The calculation uses the Mifflin–St Jeor equation for men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5. Plugging in 70 kg, 175 cm, and 25 years: - 10 × 70 = 700 - 6.25 × 175 = 1093.75 - 5 × 25 = 125, so −125 - +5 at the end Total = 700 + 1093.75 − 125 + 5 = 1673.75 kcal/day, about 1674 kcal/day. So the best choice is the one around 1674 kcal/day.

Linoleic acid is the primary omega-6 fatty acid. It is an essential fatty acid in the omega-6 family, meaning the body cannot make it and it must be obtained from the diet. Its structure is 18 carbons with two double bonds (18:2, n-6), and it serves as the main dietary source of omega-6 fats and a precursor to other omega-6 compounds. Linolenic acid, in contrast, is an omega-3 fatty acid (18:3, n-3). Arachidonic acid is a longer omega-6 fatty acid derived from linoleic acid, not the primary dietary omega-6. Palmitic acid is a saturated fatty acid (16:0) and is not an omega-6.

Nitrogen balance is the key idea here: your body’s nitrogen comes from dietary protein, and it’s lost mainly in urine as urea, plus some from sweat and feces. When the nitrogen you take in matches what you lose, you’re in nitrogen balance — no net gain or loss of body protein. The RDA for protein is set to keep healthy adults in that balanced state, roughly 0.8 g of protein per kilogram of body weight per day. So eating the RDA amount provides just enough protein to replace the nitrogen lost, maintaining equilibrium. If you consumed more protein than you lose, you’d have a positive nitrogen balance (as in growth or muscle building). If you consumed less, or if losses were higher due to illness or stress, you’d have a negative nitrogen balance. Nitrogen imbalance isn’t a normal steady state in healthy adults. So, eating the RDA amount of protein results in nitrogen balanced.

Understanding how the major digestive enzymes work across the digestive tract helps explain why this option is correct. Carbohydrates are first targeted by amylase, which starts in the mouth from the saliva and then continues in the small intestine with pancreatic amylase, breaking down starches into simpler sugars. Proteins are digested by proteases in two key places: pepsin in the stomach begins protein breakdown in the acidic environment, and in the small intestine the pancreatic proteases trypsin and chymotrypsin finish the job, producing peptides that are further digested by other enzymes. Fats are mainly digested by lipase in the small intestine, with bile salts helping to emulsify fats and allow lipase to access triglycerides effectively. This pattern—amylase for carbohydrates in the mouth and pancreas, proteases (pepsin in the stomach and trypsin/chymotrypsin in the small intestine) for proteins, and lipase for fats—matches the statement described.