Benefits
Active myrosinase that raises sulforaphane formation from cooked broccoli
In a randomized crossover in 12 healthy adults, adding 1 g of powdered brown mustard to cooked broccoli raised a urinary sulforaphane marker more than fourfold, showing more sulforaphane formed and was absorbed, not a health effect. Cooking destroys broccoli's own myrosinase, and the mustard supplied active enzyme (44.7 vs 9.8 micromoles per gram of creatinine).
Source of sinigrin and sinalbin, which release pungent isothiocyanates
Brown and black seeds are rich in sinigrin, which yields allyl isothiocyanate, and white seed in sinalbin, which yields the milder 4-hydroxybenzyl isothiocyanate. In 4 volunteers who ate brown mustard, an allyl isothiocyanate metabolite appeared in urine within 12 hours, about 5.4 mg after 10 g and 12.8 mg after 20 g.
Energy expenditure and appetite after eating mustard
In a placebo-controlled crossover in healthy adults, 10 g of prepared mustard did not raise energy expenditure, body temperature or hunger, and later food intake was unchanged. In 22 young men, 21 g of mustard in a meal gave a non-significant rise in heat production after eating versus no spice, with no change in appetite or intake.
Post-meal blood glucose with yellow mustard bran added to soup
In 10 healthy young men, a potato and leek soup with 5 g of yellow mustard bran, the seed-coat fraction, gave lower blood glucose at 15, 30 and 90 minutes than the same soup without it. This was a single test meal of bran, not whole seed; in a separate study, 10 g of prepared mustard did not change plasma glucose versus placebo.
DNA damage markers in blood cells after eating mustard
In 14 volunteers eating 20 g of mustard a day, blood cells resisted DNA damage applied in the laboratory after 3 days, with no placebo group described. In a 46-adult crossover, 10 days of prepared mustard with cabbage did not change DNA strand breaks or a urinary oxidative marker versus control, and strand breaks rose briefly 3 hours after eating.
Plasma sodium and potassium after a large serving of mustard
Some athletes eat mustard for exercise-related muscle cramps. In 9 active adults dehydrated by exercise in the heat, about 135 g of mustard (roughly 1.5 g of sodium) did not change plasma sodium, potassium or fluid balance within 60 minutes. It did not cause high potassium, nor did it fully replace the electrolytes and fluid lost in sweat.
Mechanism of action
The glucosinolate and myrosinase system is switched on by grinding and water
In whole dry seed, glucosinolates and myrosinase are kept apart. Grinding the seed and mixing it with water lets myrosinase release isothiocyanates, which give mustard its heat. A toxicology review notes this conversion still occurs in salty, acidic mustard preparations, while boiling makes sinigrin disappear.
Allyl isothiocyanate activates the TRPA1 cold receptor
Allyl isothiocyanate activates TRPA1, a receptor that senses extreme cold, which is the basis for testing mustard on heat production. In mice, injected allyl isothiocyanate raised energy expenditure by 32%, but eating up to 10 g of prepared mustard did not reproduce this in adults.
Isothiocyanates are absorbed and cleared through the urine
After a mustard meal, allyl isothiocyanate is absorbed and conjugated, and its N-acetylcysteine conjugate is excreted in urine, mostly within 8 hours and all within 12 hours, in amounts that rise with the dose. Added mustard powder can also convert glucoraphanin from cooked broccoli into sulforaphane, which then appears in urine as its own metabolite.
Clinical trials
Randomized crossover bioavailability study comparing 200 g of cooked broccoli eaten alone or with 1 g of powdered brown mustard as a source of active myrosinase; outcome was the sulforaphane metabolite SF-NAC in 24-hour urine. (Okunade et al. 2018, Mol Nutr Food Res)
12 healthy adults.
Urinary SF-NAC was 9.8 micromoles per gram of creatinine after broccoli alone and 44.7 with mustard powder added, more than four times as much. This measured how much sulforaphane formed and was absorbed from one meal; no health outcome was measured.
Small human study developing a urinary marker of allyl isothiocyanate intake after a meal containing brown mustard, with 48-hour urine collection. (Jiao et al. 1994, Cancer Epidemiol Biomarkers Prev)
4 adult volunteers.
The N-acetylcysteine conjugate of allyl isothiocyanate was found in urine from 0 to 12 hours after the meal, mostly within 8 hours, and not afterward. Average excretion was 5.4 mg after 10 g of mustard and 12.8 mg after 20 g. A measure of absorption and excretion, not of any effect.
Crossover study of 10 g of prepared mustard in capsules or by the spoon versus a capsulated placebo mixture, with energy expenditure over 150 minutes as the primary outcome; the capsule and placebo visits were randomized, and the unblinded spoonful visit was the last visit for 9 of the 11 subjects. (Langeveld et al. 2017, Am J Clin Nutr)
11 healthy adults (6 men, 5 women) randomized; 1 was excluded after the first visit and 1 withdrew after the second.
Energy expenditure did not rise with either form of mustard compared with placebo, and substrate use, core temperature, cold and hunger scores, plasma glucose and other plasma measures, and food intake at a later test meal did not differ. 10 g was the highest dose tolerated without nausea in pretesting.
Placebo-controlled, single-blind, five-way crossover comparing a brunch with mustard (21 g), horseradish, black pepper, ginger or no spice on 4-hour diet-induced thermogenesis, appetite, ad libitum energy intake and energy balance. One author was from Unilever R&D. (Gregersen et al. 2013, Br J Nutr)
22 young, normal-weight men.
No spice had a significant effect on thermogenesis. After the mustard meal it was 59 versus 52 kJ/h with no spice, a non-significant trend (P = 0.08). Appetite ratings, how much people ate at the next meal and energy balance did not differ between meals.
Randomized repeated-measures comparison of a potato and leek soup with or without 5 g of yellow mustard bran, with capillary blood glucose and satiety measured for 120 minutes. Post-meal glucose in healthy men. (Lett et al. 2013, Int J Food Sci Nutr)
10 healthy, non-smoking young men (mean age 21, mean BMI 23).
Blood glucose was significantly lower with the mustard bran at 15, 30 and 90 minutes. The abstract does not report whether the total incremental area or satiety ratings differed. One test meal, and the bran is the seed-coat fraction, not whole seed or prepared mustard.
Randomized three-period crossover on a controlled diet: control, pure allyl isothiocyanate, or 30 g of a Dijon-style prepared mustard with 150 g of cabbage daily for 10 days each, with a 17-day washout. (Charron et al. 2013, J Nutr Biochem)
46 adults completed; blood was sampled 3 and 6 hours after a dose in 20 of them.
After 10 days, DNA strand breaks in blood cells and urinary 8-oxodG did not differ between treatments. Both isothiocyanate treatments raised strand breaks 3 hours after eating compared with control, and the difference was gone by 6 hours. The isothiocyanate content of the mustard fell by 89% over the study.
Intervention study of 20 g of a mustard preparation (25 mg total isothiocyanates) daily for 4 days, testing blood cells with the comet assay and micronucleus test after laboratory exposure to DNA-damaging agents; the abstract calls the trial controlled but does not describe a placebo group. (Lamy et al. 2012, Eur J Cancer Prev)
14 volunteers (10 women, 4 men).
After 3 days of mustard, blood cells showed significantly less DNA damage and micronucleus formation when exposed to hydrogen peroxide or a benzo(a)pyrene metabolite in the laboratory. Liver tests were unchanged and cholesterol fell significantly. These are laboratory markers on blood cells, not clinical outcomes.
Crossover study after 2 hours of vigorous exercise in the heat: 1 mL/kg of pickle juice or deionized water, or an amount of mustard with sodium similar to the pickle juice, with blood sampled for 60 minutes. (Miller 2014, J Athl Train)
9 physically active adults (mean age 25).
Participants ate about 135 g of mustard (roughly 1.5 g of sodium). Plasma sodium, potassium, osmolality, plasma volume and plasma sodium content did not change within 60 minutes after any drink or food. Mustard did not raise potassium and did not fully replace the sodium and fluid lost in sweat.