5 Nutrients People Commonly Miss and How to Get Them From Food

Five nutrients show up short in national dietary surveys far more often than the rest: iron, calcium, vitamin B12, potassium and fibre. The fix is not a supplement aisle sweep. It is a small number of repeatable food habits: legumes several times a week, a calcium source at two meals, a B12 source daily, and whole grains and produce in place of refined versions. Most people can close most of the gap with ordinary food, and this guide shows what that looks like in a single day.

Why these five, and why "eat more vegetables" is not enough

"Eat more vegetables" is good advice that does not tell you anything specific. These five nutrients are worth naming because they are the ones that most often fall short even when someone is eating a reasonable diet:

• Iron, especially for menstruating adults, because plant iron is absorbed less efficiently than animal iron.
• Calcium, because dairy intake has fallen and leafy greens vary enormously in how much calcium your body can actually use.
• Vitamin B12, because it occurs naturally almost only in animal foods, which matters for anyone eating mostly plants.
• Potassium, because it is abundant in whole foods and scarce in processed ones, and most people eat the reverse.
• Fibre, because the average adult gets roughly half the recommended amount.

They also share a useful property: each one has cheap, widely available food sources. None of this requires specialty products.

Iron

What it does: carries oxygen in haemoglobin and supports energy metabolism. Low iron shows up as fatigue, breathlessness and poor concentration long before anaemia is diagnosed.

How much: adults need about 8 mg per day; menstruating adults aged 19 to 50 need about 18 mg; pregnancy needs more. These are US Dietary Reference Intake figures.

Where it comes from:

• Heme iron (best absorbed): red meat, liver, poultry, fish, shellfish.
• Non-heme iron: lentils, chickpeas, beans, tofu, spinach, fortified cereals, oats, pumpkin seeds, dark chocolate.

What changes absorption:

• Vitamin C boosts non-heme iron absorption substantially. A squeeze of lemon or a red pepper alongside lentils genuinely matters.
• Tea, coffee and calcium-rich foods inhibit it. Leave an hour between a strong coffee and your iron-rich meal if you are trying to raise your intake.
• Soaking and fermenting beans and grains reduces phytates, which improves absorption.

Calcium

What it does: builds and maintains bone, and is involved in muscle contraction, nerve signalling and blood clotting.

How much: about 1,000 mg per day for most adults, rising to 1,200 mg after 50 for women and after 70 for men.

Where it comes from:

• Dairy: milk, yoghurt and cheese are the most concentrated everyday sources.
• Fortified plant milks: check the label for calcium content; levels vary widely between brands.
• Canned fish with bones: sardines and salmon with soft bones are excellent.
• Tofu set with calcium sulfate: check the ingredient list.
• Low-oxalate greens: kale, collard greens, bok choy and broccoli. These are the greens whose calcium your body can actually use.

The oxalate catch: spinach and rhubarb are high in calcium on paper but low in bioavailability, because oxalates bind it. A day built on spinach will show a high calcium number on a spreadsheet and a low one in your body. Mix your greens.

Vitamin B12

What it does: needed for red blood cell formation, nerve function and DNA synthesis. Deficiency develops slowly and can cause irreversible nerve damage if it goes undetected for years.

How much: about 2.4 micrograms per day for adults.

Where it comes from: naturally, almost exclusively from animal foods — meat, fish, eggs, dairy and shellfish. For plant-based diets, the practical sources are fortified foods: fortified plant milks, fortified cereals, fortified nutritional yeast and some meat alternatives.

Who is at higher risk:

• Anyone eating a fully plant-based diet without fortified foods.
• Adults over 60, because absorption declines with age.
• People taking metformin or long-term acid-reducing medication.
• People with gastrointestinal conditions affecting absorption, or after bariatric surgery.

B12 absorption depends on intrinsic factor and stomach acid, so for many people at risk, fortified foods or a supplement is the reliable route rather than more of a food they cannot absorb.

Potassium

What it does: helps regulate blood pressure, fluid balance and muscle function, and it works alongside sodium.

How much: the US adequate intake is about 2,600 mg per day for women and 3,400 mg for men, and most adults fall short.

Where it comes from: potatoes, sweet potatoes, beans, lentils, bananas, spinach, tomatoes, oranges, avocado, yoghurt and fish. Notice that almost all of these are whole or minimally processed foods. A diet built on packaged food is naturally low in potassium, which is one reason the gap is so common.

Fibre

What it does: supports digestion, feeds gut bacteria, slows glucose absorption and increases satiety. Higher fibre intake is consistently associated with better cardiovascular and metabolic outcomes.

How much: about 25 g per day for women and 38 g for men, or roughly 14 g per 1,000 calories. The average adult intake is closer to 15 g.

Where it comes from: beans and lentils (the highest per serving), whole grains, oats, fruit with skin, vegetables, nuts and seeds.

The practical caution: increasing fibre quickly causes bloating and discomfort. Add it gradually over two to three weeks and increase water intake at the same time.

Worked example: a day that hits four of the five

Here is an ordinary day for one adult, with approximate values. Numbers are rounded and drawn from standard food composition data, so treat them as a demonstration rather than a precise measurement.

Breakfast: 60 g oats with 200 ml fortified soy milk, one banana, 20 g almonds.

• Fibre: about 10 g
• Calcium: about 350 mg
• B12: about 0.8 µg
• Potassium: about 900 mg
• Iron: about 3 mg

Lunch: lentil soup made with 200 g cooked lentils, two slices of wholegrain bread, one red pepper.

• Fibre: about 20 g
• Calcium: about 100 mg
• B12: 0 µg
• Potassium: about 1,150 mg
• Iron: about 8 mg

Dinner: 90 g canned sardines with bones on toast, a kale salad, 150 g plain yoghurt.

• Fibre: about 4 g
• Calcium: about 520 mg
• B12: about 9 µg
• Potassium: about 800 mg
• Iron: about 3 mg

Day totals: fibre around 34 g, calcium around 970 mg, B12 around 10 µg, potassium around 2,850 mg, iron around 14 mg.

That day reaches the target for B12 comfortably, gets close on calcium, and lands in the right range for iron, potassium and fibre — without a supplement, without a specialty product, and without a single meal that took more than twenty minutes. If you are a menstruating adult with higher iron needs, or you eat fully plant-based, the same day needs one or two deliberate additions: a fortified cereal, a second fortified milk, or a clinician-guided supplement.

Who should not simply "eat more"

Food first is the right default, but for some people it is not enough, and for others it is actively the wrong advice:

• Anyone with a diagnosed deficiency needs treatment, not dietary tweaks.
• People eating fully plant-based diets should treat B12 as a planned nutrient, usually from fortified foods or a supplement.
• Adults over 60 absorb B12 and calcium less efficiently and may need fortified foods or supplements.
• People with kidney disease often need to limit potassium, not increase it.
• People with haemochromatosis need to limit iron.
• Pregnant adults have higher requirements for iron, folate and other nutrients and should follow their clinician's guidance.

If you suspect a deficiency, a blood test is the only way to know. Fatigue has many causes, and guessing wastes time.

Limitations: what this guide does not cover

• Reference intakes are population figures. Your needs depend on age, sex, activity, pregnancy, medication and health conditions.
• Absorption varies more than content. The calcium in spinach and the iron in lentils are not equivalent to the same numbers from other foods.
• Vitamin D is deliberately missing here. It comes mainly from sunlight and fortified foods rather than from the food patterns discussed above, and it is a large enough topic to deserve its own treatment.
• Food composition data is approximate. Values vary by variety, soil, storage and cooking method.
• More is not better. Very high doses of some nutrients, particularly iron and calcium supplements, cause harm.
• This is general information, not medical advice. Individual decisions belong with your clinician.

Where this fits with the rest of your plan

Nutrients are easier to hit when the week is built around foods that carry several at once: lentils, yoghurt, sardines, oats and leafy greens each contribute to more than one of the five. The vitamins and minerals guide explains the categories, the fibre guide goes deeper on the one most people miss, and the plant protein sources guide covers the protein side of the same foods. To see how a day like the one above fits your overall targets, use the macro calculator, and to turn it into a repeatable week, open the public planner.

FAQ

Do I need supplements for these nutrients?

Most adults do not need supplements for iron, calcium, potassium or fibre if they eat a varied diet with legumes, dairy or fortified alternatives, and whole grains. Vitamin B12 is the exception for anyone eating a fully plant-based diet, where fortified foods or a supplement are the reliable route.

Are plant sources of iron useless?

No, but they are absorbed less efficiently. Pair them with vitamin C, avoid tea and coffee at the same meal, and soak or ferment beans and grains to reduce phytates.

Is spinach a good source of calcium?

It is high in calcium but low in bioavailability because of oxalates. Kale, collard greens and bok choy are better choices for usable calcium. Mix your greens rather than relying on one.

How do I increase fibre without bloating?

Add about 5 g per day per week rather than doubling overnight, increase water at the same time, and spread fibre across meals instead of concentrating it in one.

Can I get potassium from a supplement?

Potassium supplements are limited in dose for safety reasons, and high-dose potassium can be dangerous for people with kidney problems. Food is the better route, and most potassium-rich foods are cheap.

The bottom line

Iron, calcium, vitamin B12, potassium and fibre fall short in a lot of ordinary diets, and each has a cheap, everyday food source. Legumes several times a week, a calcium source at two meals, a daily B12 source, and whole grains and produce in place of refined versions will close most of the gap. For B12, for older adults and for anyone with a diagnosed deficiency, food alone may not be enough — that is a conversation with a clinician, not a guess.