Nutrients, vitamins and minerals

Triglycerides are packed with carbon–hydrogen bonds and hold about 9 kcal per gram, against about 4 for carbohydrate.

• About the same:
• About half as much:
• Correct: More than twice as much:

A coenzyme is an organic helper molecule, often made from a vitamin, that an enzyme needs to work. NAD+ and FAD are examples.

• Correct: An organic molecule an enzyme needs to catalyze its reaction:
• A second enzyme that speeds up the first:
• The part of the substrate that binds the active site:

Without bile, fats are not packed into micelles, and the vitamins that travel with fat are absorbed poorly too.

• Vitamins that dissolve in water, such as vitamin C:
• Correct: Vitamins that dissolve in fat, such as vitamins D and K:
• Vitamin B12 alone:

Carbohydrate: 45 g × 4 = 180 kcal. Protein: 10 g × 4 = 40 kcal. Fat: 5 g × 9 = 45 kcal. Total: 180 + 40 + 45 = 265 kcal.

• 220 kcal: 220 kcal leaves out the fat. Its 5 g still supply 5 × 9 = 45 kcal.
• 240 kcal: 240 kcal counts the fat at 4 kcal per gram, like carbohydrate. Fat supplies about 9 kcal per gram.
• Correct: 265 kcal: Correct. 180 + 40 + 45 = 265 kcal.
• 540 kcal: 540 kcal counts all 60 g at 9 kcal per gram. Only fat supplies 9; carbohydrate and protein supply about 4.

Vitamin C keeps the iron in the collagen-strengthening enzymes in its working form. Without it, new collagen is weak, so small vessels break (bruises, bleeding gums) and wounds cannot build strong scar tissue. This is scurvy, and a diet with no fruit or vegetables for months causes it.

• Correct: Vitamin C: the collagen made without it is weak: Correct. Bleeding gums plus a wound that will not heal point to weak collagen: scurvy.
• Vitamin K: clotting factors stay unfinished: A lack of vitamin K does cause bleeding, but it does not stop wounds from healing, and in adults it rarely comes from diet alone: it usually follows fat malabsorption or drugs such as warfarin.
• Iron: too little hemoglobin reaches the gums: Iron deficiency causes anemia and fatigue, not bleeding gums and failed wound healing.
• Vitamin B12: new blood cells cannot divide: B12 lack causes anemia with large red blood cells and nerve damage, and it takes years to appear because the liver stores so much.

Bile is needed to absorb fat, and the fat-soluble vitamins travel with fat. Blocking the bile duct lets fat pass into the feces and cuts absorption of A, D, E and K. The first sign in the blood is often slow clotting, because vitamin K stores are the smallest. Water-soluble vitamins are absorbed normally.

• Fat in the feces: up. Without bile salts, fats are poorly emulsified and cannot form micelles, so much of the dietary fat passes through unabsorbed.
• Absorption of vitamin K: down. Vitamin K dissolves in fat and enters the absorptive cells in micelles; with no micelles, little is absorbed.
• Time for the blood to clot: up. Without vitamin K, the liver cannot finish clotting factors II, VII, IX and X, so clotting slows.
• Absorption of vitamin C: no change. Vitamin C is water-soluble and is absorbed by carriers in the intestinal lining, which do not depend on bile.

This is Wernicke encephalopathy from thiamine deficiency. Thiamine is the coenzyme for the enzyme that removes CO2 from pyruvate as it enters the mitochondrion. Brain cells rely on glucose broken down this way, so without thiamine they cannot make enough ATP. Heavy alcohol use cuts both intake and absorption of thiamine.

• Vitamin A: Vitamin A lack causes night blindness and a damaged cornea, not confusion and an unsteady walk.
• Correct: Thiamine (B1): Correct. Thiamine replaces the missing coenzyme and can reverse the eye signs within hours.
• Vitamin C: Vitamin C lack causes scurvy: bleeding gums and poor healing.
• Cobalamin (B12): B12 lack also damages nerves, but it develops over years and causes numbness and anemia, not this sudden confusion with eye movement problems.

Lysine is essential: her cells cannot make it. Rice supplies some lysine, but less than her cells need. A ribosome needs every amino acid in the sequence at the moment it adds it, so protein building slows to the pace the scarce lysine allows. Amino acids are not stored for later, so the unused ones are broken down for fuel. Adding beans, which are rich in lysine, covers the gap.

• They make other amino acids into lysine as needed: Cells cannot build lysine from other amino acids; that is what makes it essential.
• They swap a different amino acid in where lysine belongs: The sequence is set by the gene, so a ribosome does not substitute another amino acid for a missing one.
• Correct: Synthesis slows, and the unused amino acids are burned: Correct. The scarce essential amino acid limits protein synthesis.
• They take lysine from stored lysine reserves: The body keeps no reserve of free amino acids set aside for later protein building.

Carbohydrate carbons already carry many oxygen atoms: they are partly oxidized. Fat is mostly carbon–hydrogen bonds, so each carbon has more electrons to give up as it is oxidized to CO2, and more energy is released per gram.

• Fat is absorbed more completely from the gut than carbohydrate is: Both are absorbed almost completely in healthy people; the difference is in the molecules, not absorption.
• Correct: Fat is less oxidized: its carbons carry fewer oxygen atoms: Correct. Fat is less oxidized to start with, so it releases more energy as it is fully oxidized.
• Fat is broken down by a longer chain of enzymes than carbohydrate: The number of enzymes does not set how much energy a molecule holds; the chemistry of its bonds does.
• Fat is stored in adipose tissue, which holds almost no water: Storage with little water makes stored fat tissue denser in energy than glycogen, but it does not change the energy in a gram of pure fat.

B vitamins supply no energy; they are parts of coenzymes. Once a well-fed person has enough coenzyme, the enzymes of fuel breakdown are not limited by it, so extra vitamin does not release more energy. The extra water-soluble vitamin leaves in her urine.

• It rises, because B vitamins are oxidized for ATP: Vitamins are not fuel. A vitamin tablet supplies 0 kcal.
• It rises, as extra coenzymes speed every reaction: Fuel breakdown is not limited by coenzyme supply in a well-fed person, so adding more does not speed it.
• Correct: It does not change, because she already has enough: Correct. Extra B vitamins do not add energy when stores are already adequate.
• It falls, because B vitamins block fat breakdown: B vitamins are coenzymes for fuel breakdown, including fat breakdown, not blockers of it.