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Module 4: Carbohydrates, Sugars, Starches, and Fiber — Vocabulary Flashcards

What Are Carbohydrates and Why Do You Need Them?

  • Found primarily in plant-based foods:
    • Grains, vegetables, fruits, nuts, legumes
    • Carbohydrate-based foods are staples in many cultures
  • Most desirable form of energy for the body:
    • Glucose is the main fuel for most cells
    • Brain and red blood cells depend heavily on glucose for energy
  • Plants convert sunlight into glucose via photosynthesis:
    • Chlorophyll in leaves absorbs energy from sunlight
    • Glucose is the most abundant carbohydrate in nature
    • Glucose units are linked to form starch stored in plants

Carbohydrate Structure and Types

  • Carbohydrates are categorized as simple and complex by the number of sugar units:
    • Simple carbohydrates contain 1 or 2 sugar units (monosaccharides and disaccharides)
    • Monosaccharides: glucose, fructose, galactose
    • Disaccharides: maltose (glucose + glucose), sucrose (glucose + fructose), lactose (glucose + galactose)
  • Complex carbohydrates are polysaccharides:
    • Long chains/branches of sugars: starch, fiber, glycogen
    • Starch is the storage form in plants
    • Amylose: straight chains of glucose
    • Amylopectin: branched chains of glucose

Monosaccharides, Disaccharides, and Polysaccharides (Overview)

  • Monosaccharides: glucose, fructose, galactose
  • Disaccharides: maltose (glucose + glucose), sucrose (glucose + fructose), lactose (glucose + galactose)
  • Polysaccharides: starch (plant storage), glycogen (animal storage), fiber (non-digestible)

Fiber: Definition, Types, and Roles

  • Fiber is a nondigestible polysaccharide:
    • Examples: cellulose, hemicellulose, lignins, gums, pectin
    • Humans lack the enzyme to digest fiber
    • Dietary fiber: naturally in foods; Functional fiber: added to foods for benefit (e.g., psyllium)
    • Total fiber = dietary fiber + functional fiber
  • Fiber can be classified by water affinity:
    • Soluble fiber: dissolves in water, fermentable by gut bacteria; viscous; slows GI transit
    • Examples: pectin, beta-glucan, gums, psyllium
    • Insoluble fiber: does not dissolve; speeds transit; laxative effect
    • Examples: cellulose, hemicellulose, lignins
  • Plant foods contain multiple fiber types, not just one type

Glycogen and Fiber Facts

  • Glycogen is the storage form of glucose in animals
    • Branched glucose units; stored in liver and muscle
    • Limited storage capacity; not accessible after animal death
  • Dietary fiber in health: supports digestion, heart health, metabolic health, and gut microbiota

How Do We Digest and Absorb Carbohydrates?

  • Digestion starts in the mouth:
    • Salivary amylase begins breaking down amylose and amylopectin into smaller starch units and maltose
  • In the small intestine:
    • Pancreatic amylase continues starch breakdown to maltose
    • Brush-border enzymes convert disaccharides to monosaccharides (glucose, fructose, galactose)
    • Monosaccharides are absorbed into the bloodstream
  • In the large intestine:
    • Fiber is not digested; some is metabolized by bacteria; most is excreted

Carbohydrate Digestion and Absorption: Diagram Summary

  • Mouth: salivary amylase acts on starches
  • Stomach: acidity inactivates salivary amylase; limited carbohydrate digestion occurs
  • Small intestine: pancreatic amylase breaks down starch to maltose; brush-border enzymes finish breakdown to monosaccharides
  • Bloodstream: monosaccharides (glucose, fructose, galactose) absorbed; liver processes glucose; excess glucose may be stored as glycogen or fat

How Glucose Is Used in the Body

  • Glucose provides energy for the body
  • Hormones regulate blood glucose levels:
    • Insulin (from the pancreas) lowers blood glucose by facilitating cellular uptake and storage
    • Glucagon (from the pancreas) raises blood glucose by promoting glycogenolysis and gluconeogenesis
  • Insulin actions:
    • Increases glucose transport into cells
    • Stimulates glycogenesis (glucose → glycogen) in liver and muscle
    • Promotes lipogenesis (glucose → triglycerides) in fat tissue
  • When glucose is scarce, the body uses glycogen stored in liver/muscle and can generate glucose from non-carbohydrate sources (gluconeogenesis) and fat becomes a major energy source via ketone bodies

Hormonal Regulation of Blood Glucose (Overview)

  • High blood glucose after a meal:
    • Insulin is secreted by the pancreas
    • Insulin increases glucose uptake into cells and storage as glycogen or fat
  • Low blood glucose between meals:
    • Glucagon is secreted by the pancreas
    • Glucagon stimulates glycogenolysis and gluconeogenesis to raise blood glucose
  • Adrenaline (epinephrine) also raises blood glucose during stress or fasting

Regulating Blood Glucose Between Meals

  • Liver glycogen stores deplete after about 18 hours of fasting; then fat breakdown and ketone production increase
  • Ketosis can occur after ~2 days of fasting as fatty acids are converted to ketone bodies
  • Prolonged fasting leads to protein breakdown to provide glucose (gluconeogenesis); brain may switch to ketone usage to spare protein

How Much Carbohydrate Do You Need? Best Food Sources

  • Minimum daily carbohydrate requirement: 130 rac{ ext{g}}{ ext{day}} for brain function
  • AMDR for carbohydrates: 45 ext{-}65 ext{ ext{-}percent of daily calories}
  • Total carbohydrate range for a typical 2000 kcal/day diet: 225 ext{ to } 325 rac{ ext{g}}{ ext{day}}
  • Daily fiber guidelines (AI) to promote heart health: 14 rac{ ext{g}}{1000 ext{ kcal}} of energy intake
  • Fiber AI by age and sex (Adequate Intake):
    • Males 19–50: 38 rac{ ext{g}}{ ext{day}}
    • Females 19–50: 25 rac{ ext{g}}{ ext{day}}
    • Males 51–70+: 30 rac{ ext{g}}{ ext{day}}
    • Females 51–70+: 21 rac{ ext{g}}{ ext{day}}
    • Pregnancy: 28 rac{ ext{g}}{ ext{day}}
    • Lactation: 29 rac{ ext{g}}{ ext{day}}
  • Most Americans consume far less fiber than recommended (around 16 rac{ ext{g}}{ ext{day}})
  • Fiber-rich foods are found in whole grains, fruits, vegetables, legumes, nuts, and seeds

Natural vs Added Sugars

  • Naturally occurring sugars are found in fruits and dairy; usually come with beneficial nutrients
  • Added sugars are added during processing or preparation and are often empty calories
    • Examples: soda, candy
  • Taste buds cannot distinguish natural from added sugars
  • Yearly consumption of added sugars has increased since 1970

Ultra-Processed Foods and Added Sugars

  • Added sugars can contribute to weight gain and higher risk of certain diseases if consumed in excess
  • Sugar does not cause hyperactivity in kids; dental caries depend on fermentable sugars and starch on teeth
  • Moderation within daily calorie needs is essential

Dental Health and Carbohydrates

  • Carbohydrates contribute to dental caries when fermentable sugars feed oral bacteria
  • Strategies to minimize caries:
    • Eat three balanced meals daily; limit snacking
    • Choose whole fruits and raw vegetables for snacks
    • Include cheese (protein, calcium, phosphorus) to aid remineralization
    • Practice good dental hygiene; drink water; avoid sugar-sweetened beverages

Sugar Substitutes: Forms and Safety

  • Sugar substitutes are sweeter than sugar but provide fewer calories and are FDA-approved for safety
  • They come in several categories:
    • Reduced-calorie sweeteners (polyols): sorbitol, mannitol, xylitol; absorbed slowly; may cause digestive issues in large amounts
    • Calorie-free sweeteners: saccharin, aspartame, neotame, acesulfame-K, sucralose, steviol glycosides (rebaudioside A, M, etc.), monk fruit extracts, advantame, allulose (calorie-free or near-zero in small amounts)
  • Some examples and facts:
    • Sucrose: 4 kcal/g; trade name Table Sugar
    • Sorbitol: 2.6 kcal/g; 50%–70% as sweet as sucrose; may cause diarrhea at high intakes
    • Aspartame: ~200× sweeter than sucrose; PKU must monitor phenylalanine intake
    • Sucralose: 0 kcal/g; ~600× sweeter; not absorbed
    • Steviol glycosides (stevia): 240× sweeter; may have aftertaste
    • Monk fruit extracts: 150–300× sweeter
    • Advantame: ~20,000× sweeter; very high sweetness
  • Table 4.3 (Oh So Sweet!) provides relative sweetness and calories per gram for various sweeteners

How Sugar Substitutes Are Labeled

  • Added sugars can be hidden under many names (e.g., corn syrup, dextrose, fructose, honey, molasses, invert sugar, etc.)
  • Nutrition labels list total sugars and added sugars; naturally occurring sugars are not distinguished on standard panels

Diabetes: Types, Prediabetes, and Management

  • Diabetes mellitus: chronic high blood glucose due to insufficient insulin or insulin resistance
  • Insulin resistance: glucose cannot enter cells efficiently
  • Type 1 diabetes:
    • Autoimmune destruction of insulin-producing cells
    • Usually begins in childhood or young adulthood
    • Requires insulin injections
    • Accounts for about 5–10% of cases
  • Type 2 diabetes:
    • Characterized by insulin resistance and eventual impaired insulin production
    • Accounts for about 90–95% of cases
    • Commonly diagnosed in people aged 45+ or those at risk; testing recommended for at-risk individuals
  • Prediabetes: higher-than-normal blood glucose but not yet diabetes; risk for heart disease and other issues
  • Consequences of chronic high blood glucose include nerve damage, eye damage, kidney damage, cardiovascular disease, infections, and poor wound healing; risk of diabetic ketoacidosis if insulin is severely deficient
  • Hypoglycemia (low blood glucose) can occur if glucose is too low due to inadequate intake or excess medication; symptoms include hunger, shakiness, dizziness; potentially life-threatening if untreated
  • Management: blood glucose control, nutrition, physical activity, and medications when needed

Glycemic Index (GI) and Glycemic Load (GL)

  • GI classifies how carbohydrate-containing foods affect blood glucose relative to pure glucose
  • GL adjusts GI to account for the amount of carbohydrate in a typical serving
  • Pairing carbohydrate-rich foods with protein or fat can lower the overall glycemic response
  • Total calories, not just GI/GL, determine weight management outcomes

Carbohydrates During Fasting and Ketosis Risk

  • Liver glycogen stores deplete after about t \approx 18 ext{ hours} of fasting
  • Without glucose, fat breakdown increases and ketone bodies accumulate (ketosis) after about two days of fasting
  • Prolonged fasting leads to muscle and organ protein breakdown to maintain glucose needs; brain may shift to ketone bodies to spare protein

Practical Guidelines: Food Sources and Daily Choices

  • Daily carbohydrate needs:
    • Minimum: 130 rac{ ext{g}}{ ext{day}} for brain function
    • Total daily carbohydrate range (typical 2000 kcal): 225 ext{ to } 325 rac{ ext{g}}{ ext{day}}
  • Emphasize nutrient-dense sources:
    • Whole grains (bread, cereals) with ample fiber
    • Fruits and vegetables for natural sugars, starch, and fiber
    • Legumes, nuts, and seeds for both carbs and fiber
    • Low-fat and fat-free dairy provide some simple sugars
  • Be mindful of packaged foods that may provide added sugars, salt, and fats

Fiber: Real-World Dietary Guidance

  • Fiber AI and daily goals (Adequate Intake):
    • Males 19–50: 38 rac{ ext{g}}{ ext{day}}
    • Females 19–50: 25 rac{ ext{g}}{ ext{day}}
    • Males 51–70+: 30 rac{ ext{g}}{ ext{day}}
    • Females 51–70+: 21 rac{ ext{g}}{ ext{day}}
    • Pregnancy: 28 rac{ ext{g}}{ ext{day}}
    • Lactation: 29 rac{ ext{g}}{ ext{day}}
  • Aim for fiber intake of about 14 ext{ g per 1{,}000 kcal} of daily energy
  • Gradually increase fiber to reduce digestive discomfort; increase fluids accordingly
  • Easy substitutions to boost fiber: choose whole grains, fruits with skin, vegetables, beans, and a variety of fiber-rich foods

Real-World Food Sources of Fiber and Carbohydrates

  • Food groups contributing to carbohydrate and fiber intake:
    • Fruits, vegetables, dairy, grains, and protein foods
    • Emphasis on whole-grain options and fiber-rich choices
  • MyPlate guidance and typical serving sizes help plan daily targets
  • Examples of high-fiber foods include: oats, beans, whole-grain bread, brown rice, fruits with edible skins, vegetables like broccoli and carrots

Natural vs Added Sugars: Summary and Labeling Notes

  • Natural sugars come with nutrients and fiber (e.g., in fruit and dairy)
  • Added sugars provide little nutritional value beyond calories
  • Sugar labeling difficulty: many names can mask added sugars; education on reading labels helps reduce intake

Sugar and Health: Behavioral and Nutritional Implications

  • Moderation is key: total daily calories matter more than a single nutrient
  • High intake of added sugars is linked to weight gain and higher risk of metabolic diseases; however, evidence on beverages alone driving obesity is inconclusive; focus on overall energy balance
  • Drinking sugar-sweetened beverages contributes to daily sugar intake; portion sizes and frequency matter

Tables, Figures, and Practical References (What They Show)

  • Figure references illustrate: photosynthesis, carbohydrate construction, fiber types, digestion, and energy pathways
  • Table 4.2 (Sugar Smacked!): typical teaspoons of added sugar in common foods and beverages
  • Table 4.3 (Oh So Sweet!): sweetness, calories per gram, trade names, and sweetening power for various sweeteners
  • Table 4.4 provides examples of viscous fiber sources for dietary planning
  • Figure 4.9, 4.10, and 4.11 illustrate added sugars labeling and the myriad names used on ingredient lists

Practical Substitutions for Higher Fiber Intake (Made Over Made Better)

  • Oatmeal or bran flakes instead of corn flakes
  • Whole-grain crackers instead of cheese crackers
  • Whole wheat tortilla instead of white flour tortilla
  • Popcorn instead of pretzels

Quick Reference: Key Numerical Constants and Ranges

  • Brain carbohydrate requirement: 130 rac{ ext{g}}{ ext{day}}
  • AMDR for carbohydrates: 45 ext{-}65 ext{ ext{-}percent of daily calories}
  • Daily carbohydrate range for a 2000 kcal diet: 225 ext{ to } 325 rac{ ext{g}}{ ext{day}}
  • Fiber intake guidance: 14 rac{ ext{g}}{1000 ext{ kcal}}; AI values by demographic group as listed above
  • Added sugar guidelines: less than 10 ext{ ext{-}percent of daily calories}; For U.S. adults, average added sugar intake is roughly 68 rac{ ext{g}}{ ext{day}} (~16 ext{ teaspoons})
  • Sugar substitutes: varying sweetness powers, from as low as 0 kcal/g to about 20{,}000× sweeter than sucrose (Advantame)
  • Ketosis timeframe: fasting-induced ketosis around t \approx 18 ext{ hours}; full ketosis with prolonged fasting (~2 days)