| Course | NS230 Macronutrient Metabolism |
|---|---|
| Unit | Unit 9 |
| Paper type | Fed and fasted comparison |
| Length | About 1,110 words, 7 pages double-spaced |
| Format | APA 7 student paper |
| School | Purdue University Global |
| Program | BS in Nutrition Science |
| Updated | October 2026 |
Free sample paper for NS230 Unit 9
Two Hours After a Meal, Twenty-Four Hours Into a Fast: A Unit 9 Fed and Fasted Comparison, Tissue by Tissue
[Student Name]
Purdue University Global
NS230: Macronutrient Metabolism
Unit 9 Fed and Fasted Comparison
[Instructor Name]
[Date]
The comparison describes typical adult physiology from the sources cited; values are approximate.
The Two Moments
Moment A: two hours after a mixed meal of about 700 kilocalories, with carbohydrate, protein and fat. Blood glucose is near its post-meal peak or just past it. Insulin is high; glucagon is low.
Moment B: twenty-four hours after the last meal, with only water since. Blood glucose is in the low-normal range. Insulin is low; glucagon is high. Liver glycogen is largely depleted.
Hormonal Setting
Moment A. Insulin dominates. It promotes uptake and storage of glucose, fat synthesis and protein synthesis, and it suppresses fat release from adipose tissue and glucose output from the liver.
Moment B. Glucagon dominates in the liver, with low insulin removing the brakes on fat release and glucose production. Cortisol and, during any activity, epinephrine support fuel mobilization (Cahill, 2006).
Liver
Moment A. The liver takes up glucose from the portal vein and stores it as glycogen through glycogen synthase. It runs glycolysis, and some glucose carbon goes to fatty acid synthesis. Gluconeogenesis is suppressed. Amino acids are used for protein synthesis, and surplus amino acid nitrogen goes to urea. Fat made in the liver is exported in very low density lipoproteins.
Moment B. The liver releases glucose. Glycogen breakdown, which supplied much glucose overnight, has largely run its course, and gluconeogenesis now supplies most of the glucose the liver releases. Measurements in fasting humans found gluconeogenesis accounted for most glucose production within the first day of fasting (Rothman et al., 1991). The liver oxidizes fatty acids arriving from adipose tissue to power gluconeogenesis and begins to make ketone bodies from the surplus acetyl-CoA.
Skeletal Muscle
Moment A. Muscle takes up glucose through insulin-stimulated transporters and stores it as glycogen. It takes up amino acids and builds protein. It uses glucose as a major fuel at rest.
Moment B. Muscle relies mainly on fatty acids for fuel at rest, sparing glucose for the brain. It breaks down some protein, releasing amino acids, especially alanine and glutamine, which travel to the liver and kidney for gluconeogenesis (Felig, 1973). Muscle keeps its glycogen for its own use, since it cannot release free glucose.
Adipose Tissue
Moment A. Adipose tissue takes up fatty acids from chylomicrons through lipoprotein lipase, which insulin activates, and stores them as triglyceride. Insulin strongly suppresses lipolysis.
Moment B. With insulin low, lipolysis is active. Adipose tissue releases fatty acids and glycerol into the blood. Fatty acids fuel muscle and the liver; glycerol goes to the liver for gluconeogenesis.
Brain
Moment A. The brain uses glucose, about 120 grams a day, supplied abundantly from the meal.
Moment B. The brain still uses glucose almost entirely, supplied by liver gluconeogenesis. Ketone bodies are beginning to rise but supply only a small share of the brain's energy this early; their contribution grows over several days of fasting (Cahill, 2006).
Red Blood Cells
Moment A. Red blood cells use glucose by glycolysis, producing lactate.
Moment B. The same; they have no alternative. The lactate they produce returns to the liver for gluconeogenesis, so their glucose use costs the body little net glucose.
At Moment A every tissue is building, with insulin telling liver, muscle and fat to store what the meal supplied, while at Moment B the same tissues are releasing, with the liver making glucose from muscle amino acids and fat-derived glycerol so that the brain, which cannot yet run on much else, is still fed.
Heart and Other Tissues
Moment A. The heart uses a mix of fatty acids and glucose, with glucose's share higher after a meal when insulin is high.
Moment B. The heart relies mainly on fatty acids and begins to use some ketone bodies. Like skeletal muscle, it spares glucose for the tissues that depend on it.
The Transition Between the Two
The body does not jump from Moment A to Moment B. Over the hours after the meal, insulin falls gradually and glucagon rises. Liver glycogen storage slows and then reverses into breakdown, usually within four to six hours of eating. Overnight, glycogen breakdown and gluconeogenesis share the work. By the next afternoon, glycogen is largely spent and gluconeogenesis dominates. The two moments in this comparison are snapshots of a continuous shift.
Fuel Flows Summarized
1. Glucose: Moment A, into liver, muscle and adipose storage; Moment B, out of the liver, made mostly from lactate, glycerol and amino acids.
2. Fatty acids: Moment A, into adipose storage; Moment B, out of adipose tissue to muscle and liver.
3. Amino acids: Moment A, into protein; Moment B, out of muscle protein to the liver for glucose.
4. Ketone bodies: Moment A, negligible; Moment B, rising, a small but growing fuel.
Kidney and Intestine
Moment A. The kidney filters glucose and reabsorbs it almost completely. The intestine absorbs the meal's nutrients and uses some glutamine as fuel.
Moment B. The kidney begins to contribute to glucose production through gluconeogenesis, a role that grows with longer fasting, and it uses glutamine's nitrogen in handling acid. The intestine, with no food arriving, relies on glutamine and other fuels from the blood.
Why Keeping the States Separate Matters
Writing about both states in the same paragraph invites errors, such as saying the liver both stores and releases glucose without saying when. Keeping the states in facing sections forces each statement to belong to one time point, and it makes the reversal clear. The underlying regulation, insulin promoting storage and glucagon promoting release through phosphorylation of key enzymes, is the same in both columns; what differs is which signal dominates (Petersen et al., 2017).
A Common Confusion
A frequent error is to describe the fasted liver as breaking down glycogen to supply glucose. That was true overnight, but by twenty-four hours liver glycogen is largely exhausted, and the glucose the liver releases comes mostly from gluconeogenesis. Another is to say the fasted brain runs on ketones. At twenty-four hours, ketones supply only a small share of the brain's energy; the large shift comes days later. Keeping the time points precise prevents both errors.
What Happens Beyond Twenty-Four Hours
If the fast continues, the liver's output of ketone bodies rises substantially, and over several days the brain shifts to using ketones for a large share of its energy. That shift reduces the need for gluconeogenesis from amino acids, sparing muscle protein, one of the most important adaptations to prolonged fasting (Cahill, 2006).
References
Cahill, G. F., Jr. (2006). Fuel metabolism in starvation. Annual Review of Nutrition, 26, 1-22. https://doi.org/10.1146/annurev.nutr.26.061505.111258
Felig, P. (1973). The glucose-alanine cycle. Metabolism, 22(2), 179-207. https://doi.org/10.1016/0026-0495(73)90269-2
Petersen, M. C., Vatner, D. F., & Shulman, G. I. (2017). Regulation of hepatic glucose metabolism in health and disease. Nature Reviews Endocrinology, 13(10), 572-587. https://doi.org/10.1038/nrendo.2017.80
Rothman, D. L., Magnusson, I., Katz, L. D., Shulman, R. G., & Shulman, G. I. (1991). Quantitation of hepatic glycogenolysis and gluconeogenesis in fasting humans with 13C NMR. Science, 254(5031), 573-576. https://doi.org/10.1126/science.1948033
NS230 Unit 9 instructions, in plain terms
The comparison unit asks students to contrast metabolism in the fed and fasted states. Prompts usually expect the hormonal setting and the activity of each major tissue in both states, often with fuel flows between them. Define the two time points precisely. Write each tissue's section in two parts, one per state, so that no sentence describes both. Include the liver, muscle, adipose tissue and brain at minimum, and add other tissues where they matter. Explain the dominant hormones and how they act. Note how the body transitions between states. Correct common confusions about timing, such as when liver glycogen runs out. Draw on reviews of fasting physiology; most comparisons fill about four or five pages. Give approximate times for each shift.
How the NS 230 Unit 9 example is put together
The comparison defines the two moments and their hormonal settings. Facing sections follow for the liver, muscle, adipose tissue, brain and red blood cells, each with a Moment A and a Moment B, and the liver section cites fasting measurements showing gluconeogenesis dominating. The highlighted sentence captures the reversal. Sections add the kidney, intestine and heart. A four-line summary of fuel flows follows. A section describes the hours between the two moments, another explains why keeping the states separate matters, a section corrects two common confusions and the comparison ends with the shift to ketones over several days. No sentence in the comparison describes both moments at once.
NS230 Unit 9 rubric: what earns full points
NS230 fed and fasted comparisons are usually scored on accuracy for each tissue in each state and on clarity of contrast. Points go to correct hormonal settings, correct fuel use by tissue and accurate timing, such as the role of gluconeogenesis at twenty-four hours. Keeping the states separate in the writing is often explicitly assessed. Including tissues beyond the core three earns credit for completeness. Explaining the transition and correcting common errors shows depth. Cited sources and clear organization complete the rubric. Comparisons that say the fasted brain runs mostly on ketones at one day, or that blend the two states in single sentences, generally lose points.
Common NS230 Unit 9 mistakes, and how to avoid them
Fed and fasted comparisons often mix states in the same sentence, such as saying the liver stores and releases glucose, without saying when. Another frequent error is placing the brain's shift to ketones at one day rather than several. Students sometimes describe liver glycogen as the main glucose source at twenty-four hours, when it is largely gone. Red blood cells and the kidney are often forgotten. The hours between meals and fasting are rarely discussed. If you are drafting the comparison, set up two columns for each tissue before writing anything, and our writers can help you fill each column without letting one state drift into the other.
Get an NS230 Unit 9 example written to your instructions
Tell us the two time points your Unit 9 prompt sets, or whether it leaves the choice open, and add the rubric. The comparison is written in facing columns for those moments, tissue by tissue, with the hormonal row in place, and arrives in 24-48h. Nothing is owed for the first one. 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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NS230 Unit 9 questions, answered
Why compare at twenty-four hours rather than overnight?
Either works if your prompt allows it, but a day without food makes the contrast sharper. By then liver glycogen is largely used, gluconeogenesis carries most of the glucose supply and ketone production has started to rise. An overnight fast sits between states, which makes a clean two-column comparison harder. Whatever point you choose, state it and keep every cell consistent with it.
Does the brain really need glucose during a fast?
In the first day, yes, almost entirely, because fatty acids do not cross into brain tissue in useful amounts. Over several days the brain takes a growing share of its energy from ketone bodies made by the liver, which lowers the demand for glucose and spares muscle protein. Keep that later shift in a separate section so it does not blur your one-day column.
Should the comparison include exercise?
Not unless the prompt asks. Exercise adds a third set of signals, epinephrine and local muscle signals, on top of either state, and folding it into a fed-fasted comparison makes both columns harder to read. If your prompt does include it, give it its own row or a separate short section, clearly labeled, rather than mixing it into the tissue cells.
Where can I find a free NS230 Unit 9 sample paper?
This page holds a complete Unit 9 fed and fasted comparison, tissue by tissue at two hours after a meal and twenty-four hours into a fast, with APA references.
Where does blood glucose come from after twenty-four hours without food?
Mostly from gluconeogenesis in the liver, using lactate, glycerol and amino acids, since liver glycogen is largely depleted by then. The kidney begins to contribute as fasting continues.