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ACE Fitness Nutrition study materials
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ACE Fitness Nutrition practice questions

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Question 1Nutrition Science Foundations and Nutrient Requirements

How many kilocalories does one gram of dietary fat provide?

  1. 2
  2. 9 Correct answer.
  3. 7
  4. 4

Explanation

Fat is the most energy-dense macronutrient, yielding about 9 kcal per gram. Carbohydrate and protein each supply roughly 4 kcal per gram, so fat delivers more than twice the energy per gram.

Question 2Nutrition Science Foundations and Nutrient Requirements

How many amino acids are considered indispensable (essential) for healthy adults?

  1. 4
  2. 9 Correct answer.
  3. 20
  4. 22

Explanation

Nine amino acids cannot be made by the adult body in sufficient amounts and must be supplied by food: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. The remaining amino acids are dispensable or conditionally indispensable.

Question 3Nutrition Science Foundations and Nutrient Requirements

Which list contains only fat-soluble vitamins?

  1. C, D, B3, K
  2. B12, folate, C, choline
  3. A, D, E, K Correct answer.
  4. B1, B2, B6, C

Explanation

Vitamins A, D, E, and K dissolve in fat and are absorbed with dietary lipids, so they depend on normal fat digestion and bile. The B vitamins and vitamin C are water-soluble.

Question 4Nutrition Science Foundations and Nutrient Requirements

Vitamin K is required for the synthesis of which type of compound?

  1. Thyroid hormones
  2. Blood-clotting factors Correct answer.
  3. Collagen cross-links
  4. Red blood cell membranes

Explanation

Vitamin K is a cofactor for the carboxylation of glutamate residues in several clotting proteins, including prothrombin and factors VII, IX, and X. Without it, these proteins cannot bind calcium properly and clotting is impaired.

Question 5Nutrition Science Foundations and Nutrient Requirements

What is the approximate adequate total water intake per day for adult men, including water from food and beverages?

  1. 5.5 liters
  2. 2.0 liters
  3. 3.7 liters Correct answer.
  4. 1.5 liters

Explanation

The adequate intake for total water is about 3.7 liters per day for men and 2.7 liters per day for women, with roughly 20 percent typically coming from food. Needs rise with heat, humidity, and high sweat losses during exercise.

Question 6Nutrition Science Foundations and Nutrient Requirements

Which food component is a carbohydrate that human digestive enzymes cannot break down?

  1. Sucrose
  2. Dietary fiber Correct answer.
  3. Starch
  4. Glycogen

Explanation

Dietary fiber consists of carbohydrate structures that resist digestion by human enzymes, though some fractions are fermented by gut bacteria. Starch, glycogen, and sucrose are all digested and absorbed as glucose or its components.

Question 7Nutrition Science Foundations and Nutrient Requirements

What is the RDA for protein for healthy sedentary adults?

  1. 1.6 g/kg body weight per day
  2. 2.2 g/kg body weight per day
  3. 0.4 g/kg body weight per day
  4. 0.8 g/kg body weight per day Correct answer.

Explanation

The protein RDA for adults is 0.8 g per kilogram of body weight per day, which meets the needs of nearly all healthy sedentary people. Higher intakes are used for athletes, pregnancy, and recovery from illness or injury.

Question 8Nutrition Science Foundations and Nutrient Requirements

Vitamin C enhances the intestinal absorption of which mineral?

  1. Magnesium
  2. Calcium
  3. Zinc
  4. Iron Correct answer.

Explanation

Vitamin C reduces ferric iron to the more absorbable ferrous form and forms a soluble complex with non-heme iron, improving uptake in the small intestine. This effect is most useful for plant sources of iron.

Question 9Nutrition Science Foundations and Nutrient Requirements

A client wants a breakfast with a lower glycemic response. Which change is most likely to lower the glycemic index of the meal?

  1. Swapping a whole orange for orange juice
  2. Stirring refined sugar into the oatmeal
  3. Replacing white bread with steel-cut oats Correct answer.
  4. Choosing instant white rice instead of parboiled rice

Explanation

Steel-cut oats are a minimally processed, high-fiber grain with a lower glycemic index than white bread, so glucose rises more slowly. Refined sugar, instant rice, and juice all push the meal toward a faster glucose rise.

Question 10Nutrition Science Foundations and Nutrient Requirements

A vegetarian client's iron intake looks adequate on paper, but absorption is a concern. Which food pairing best improves non-heme iron absorption?

  1. Tofu taken with a calcium supplement
  2. Spinach salad with a cup of black tea
  3. Black beans topped with tomato salsa Correct answer.
  4. Lentils with whole-grain pita bread

Explanation

The vitamin C in tomato salsa enhances absorption of the non-heme iron in black beans. Tannins in tea, phytates in whole grains, and calcium all inhibit non-heme iron uptake when eaten at the same meal.

Question 11Nutrition Science Foundations and Nutrient Requirements

A diet built mainly on rice supplies enough total protein but is low in lysine. What is the best description of lysine in this diet?

  1. An essential fatty acid
  2. A conditionally essential amino acid
  3. A nitrogen-balance marker
  4. The limiting amino acid Correct answer.

Explanation

When a protein source is short on one indispensable amino acid, that amino acid limits how efficiently the protein can be used for tissue synthesis and is called the limiting amino acid. In rice-dominant diets, lysine is typically the one in shortest supply.

Question 12Nutrition Science Foundations and Nutrient Requirements

During steady-state aerobic exercise a client's respiratory exchange ratio is 0.82. What does this value indicate about fuel use?

  1. Almost exclusively carbohydrate oxidation
  2. Mixed fat and carbohydrate oxidation Correct answer.
  3. Almost exclusively fat oxidation
  4. Protein as the dominant fuel

Explanation

A respiratory exchange ratio near 0.70 reflects mostly fat oxidation and near 1.00 mostly carbohydrate oxidation. A value of 0.82 falls between them, showing that both fuels are being used and that fat still supplies a substantial share.

Question 13Nutrition Science Foundations and Nutrient Requirements

Which client is at highest risk of vitamin D deficiency?

  1. A young adult who takes a daily multivitamin
  2. A person who drinks fortified milk daily and eats oily fish twice weekly
  3. An office worker with dark skin who rarely goes outdoors Correct answer.
  4. A lifeguard who works outside in summer

Explanation

Vitamin D is made in the skin when it is exposed to ultraviolet B light, and darker skin pigment and limited sun exposure both reduce that synthesis. Fortified foods, oily fish, and supplements supply meaningful amounts and lower risk.

Question 14Nutrition Science Foundations and Nutrient Requirements

Vitamin B12 absorption in the small intestine requires which carrier protein?

  1. Transferrin
  2. Albumin
  3. Retinol-binding protein
  4. Intrinsic factor Correct answer.

Explanation

Parietal cells in the stomach secrete intrinsic factor, which binds dietary B12 and carries it to specific receptors in the terminal ileum. Without intrinsic factor, B12 absorption fails even when intake is adequate.

Question 15Nutrition Science Foundations and Nutrient Requirements

Protein has the highest thermic effect of food among the macronutrients. What does this mean for energy balance?

  1. More of protein's energy is lost as heat during metabolism Correct answer.
  2. Protein energy is stored as body fat more readily than carbohydrate energy
  3. Protein is the strongest known suppressant of appetite
  4. Protein supplies more kilocalories per gram than fat does

Explanation

The thermic effect of food is the energy spent digesting, absorbing, and metabolizing nutrients. Protein costs roughly 20 to 30 percent of its own energy content, so a larger share is dissipated as heat than with carbohydrate or fat.

Question 16Nutrition Science Foundations and Nutrient Requirements

A 2,000-kcal diet provides 90 g of fat per day. How does this compare with the acceptable macronutrient distribution range for fat?

  1. No, because it falls below the 20% lower limit
  2. No, because it exceeds the 35% upper limit Correct answer.
  3. Yes, because fat intake is below 45% of energy
  4. Yes, because 90 g of fat is under a 100-g daily cap

Explanation

Ninety grams of fat provides 810 kcal, which is about 40.5 percent of a 2,000-kcal diet. The acceptable macronutrient distribution range for fat is 20 to 35 percent of energy, so this intake is above the upper bound.

Question 17Nutrition Science Foundations and Nutrient Requirements

A client with elevated LDL cholesterol is advised to add a soluble fiber source. Which food best matches that advice?

  1. Wheat bran
  2. Celery
  3. White rice
  4. Oat bran Correct answer.

Explanation

Soluble fibers such as beta-glucan in oat bran bind bile acids in the gut, increasing their excretion and prompting the liver to use cholesterol to make more. Wheat bran and celery are predominantly insoluble fiber, which mainly adds bulk.

Question 18Nutrition Science Foundations and Nutrient Requirements

A client maintains a daily energy deficit of 500 kcal. Using the estimate of 3,500 kcal per pound of body fat, about how much fat could this deficit support losing in one week?

  1. About 0.5 pound
  2. About 1 pound Correct answer.
  3. About 2 pounds
  4. About 3.5 pounds

Explanation

A 500-kcal daily deficit accumulates to 3,500 kcal over seven days, which corresponds to about one pound of stored fat under the standard estimate. Real-world loss varies as the body adapts and lean tissue changes.

Question 19Nutrition Science Foundations and Nutrient Requirements

Which dietary change best reflects a DASH-style eating pattern for lowering blood pressure?

  1. Replacing fruit with refined grain products
  2. Raising sodium intake to match estimated sweat losses
  3. Fruits, vegetables, and low-fat dairy with less sodium Correct answer.
  4. Adding a potassium supplement without other changes

Explanation

The DASH pattern emphasizes fruits, vegetables, whole grains, and low-fat dairy, which supply potassium, calcium, and magnesium, while limiting sodium. This combination lowers blood pressure more than any single nutrient change alone.

Question 20Nutrition Science Foundations and Nutrient Requirements

A 70-kg endurance athlete targets 1.2 to 1.4 g of protein per kilogram of body weight per day. Roughly what daily protein intake does this represent?

  1. 140–175 g
  2. 56–70 g
  3. 84–98 g Correct answer.
  4. 42–56 g

Explanation

Multiplying 70 kg by 1.2 and 1.4 g/kg gives a range of 84 to 98 g of protein per day. This is above the 0.8 g/kg adult RDA and reflects the higher needs of regular endurance training.

Question 21Nutrition Science Foundations and Nutrient Requirements

A client drinks several cups of strong tea with meals. Which effect on mineral status is most plausible?

  1. Increased calcium absorption because of caffeine
  2. Increased vitamin C status because of antioxidants
  3. Enhanced zinc absorption because of polyphenols
  4. Lower non-heme iron absorption from tannins Correct answer.

Explanation

Tannins and related polyphenols in tea bind non-heme iron in the intestinal lumen and reduce its absorption when consumed with food. Tea also contains caffeine, but caffeine does not increase calcium absorption, and its polyphenols do not enhance zinc uptake.

Question 22Nutrition Science Foundations and Nutrient Requirements

For a given nutrient the estimated average requirement is 60 mg per day and the RDA is 75 mg per day. What does the RDA value represent?

  1. The maximum intake unlikely to cause adverse effects
  2. An intake covering about 97–98% of healthy people Correct answer.
  3. The average daily intake that meets the requirement of half the population
  4. The intake needed to prevent overt deficiency signs in everyone

Explanation

The RDA is set at the estimated average requirement plus two standard deviations, so it meets the needs of roughly 97 to 98 percent of healthy individuals in the group. It is a planning and assessment target, not a minimum threshold for avoiding symptoms.

Question 23Nutrition Science Foundations and Nutrient Requirements

When carbohydrate intake is very low for several days, which metabolic change most directly supports the brain's fuel supply?

  1. Increased protein oxidation to supply glucose
  2. Increased gluconeogenesis from fatty acids
  3. Increased ketone body production by the liver Correct answer.
  4. Increased muscle glycogen synthesis

Explanation

Fatty acids cannot be converted to glucose in humans, but the liver can convert them into ketone bodies, which the brain uses when glucose availability falls. Muscle glycogen cannot help because muscle lacks glucose-6-phosphatase and cannot release free glucose into the blood.

Question 24Nutrition Science Foundations and Nutrient Requirements

A client takes a calcium supplement with a meal that is also high in iron. What is the most likely interaction?

  1. Calcium has no effect on iron absorption
  2. Calcium inhibits iron absorption when taken at the same time Correct answer.
  3. Calcium converts iron to the heme form
  4. Calcium increases iron absorption when the two are taken together

Explanation

Calcium and iron share absorptive pathways in the small intestine, and a large calcium dose taken with a meal can reduce both heme and non-heme iron absorption. Separating the supplement from iron-rich meals by a couple of hours limits the effect.

Question 25Nutrition Science Foundations and Nutrient Requirements

Thiamin deficiency most directly impairs which process?

  1. Regeneration of rhodopsin
  2. Collagen synthesis
  3. Pyruvate dehydrogenase activity and glucose metabolism Correct answer.
  4. Activation of prothrombin

Explanation

Thiamin is a coenzyme (as thiamin pyrophosphate) for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase, all central to carbohydrate metabolism. Deficiency therefore hits glucose-dependent tissues such as nerves and the heart hardest.

Question 26Nutrition Science Foundations and Nutrient Requirements

How many kilocalories are provided by one gram of pure alcohol?

  1. 4 kcal
  2. 7 kcal Correct answer.
  3. 9 kcal
  4. 2 kcal

Explanation

Alcohol supplies about 7 kcal per gram, which places it between carbohydrate and fat in energy density. It is not a nutrient that builds or repairs tissue, but its energy still contributes to daily intake.

Question 27Nutrition Science Foundations and Nutrient Requirements

Which pair of fatty acids is essential for healthy adults?

  1. Arachidonic acid and docosahexaenoic acid
  2. Linoleic acid and alpha-linolenic acid Correct answer.
  3. Oleic acid and stearic acid
  4. Palmitic acid and lauric acid

Explanation

Linoleic acid (omega-6) and alpha-linolenic acid (omega-3) cannot be synthesized by the human body and must come from the diet. Other fatty acids can be made endogenously or derived from these essential precursors.

Question 28Nutrition Science Foundations and Nutrient Requirements

Iodine is required for the synthesis of which compounds?

  1. Red blood cells
  2. Thyroid hormones Correct answer.
  3. Vitamin D
  4. Digestive enzymes

Explanation

Iodine is incorporated into the thyroid hormones triiodothyronine and thyroxine, which regulate metabolism and growth. Without adequate iodine, thyroid hormone production falls and goiter or developmental problems can occur.

Question 29Nutrition Science Foundations and Nutrient Requirements

Vitamin K is best known for which function?

  1. Hemoglobin oxygen transport
  2. Intestinal calcium absorption
  3. Membrane antioxidant protection
  4. Clotting factor activation Correct answer.

Explanation

Vitamin K serves as a cofactor for gamma-carboxylation of glutamate residues in several clotting factors, including prothrombin. This modification allows the factors to bind calcium and function properly in the coagulation cascade.

Question 30Nutrition Science Foundations and Nutrient Requirements

The primary function of vitamin E in the body is to provide what?

  1. Hormone precursor activity
  2. Antioxidant protection of cell lipids Correct answer.
  3. Nerve impulse transmission
  4. Coenzyme role in energy metabolism

Explanation

Vitamin E is a lipid-soluble antioxidant that protects polyunsaturated fatty acids in cell membranes from oxidative damage. It neutralizes free radicals and helps maintain membrane integrity.

Question 31Nutrition Science Foundations and Nutrient Requirements

A nutrient-dense food is best described as one that does what?

  1. Has high nutrients per calorie Correct answer.
  2. Provides many calories per gram
  3. Has a low water content
  4. Contains only one macronutrient

Explanation

Nutrient density compares the amount of a nutrient to the energy the food provides. Foods with high nutrient density deliver vitamins, minerals, protein, or fiber with relatively few calories.

Question 32Nutrition Science Foundations and Nutrient Requirements

Which function is performed by water in the body?

  1. It stores energy as glycogen
  2. It yields 4 kcal per gram
  3. It is a solvent and coolant Correct answer.
  4. It forms bone mineral crystals

Explanation

Water acts as a solvent for nutrients and waste products and helps regulate body temperature through sweating and evaporation. It also participates in transport, lubrication, and many metabolic reactions.

Question 33Nutrition Science Foundations and Nutrient Requirements

A complete protein is one that does what?

  1. Supplies all essential amino acids adequately Correct answer.
  2. Contains only nonessential amino acids
  3. Is derived exclusively from animal sources
  4. Has been refined to remove fat

Explanation

A complete protein provides all nine indispensable amino acids in amounts adequate to support protein synthesis. Plant-based combinations can also be complete even though individual plant foods may be limiting.

Question 34Nutrition Science Foundations and Nutrient Requirements

When blood calcium falls, which hormonal response is most direct?

  1. Calcitonin raises bone deposition and calcium excretion
  2. Insulin raises cellular calcium uptake
  3. Aldosterone raises intestinal calcium absorption
  4. PTH raises bone resorption and renal reabsorption Correct answer.

Explanation

Parathyroid hormone responds to low blood calcium by increasing bone resorption, increasing renal calcium reabsorption, and activating vitamin D to enhance intestinal absorption. These actions restore serum calcium toward normal.

Question 35Nutrition Science Foundations and Nutrient Requirements

Adequate folate before and during early pregnancy most directly reduces the risk of which outcome?

  1. Gestational diabetes
  2. Preterm birth
  3. Iron-deficiency anemia
  4. Neural tube defects Correct answer.

Explanation

Folate is required for DNA synthesis and cell division, and the neural tube closes very early in pregnancy. Adequate folate intake before conception and in early pregnancy reduces the risk of neural tube defects such as spina bifida.

Question 36Nutrition Science Foundations and Nutrient Requirements

Zinc deficiency most commonly impairs which process?

  1. Thyroid hormone synthesis
  2. Blood clotting
  3. Oxygen transport
  4. Wound healing and immune function Correct answer.

Explanation

Zinc is a cofactor for many enzymes involved in cell division, DNA synthesis, immunity, and tissue repair. Deficiency can therefore slow wound healing and increase susceptibility to infection.

Question 37Nutrition Science Foundations and Nutrient Requirements

Magnesium is required for which of the following?

  1. Absorption of vitamin B12 in the ileum
  2. Formation of hemoglobin in red cells
  3. Cofactor for ATP and muscle relaxation Correct answer.
  4. Synthesis of thyroid hormones and melatonin

Explanation

Magnesium is a cofactor for more than 300 enzyme systems, including many that use ATP. It also supports neuromuscular function and helps regulate muscle contraction and relaxation.

Question 38Nutrition Science Foundations and Nutrient Requirements

Phosphorus is a structural component of which molecules?

  1. Bile acids and steroid hormones
  2. Hemoglobin and myoglobin
  3. Thyroid hormones and melatonin
  4. ATP and bone mineral Correct answer.

Explanation

Phosphorus is part of ATP, phospholipids, DNA, and the calcium phosphate mineral in bone. It is therefore central to energy transfer and skeletal structure.

Question 39Nutrition Science Foundations and Nutrient Requirements

A diet high in potassium-rich foods is most likely to do what?

  1. Reduce vitamin D synthesis in the skin
  2. Raise blood pressure through sodium retention
  3. Lower blood pressure and lessen sodium effect Correct answer.
  4. Increase iron absorption from mixed meals

Explanation

Potassium promotes sodium excretion and helps relax blood vessel walls, which can lower blood pressure. This is why potassium-rich fruits, vegetables, and legumes are emphasized in blood-pressure-lowering eating patterns.

Question 40Nutrition Science Foundations and Nutrient Requirements

Iron is essential because it does what?

  1. Enables oxygen transport as part of hemoglobin Correct answer.
  2. Serves as a cofactor for thyroid hormone synthesis
  3. Acts as an antioxidant in cell membranes
  4. Forms the mineral matrix of teeth

Explanation

Iron is part of the heme group in hemoglobin and myoglobin, allowing red blood cells to transport oxygen and muscle cells to use it. Iron also participates in electron transport and other metabolic reactions.

Question 41Nutrition Science Foundations and Nutrient Requirements

Which tissue relies most heavily on glucose for fuel under normal conditions?

  1. Brain and red blood cells Correct answer.
  2. Skeletal muscle at rest
  3. Liver during fasting
  4. Adipose tissue

Explanation

The brain and red blood cells depend heavily on glucose under normal conditions, although the brain can adapt to use ketones during prolonged fasting. Red blood cells lack mitochondria and therefore rely on glucose for energy.

Question 42Nutrition Science Foundations and Nutrient Requirements

Which of the following is a primary function of dietary protein?

  1. Providing the main stored fuel in adipose tissue
  2. Supplying amino acids for enzyme and tissue synthesis Correct answer.
  3. Serving as the precursor for all steroid hormones
  4. Acting as the body's primary solvent

Explanation

Dietary protein supplies amino acids that the body uses to synthesize enzymes, hormones, structural proteins, and tissues. Amino acids also participate in transport and immune function.

Question 43Nutrition Science Foundations and Nutrient Requirements

The tolerable upper intake level (UL) is best defined as which of the following?

  1. Intake meeting the needs of 50% of healthy people
  2. Intake that supplies 10% of daily energy
  3. Minimum intake needed to prevent deficiency symptoms
  4. Highest daily intake unlikely to cause adverse effects Correct answer.

Explanation

The UL is the highest average daily nutrient intake that is likely to pose no risk of adverse health effects to almost all individuals in a specified group. It is not a recommended intake target and is used to guard against excessive intake.

Question 44Nutrition Science Foundations and Nutrient Requirements

An adequate intake (AI) is used when which condition applies?

  1. Evidence is insufficient to set an EAR and RDA Correct answer.
  2. A nutrient is needed only in pregnancy
  3. A nutrient already has a well-established RDA
  4. A nutrient is toxic at low doses

Explanation

An AI is set when there is not enough evidence to calculate an estimated average requirement and therefore an RDA. It is based on observed or experimentally determined approximations of nutrient intake by a healthy group.

Question 45Nutrition Science Foundations and Nutrient Requirements

Bioavailability of a nutrient refers to which of the following?

  1. The nutrient's effect on blood glucose
  2. The fraction absorbed and used by the body Correct answer.
  3. The nutrient's energy value per gram
  4. The total amount of nutrient in a food

Explanation

Bioavailability describes how much of a nutrient from a food or supplement is absorbed and becomes available for physiological use. It accounts for factors such as chemical form, food matrix, and absorption enhancers or inhibitors.

Question 46Nutrition Science Foundations and Nutrient Requirements

Phytic acid in whole grains and legumes most strongly reduces the absorption of which minerals?

  1. Iodine and selenium
  2. Sodium, potassium, and chloride
  3. Iron, zinc, and calcium Correct answer.
  4. Fluoride and chromium

Explanation

Phytic acid binds multivalent cations such as iron, zinc, and calcium in the intestine, forming complexes that are poorly absorbed. Processing methods such as soaking, sprouting, and fermentation can reduce phytate and improve mineral absorption.

Question 47Nutrition Science Foundations and Nutrient Requirements

Which measure compares a protein's amino acid profile with a reference pattern and adjusts for digestibility?

  1. Respiratory exchange ratio
  2. Glycemic index
  3. PDCAAS Correct answer.
  4. Thermic effect of food

Explanation

The Protein Digestibility Corrected Amino Acid Score (PDCAAS) compares a protein's essential amino acid profile with a reference pattern and corrects for fecal digestibility. It is used to evaluate protein quality in foods and diets.

Question 48Nutrition Science Foundations and Nutrient Requirements

A food provides 20 g of carbohydrate, 5 g of protein, and 4 g of fat. What is its total energy content?

  1. 106 kcal
  2. 136 kcal Correct answer.
  3. 146 kcal
  4. 116 kcal

Explanation

Carbohydrate and protein each supply about 4 kcal per gram, while fat supplies about 9 kcal per gram. The calculation is (20 × 4) + (5 × 4) + (4 × 9) = 80 + 20 + 36 = 136 kcal.

Question 49Nutrition Science Foundations and Nutrient Requirements

A healthy adult consuming adequate protein and energy is most likely to be in which state?

  1. Negative nitrogen balance
  2. Positive nitrogen balance from growth
  3. Nitrogen equilibrium Correct answer.
  4. Zero energy balance

Explanation

A healthy adult with adequate protein and energy intake is typically in nitrogen equilibrium, meaning nitrogen intake equals nitrogen excretion. Positive nitrogen balance occurs during growth, pregnancy, or recovery, while negative balance occurs with inadequate intake or catabolic stress.

Question 50Nutrition Science Foundations and Nutrient Requirements

How many amino acids are considered indispensable, or essential, for healthy adults?

  1. 9 Correct answer.
  2. 4
  3. 15
  4. 20

Explanation

Nine amino acids are indispensable for adults because the body cannot synthesize them in adequate amounts. These must be supplied by the diet to support protein synthesis and nitrogen balance.