| Course | NS235 Micronutrient Metabolism |
|---|---|
| Unit | Unit 3 |
| Paper type | Bioavailability comparison |
| Length | About 870 words, 6 pages double-spaced |
| Format | APA 7 student paper |
| School | Purdue University Global |
| Program | BS in Nutrition Science |
| Updated | October 2026 |
Free sample paper for NS235 Unit 3
Same Calcium on Paper, Different Calcium in the Body: A Unit 3 Bioavailability Comparison of a Spinach Dish and Yogurt With Kale
[Student Name]
Purdue University Global
NS235: Micronutrient Metabolism
Unit 3 Bioavailability Comparison
[Instructor Name]
[Date]
The two meals are composite with values rounded from standard tables; absorption fractions come from the isotope studies cited, and the estimates are illustrations.
The Two Meals
Meal A: a spinach and white bean skillet. One cup of cooked spinach supplies about 245 milligrams of calcium; half a cup of cooked white beans supplies about 60 milligrams. Total: about 305 milligrams.
Meal B: yogurt with kale. Six ounces of plain low-fat yogurt supplies about 210 milligrams of calcium; one cup of cooked kale supplies about 95 milligrams. Total: about 305 milligrams.
On a food label or in a diet analysis program, the two meals look identical for calcium. The question is how much of each meal's calcium the body actually absorbs.
What Determines Calcium Absorption
Calcium is absorbed in the small intestine by two routes. An active, saturable route, regulated by vitamin D, works mainly in the duodenum and is most important at low and moderate intakes. A passive route, between cells, works along the length of the intestine and increases with the amount of calcium present. Because the active route saturates, the fraction absorbed falls as the calcium load in a single meal rises (Institute of Medicine, 2011).
Food components matter as much as the amount. Oxalate, found in high amounts in spinach, rhubarb and beet greens, binds calcium in the gut, forming insoluble calcium oxalate that is poorly absorbed. Phytate, found in beans, whole grains and seeds, also binds calcium, though less strongly. Foods low in oxalate and phytate, such as kale, broccoli and bok choy, release calcium readily (Weaver et al., 1999).
Absorption Fractions From the Research
Isotope studies have measured how much calcium is absorbed from specific foods. In a crossover study using labeled calcium, absorption from spinach was a small fraction of absorption from milk, consistent with spinach's high oxalate content (Heaney et al., 1988). In a similar study, absorption from kale averaged about 41 percent, compared with about 32 percent from milk in the same women (Heaney & Weaver, 1990). Reviews of plant sources of calcium place spinach near 5 percent absorbed, beans near 17 percent, dairy near 32 percent and low-oxalate greens such as kale around 40 percent or more (Weaver et al., 1999).
Estimating Meal A
1. Spinach: 245 milligrams times about 0.05 equals about 12 milligrams absorbed.
2. White beans: 60 milligrams times about 0.17 equals about 10 milligrams absorbed.
3. Meal A total: about 22 milligrams absorbed from 305 milligrams eaten, about 7 percent.
Estimating Meal B
1. Yogurt: 210 milligrams times about 0.32 equals about 67 milligrams absorbed.
2. Kale: 95 milligrams times about 0.41 equals about 39 milligrams absorbed.
3. Meal B total: about 106 milligrams absorbed from 305 milligrams eaten, about 35 percent.
On paper the two meals supply identical calcium, but the yogurt and kale meal delivers roughly five times as much to the body, because spinach's oxalate locks most of its calcium away while kale and dairy release theirs.
The Saturable Route
Both estimates assume each meal's calcium is absorbed as if eaten alone. If a person ate both meals at once, about 610 milligrams in one sitting, the active route would be more saturated and the fraction absorbed would fall. Spreading calcium-rich foods across meals generally improves total absorption, which is why many supplements are advised in doses of 500 milligrams or less at a time (Institute of Medicine, 2011).
Does Spinach Interfere With Other Foods?
A common question is whether spinach's oxalate binds calcium from other foods eaten at the same meal. Spinach contains more oxalate than it needs to bind its own calcium, so some excess oxalate could bind calcium from other foods in the gut, though the size of this effect in mixed meals is modest. The safer conclusion is that spinach should not be counted as a calcium source, not that it must be avoided.
How Vitamin D Changes the Picture
The active route for calcium absorption depends on vitamin D. Without enough vitamin D, the intestine makes less of the transport proteins that carry calcium into cells, and the fraction absorbed falls for any food. A person with low vitamin D status would therefore absorb less from both meals. This is one reason calcium and vitamin D recommendations are set together.
Limits of the Estimates
The absorption fractions come from isotope studies in small groups of healthy adults, often with single foods. Real meals combine foods, and individual absorption varies with age, vitamin D status and habitual intake. The estimates are therefore illustrations of direction and size, not precise predictions for any person.
Practical Meaning
For someone relying on plant foods for calcium, the choice of greens matters greatly. Kale, bok choy, broccoli and collards are good calcium sources; spinach, despite its high label value, is not. Calcium-set tofu and fortified plant milks can also contribute substantially (Weaver et al., 1999). Diet analysis programs that report calcium content without absorption can mislead anyone who eats a lot of spinach.
References
Heaney, R. P., & Weaver, C. M. (1990). Calcium absorption from kale. The American Journal of Clinical Nutrition, 51(4), 656-657. https://doi.org/10.1093/ajcn/51.4.656
Heaney, R. P., Weaver, C. M., & Recker, R. R. (1988). Calcium absorbability from spinach. The American Journal of Clinical Nutrition, 47(4), 707-709. https://doi.org/10.1093/ajcn/47.4.707
Institute of Medicine. (2011). Dietary reference intakes for calcium and vitamin D. National Academies Press. https://doi.org/10.17226/13050
Weaver, C. M., Proulx, W. R., & Heaney, R. (1999). Choices for achieving adequate dietary calcium with a vegetarian diet. The American Journal of Clinical Nutrition, 70(3, Suppl.), 543S-548S. https://doi.org/10.1093/ajcn/70.3.543s
What the NS235 Unit 3 assignment asks for
The bioavailability unit asks students to compare how much of a nutrient two foods or meals actually deliver. Prompts usually provide or invite meals with similar nutrient content and expect an explanation of absorption, the factors that enhance or inhibit it and calculated estimates of absorbed amounts. Choose meals that differ in a known inhibitor or enhancer. Explain the absorption routes, including any that saturate. Take absorption fractions from published isotope studies, cited, rather than guessing. Multiply each component's content by its fraction and total each meal. Discuss factors the estimates do not capture, such as vitamin D status or mixing meals. Draw a practical conclusion. Three to four pages is common.
How this NS235 Unit 3 example is built
The two meals are set out with their calcium content. A section explains active and passive absorption and how oxalate and phytate bind calcium. Absorption fractions are drawn from a spinach study, a kale study and a review of plant sources. Each meal is estimated line by line, and the highlighted sentence states that the second meal delivers about five times as much. Sections explain saturation when both meals are eaten together, whether spinach affects other foods and how vitamin D status changes absorption. Limits of the estimates and practical meaning for plant-based eaters close the comparison. Every estimate shows the milligrams eaten, the fraction and the milligrams absorbed.
NS235 Unit 3 rubric: what earns full points
NS235 bioavailability rubrics generally reward correct explanation of absorption and its modifiers, accurate calculation of absorbed amounts and appropriate use of published absorption data. Points go to identifying the specific inhibitor or enhancer that drives the difference. Showing the arithmetic for each component is scored under accuracy. Discussing saturation, vitamin D and the limits of single-food studies earns credit for critical thinking. A practical conclusion counts under application. Cited isotope studies and a tidy layout finish the scoring. Comparisons that assert one meal is better without numbers, or use invented absorption fractions, usually lose points. Naming the specific inhibitor behind each difference is often decisive. Showing the arithmetic for each absorbed amount lets a grader confirm every figure in seconds.
NS235 Unit 3 help: mistakes that cost points
Bioavailability comparisons often stop at saying spinach contains oxalate, without estimating how much calcium is lost. Another weakness is using absorption fractions without sources, or applying one fraction to all foods. Students sometimes forget that absorption falls as the calcium load rises. Vitamin D's role is frequently omitted. Conclusions can overstate, implying spinach should be avoided. If you have two meals and their nutrient totals, find published absorption figures for each food first, and a writer can help you set out the estimate line by line. Spreading calcium across meals, rather than one large dose, is a point many comparisons miss.
Get an NS235 Unit 3 example written to your instructions
Share the two meals your Unit 3 prompt supplies, or the mineral and foods you would compare where it leaves that open, together with the rubric. The comparison comes back with absorbed amounts worked row by row and every figure sourced, inside 24-48h, and a first comparison costs nothing, however the meals are built. The paper above is an original model document written by our desk, not a submitted student paper and not an official Purdue University Global document.
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NS235 Unit 3 questions, answered
Where do fractional absorption figures come from?
Mostly from isotope studies, in which calcium in a test food is labeled and its appearance in blood or urine is measured. Published reviews collect these figures by food. Cite the study or review directly, note the population it measured, and treat each value as an estimate. Figures without a source are among the most common reasons these comparisons lose accuracy credit.
Does the comparison need to calculate absorbed milligrams?
In most sections, yes. Multiply each component's listed calcium by its estimated fractional absorption, show the working in the table, and total each meal. The absorbed figure is what makes the comparison meaningful. Round consistently and say how, because a grader will usually recheck at least one row against the figures you cited.
Can I compare a different mineral?
If the prompt allows, yes. Iron and zinc both compare well across meals, each with its own inhibitors and enhancers, phytate among them. Choose a mineral where published absorption data exist for the foods you pick, so the estimate rests on evidence. Send the prompt with the mineral and meals you have in mind, and the comparison is built on those.
Where can I find a free NS235 Unit 3 sample paper?
This page holds a complete Unit 3 bioavailability comparison of calcium from a spinach dish and from yogurt with kale, with estimates, margin notes and APA references.
Why is calcium from spinach poorly absorbed?
Spinach is high in oxalate, which binds calcium in the gut into calcium oxalate, a form that is poorly absorbed. Isotope studies found only a small fraction of spinach calcium absorbed compared with milk.