How Your Body Absorbs Nutrients: Bioavailability Explained

Nutrient absorption from food is a more complicated story than most labels let on. The scientific term is bioavailability: how much of a nutrient actually gets absorbed and becomes available for the body to use, out of the total amount you consumed. It is not the same as how much is on the label. A number on a nutrition panel tells you what went in. Bioavailability is about what makes it through digestion and into circulation, and research shows that number moves around depending on the food, the person, and the dose.

This article lays out what the research on bioavailability actually shows, and just as importantly, what it does not show. We are not going to claim a percentage for our own product, because we have not measured one. We think that honesty is worth more than a marketing number.

What bioavailability actually means

Researchers generally separate two ideas. Bioaccessibility is the portion of a nutrient that gets released from food during digestion and becomes available for absorption. Bioavailability is the portion that is actually absorbed and used by the body. A nutrient can be present in a food and still be poorly bioaccessible, for example if it is physically locked inside plant cell walls, or poorly bioavailable, for example if it is bound to a compound that blocks its uptake (Bioavailability of Micronutrients From Nutrient-Dense Whole Foods, PMC, 2020).

This is a field of study, not a fixed constant. Bioavailability studies measure averages across groups of people under controlled conditions. Individual results vary by digestion, gut microbiome, age, and overall diet. Any single number you see quoted is a study result, not a guarantee for any one person.

Why food form changes the outcome

The structure a nutrient sits inside matters. Researchers call this the food matrix: the physical and chemical scaffolding of a whole food that surrounds its nutrients and affects how easily they are released during digestion (Overview: the food matrix and its role in the diet, Critical Reviews in Food Science and Nutrition, 2025). Isolating a nutrient and putting it in a capsule removes that scaffolding entirely. That is a structural difference worth naming plainly: a capsule has to break down and release an isolated compound before absorption can even begin, while a whole food, or a puree made from one, arrives at digestion already in food form, with its natural matrix intact. Naming that structural difference is not the same as claiming what happens next inside any specific body, and we are not making that claim.

Food form cuts both ways, though, and the honest picture is not simple. One frequently cited comparison found carotenoids were absorbed roughly five times more efficiently when dissolved in oil alone than when left inside the dense matrix of a raw carrot (see review discussion in PMC, 2020). Cooking and processing can also change bioaccessibility, sometimes for the better. The lesson from the literature is not "whole food always wins." It is that form matters, results vary by nutrient and by food, and nobody should be handed an oversimplified rule.

Fat-soluble versus water-soluble nutrients

Nutrients split broadly into two absorption categories, and they behave differently.

Fat-soluble nutrients, including carotenoids (the pigments behind orange and red plant color) and vitamin E, are absorbed along with dietary fat. During digestion they are packaged into micelles, tiny fat-carrying particles, and taken up by the intestine that way. Multiple controlled studies in the American Journal of Clinical Nutrition have found that adding fat improves carotenoid uptake, and that low-fat or fat-free versions of the same meal absorb these nutrients less well (Carotenoid bioavailability is higher from salads ingested with full-fat than with fat-reduced salad dressings, American Journal of Clinical Nutrition; Effects of dietary fat type and emulsification on carotenoid absorption: a randomized crossover trial, American Journal of Clinical Nutrition, 2023). A whole fruit puree naturally carries its own fat content alongside its carotenoids and vitamin E, which is a structural feature worth noting. We are not claiming a measured absorption outcome for our product from this; we are describing what the published research says about fat and fat-soluble nutrients generally.

Water-soluble nutrients, like vitamin C, dissolve in water rather than fat and are absorbed through a different route in the gut lining, largely independent of dietary fat.

Absorption is often saturable, using vitamin C as the example

One of the clearest illustrations in the bioavailability literature is vitamin C, thanks to a classic body of pharmacokinetic work by Levine and colleagues. Their controlled dosing studies in healthy volunteers found that vitamin C absorption follows a saturable, sigmoid curve rather than a straight line. Absorption was essentially complete at a 200 mg single dose. At single doses of 500 mg and above, the absorbed percentage declined and the extra amount was simply excreted by the kidneys rather than retained (Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance, PNAS, 1996; see also the review in The Pharmacokinetics of Vitamin C, PMC).

In plain terms: more is not simply more. Both gut absorption and kidney reabsorption of vitamin C are saturable processes, meaning the body has a ceiling on how much it takes up and holds onto at once, and megadosing past that ceiling mostly produces expensive urine, not proportionally higher vitamin C status. This is the kind of nuance a simple percentage claim tends to erase.

What bioavailability research can and cannot tell you

Bioavailability studies have real limits worth naming honestly. They typically measure a narrow window, blood plasma levels after a single dose or a short feeding period, not long-term nutritional status. Results are reported as group averages, and individual variation can be large. Most studies test one nutrient in isolation under lab conditions, which does not necessarily reflect a full, mixed diet. A study finding higher blood levels of a nutrient does not, on its own, establish what that means for any one person's health outcome over time.

We think the field deserves that kind of plain description rather than a simplified marketing pitch. Human Renaissance sea buckthorn puree is made with no liposomes and no proprietary absorption blend. We have not run an absorption study on our product, so we do not claim an absorption percentage for it, measured or estimated. What we can tell you is what is actually on the label: 190+ bioactive compounds naturally occurring in the berry, the full omega 3-6-7-9 profile, 201 mg of vitamin C per serving (223% NRV), and 0 g of sugar. The research base behind sea buckthorn and its individual compounds now runs past 1,200 published studies. You can review the label detail on our What's Inside page and the research we draw on at Research.

Frequently asked questions

What does bioavailability mean in simple terms?

Bioavailability is the portion of a nutrient you consume that actually gets absorbed and becomes available for the body to use. It is different from the total amount listed on a label, because digestion, food form, and individual differences all affect how much makes it through.

Does whole food always absorb better than a supplement pill?

Not universally, and research results vary by nutrient. Some studies find whole-food forms absorb better; others, like the carrot versus oil carotenoid comparison, find the opposite for a specific nutrient. What is consistent across the literature is that food form, fat content, and co-occurring compounds all influence the outcome, and a blanket rule in either direction oversimplifies real findings.

Why does fat matter for absorbing some nutrients?

Fat-soluble nutrients such as carotenoids and vitamin E are absorbed through the same digestive pathway as dietary fat, packaged into fat-carrying particles called micelles in the gut. Published trials in the American Journal of Clinical Nutrition have repeatedly found that meals with more fat improve uptake of these nutrients compared to fat-reduced versions of the same meal.

Is it true that taking more vitamin C doesn't help once you hit a certain dose?

Classic pharmacokinetic research on vitamin C found that absorption is a saturable process. Absorption efficiency is high at doses around 200 mg, and declines at single doses of 500 mg or more, with the surplus excreted by the kidneys rather than retained. This is a well-documented finding in the dosing literature, not a claim about any specific product.

Does Human Renaissance claim its puree absorbs better than a supplement?

No. We do not state an absorption percentage for our product because we have not measured one. We can tell you what is structurally true, that our puree is a whole-food product with no liposomes or proprietary absorption blends, and we can point you to the general research on bioavailability. What we will not do is attach an invented number to make the story sound more definitive than the evidence allows.

Related reading

• Whole food versus isolated nutrients
• What is omega-7
• Sea buckthorn versus fish oil
• Why we talk about longevity research

You can see the full compound and label breakdown on our sea buckthorn puree product page.

References

• Levine M, et al. Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. PNAS, 1996.
• Padayatty SJ, Levine M. The Pharmacokinetics of Vitamin C. PMC.
• Brown MJ, et al. Carotenoid bioavailability is higher from salads ingested with full-fat than with fat-reduced salad dressings. American Journal of Clinical Nutrition.
• Effects of dietary fat type and emulsification on carotenoid absorption: a randomized crossover trial. American Journal of Clinical Nutrition, 2023.
• Bioavailability of Micronutrients From Nutrient-Dense Whole Foods: Zooming in on Dairy, Vegetables, and Fruits. PMC, 2020.
• Overview: the food matrix and its role in the diet. Critical Reviews in Food Science and Nutrition, 2025.