Magnesium-Rich Foods and Deficiency Signs: USDA FoodData Central Analysis (2026)

Disclaimer: This article is for informational purposes only and is not medical advice. Consult a qualified healthcare provider before changing your diet, starting supplements, or treating any suspected deficiency. The data and references below describe nutrient content from public databases and do not diagnose or treat any condition.

Building HealthSavvyGuide on top of the USDA FoodData Central (FDC) API, I spent the last six weeks indexing nutrient profiles for 1,465 foods. One mineral kept surfacing in the deficiency-related queries my readers run: magnesium. The National Institutes of Health Office of Dietary Supplements estimates that nearly half of Americans consume less than the Estimated Average Requirement for magnesium, and the USDA's What We Eat in America (NHANES 2017-2018) data confirms the gap is widest in adolescents and adults over 70.

This article is not a diet plan. It is an engineer's read of what the USDA FDC database actually says about magnesium content in whole foods, what the NIH and CDC say about deficiency signs, and where the database fields can mislead you if you take the first row of a search result at face value.

Why Magnesium Matters: What NIH and Mayo Clinic Say

According to the NIH Office of Dietary Supplements fact sheet on magnesium, the mineral is a cofactor for more than 300 enzyme systems involved in protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation. Mayo Clinic notes that magnesium is also required for energy production and the structural development of bone.

The Recommended Dietary Allowance (RDA) varies by age and sex. Per the NIH ODS table:

• Adult men 19-30: 400 mg/day
• Adult men 31+: 420 mg/day
• Adult women 19-30: 310 mg/day
• Adult women 31+: 320 mg/day
• Pregnant women 19-30: 350 mg/day
• Pregnant women 31-50: 360 mg/day

The body stores roughly 25 grams of magnesium total, with 50-60% in bone and the rest distributed in soft tissue. Less than 1% sits in serum, which is why a normal serum magnesium test does not rule out a chronic intake gap. The CDC's National Report on Biochemical Indicators of Diet and Nutrition flagged this exact measurement limitation in its 2012 review and the limitation has not changed.

Deficiency Signs the NIH and Cleveland Clinic Document

Early magnesium inadequacy rarely produces dramatic symptoms, which is part of why the gap is easy to miss. Both the NIH ODS and Cleveland Clinic patient education materials list the following signs that may appear as deficiency progresses:

• Loss of appetite, nausea
• Fatigue and general weakness
• Muscle cramps, especially in the calves and feet at night
• Numbness or tingling
• Abnormal heart rhythms
• Personality changes including irritability or low mood
• Seizures in severe, prolonged cases

Risk factors flagged by the NIH include gastrointestinal diseases such as Crohn's disease and celiac disease, type 2 diabetes, chronic alcohol use disorder, long-term proton pump inhibitor use, and older age (intestinal absorption drops while urinary excretion rises). None of these are self-diagnose situations. They are reasons to ask a primary care provider for a full magnesium workup, not to start aggressive supplementation on your own.

Top Magnesium-Rich Foods From USDA FoodData Central

Here is the part I actually verified row-by-row in the FDC API. The nutrient ID for magnesium in the FDC schema is 1090, expressed in milligrams per 100 grams of edible portion. All values below are from FDC SR Legacy and Foundation Foods entries, which are the most rigorously sourced subsets in the database. I'm listing per-100g and per-typical-serving so you can see how serving size changes the picture.

1. Pumpkin Seeds, Roasted Without Salt

USDA FDC entry: pumpkin seed kernels, roasted, without salt. Magnesium content lands at roughly 550 mg per 100 g, which is the highest density I encountered in the SR Legacy nut and seed category. A practical serving is 28 g (about a quarter cup), delivering around 156 mg, or roughly 37% of the adult male RDA.

One engineering note: the FDC database has multiple pumpkin seed entries with different processing (in shell vs kernel only, salted vs unsalted, dried vs roasted). The kernel-only roasted entry is the one most home cooks actually buy in bags labeled "pepitas." If you query the database without filtering, the in-shell entry will pull down your average because it includes the inedible shell mass.

2. Chia Seeds

FDC reports chia seeds at approximately 335 mg of magnesium per 100 g. A 28 g serving (about 2 tablespoons) yields around 95 mg. Chia also contributes about 10 g of fiber per 28 g, most of it soluble, which the Harvard T.H. Chan School of Public Health notes can slow nutrient absorption from a single sitting. Spreading chia across two meals rather than one large pudding is a small but evidence-supported pattern.

3. Almonds, Dry Roasted

USDA FDC value: 268 mg per 100 g. A 28 g serving (about 23 almonds) provides 75 mg. Almonds also bring vitamin E and monounsaturated fat. The dry-roasted entry without added salt is the cleanest comparison; oil-roasted and salted versions differ in sodium but not significantly in magnesium.

4. Cashews, Raw

FDC entry shows 292 mg per 100 g for raw cashews. The 28 g serving delivers 82 mg. Note that retail "raw" cashews are technically steamed during processing because the natural shell oil is irritant; the USDA "raw" designation reflects pre-roast state.

5. Boiled Spinach

This one surprised the readers I tested it on. Raw spinach lists 79 mg per 100 g in the FDC, but cooked (boiled, drained) spinach jumps to 87 mg per 100 g. The reason is straightforward: boiling collapses the leaf volume, concentrating mineral content per gram. A standard cooked half-cup serving (90 g) delivers about 78 mg of magnesium, which is more than most people get from any single salad serving of raw leaves.

The trade-off: oxalates in spinach bind magnesium and reduce absorption. The Linus Pauling Institute at Oregon State has reviewed the bioavailability data and concluded that absorption from spinach is real but lower per milligram than from nuts and seeds. Eat the spinach, but don't count it as your only magnesium source.

6. Black Beans, Cooked

FDC value: 70 mg per 100 g cooked. A typical one-cup serving (172 g) yields about 120 mg, or 38% of the adult female RDA. Beans also contribute potassium, folate, and resistant starch. From an aggregation standpoint, beans are the most calorie-efficient magnesium source in the database for people watching weight: 227 kcal per cup versus 470+ kcal for an equivalent magnesium dose from nuts.

7. Dark Chocolate (70-85% Cacao)

FDC reports 228 mg per 100 g. A 28 g serving (one square of most retail bars) delivers about 64 mg. The catch is energy density: that same 28 g brings around 170 kcal and 12 g of saturated fat. Mayo Clinic dietitians have written about this trade-off; dark chocolate is a real magnesium source, just not a free one.

8. Avocado

FDC entry for raw Hass avocado: 29 mg of magnesium per 100 g. A medium avocado weighs roughly 200 g of edible flesh, which works out to about 58 mg. Avocado is not the densest source per gram, but it is one of the most commonly consumed and pairs well with leafy greens to compound intake at a single meal.

9. Mackerel, Atlantic, Cooked

FDC value: 97 mg per 100 g cooked. A standard 6-oz fillet (170 g) provides 165 mg. Mackerel also contributes EPA and DHA omega-3s, which I covered separately in the omega-3 article published earlier this month.

10. Brazil Nuts

FDC reports 376 mg per 100 g. The catch with Brazil nuts is selenium: a single nut can exceed the daily upper limit for selenium intake, so portion control here is not optional. Treat Brazil nuts as a magnesium contributor of 1-2 nuts per day, not a primary source.

What the Aggregator View Reveals That Single-Article Lists Miss

When I ran a sort across the FDC magnesium field for the entire SR Legacy dataset, three patterns stood out that most "best magnesium foods" lists do not surface:

Pattern 1: Refined grains lose 80-90% of native magnesium. Whole wheat flour lists at 138 mg per 100 g; all-purpose white flour drops to 22 mg per 100 g. The milling process removes the bran and germ where most of the mineral sits. If your daily carbohydrate base is white bread or white pasta, you are eating a magnesium-stripped staple.

Pattern 2: Tap water and mineral water are unlogged sources. The USDA does not enter tap water magnesium because it varies by municipality, but European studies cited by the World Health Organization have shown that hard-water regions can contribute 30-50 mg per liter, a non-trivial daily addition. The WHO's 2009 report Calcium and Magnesium in Drinking Water reviewed this in depth.

Pattern 3: Bioavailability is not in the FDC schema. The database tells you what is in the food. It does not tell you what your gut absorbs. Phytic acid in whole grains, oxalates in spinach and chard, and high-dose calcium consumed at the same meal all reduce magnesium absorption. The NIH ODS fact sheet estimates dietary magnesium absorption ranges from 30% to 40% across mixed diets. Plan intake accordingly: hitting the RDA on paper does not mean hitting it biochemically.

Practical Daily Pattern (Not a Prescription)

Stitching the above together, an adult could plausibly hit the RDA with food alone via a pattern like this: 28 g pumpkin seeds on morning yogurt (156 mg), one cup cooked black beans at lunch (120 mg), half a cooked avocado in a salad (58 mg), and a 6-oz mackerel fillet at dinner (165 mg). That stacks to roughly 499 mg before counting any whole grains or leafy greens.

This is an example of how the numbers compose, not a meal plan I am prescribing. Individual needs differ, and anyone with kidney disease, GI absorption issues, or who takes medications that affect mineral handling should not increase magnesium intake without talking to a clinician. The NIH ODS fact sheet specifically flags that supplemental magnesium has interactions with bisphosphonates, certain antibiotics, diuretics, and proton pump inhibitors.

Should You Supplement?

The NIH ODS position is clear: food first. Magnesium from food has no Tolerable Upper Intake Level because excess intake from whole foods is rapidly excreted by healthy kidneys. Supplemental magnesium is capped at a UL of 350 mg per day from non-food sources because higher doses cause diarrhea and, in extreme cases or in people with kidney impairment, toxicity.

If a clinician confirms a deficiency, the supplement form matters. Cleveland Clinic and the Linus Pauling Institute both note that magnesium oxide is poorly absorbed, while magnesium citrate, glycinate, and lactate are better tolerated and more bioavailable. I'm not making a recommendation here; I am pointing at the published bioavailability data so you can have an informed conversation with the person who actually knows your medical history.

Frequently Asked Questions

Can I get enough magnesium from a vegan diet?

Yes, in principle. The top USDA FDC magnesium sources include pumpkin seeds, chia seeds, almonds, cashews, black beans, cooked spinach, and dark chocolate, all plant-based. The NIH ODS does not flag plant-based diets as a deficiency risk on the macronutrient level, but absorption may be lower if the diet is also high in phytic acid from unsoaked legumes and grains. Soaking and sprouting reduce phytate.

Does coffee deplete magnesium?

Coffee mildly increases urinary magnesium excretion, but the effect at typical 2-3 cup daily intakes is small per the NIH ODS review. Heavy alcohol use is a much larger driver of magnesium loss and is on the official risk-factor list.

Are magnesium-fortified foods worth seeking out?

Some breakfast cereals and plant milks are fortified. Check the Nutrition Facts panel for the milligram amount, not just the percent Daily Value, because the FDA still uses the older 400 mg DV reference. Whole-food sources tend to come bundled with fiber, potassium, and other co-factors that fortified products do not replicate.

Why does the FDC have multiple entries for the same food with different magnesium values?

Different entries reflect different sample lots, different analytical labs, and different processing states. The Foundation Foods subset is the newest and most rigorously sourced. SR Legacy is older but still widely used. Branded Foods entries come from manufacturers and have wider variance. If you build anything on top of the FDC API, filter by data type to keep your analysis consistent.

Is a serum magnesium test enough to rule out deficiency?

No. As noted above, less than 1% of body magnesium is in serum. The CDC's biochemical indicators report and the NIH ODS fact sheet both flag this. Red blood cell magnesium and ionized magnesium tests are alternatives, though access varies by lab. This is a conversation for a physician, not a self-test decision.

The Engineer's Bottom Line

Magnesium is one of the cleanest examples I have indexed of a nutrient where the database, the dietary guidelines, and the absorption science point in the same direction: most adults underconsume it, whole foods are the safer source, and the highest-density entries in the USDA FDC are seeds, nuts, legumes, fatty fish, and cooked leafy greens. The gap between what the database reports and what your gut absorbs is real, which is why "I ate the RDA" and "my body got the RDA" are not the same statement.

Treat this as one engineer's reading of the public data, not as medical advice. If anything in the deficiency signs section sounds familiar, the next step is a clinician, not a supplement aisle.

Sources

• NIH Office of Dietary Supplements: Magnesium Fact Sheet for Health Professionals — ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/
• USDA FoodData Central — fdc.nal.usda.gov
• CDC Second National Report on Biochemical Indicators of Diet and Nutrition — cdc.gov/nutritionreport
• Cleveland Clinic Health Library: Magnesium Deficiency
• Mayo Clinic: Magnesium overview, drug interactions reference
• Linus Pauling Institute, Oregon State University: Magnesium
• WHO: Calcium and Magnesium in Drinking Water — Public Health Significance, 2009
• Harvard T.H. Chan School of Public Health: The Nutrition Source — Magnesium