Quiz 20 — Food and Health

The Guide

Materials and fuel

This quiz is about food: what it is made of, how the body uses it, and how to read a nutrition label. Everything the body does costs something. Muscles pull, kidneys filter, marrow makes red cells, the immune system builds antibodies, and holding your temperature at 98.6 runs day and night whether you are working or asleep. All of it needs energy to run on and materials to be made from, and both arrive as food.

So there are two questions in this topic, and the test asks both. What does the body need, and what happens when it gets too little of something, or too much?

Six kinds of nutrient

A nutrient is anything in food the body needs. There are six kinds, and the first useful division is between the three that supply energy and the three that do not.

Carbohydrates: The body's main fuel — sugars and starches, taken apart into glucose, which is what the cells burned in Quiz 12. Fiber is a carbohydrate too, and the one the body cannot digest at all; it passes through and keeps the large intestine's work moving, which is why it appears on a label even though it supplies you with nothing.
Proteins: The building material. Muscle is protein, and so are enzymes, antibodies and the hemoglobin in your red cells. Protein from food is broken into amino acids and reassembled into whatever the body needs, and a few of those amino acids cannot be made by the body at all, so they have to arrive in what you eat.
Fats: Energy in concentrated form — more than twice as much per gram as the other two. Fat also insulates, cushions organs, forms part of every cell membrane from Quiz 10, and is needed to absorb certain vitamins.
Vitamins: Needed in very small amounts, each for a particular job, and mostly not made by the body. Missing one produces a specific illness rather than general weakness, which is the fact the next section turns on.
Minerals: Elements the body cannot make or break down. Calcium builds the skeleton from Quiz 17; iron sits at the center of hemoglobin and carries the oxygen from Quiz 15; sodium and potassium make nerve signals possible, from Quiz 16; iodine is required by the thyroid, from Quiz 16 as well.
Water: Not a source of energy and still the one you die without soonest. It is the medium every chemical step happens in, the basis of blood and of the fluid around every cell, and the thing the kidneys spend all day defending.

Energy in and energy out

A calorie is a unit of energy, in the same way that an inch is a unit of length. It is not an ingredient. When a label says a serving contains 250 calories, it means that much energy is available from it.

Energy leaves the body in two ways. Some goes into what you do — walking, lifting, climbing stairs. Rather more goes into what you never notice: the heart pumping, breathing, the kidneys filtering, the immune system running, and above all holding your temperature steady, which is the largest standing cost of being warm-blooded. That is why a body still uses a great deal of energy asleep.

When more energy arrives than leaves, the surplus is stored, chiefly as fat, and as glycogen in the liver and the muscles. When less arrives than leaves, the body draws on those stores. The relationship is worth knowing plainly, and it is also more complicated in a real life than in a sentence: how much energy a given body uses varies with size, age, health, medicines, sleep and the work it does.

What missing one nutrient does

Because each vitamin and mineral has a particular job, missing one produces a particular illness. These are called deficiency diseases, and each of the four below points back at a quiz you have already taken.

Missing	What it was needed for	What follows
Vitamin C	Building the fibers that hold tissue together	Scurvy: wounds that will not heal, bleeding gums, teeth loosening
Vitamin D or calcium	Absorbing calcium, and building bone	Rickets in children, soft and weakened bone in adults
Iron	Making hemoglobin to carry oxygen	Anemia: tiredness, breathlessness, pale skin
Iodine	Making the thyroid's hormone	The thyroid enlarges, and the body's energy use slows

Two things are worth taking from that table. The first is that a deficiency is specific: it is not general poor health but a named job that cannot be done. The second is that the symptoms follow from the job. Iron carries oxygen, so too little iron means too little oxygen delivered, so a person is tired and out of breath climbing stairs. You can reason your way from the nutrient to the symptom without memorizing either.

Reading a label

Every packaged food in the United States carries the same label, and the test asks about it because everyone meets it. There is one line to read first, and skipping it makes every other number wrong.

This is the main thing to know about a label, and nearly every label question on the test turns on it. The numbers are per serving, and the container may hold more than one serving. A package that looks like a single snack can hold two and a half of them.

Zero does not mean none of anything. A label reading 0 grams of trans fat tells you about trans fat and nothing else — the same food has 8 grams of fat in total. Labels also carry percentages that compare a serving against a general daily figure for an adult; those are a rough guide, and the figure they compare against is not tailored to any particular person.

Long-term conditions, and what they turn on

Some conditions develop over years and are connected to what people eat. Type 2 diabetes is the blood sugar loop from Quiz 16 working poorly, with the cells responding weakly to insulin. High blood pressure puts a standing strain on the vessels and the heart from Quiz 15, and salt intake is one of several things that affect it.

Two honest qualifications belong with that. These conditions have many causes at once — inherited tendency, age, medicines, sleep, the amount of standing or sitting a job requires — so no single food explains any of them. And what a person eats is shaped by what is affordable, what is sold nearby, and how many hours are left in a day after work. A quiz can tell you what the body does with food. It cannot tell you what was available.

The short version

Six kinds of nutrient: carbohydrate, protein and fat supply energy, at about 4, 4 and 9 calories per gram; vitamins, minerals and water supply none and are still required. Energy arrives as food and leaves as movement and as the constant work of staying alive, with the surplus stored and the shortfall drawn from stores. Missing one vitamin or mineral produces a specific illness, because each has a specific job. And on a label, the serving size is read first, because every other number depends on it.

Worked Examples

Two questions, worked through

Example 1. A portion of food contains 20 grams of carbohydrate, 10 grams of protein and 10 grams of fat. How much energy does it supply?

Take the three separately, using 4 calories a gram for carbohydrate, 4 for protein and 9 for fat.

Carbohydrate: 20 times 4 is 80. Protein: 10 times 4 is 40. Fat: 10 times 9 is 90. Add them: 80 plus 40 plus 90 is 210.

Notice what the arithmetic shows. The fat weighs the same as the protein and supplies more than twice the energy, which is what "9 calories a gram" means in practice.

210 calories. Multiply each nutrient's grams by its calories per gram, then add. The only thing to memorize is 4, 4 and 9, and knowing which one is 9 does most of the work.

Example 2. A man is tired all the time and short of breath on stairs. A blood test shows low hemoglobin and low iron. Why would too little of a mineral cause breathlessness?

Follow the job of the nutrient rather than the name of the symptom. Iron sits at the center of hemoglobin, and hemoglobin is what red blood cells use to carry oxygen — Quiz 15's point that plasma alone cannot carry nearly enough.

With less hemoglobin, each unit of blood carries less oxygen. The muscles doing the work of climbing still need what they need, so the body compensates the only ways it can: breathe harder and pump faster. Breathlessness on stairs is the shortfall showing up under load.

Because iron is needed to make hemoglobin, and hemoglobin carries the oxygen. Deficiency questions are answered by naming the nutrient's job and then asking what fails when the job goes undone.

The Quiz

Ten questions

Answer all ten, then press the button at the bottom. Nothing is timed.

Label — questions 1 to 4

Use the nutrition label from the Guide above. Its figures: 2.5 servings per container; serving size 1 cup; per serving — 250 calories, total fat 8 g, trans fat 0 g, sodium 470 mg, total carbohydrate 31 g, dietary fiber 4 g, protein 5 g.

1.A person eats the entire container. How many calories have they taken in?

A250
B500
C625
DThere is no way to tell from the label.

2.What does the serving size line tell you?

AHow much a person ought to eat at one time
BThe amount that every other number on the label refers to
CThe total contents of the package
DThe weight of the packaging and the food together

3.Someone eats two servings. How much sodium is that?

A235 mg
B470 mg
C705 mg
D940 mg

4.A shopper sees "Trans Fat 0 g" and says the food contains no fat. How should that be judged?

AWrong — the label lists 8 g of total fat per serving.
BRight, because trans fat is the only fat that is measured.
CRight, because a zero on a label applies to the whole food.
DImpossible to judge without knowing the serving size.

Table — questions 5 to 7

Three items from one meal. Use 4 calories per gram for carbohydrate, 4 for protein and 9 for fat.

Item	Carbohydrate	Protein	Fat
Rice and beans	60 g	12 g	3 g
Grilled chicken	0 g	30 g	8 g
Can of soda	39 g	0 g	0 g

5.How much energy does the can of soda supply?

A39 calories
B156 calories
C351 calories
DNone, since it contains no protein or fat.

6.Which item supplies the most protein, and what is protein mainly used for?

ARice and beans; it is the body's main fuel.
BThe soda; it is stored as fat.
CThe chicken; it is building material for muscle, enzymes and other proteins.
DThe chicken; it is the only nutrient that supplies energy.

7.A student says the chicken must supply more energy than the rice and beans, because it has more fat and fat has the most calories per gram. Is that right?

ANo — the chicken supplies 192 calories and the rice and beans 315.
BYes, because fat supplies 9 calories per gram.
CYes, because protein and fat together always outweigh carbohydrate.
DThere is not enough information to work it out.

Passage — questions 8 to 10

In the eighteenth century, sailors on long voyages developed scurvy: wounds stopped healing, old scars opened, gums bled and teeth loosened. On some crossings it killed more men than storms and enemies together.

In 1747 a naval surgeon, James Lind, took twelve sailors already ill with scurvy and divided them into six pairs. Every pair ate the same food and slept in the same quarters. Each pair was given one addition to the diet: cider, or vinegar, or seawater, or a mixture of spices, or a weak acid, or two oranges and a lemon. Within a week the pair given the fruit were fit for duty. No other pair recovered.

The reason was not understood for another two centuries. Vitamin C, which the fruit supplied, is needed to build the fibers that hold tissue together, and the human body cannot make it.

8.Why did Lind keep the food, the quarters and the illness the same across all six pairs?

ATo make the sailors more comfortable during the test
BBecause the navy required identical treatment of all crew
CTo make the experiment finish more quickly
DSo that the one addition to the diet was the only thing that differed between pairs

9.Scurvy causes wounds to stop healing. Which explanation does the passage support?

AWithout vitamin C the blood cannot carry oxygen to the wound.
BWithout vitamin C the body cannot build the fibers that hold tissue together.
CWithout vitamin C the immune system attacks healthy tissue.
DWithout vitamin C the body stores too much iron.

10.Which conclusion does the passage best support?

AA treatment cannot be trusted until the reason it works is understood.
BScurvy was caused by conditions aboard ship rather than by diet.
CA comparison can show what works long before anyone can explain why.
DTwelve sailors is too few for the result to mean anything at all.

Send this line to your teacher

The line records which questions you missed and which answer you chose. That is more useful to your teacher than the score, because it shows where a question went wrong. If a question felt unclear even though you got it right, add its number with a question mark — for example 5? — before you send it.

Score ______ / 10 Missed — write the question number and the letter you chose:
______________________________________________________________

The Key

Answers, and the trap in each one

1. C — 625. 250 calories per serving, 2.5 servings in the container: 250 times 2.5 is 625. Half of 250 is 125, so two servings and a half is 500 plus 125. A is the answer you get by reading the big number and stopping, and it is the mistake the label's layout invites. B rounds the servings to two. Whenever a label question mentions the whole package, the servings-per-container line is doing the work.

2. B — the amount every other number refers to. The serving size is the unit the rest of the label is measured in. Change it and every figure below it would change. A reads it as a recommendation, which is the commonest misunderstanding of a label. It is a measuring unit, not advice about how much to eat, and the manufacturer does not know who is eating.

3. D — 940 mg. 470 per serving, doubled. B is the number printed on the label, chosen without multiplying. The arithmetic here is trivial and the reading is not — the question is whether you noticed that two servings were eaten.

4. A — wrong; there are 8 g of total fat. A zero on one line reports on that line. Trans fat is a particular kind of fat, and the total fat line is right above it. B and C both take a specific claim as a general one, which is the same error as reading "no added sugar" as "no sugar." Labels are precise about narrow things, and the precision is easy to mistake for a broader promise.

5. B — 156 calories. 39 grams of carbohydrate times 4 calories a gram is 156. There is no protein and no fat to add. A uses the grams as though grams were calories, which is the most common slip on this kind of item — they are different units, one of weight and one of energy. And D reasons that a food with only carbohydrate supplies no energy, when carbohydrate is the body's main fuel.

6. C — the chicken, and protein is building material. 30 grams against 12 and 0. Protein is what muscle, enzymes, antibodies and hemoglobin are made of; the body can burn it for energy, but that is not what it is chiefly for. D names the right item for the wrong reason, so it is marked wrong. Carbohydrate and fat both supply energy too — protein is not the only one, and it is not even the body's first choice.

7. A — no; 192 against 315. Chicken: 30 times 4 is 120, plus 8 times 9 is 72, giving 192. Rice and beans: 60 times 4 is 240, plus 12 times 4 is 48, plus 3 times 9 is 27, giving 315. B is true about a gram and false about a plate. Fat does supply more per gram, and there are only 8 grams of it here against 60 grams of carbohydrate. This is the item worth the most in the quiz, because it is the difference between knowing a rate and knowing a total — and that difference runs through the whole science test, not only this topic.

8. D — so the one addition was the only difference. This is the controlled comparison from Quiz 5, at sea in 1747. Same food, same quarters, same illness, one thing different — so when one pair recovered, the difference had somewhere to point. A and B give humane or administrative reasons for a choice that was made for a logical one. If the pairs had differed in several ways at once, the recovery could not have been traced to any of them.

9. B — the fibers that hold tissue together. The passage's last line names the job, and the symptoms follow from it: a wound heals by building new tissue, and old scars are held by the same fibers, which is why they reopen. A borrows the mechanism from iron deficiency, which is a real thing and a different one. Deficiency questions reward matching the nutrient to its own job rather than to a job you have heard of.

10. C — a comparison can show what works before anyone can explain why. The fruit cured scurvy in 1747 and vitamin C was not identified until the 1930s. The evidence was good long before the explanation existed. A sounds cautious and would have cost lives — the Royal Navy waited more than forty years to make lemon juice standard, and men died of a curable illness in the meantime. D dismisses twelve sailors as too few, and while a larger trial would be better, this one had a clean design and an unmistakable result. Small evidence and no evidence are not the same thing.

Your Score

What the number means

8 to 10	Solid. Check topic 20 on your map. That completes Part III.
6 or 7	Close. Read the whole key, then take this again in a few days before you check the box.
5 or fewer	Worth another pass. Write out 4, 4 and 9 and which nutrient each belongs to, then find a real package in your kitchen and work out what the whole container contains.

Misses on 1 to 4 are label reading, and the fix is a habit rather than knowledge: find the servings per container before looking at anything else. Misses on 5 to 7 are arithmetic, and question 7 is the one to study, since knowing a rate is not the same as knowing a total. Misses on 8 to 10 belong to Part I as much as to this topic — what a controlled comparison shows, and how far the evidence lets you go.

Part III ends here

Seven quizzes ago the body was a set of separate systems. It should look like fewer than that now. Food is broken down until it can cross into the blood; the blood carries it and the oxygen to every cell; the cells use them and hand back waste; the kidneys, lungs and skin get rid of it. Nerves and hormones coordinate the whole business, bones and muscles move it around, the immune system defends it, and every one of those systems is held inside narrow limits by loops that push back whenever a level drifts.

Part IV is heredity, and it starts one step behind everything you have just read: where the instructions for building all of it come from, and how they are passed on.

Twelve sailors

James Lind's trial aboard the Salisbury in 1747 is often called the first controlled clinical trial, and its design was better than its century. He took men already ill, kept everything about their lives the same, changed one thing between pairs, and watched. The pair given oranges and a lemon recovered so quickly that one of them was nursing the others within six days.

Lind published his findings in 1753 and the Royal Navy adopted lemon juice as standard in 1795 — forty-eight years after the experiment, and long after the deaths of a great many sailors from a condition that two oranges could hold off. Lind himself never quite believed his own result was the whole story, and went on recommending other remedies alongside it.

The vitamin was not isolated until the 1930s, by Albert Szent-Györgyi and, independently, Charles Glen King. By then the practical lesson had been available for nearly two hundred years, which is worth remembering whenever someone says a finding cannot be acted on until the mechanism is understood.