The Words on Your Plate, Explained PlainlyAn A to Z glossary of protein, fiber, magnesium, potassium, iron and the B vitamins

The sub terms hiding inside those four

Complete protein

A food carrying all nine essential amino acids in useful proportions. Animal foods and soy qualify on their own. Most single plants are short on one or two, which matters far less than it sounds, because eating legumes and grains across the same day covers the gaps.

Saturated and unsaturated fat

A description of chemical structure, not of virtue. Saturated fats are solid at room temperature and raise LDL cholesterol; the guidance is to keep them low. Unsaturated fats, from olive oil, nuts, seeds, avocado and fish, are the ones to build around.

Added sugar

Sugar put into a food during processing, as distinct from the sugar naturally present in fruit or milk. Your bloodstream cannot tell them apart, but the package around them differs enormously: an orange carries fiber, water and potassium, and a soda carries none of it.

Soluble and insoluble fiber

Soluble fiber, in oats, beans, apples and citrus, dissolves into a gel that slows digestion and helps lower LDL cholesterol. Insoluble fiber, in wheat bran, nuts and vegetable skins, adds bulk and speeds transit. Most fiber rich foods carry both.

Glycemic response

How much and how fast a food raises your blood glucose. It is a property of the whole meal rather than the single food. Fat, protein, fiber and acidity all slow it, which is why bread with olive oil behaves differently from bread alone.

Essential fatty acids

Linoleic acid and alpha linolenic acid, the two fats your body cannot manufacture. Alpha linolenic acid is the omega 3 in walnuts, flax and chia; the target is 0.6 to 1.2 percent of calories. EPA and DHA, from fatty fish and algae, are the forms your body uses most directly.

A through I

A · Amino acids

The twenty building blocks that proteins are made from. Nine are essential, meaning your body cannot manufacture them and food has to supply them. Protein quality is simply the question of whether all nine turn up in useful amounts.

B · Bioavailability

How much of a nutrient actually crosses out of your gut and into your blood, as opposed to how much was printed on the label. Iron is the clearest illustration: 14 to 18 percent absorbed from a mixed diet containing meat and vitamin C, and 5 to 12 percent from a vegetarian one.

C · Carbohydrate

Sugars, starches and fiber. Your default fuel source, with an acceptable range of 45 to 65 percent of calories. Everything interesting about a carbohydrate is in what surrounds it.

D · Dietary fiber

Carbohydrate your own enzymes cannot break down, so it reaches the large intestine intact and feeds the bacteria there. Targets are 25 g for women and 38 g for men aged 19 to 50. US adults average 16 g.

E · Electrolytes

Minerals that carry an electrical charge when dissolved in body fluid: potassium, sodium, magnesium, calcium, chloride and phosphate. They run nerve signals, muscle contraction and fluid balance. Sports drinks did not invent them.

F · Fat, dietary

Nine calories per gram, the structural material of cell membranes, the raw stock for hormones, and the carrier that moves vitamins A, D, E and K plus carotenoids into your bloodstream. Acceptable range 20 to 35 percent of calories.

G · Glycemic response

How much and how quickly a food lifts your blood glucose. A property of the entire meal, not of the single item, since fat, protein, fiber and acid all slow it down.

H · Heme iron

Iron held inside the hemoglobin and myoglobin of meat, poultry and seafood. Absorbed efficiently and largely indifferent to the rest of the plate, which is what makes it different from every other form of dietary iron.

I · Iron

Carries oxygen through your blood and sits inside the enzymes that generate energy. RDA of 8 mg for men, 18 mg for women aged 19 to 50, and 8 mg from 51 onward. Shortfall shows up as fatigue long before anything more dramatic.

J through R

J · Joule

The metric unit of food energy. One food calorie, properly a kilocalorie, is about 4.18 kilojoules. Labels outside the United States often lead with kilojoules, which is why a foreign package can look alarming until you do the arithmetic.

K · Potassium, symbol K

From the Latin kalium, which is why the letter on a lab report bears no resemblance to the word. Adequate Intake of 3,400 mg for men and 2,600 mg for women. Average US intakes fall below both.

L · Legumes

Beans, lentils, peas, chickpeas and peanuts. The only common food group that supplies protein, fiber, potassium, magnesium, folate and iron all in the same serving, which is why they show up in almost every recommendation ever written.

M · Magnesium

A cofactor in more than 300 enzyme systems covering protein synthesis, nerve and muscle function, blood glucose control and blood pressure. Around 48 percent of Americans take in less than their estimated requirement.

N · Nonheme iron

The iron in plants, eggs, dairy and fortified foods. Absorbed at 5 to 12 percent and highly responsive to what shares the meal with it, for better and for worse. This is the form nearly all pairing advice is about.

O · Omega 3 fatty acids

A family of unsaturated fats. Alpha linolenic acid, from walnuts, flax and chia, is essential; the target is 0.6 to 1.2 percent of calories. EPA and DHA, from fatty fish and algae, are the forms the body uses most directly, and conversion from the plant form is limited.

P · Protein

Chains of amino acids rebuilt into muscle, enzymes, antibodies and hormones. RDA of 0.8 g per kilogram of body weight, roughly 46 g for women and 56 g for men, within an acceptable range of 10 to 35 percent of calories.

Q · Quinoa

Worth a glossary entry because it carries all nine essential amino acids in usable amounts, which most single plant foods do not. A convenient example rather than a requirement; variety across the day achieves the same thing.

R · RDA

Recommended Dietary Allowance: the amount that meets the needs of 97 to 98 percent of healthy people. Distinct from an Adequate Intake, used when the evidence is too thin to set an RDA, and from an Upper Limit.

S through Z

S · Sodium

Necessary in small amounts and oversupplied in most diets. For blood pressure, what matters is its balance against potassium rather than the sodium figure by itself, which is why adding potassium rich foods does real work even when the salt shaker stays put.

T · Thiamin, vitamin B1

Cofactor for five enzymes in glucose, amino acid and fat metabolism. RDA of 1.2 mg for men and 1.1 mg for women. No upper limit has been set, since no reliable harm from high intakes has been documented.

U · Upper limit

Tolerable Upper Intake Level: the highest daily amount unlikely to cause harm in most people. It applies almost entirely to supplements and fortified foods, because that is where excess actually happens. Whole food rarely gets anyone near one.

V · Vitamin C

Builds collagen, works as an antioxidant, supports immune function, and sharply improves nonheme iron absorption within a single meal. RDA of 90 mg for men and 75 mg for women, plus 35 mg more for smokers. Upper limit 2,000 mg.

W · Whole grain

A grain with its bran, germ and endosperm all still present. The bran carries the fiber and much of the magnesium, the germ carries the fat and B vitamins, and refining discards both to leave the starch.

X · Xanthophylls

The yellow carotenoids, chiefly lutein and zeaxanthin, concentrated in leafy greens, corn and egg yolk and in the macula of your eye. Fat soluble, so a meal with no fat in it leaves most of them behind.

Y · Yeast, nutritional

Deactivated yeast flakes, usually fortified with B12. A quarter cup supplies 8.3 to 24 mcg against an RDA of 2.4 mcg, which makes it one of the very few plant foods that solves the B12 problem outright.

Z · Zinc

Required by hundreds of enzymes and central to immune function, wound healing and the sense of taste. RDA of 11 mg for men and 8 mg for women. Phytates in beans and grains bind it, and the upper limit is 40 mg.