach, and apple plus spinach, with acute measurements after each. (Bondonno et al. 2012, Free Radic Biol Med)
30 healthy men and women.
Compared with control, spinach raised plasma nitrite and other nitric oxide markers, raised flow-mediated dilation and lowered pulse pressure and systolic blood pressure (P < 0.05). Diastolic pressure did not change. Combining apple and spinach gave no additional effect. Single servings only.
Randomized, controlled crossover trial of a 7-day high-nitrate diet (at least 300 mg a day more nitrate from green leafy vegetables) versus a 7-day low-nitrate diet. This tested nitrate-rich leafy greens as a group, not spinach alone. (Bondonno et al. 2014, Free Radic Biol Med)
38 men and women aged 30 to 70 with systolic blood pressure of 120 to 139 mmHg.
Salivary and plasma nitrate and nitrite rose at least fourfold, yet ambulatory, home and office blood pressure and arterial stiffness did not differ between the high-nitrate and low-nitrate diets. The authors concluded that more dietary nitrate may not be an effective short-term way to lower blood pressure in this group.
Two 8-week pilot studies; in the food study, participants were randomized to spinach powder (rich in lutein and zeaxanthin) or carrot juice (rich in carotene). A second study tested lutein supplements against placebo. (Graydon et al. 2012, Br J Nutr)
52 healthy volunteers in the food study (75 in the supplement study).
Spinach powder had no significant effect on macular pigment level or on blood markers of endothelial activation, inflammation and oxidation. A rise in serum lutein tended to go with a rise in macular pigment (r 0.40, P = 0.05), and people with low starting macular pigment gained more.
Dietary modification study without a control group: 11 subjects added 60 g of spinach a day (10.8 mg lutein) for up to 15 weeks, 10 of them also adding 150 g of corn; 2 others ate corn only. (Hammond et al. 1997, Invest Ophthalmol Vis Sci)
13 adults.
Of the 11 who ate spinach, 8 raised serum lutein (mean 33%) and macular pigment density (mean 19%), 2 raised serum lutein without a rise in macular pigment, and 1 showed no change in either. Where macular pigment rose, it stayed raised for several months after the usual diet resumed. With no control group, the size of the effect is uncertain.
Randomized, placebo-controlled trial of 5 g of green-plant membranes (spinach thylakoid extract) once daily before breakfast for 12 weeks, with advice to eat three meals without snacking and to be more active. Two corrections to the paper were later published. (Montelius et al. 2014, Appetite)
38 women aged 40 to 65 with a body mass index of 25 to 33.
Weight loss was 5.0 kg with the extract versus 3.5 kg with placebo (p < 0.01), and total and LDL cholesterol fell more than with placebo. GLP-1 release after a test breakfast rose and the urge for sweets fell on day 1 and day 90. Waist circumference, body fat and leptin fell in both groups with no difference between them.
Randomized, double-blind, placebo-controlled trial of a branded spinach leaf water extract (Spisar, Euromed; batch contained 1600 ppm 20-hydroxyecdysone) at 2 g a day, or maltodextrin placebo, alongside a moderate-intensity training program 3 times a week. No external funding was reported. (Pérez-Piñero et al. 2021, Nutrients)
45 adults over 50 (23 extract, 22 placebo).
Strength rose in both groups, but more with the extract, with between-group differences in most isokinetic and isometric knee-extension measures (for example, peak torque at 60 degrees per second, p < 0.007). Lean and muscle mass rose in both groups without a significant between-group difference. No adverse events. Small, exploratory and in a training context.