Most American adults fall short on four things: calcium, potassium, dietary fiber and vitamin D. Those are the ones the federal Dietary Guidelines name, and the national intake surveys support the choice. Most of the rest of the diet is adequate for most people.
That narrows the problem usefully. Instead of chasing every nutrient with a marketing budget behind it, there are perhaps seven worth attention, and most are settled in the produce aisle. What follows is what the shortfalls are, which are genuinely hard to fix with food, and where a supplement is the sensible answer rather than the lazy one.
What the guidelines name, and what the intake data shows
The 2020–2025 Dietary Guidelines identified calcium, potassium, dietary fiber and vitamin D as underconsumed dietary components of public health concern, and added iron for infants from about six months fed mostly human milk, and for people who are pregnant. The tenth edition, covering 2025–2030, was published in January 2026 and rebuilt the advice around whole foods: three servings of vegetables and two of fruit a day on a 2,000-calorie pattern, protein at 1.2 to 1.6 grams per kilogram of body weight, and an instruction to avoid highly processed food.
The numbers underneath are specific. In NHANES 2013–2016 data, 48% of Americans of all ages took in less magnesium than their estimated average requirement. For calcium, 39% of people aged four and over fell below the EAR, rising to 49% among children and teenagers, and about 72% of US calcium intake comes from dairy products and foods made with them.
The potassium adequate intake is 3,400 mg a day for men and 2,600 mg for women; NHANES 2013–2014 recorded averages of 3,016 mg and 2,320 mg. Vitamin D is the widest miss: 5.1 mcg in men and 4.2 mcg in women from food and drink, against an RDA of 15 mcg for adults up to age 70.
Fiber is the one almost nobody meets. A 2015 review in the American Journal of Lifestyle Medicine put the share of the US population reaching recommended intake at about 5%, against a Daily Value of 28 grams. Choline sits just outside the official list on similar arithmetic: an adequate intake of 550 mg for men and 425 mg for women against average intakes of 402 mg and 278 mg.
What those percentages do not mean
An intake below the estimated average requirement is not a diagnosis. The EAR is the level that meets the needs of half a healthy population, so falling under it raises the probability of inadequacy without establishing it in any one person. Someone under the EAR for magnesium is not thereby magnesium deficient.
The measurement is softer than the decimal places suggest. These figures come from 24-hour dietary recalls, and people under-report what they eat unevenly and in patterned ways. The databases carry their own error, since the mineral content of a plant varies with the soil it grew in.
Blood status is a separate question, and often a more reassuring one. On serum 25-hydroxyvitamin D measured in 2011–2014, 18% of Americans were at risk of inadequacy and 5% at risk of deficiency, well below the share whose intake looks alarming on paper, because skin makes most of the rest. Intake data says where to look. It does not say what is wrong with you.
The nutrients that are genuinely hard to get from food
Most shortfalls are habit-and-access problems rather than chemistry problems. Potassium, fiber, magnesium and calcium are abundant in food that is cheap, shelf-stable and sold everywhere. Three nutrients are different in kind.
Vitamin D is the clearest case. Few foods contain it naturally, and fortified milk carries roughly 3 mcg per cup, so reaching 15 mcg from diet alone means about five cups a day. Skin synthesis normally covers the difference, which is why latitude, season, clothing and skin tone matter more here than the grocery list. Our piece on vitamin D and sunlight covers the exposure side.
Vitamin B12 is the second. Natural sources are limited to animal foods, and roughly 3.6% of US adults are deficient and 12.5% insufficient. Absorption is frequently the constraint rather than intake: metformin can reduce serum B12, proton pump inhibitors interfere with its release from food, and the capacity to free B12 from protein declines with age. Anyone eating plant-based needs a reliable outside source, one of the main things that changes on a plant-based diet.
Iron is the third, and only for some people. The RDA is 8 mg a day for adult men and 18 mg for women aged 19 to 50, and the requirement is 1.8 times higher again for people who avoid animal foods, because non-heme iron is absorbed less readily than heme iron.
Why food first is a mechanical argument, not a sentimental one
Food-first advice usually arrives as a moral preference. It holds up better as an engineering one, because several of the things food does are not reproducible in a capsule.
Fiber is the plainest example. There is no practical way to take 28 grams a day of it as a supplement, and no isolated fiber behaves like the mix of soluble and insoluble fractions in a bowl of beans. Absorption is contextual too: vitamin C in the same meal increases uptake of non-heme iron, while phytate in grains and legumes and certain polyphenols reduce it. Whether the lentils come with lemon or with tea changes the arithmetic.
Form appears to matter even when the label numbers match. In a 2019 inpatient randomized trial at the NIH Clinical Center, 20 adults ate ultra-processed and minimally processed diets for two weeks each, matched for calories, sugar, fat, fiber and carbohydrate and served without limit. On the ultra-processed arm they ate about 500 more calories a day and gained 0.9 kg, losing roughly the same amount on the other arm.
That trial enrolled 20 people and ran four weeks in a metabolic ward, which is not a life. It remains the cleanest demonstration that nutrient totals do not fully describe a diet. Whether nutrient form changes what the body does with it is a narrower question, taken apart in whole-food versus synthetic nutrient forms.
Where the four shortfalls actually come from
| Nutrient | Adult reference | What US intake looks like | Foods that move it fastest |
|---|---|---|---|
| Dietary fiber | 28 g Daily Value | About 5% of the population meets the recommendation | Beans, lentils, split peas, whole grains, pears, raspberries |
| Potassium | 3,400 mg men, 2,600 mg women | 3,016 mg and 2,320 mg on average | Potatoes, beans, lentils, dried apricots, milk |
| Calcium | 1,000–1,200 mg | 39% of people aged 4 and over below the EAR | Dairy, fortified alternatives, canned sardines with bones, kale |
| Vitamin D | 15 mcg (600 IU) | 5.1 mcg in men, 4.2 mcg in women from food | Oily fish, fortified milk, sun exposure |
| Magnesium | 310–420 mg | 48% below the EAR | Pumpkin seeds (156 mg per ounce), chia (111 mg), almonds (80 mg), spinach |
Two habits move most of this at once. Beans, lentils or peas at one meal a day covers a large share of the fiber and potassium gap and contributes magnesium. A serving of dairy or a fortified alternative at two meals covers most of the calcium gap, given how concentrated US calcium intake already is in that one food group.
When a supplement is the sensible answer
The 2025–2030 guidelines put the threshold plainly: when dietary intake or absorption is insufficient, fortified foods or supplements may be needed under medical supervision. That is a narrower brief than the supplement aisle implies, and it points at four situations rather than a general policy of insurance.
- Vitamin D, where sun exposure is limited by latitude, season, work indoors, clothing or skin tone, and food cannot close a 10 mcg gap.
- Vitamin B12, for anyone eating plant-based, anyone over about 50, and anyone on long-term metformin or a proton pump inhibitor.
- Iron, but only on the basis of a blood test, because unnecessary iron is not benign.
- Folic acid before and during early pregnancy, which is a settled clinical recommendation rather than a nutritional preference.
Everything on that list shares a shape: a named gap with a measurable marker or an obvious mechanism, and a specific answer. A supplement taken because a diet is generally poor has no target to hit, which is why it usually misses.
What a greens powder does here, and what it does not
Being straight about this matters more than the sale. A greens powder is a concentrated dried plant food, and a daily scoop typically runs 5 to 10 grams: a serious amount of plant variety, a trivial amount of bulk.
So it does not fix the four shortfalls above. It is not a meaningful source of calcium against a 1,000 mg target, contributes no vitamin D unless one is added, and cannot supply a useful fraction of 28 grams of fiber from a 10 gram scoop. What it can do is widen the range of plants in a diet that has very few, which is a separate benefit worth having on its own terms. The case and its limits are in the evidence on greens powders.
Common questions
How do I know whether I am actually short of something?
A blood test ordered by a clinician, not a symptom checklist. Fatigue, poor sleep and low mood are compatible with almost every deficiency and with none of them, which is why they open so much supplement advertising. Vitamin D, B12, ferritin and a full blood count answer most of the practical questions in one draw.
Is a multivitamin worth taking?
As a hedge against a named risk, sometimes. As general insurance against a diet already known to be poor, it is aimed at nothing in particular. Shortfalls in the intake data cluster in four or five nutrients, and those have targeted answers a broad-spectrum tablet delivers only incidentally.
Should I worry about magnesium?
It is the most common intake shortfall in the survey data, at 48% below the EAR, and one of the easiest to close from food. An ounce of pumpkin seeds carries 156 mg, chia 111 mg and almonds 80 mg, so a handful of seeds plus a serving of beans covers much of the day without a bottle.
The short version
Four nutrients, plus B12 and iron for specific groups, account for most of what is missing from American diets. Beans, seeds, dairy or its fortified equivalents, and a considered answer on vitamin D handle nearly all of it. Supplements belong where a real gap has been identified and food genuinely cannot reach it.
Where a diet is persistently short on plant variety rather than on any single nutrient, a concentrated greens powder is one reasonable addition, and our formulas and their full panels are at Greens Plus.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.
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