NS105 Unit 4 Carbohydrate Profile Example

Both End as Glucose, So the Difference Has to Be Argued: A Unit 4 Carbohydrate Profile of Sugars, Starches and Fiber

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Purdue University Global

NS105: Fundamentals of Nutrition

Unit 4 Carbohydrate Profile

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[Date]

The food examples are typical values rounded from standard tables; the reference intakes, guidelines and fiber review cited are real.

What Carbohydrates Are

Carbohydrates are compounds of carbon, hydrogen and oxygen built from sugar units. They are grouped by size. Simple carbohydrates include monosaccharides, single sugar units such as glucose, fructose and galactose, and disaccharides, pairs such as sucrose, lactose and maltose. Complex carbohydrates include starches, long chains of glucose that plants store for energy, and fibers, plant carbohydrates that human enzymes cannot break down (Institute of Medicine, 2005).

What Carbohydrates Supply

Digestible carbohydrates supply about 4 kilocalories per gram, and glucose is the preferred fuel of the brain and red blood cells. The Recommended Dietary Allowance for carbohydrate, 130 grams a day for adults, is set from the brain's average glucose use, not from the amount most people eat or should eat. The Acceptable Macronutrient Distribution Range allows carbohydrate to supply 45 to 65 percent of daily energy (Institute of Medicine, 2005). Fiber supplies little energy but has its own functions, discussed below.

Sugars

Sugars arrive in the blood quickly, since they need little or no digestion before absorption. Glucose is absorbed directly; sucrose is split into glucose and fructose; lactose is split into glucose and galactose if lactase is present.

The distinction that matters most is not between kinds of sugar but between sugars that occur naturally in foods and sugars added during processing or preparation. Naturally occurring sugars in fruit and milk come packaged with water, fiber, vitamins, minerals and, in milk, protein. Added sugars, such as table sugar, honey, syrups and fruit juice concentrates used as sweeteners, supply energy with few other nutrients. The Dietary Guidelines recommend limiting added sugars to less than 10 percent of daily energy, about 50 grams in a 2,000-kilocalorie diet, and the Nutrition Facts label now lists added sugars separately (U.S. Department of Agriculture & U.S. Department of Health and Human Services, 2020).

Example. A medium apple contains about 19 grams of sugar, naturally occurring, with about 4 grams of fiber and roughly 95 kilocalories. A 12-ounce cola contains about 39 grams of added sugar, no fiber and about 140 kilocalories. Both supply sugar; only one supplies anything else.

Starches

Starches arrive more slowly than sugars, because amylase must break their chains before glucose can be absorbed. How slowly depends on the food. Starch in cooked white rice or white bread is broken down quickly. Starch in whole grains, beans and lentils is digested more slowly, partly because it is enclosed in plant cell walls and accompanied by fiber. Some starch, called resistant starch, escapes digestion entirely and behaves like fiber in the colon.

Example. A cup of cooked white rice supplies about 45 grams of carbohydrate with less than 1 gram of fiber. A cup of cooked lentils supplies about 40 grams of carbohydrate with about 16 grams of fiber and 18 grams of protein.

Fiber

Fiber is the carbohydrate the body cannot digest, and that is precisely its value. Soluble fibers, such as those in oats, beans and apples, form gels that slow digestion and can lower blood cholesterol. Insoluble fibers, such as those in wheat bran and vegetable skins, add bulk and speed the passage of material through the colon. Bacteria in the colon ferment much fiber, producing compounds that nourish colon cells.

A large series of systematic reviews and meta-analyses linked the highest fiber intakes with death and disease rates roughly a sixth to almost a third below those seen at the lowest intakes, with the greatest benefit at about 25 to 29 grams a day (Reynolds et al., 2019). The Adequate Intake for fiber is 25 grams a day for women and 38 for men aged 19 to 50, set from its link with lower heart disease risk (Institute of Medicine, 2005).

How Fast It Arrives, and What Comes With It

The argument for distinguishing forms of carbohydrate rests on two points: speed and company.

Speed. Sugars and quickly digested starches raise blood glucose rapidly; slowly digested starches and fiber-rich foods raise it more gradually. For most healthy people, the body handles both. The speed matters more for people with diabetes and for satiety: foods that digest slowly tend to keep people full longer.

Company. More important for most people is what travels with the carbohydrate. Whole grains, beans, fruit, vegetables and milk deliver carbohydrate along with fiber, vitamins, minerals and other compounds. Added sugars and refined starches deliver carbohydrate with little else.

Sugars and starches end as the same glucose, but the foods that carry them do not: an apple and a cola both deliver sugar, and only one delivers fiber, water and vitamins along with it, which is why the useful distinction is between whole and refined sources rather than between sugar and starch.

Why Glycemic Index Is Not Enough

Some people judge carbohydrate foods by their glycemic index, a measure of how much a food raises blood glucose compared with pure glucose. The measure has uses, especially for people managing diabetes, but it has limits as a general guide. It is measured for single foods eaten alone, yet people eat foods in meals where fat, protein and fiber change the response. Some low-index foods, such as ice cream, are low partly because of their fat, and some high-index foods, such as baked potatoes, carry potassium and fiber. The index also says nothing about vitamins, minerals or added sugars. For most people, asking whether a carbohydrate comes from a whole food or a refined one answers more than its index does.

Where Americans Stand

Most Americans eat carbohydrate within the acceptable range, but the forms are uneven. Average intakes of added sugars exceed the guideline limit, and most adults eat far less fiber than the Adequate Intake (U.S. Department of Agriculture & U.S. Department of Health and Human Services, 2020). Whole grains make up a small share of grain intake for most people.

A Day Compared

Consider two days that each supply 250 grams of carbohydrate, about half of a 2,000-kilocalorie diet. Day A comes from white bread, sweetened cereal, a soda and white rice: about 12 grams of fiber and 60 grams of added sugar. Day B comes from oatmeal, whole-wheat bread, an orange, lentil soup and brown rice: about 35 grams of fiber and 10 grams of added sugar. The carbohydrate totals are identical; the profiles are not.

Conclusion

Carbohydrates are the body's main fuel, and the published figures place them at about half of daily energy. The forms differ in how quickly they arrive and, more importantly, in what comes with them. Fiber, which the body cannot digest, has the strongest evidence of benefit. The practical distinction is between carbohydrate from whole foods and carbohydrate from added sugars and refined grains.

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

Reynolds, A., Mann, J., Cummings, J., Winter, N., Mete, E., & Te Morenga, L. (2019). Carbohydrate quality and human health: A series of systematic reviews and meta-analyses. The Lancet, 393(10170), 434-445. https://doi.org/10.1016/S0140-6736(18)31809-9

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