Nutrition: Macronutrients and Carbohydrates Quiz

Macronutrients and Micronutrients

• Macronutrients are needed in larger quantities than micronutrients
• Macronutrients include carbohydrates, proteins, and fats
• Micronutrients include vitamins and minerals

Carbohydrate Sources

• Sucrose (cane sugar) is a disaccharide
• Lactose is a disaccharide found in milk
• Starches are large polysaccharides
• Cellulose is a large amount of polysaccharide
• Amylose, glycogen, alcohol, lactic acid, pyruvic acid, pectins, dextrins, and minor carbohydrate derivatives are also found in meats

Simple Carbohydrates

• Simple carbohydrates are found in fruits, milk, and vegetables
• Cake, candy, and refined sugars are simple carbohydrates
• Simple carbohydrates provide energy but lack vitamins, minerals, and fiber

Dietary Carbohydrates and Blood Glucose

• Some carbohydrate-containing foods cause a rapid rise and fall in blood glucose
• Other foods result in a gradual rise and fall in blood glucose levels
• The glycemic index (GI) measures these differences in the speed of post-prandial glucose concentration

Glycemic Index (GI)

• The GI measures the area under the blood glucose curve after consuming a carbohydrate-rich meal
• It's compared with the area under a blood glucose curve after consuming the same amount of glucose
• A low GI (<55) results in a slower increase in blood glucose compared to a high GI (270)
• A low GI diet can improve glycemic control in diabetic individuals
• The glycemic load (GL) measures how much a typical serving size of a food raises blood glucose

Carbohydrate Digestion

• Digestion occurs in the mouth and the intestinal lumen
• Specific glycosidases hydrolyze polysaccharides and oligosaccharides
• Disaccharidases hydrolyze tri- and disaccharides into reducing sugars
• The final digestion products are glucose, galactose, and fructose

Hydrolysis of Carbohydrates

• Carbohydrates in our diet are large polysaccharides or disaccharides
• Digestive enzymes hydrolyze these molecules by returning hydrogen and hydroxyl ions from water to separate the monosaccharides from each other

Digestion of Carbohydrates

• In the mouth, the digestive enzyme ptyalin (α-amylase) hydrolyzes some starches into the disaccharide maltose
• In the mouth, not more than 5% of the starches are hydrolyzed via ptyalin
• In the stomach, between 30 and 40% of the starches are hydrolyzed
• The digestion in the stomach halts when the acidic contents reach the small intestine
• Pancreatic amylase (several times powerful than salivary amylase) works on the carbohydrates that are entering the small intestine (duodenum)
• Carbohydrates are almost completely transformed to maltose and/or other smaller glucose polymers entering the upper jejunum by the pancreatic amylase

Hydrolysis of Disaccharides

• Enterocytes lining the small intestine contain four enzymes (lactase, sucrase, maltase, and α-dextrinase) that hydrolyze lactose, sucrose, and maltose into monosaccharides
• Lactose produces glucose and galactose molecules
• Sucrose splits into fructose and glucose molecules
• Maltose and other small glucose polymers are split into molecules of glucose

Absorption of Carbohydrates

• Carbohydrates are absorbed as monosaccharides
• Glucose accounts for more than 80% of carbohydrate calories absorbed
• Remaining 20% are mostly galactose and fructose

Absorption of Glucose

• Glucose is absorbed via a sodium co-transport mechanism
• Sodium ions are actively transported across the basolateral membranes of the intestinal cells, reducing intracellular sodium
• The decreased intracellular sodium concentration causes sodium ions from the intestinal lumen to move through the brush border of the cells to the blood
• Glucose molecules are transported with the sodium ions to the interior of the cell
• Other transport proteins and enzymes facilitate glucose diffusion into the interstitial fluid and then into the blood

Absorption of Other Monosaccharides

• Fructose is absorbed via facilitated diffusion and does not rely on sodium transport
• Fructose enters the cell and is phosphorylated into a glucose form
• Galactose absorption follows the same mechanism as glucose

Absorption of Carbohydrates (duodenum and jejunum)

• Absorption of carbohydrates occurs in the duodenum and upper jejunum
• Different sugars have different absorption mechanisms
• Galactose and glucose are absorbed via sodium-dependent glucose cotransporter (SGLT-1)
• Fructose requires a sodium-independent monosaccharide transporter (GLUT-5)

Clinical Aspect - Defects

• Defects in disaccharidase activity can impair carbohydrate digestion, leading to undigested carbohydrates entering the large intestine
• Various intestinal diseases, malnutrition, and certain drugs can also disrupt disaccharide digestion

Lactose Intolerance

• Lactose intolerance is prevalent in many adults, commonly due to a deficiency of lactase, the enzyme needed to digest lactose
• Lactose intolerance can cause symptoms like bloating, pain, gas, and diarrhea from undigested lactose entering the large intestine (fermentation)
• People dealing with this condition can reduce consumption of lactose-containing foods, substitute with alternative sources to maintain energy, use lactase products, or eat yogurt with live and active cultures
• Lactose intolerance is sometimes age-dependent and related to the DNA sequence on chromosome 2 that influences lactase expression

Protein Digestion

• Dietary proteins are hydrolyzed by proteolytic enzymes to amino acids for absorption
• These enzymes include pepsin in the stomach and various pancreatic proteases and peptidases in the small intestine
• Protein digestion in the stomach starts with pepsin, which denatures proteins
• Enzymes in the small intestine further hydrolyze polypeptides to release various amino acids

Digestion in small intestine - steps

• Pepsin begins protein digestion in the stomach
• Pancreatic enzymes act on proteins in the small intestine: Trypsin, chymotrypsin and others hydrolyze polypeptides further
• Peptidases in the small intestine break down peptides into amino acids.

Protein Absorption

• Proteins are absorbed in their di-, tri-peptide forms or as free amino acids
• Sodium co-transport mechanism facilitates di- and tri-peptide absorption
• Amino acids are absorbed via facilitated diffusion

Diseases Associated with Protein Digestion

• Pancreatic insufficiency (acute/chronic pancreatitis, cystic fibrosis, surgical removal of the pancreas) can lead to protein maldigestion
• Celiac disease damages the intestinal villi leading to malabsorption of dietary components such as proteins

Other Notes:

• Carbohydrates, proteins, and fats are the three major food types digested and absorbed in the body in their constituent parts. Their amounts and percentages might be different
• The images show diagrams and figures showing the process
• The listed enzymes, some with their inactive form, are produced in one part of the body and their actions occur in another part of the body.

Test your knowledge on macronutrients and their carbohydrate sources with this quiz. Explore the differences between simple and complex carbohydrates, as well as their effects on blood glucose levels. Ideal for students studying nutrition or health sciences.