NS105 Unit 5 Fat and Protein Comparison Example

Two Energy Sources, Different Jobs: A Unit 5 Fat and Protein Comparison

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Purdue University Global

NS105: Fundamentals of Nutrition

Unit 5 Fat and Protein Comparison

[Instructor Name]

[Date]

Food examples use typical values rounded from standard tables; the reference intakes, fat advisory and guidelines cited are real.

Structure in Brief

Dietary fats are mostly triglycerides: three fatty acids attached to a glycerol backbone. Fatty acids differ in chain length and in the number of double bonds: saturated fatty acids have none, monounsaturated one and polyunsaturated two or more. Two polyunsaturated fatty acids, linoleic acid, an omega-6, and alpha-linolenic acid, an omega-3, are essential because the body cannot make them (Institute of Medicine, 2005).

Proteins are chains of amino acids. Of the twenty amino acids in human proteins, nine are essential and must come from food. A protein's quality depends on whether it supplies all nine in useful proportions and how well it is digested.

Dimension 1: The Work Each Does

Fat. Fat is the body's most concentrated energy store, supplying 9 kilocalories per gram. Stored body fat cushions organs and insulates. Dietary fat carries the four vitamins that dissolve in fat and helps the body absorb them. Fatty acids form part of every cell membrane, and the essential fatty acids are precursors of signaling compounds involved in inflammation, blood clotting and blood pressure.

Protein. Protein supplies 4 kilocalories per gram, but energy is not its main job. Proteins build and maintain muscle, skin, bone matrix and organs. Enzymes, the catalysts behind most of the body's chemistry, are proteins, as are several hormones, antibodies and transport molecules such as hemoglobin. The body has no protein store comparable to fat; amino acids beyond immediate needs are broken down, and their nitrogen is excreted.

Fat's chief work is to store and supply energy and to carry what dissolves in it, while protein's chief work is to build and run the body, so that burning protein for energy is a fallback and burning fat is the plan.

Dimension 2: What Happens When Intake Runs Short

Fat. A diet very low in fat can fail to supply the essential fatty acids, leading over time to scaly skin, poor wound healing and, in children, poor growth. Absorption of fat-soluble vitamins can also fall. True essential fatty acid deficiency is rare in people eating varied diets, since only small amounts are needed.

Protein. When protein intake is too low, the body breaks down its own proteins, starting with muscle, to supply amino acids for essential functions. Prolonged shortfall leads to muscle wasting, weakened immunity, poor wound healing and, in severe cases among children, the swelling and growth failure of kwashiorkor. When total energy intake is also too low, the body uses protein for energy, which worsens the shortfall.

Dimension 3: Which Foods Carry Each

Fat. Oils, butter, nuts, seeds, avocados, fatty fish, meat, cheese and whole milk carry most dietary fat. The type differs: olive and canola oils are mostly monounsaturated; soybean, corn and sunflower oils mostly polyunsaturated; butter, coconut oil and fatty meat mostly saturated; salmon and sardines supply omega-3 fatty acids.

Protein. Meat, poultry, fish, eggs and dairy supply protein with all essential amino acids. Beans, lentils, soy, nuts, seeds and grains supply protein as well; most plant proteins are lower in one or more essential amino acids, but eating a variety across the day supplies all of them.

Example comparison. A tablespoon of olive oil supplies about 14 grams of fat and no protein. A three-ounce piece of salmon brings roughly 22 grams of protein with a few grams of fat, much of it omega-3. A cup of black beans supplies about 15 grams of protein, less than 1 gram of fat and 15 grams of fiber.

Dimension 4: How the Published Figures Differ in Form

The two nutrients' intake figures are expressed in different ways, and the difference is instructive.

Protein's allowance for adults is expressed as grams per kilogram, set at 0.8, about 56 grams for a 70-kilogram person. It is set per kilogram because protein needs scale with the body's size. Protein may also supply anywhere from a tenth to about a third of daily energy under its acceptable range (Institute of Medicine, 2005).

Fat has no Recommended Dietary Allowance in grams for adults, because there is no single amount the body requires beyond the small amounts of essential fatty acids. Instead it has an Acceptable Macronutrient Distribution Range of 20 to 35 percent of energy and Adequate Intakes for linoleic and alpha-linolenic acids. The Dietary Guidelines recommend limiting saturated fat to less than 10 percent of energy (U.S. Department of Agriculture & U.S. Department of Health and Human Services, 2020). The American Heart Association's advisory found heart risk falling when polyunsaturated fat takes saturated fat's place in the diet, but not when refined carbohydrate does (Sacks et al., 2017).

So protein's figure tells a person how much to eat; fat's figures tell a person how much of their energy fat may supply and which kinds to favor.

A Day in Practice

A typical adult eating 2,000 kilocalories might get about 30 percent of energy from fat, roughly 67 grams, and about 15 percent from protein, roughly 75 grams. The fat might come from cooking oil, a handful of nuts, cheese and the fat in meat; the protein from eggs at breakfast, chicken at lunch, beans at dinner and milk throughout the day. Both figures fall within their ranges, and the protein comfortably exceeds the allowance for most adults. What a day like this reveals is that protein targets are easy for most Americans to meet, while the type of fat, not its amount, is where most diets could improve.

Side-by-Side Summary

1. Energy: fat 9 kilocalories per gram; protein 4.

2. Main job: fat stores energy and carries fat-soluble vitamins; protein builds and runs the body.

3. Storage: fat stored in large amounts; protein not stored as such.

4. Shortfall: fat, rare essential fatty acid deficiency; protein, muscle loss and impaired function.

5. Reference form: fat, a range of energy share plus limits on saturated fat; protein, grams per kilogram plus a range.

Conclusion

Fat and protein both supply energy, but their functions, their behavior when intake falls short and the way their recommended intakes are expressed reflect fundamentally different roles. Fat is the body's energy reserve and carrier; protein is its building material and machinery. A diet that supplies enough protein at about 0.8 grams per kilogram and draws fat mostly from unsaturated sources meets both sets of figures.

References

Institute of Medicine. (2005). Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids. National Academies Press. https://doi.org/10.17226/10490

Sacks, F. M., Lichtenstein, A. H., Wu, J. H. Y., Appel, L. J., Creager, M. A., Kris-Etherton, P. M., Miller, M., Rimm, E. B., Rudel, L. L., Robinson, J. G., Stone, N. J., & Van Horn, L. V. (2017). Dietary fats and cardiovascular disease: A presidential advisory from the American Heart Association. Circulation, 136(3), e1-e23. https://doi.org/10.1161/CIR.0000000000000510

U.S. Department of Agriculture & U.S. Department of Health and Human Services. (2020). Dietary guidelines for Americans, 2020-2025 (9th ed.). https://www.dietaryguidelines.gov