Four vegetarian bentos that all carry the label balanced meal can deliver anywhere from 417 to 642 kcal and from 0 to 5.7 g of salt. Calculated on the Swiss Food Composition Database, the four menus on this page rank like this: the lentil and roasted vegetable box adds no salt at all, the quinoa and marinated tofu box reaches 4.4 g as soon as the marinade is poured in whole, and the maki box hits 5.7 g, which is 95 % of the 6 g daily reference intake. That same maki box supplies 310 µg of iodine from two sheets of nori, more than double the nutrient reference value. None of these gaps come from the vegetables. They come from three ingredients: soy sauce, salted cooking water and seaweed.

What the four bentos on this page actually weigh

The figures below are calculated from the Swiss Food Composition Database V7.1 published by the Federal Food Safety and Veterinary Office, using the quantities written in the recipes on this page, one portion per bento. Percentages refer to the daily reference intakes in Annex 10 of the Swiss ordinance on food information: 6 g of salt, 50 g of protein, 14 mg of iron, 150 µg of iodine, 80 mg of vitamin C.

Bento	Energy	Protein	Salt	Iron	Iodine	Fibre
1. Quinoa and marinated tofu	642 kcal	30.0 g (60 %)	4.4 g (73 %)	5.7 mg (41 %)	10 µg (7 %)	9.0 g
2. Makis and crunchy salad	417 kcal	10.7 g (21 %)	5.7 g (95 %)	3.1 mg (22 %)	310 µg (207 %)	7.2 g
3. Vegetable patties and hummus	469 kcal	16.8 g (34 %)	1.3 g (22 %)	4.1 mg (29 %)	18 µg (12 %)	13.7 g
4. Lentils and roasted vegetables	510 kcal	19.8 g (40 %)	0.0 g	5.7 mg (41 %)	3 µg (2 %)	21.6 g

Three things stand out. The maki box, which looks lightest at 417 kcal, carries the most salt and by far the most iodine. The lentil box, which looks the most rustic, delivers two and a half times more fibre than the makis and not a gram of added salt. And the quinoa box, at 30.0 g of protein, is the only one covering more than half the protein reference intake, but it pays for that with 73 % of the salt reference intake in a single meal.

None of these four compositions is bad. They simply are not interchangeable, and the word balanced says nothing about what separates them.

Salt is the real problem in a bento, not calories

Soy sauce in the Swiss database contains 14 g of salt per 100 g. One tablespoon weighs roughly 15 g. Two tablespoons, the amount written in the quinoa bento marinade, therefore deliver 4.2 g of salt, or 70 % of the 6 g daily reference intake from a single seasoning. The World Health Organization recommends staying below 2 000 mg of sodium per day, the equivalent of less than 5 g of salt, and puts the global adult mean at 4 278 mg of sodium per day in 2021, more than double its own recommendation.

Rice creates the same problem by another route. Polished rice cooked in salted water contains 1.3 g of salt per 100 g according to the Swiss database. The 250 g of cooked rice in a maki bento therefore contributes 3.25 g of salt on its own, before any dipping sauce and before the nori, which itself holds 5 g of salt per 100 g. That accumulation, rather than any single ingredient, is what pushes bento 2 to 5.7 g.

The fix is straightforward and changes neither the taste nor the recipe:

• Cook rice and quinoa in unsalted water. Sushi rice is seasoned after cooking anyway, with the vinegar, sugar and salt mixture, and that seasoning is enough.
• Cut the tofu marinade back to one tablespoon of soy sauce for 110 g of tofu, which is 0.7 g of salt, and replace the volume with lemon juice, grated ginger and garlic. The marinade still reads as salty because acidity amplifies perceived saltiness.
• Serve the dipping sauce separately in a small container rather than pouring it over the rice. People then typically use 5 g instead of 15.

With those three moves, the quinoa bento drops from 4.4 to 1.6 g of salt while keeping 28.3 g of protein. The principle goes beyond bentos: our page on seasoning without salt covers the acid and aromatic levers that genuinely replace salt, and the one on salt-free cooking deals with the case where the target is genuinely low.

Two sheets of nori exceed the iodine reference value

This is the most surprising line in the table. Dried nori contains 5 100 µg of iodine per 100 g according to the Swiss database. One sheet weighs around 3 g. Two sheets, the amount needed to roll the makis for one bento, therefore deliver 306 µg of iodine, or 204 % of the 150 µg nutrient reference value set in Annex 10 of the ordinance.

Two opposite qualifications matter here, and both are real.

On one side, iodine is a critical nutrient in vegetarian and vegan diets in Switzerland, and the main dietary source for the population remains iodised table salt. A one-off dose of 306 µg stays well below the safety ceiling: the European Food Safety Authority uses a tolerable upper intake level of 600 µg per day for adults, a value carried over from the Scientific Committee on Food, and sets the adequate intake at 150 µg per day. An occasional maki bento puts nobody at risk of excess.

On the other side, the margin closes quickly once seaweed becomes a habit. A Norwegian clinical study published in the European Journal of Nutrition in 2026 followed 49 habitual seaweed consumers before and after a six-week cessation period. Their median estimated iodine intake was 658 µg per day before cessation, with an upper quartile at 1 516 µg, above the tolerable upper intake level. After six weeks without seaweed, median intake fell to 189 µg per day and median serum TSH dropped significantly, with the largest decrease among participants who had the highest intakes to begin with. The authors conclude that eating seaweed with high iodine content could push intake past the upper limit. The study had neither randomisation nor a control group, which limits how far the result carries, but the direction matches the known mechanism.

The German Federal Institute for Risk Assessment goes further on the regulatory side: it considers dried seaweed products containing 20 mg of iodine per kilogram or more to be capable of damaging health and not marketable as such, on the grounds that a 10 g portion is then enough to cause excessive intake. The nori in the Swiss database sits at 51 mg per kilogram, well above that threshold.

In practical terms, for a maki bento:

• One 3 g sheet of nori delivers 153 µg of iodine, roughly one reference value. That is a sensible amount for one meal.
• Two sheets deliver 306 µg. That remains acceptable occasionally.
• A maki bento two or three times a week, on top of iodised salt and other seaweed, gets seriously close to the 600 µg daily limit.
• Anyone being followed for Hashimoto’s thyroiditis, hyperthyroidism or thyroid autonomy should discuss seaweed consumption with their doctor before making it a habit, because the response to iodine differs in these conditions.

Our page on iodine in a vegetarian diet covers the relationship between iodised salt and seaweed, and the one on avoiding iodine deficiency without fish handles the opposite situation, inadequate intake.

Cold rice and Bacillus cereus: the one microbiological risk specific to bentos

A bento almost always contains rice, pasta or a cooked grain that has been cooled. That is exactly the food profile associated with Bacillus cereus. This soil bacterium frequently contaminates raw rice as spores, and the spores survive cooking. A review published in Foods in 2021 on the risk linked to rice and its derivatives notes that B. cereus can multiply in rice-based foods that have been cooked or subjected to treatments short of commercial sterility, at temperatures as low as 4 °C, and that it produces diarrhoeal or emetic toxins.

The decisive step is cooling, not reheating. An experimental study published in Foods in 2025 inoculated B. cereus spores into six hot dishes and held them at 40, 50 and 60 °C for half an hour up to four hours. The tested strain exceeded 6.0 log CFU/g within four hours at 40 °C in dishes with a pH above 6.0. The two dishes with a pH of 4.6, tomato sauce and ratatouille, showed no such growth. In other words, a dish sitting between 40 and 50 °C for several hours is the problem scenario, and acidity slows the process down.

That dictates specific habits:

• Spread cooked rice or quinoa in a thin layer on a tray or in a wide dish as soon as it is drained, instead of letting it cool as a mass in the pan. A compact mass stays warm at the centre for hours.
• Get it into the fridge within one to two hours of cooking. The UK Food Standards Agency recommends cooling cooked food at room temperature and then refrigerating it within one to two hours, and dividing large quantities into portions to speed cooling up.
• Keep the fridge between 0 and 5 °C, and check it with a thermometer.
• Eat leftovers within 48 hours or freeze them.
• Do not keep chilled food out of the fridge for more than four hours in total during preparation.

Seasoning sushi rice plays a role here that goes past flavour. Rice vinegar lowers the pH of the rice, and that is precisely the factor that blocked growth in the two acidic dishes of the study. Seasoning sushi rice is not a decorative finishing step.

For transport, the practical rule is simple: a bento that spends more than two hours out of the fridge needs an ice pack in the bag, and a bento prepared the night before must have spent that night in the fridge, not on the counter.

Bento 1: quinoa and marinated tofu, 642 kcal or 603 kcal depending on the marinade

This is the highest-protein bento on the page: 30.0 g of protein in the original version, 60 % of the 50 g reference intake, with 19 % of its energy coming from protein. The ordinance reserves the claim high in protein for foods where at least 20 % of the energy comes from protein, and this composition sits just short of it.

Ingredients for one portion:

• 80 g of quinoa dry weight, giving roughly 240 g cooked
• 110 g of plain firm tofu
• Marinade: 1 tablespoon of soy sauce (15 g), 1 teaspoon of maple syrup, 1 tablespoon of sesame oil, 1 minced garlic clove, 1 teaspoon of grated ginger, the juice of half a lemon
• 60 g of cucumber, 50 g of grated carrot, a few cherry tomatoes, some radishes
• 1 tablespoon of sesame seeds

Method:

1. Press the tofu between two plates under a weight for 15 minutes. This is not cosmetic: firm tofu still holds a lot of water, and pressed tofu absorbs the marinade instead of letting it bead on the surface.
2. Cut into 2 cm cubes, mix the marinade and leave for at least 30 minutes, ideally overnight in the fridge.
3. Rinse the quinoa under clear water to remove the saponins that cause bitterness. Cook for 15 minutes in two volumes of unsalted water, then spread it out to cool quickly.
4. Brown the tofu cubes for 8 to 10 minutes in a pan with a little oil over medium-high heat. Leftover marinade can be reduced in the pan for a minute and spooned over the tofu.
5. Assemble cold. Sesame seeds go on last so they stay crunchy.

Quinoa is a pseudo-cereal that the Swiss database credits with 13.3 g of protein per 100 g raw, alongside 3.6 mg of iron and 8.3 g of fibre. Cooked, it drops to 4.4 g of protein per 100 g, simply because it absorbs water. That is the same amount of protein spread across more mass, and a frequent source of confusion when people compare figures found at random.

One note on the starch portion: the Swiss dietary recommendations from the FSVO define a cereal portion as 45 to 75 g dry weight. The 80 g of quinoa in this recipe edges past the upper end, which explains part of the 642 kcal. If the bento needs to be lighter, that is where to cut, not on the tofu.

Bento 2: vegetarian makis, the lightest in calories and the heaviest in salt and iodine

At 417 kcal, this is the least energy-dense of the four, but also the only one supplying just 10.7 g of protein, 21 % of the reference intake and only 10.4 % of its energy as protein. White rice, seaweed, avocado and raw vegetables do not add up to a protein-bearing meal.

Ingredients for one portion:

• 100 g of round sushi rice dry weight, giving roughly 250 g cooked, cooked without salt
• Rice seasoning: 1 tablespoon of rice vinegar, 1 teaspoon of sugar, a pinch of salt
• One 3 g sheet of nori
• 50 g of sliced avocado, 40 g of cucumber, 40 g of carrot sticks
• 100 g of cooked chickpeas, added to the salad
• Crunchy salad: lettuce, shredded red cabbage, grated carrot, sprouted seeds
• Dipping sauce served separately: 1 teaspoon of soy sauce, wasabi, pickled ginger

With this version the bento comes to 535 kcal, 16.2 g of protein, 14.4 g of fibre, 4.1 g of salt and 157 µg of iodine, which is a clearly better composition than the original on every axis except calories, and those rise because actual food was added. The remaining 4.1 g of salt comes almost entirely from the rice if it was cooked in salted water: cooking it unsalted takes off roughly another 3.2 g.

Method:

1. Rinse the rice until the water runs almost clear. This removes surface starch and prevents the rice from turning uncontrollably sticky.
2. Cook in 1.2 volumes of unsalted water with the lid on, then rest off the heat for 10 minutes without lifting the lid.
3. Pour the vinegar, sugar and salt mixture over the still-hot rice, fold it in with a spatula using cutting motions rather than crushing, and let it cool spread out.
4. Lay the nori sheet on the mat, rough side up. Spread a thin layer of rice with damp hands, leaving 2 cm clear at the top edge.
5. Arrange the filling across the lower third, roll tightly, moisten the free edge to seal, and rest for two minutes before slicing.
6. Slice with a knife moistened between each cut.

If rolling feels like too much, the deconstructed bowl gives exactly the same nutritional result: seasoned rice at the bottom, filling on top, crumbled nori over it. It also travels better in a bag.

Bento 3: vegetable patties and hummus, the most even of the four

This box delivers 469 kcal, 16.8 g of protein, 13.7 g of fibre, 30.9 mg of vitamin C and only 1.3 g of salt, most of it from the hummus. It is the most consistent composition of the set: nothing excessive, nothing missing.

Patties, for four pieces:

• 160 g of grated carrot, 200 g of grated courgette, 70 g of finely chopped onion
• 20 g of oats, 30 g of spelt, wheat or chickpea flour
• 1 egg, or 1 tablespoon of ground flaxseed in 3 tablespoons of water, rested for 10 minutes
• Salt, pepper, paprika, cumin
• 10 g of oil for frying

One patty works out at roughly 118 kcal and 4.4 g of protein. Two patties make up this bento’s share.

The move that decides whether these work: salt the grated courgette, let it drain in a sieve for 15 minutes, then squeeze it by hand. Courgette is over 90 % water, and that water is the number one reason patties fall apart in the pan. Squeezing first also lets you use less flour, so the patty tastes of vegetable rather than of dough.

Hummus, for about 250 g:

• 200 g of cooked, drained chickpeas
• 30 g of tahini
• 1 garlic clove, the juice of half a lemon, 2 tablespoons of olive oil
• Chickpea cooking liquid to adjust

Shop-bought hummus measured in the Swiss database contains 1.1 g of salt per 100 g. Home-made hummus with no added salt sits well below that, and it is an easy lever since the tahini and lemon already carry the flavour. For texture, cold chickpea cooking liquid gives a creamier result than tap water because it holds dissolved starch.

Our guide to batch cooking legumes covers the soaking and cooking times that let you prepare chickpeas ahead for the week.

Bento 4: green lentils and roasted vegetables, the highest in fibre and the only one with no added salt

510 kcal, 19.8 g of protein, 21.6 g of fibre, 5.7 mg of iron at 41 % of the reference value, 137.6 mg of vitamin C at 172 % of the reference value, and zero added salt. The fibre in this box alone accounts for a large share of a desirable daily intake, which also makes it the most filling of the four.

Ingredients for one portion:

• 80 g of green lentils dry weight, giving roughly 190 g cooked
• 90 g of aubergine, 80 g of courgette, 80 g of red pepper, 40 g of red onion
• 25 g of olive oil in total, across the vegetables and the dressing
• Dressing: mustard, balsamic vinegar, pepper, herbs

Method:

1. Rinse the lentils, cover with three times their volume of cold unsalted water, bring to the boil and simmer for 20 to 25 minutes. Salting the water at the start toughens the skins and lengthens the cooking time; add salt or acid at the end, or not at all.
2. Preheat the oven to 200 °C rather than 180 °C. At 180 °C the vegetables release their water and steam; at 200 °C they caramelise. That is the difference between tender vegetables and soggy ones.
3. Cut the vegetables into similar-sized pieces and spread them out on a tray without overlapping. An overloaded tray produces steam.
4. Roast for 25 to 30 minutes, stirring halfway through.
5. Dress cold, just before closing the bento.

Red pepper alone supplies 149 mg of vitamin C per 100 g according to the Swiss database, more than the daily reference value in an 80 g portion. That has a direct consequence for the iron in the lentils. Vitamin C eaten in the same meal improves the absorption of non-haem iron, the plant form, by reducing it to a more absorbable state and by limiting the inhibitory effect of phytates. A review published in Frontiers in Nutrition in 2025 on micronutrient bioavailability confirms this interaction among the dietary factors that genuinely change absorption. The benefit applies to absorption during that meal, not to iron status in general, and the size of the effect varies considerably with the composition of the meal. Our page on plant-based iron absorption separates what has been measured from what circulates as advice.

This bento is therefore the best built of the four for iron: the lentils supply the mineral, the roasted pepper supplies the vitamin C in the same box, and nothing in the composition introduces tea or coffee to hold absorption back.

How much protein a bento actually needs

The question of protein per meal deserves a number rather than a formula. An analysis of the Dutch National Food Consumption Survey 2019-2021, published in Current Developments in Nutrition in 2026 covering 1 747 adults, examined protein quantity and quality meal by meal. The result: only 3 % of all meals simultaneously reached 20 g of protein, a share of at least 60 % plant protein and a protein quality judged optimal. When quality was low, lysine was the most frequent limiting amino acid.

Two practical lessons follow for a bento.

First, the 20 g per meal threshold is a usable benchmark. Across the four bentos on this page, only the quinoa and tofu box clears it comfortably, the lentil box comes close at 19.8 g, the patty box sits at 16.8 g and the maki box at 10.7 g in its original form.

Second, limiting lysine explains why cereals alone do not suffice. Cereals are low in lysine and legumes are rich in it; tofu, lentils and chickpeas supply exactly what rice and quinoa lack. This is not a matter of combining them within the same meal to the minute, since the amino acid pool replenishes across the day, but in a bento that is a complete and isolated meal, having a legume or a soy product in the box remains the most direct way to get both. Our page on essential amino acids explains this mechanism, and the plant protein guide gives the content source by source.

The Swiss dietary recommendations from the FSVO define one portion of protein-rich food as 120 g of tofu, tempeh or plain seitan, or 60 g of legumes dry weight. The 110 g of tofu in bento 1 and the 80 g of dry lentils in bento 4 sit comfortably in that range.

What makes a bento balanced, in practice

The FSVO recommends for adults three portions of vegetables and two of fruit per day, three portions of cereal products or potatoes with at least half of them wholegrain, one daily portion of protein-rich food with legumes at least once a week, a small handful of seeds or nuts, and two tablespoons of vegetable oil including at least one of rapeseed oil.

Translated into a box, that gives a short checklist:

• A legume or soy product: lentils, chickpeas, beans, tofu, tempeh. This is the point bentos miss most often.
• A grain, preferably wholegrain for at least half the day’s portions.
• Two different vegetables, ideally one raw and one cooked. The raw one carries vitamin C, which is more stable than after cooking.
• A source of fat: oil, nuts, seeds, avocado.
• A piece of fruit, eaten separately or packed in.

And above all, one thing that appears in no food pyramid: a seasoning that does not rest entirely on salt. That is where the difference between a 0 g bento and a 5.7 g bento is decided.

The mistakes that come up most often

Salting the cooking water for starches out of habit. This is the most invisible salt source in a bento, because you never see it on the plate. 250 g of rice cooked in salted water is 3.25 g of salt before any seasoning.

Pouring the whole marinade into the box. The marinade exists to flavour the tofu while it rests. The leftover liquid, tipped into the bento, adds its salt without adding taste, since the tofu has already taken up what it could. Reduce it in the pan or discard it.

Treating nori as packaging. Two sheets supply 306 µg of iodine. It is an active ingredient, not a wrapper.

Letting rice cool in the pan. A compact mass of rice stays in the warm zone for hours, which is precisely the growth scenario for B. cereus demonstrated at 40 °C.

Dressing raw vegetables the night before. Dressing softens raw vegetables by osmosis. It travels separately in a small container and goes on at the table.

Assuming light means balanced. The least caloric bento on this page is also the least protein-bearing and the saltiest.

Adapting to different situations

Work with no fridge. An ice pack is mandatory, and acidic or dry compositions are preferable: hummus with crudités, a dressed lentil salad, cold patties. Rice-based preparations are the most demanding on the cold chain. For the hot version, our page on hot thermos lunchboxes covers temperature holding, which follows the opposite rules.

Pregnancy. Iodine requirements rise, but the variability of seaweed makes it a poorly controlled source. Iodised salt and medical advice on supplementation are more reliable than a sheet of nori whose exact content is unknown.

Known thyroid condition. Seaweed deserves a medical conversation before it becomes a habit. The iodine content per sheet varies widely between products and the labelling is often silent on this.

High blood pressure or a low-sodium diet. The lentil bento is the simplest base, because it starts from zero added salt. Reduced-sodium soy sauce, served separately, and acidity as a replacement.

A day with training. The quinoa and tofu bento, with its 30 g of protein and 642 kcal, is the only one of the four calibrated for that without additions.

Children. Portions shrink, but seaweed deserves more limitation than for adults since the iodine reference value is lower. Our page on allergen-free lunchboxes for children covers the allergy case.

Preparing several bentos ahead

The useful principle is not cooking four complete meals on Sunday but preparing components that recombine. One pot of lentils, one tray of roasted vegetables, one block of marinated tofu and a hummus cover four different bentos without repetition, because it is the seasonings that change.

Three real constraints frame this practice:

• Cooked preparations keep for 48 hours in the fridge according to the UK guidance on leftovers, beyond which freezing is better. In concrete terms, the Sunday batch covers Monday and Tuesday, not Thursday.
• Components are stored separately, not assembled. A bento built three days ahead loses its texture and blends its flavours.
• Raw vegetables are cut the same morning. Grated carrot and sliced cucumber oxidise and release water.

Our page on batch cooking for work lunchboxes covers this organisation, and the one on jar salads deals with the format that genuinely holds for several days.

The limits of this page

The nutritional values presented here are calculated, not measured. They combine the generic figures from the Swiss Food Composition Database with the quantities written in the recipes. A specific tofu, nori or hummus can deviate substantially from the average: the iodine content of seaweed varies by a large factor depending on species, origin and batch, and the salt content of shop-bought hummus depends entirely on the brand. Reading the label on the product you bought stays more accurate than any generic calculation, and our page on reading nutrition labels explains how.

The cooked weights, notably the conversion of 80 g of dry quinoa into 240 g cooked and 80 g of dry lentils into 190 g cooked, are usual orders of magnitude and vary with cooking time and draining.

The Norwegian study on seaweed consumers covered 49 people with neither randomisation nor a control group. The Bacillus cereus study relied on artificial inoculation in a laboratory, under conditions that probably overstate the initial contamination compared with a home kitchen. The regulatory thresholds cited belong to Swiss and European food law and govern the labelling of products for sale, not preparations made at home. They serve here as comparison points, not as rules applicable to a lunchbox.

Frequently asked questions

How many sheets of nori per week without exceeding the iodine limit? At 153 µg per 3 g sheet and with a 600 µg daily upper limit set by EFSA, one or two sheets at a meal poses no problem for someone without a thyroid condition. Risk appears with daily seaweed consumption, especially if species richer in iodine than nori enter the diet.

Is cold rice dangerous? No, provided the cooling was fast and the storage cold. The problem is not the cold but the time spent between cooking and refrigeration, plus prolonged stays in the warm zone.

Can makis be made the night before? Yes, if the bento spends the night in the fridge. Nori softens in contact with damp rice; that is a texture flaw, not a safety issue. Rolling in the morning gives a better result.

How do you reach 20 g of protein without tofu? 100 g of cooked chickpeas supply 7.3 g, 190 g of cooked lentils supply 16.7 g. A legume base with seeds and a grain clears the threshold without any soy product.

Does quinoa really contain as much protein as claimed? 13.3 g per 100 g raw according to the Swiss database, 4.4 g per 100 g once cooked. Both figures are correct and describe the same food at two hydration states.

Does a bento have to be eaten cold? Nothing requires it. A bento reheated in the microwave should be heated through in one go, with no repeated reheating.

Should soy sauce be avoided entirely? No. One teaspoon served separately supplies 0.7 g of salt, which is reasonable in a meal. The tablespoon poured over the whole box is the version that creates the problem.

Are sprouted seeds a problem in a bento? They keep less well than whole vegetables and need careful rinsing plus cold transport. In a bento with no ice pack, firm raw vegetables are the better swap.

Sources

• Swiss Food Composition Database, FSVO
• Swiss dietary recommendations for adults, FSVO
• Swiss ordinance on food information (OIDAl), SR 817.022.16
• EFSA, Scientific Opinion on Dietary Reference Values for iodine, 2014
• BfR, health risks from excessive iodine in dried seaweed
• WHO, salt reduction fact sheet
• Food Standards Agency, How to chill, freeze and defrost food safely
• Impact of habitual seaweed consumption on iodine nutrition and thyroid function, European Journal of Nutrition, 2026
• Risk of Bacillus cereus in Relation to Rice and Derivatives, Foods, 2021
• The Germination and Growth of Two Strains of Bacillus cereus in Selected Hot Dishes After Cooking, Foods, 2025
• Differences in Protein Quantity and Quality Across a Spectrum of Plant-Based Meals, Current Developments in Nutrition, 2026
• Micronutrient bioavailability: concepts, influencing factors, and strategies for improvement, Frontiers in Nutrition, 2025