**Core Concept**
During lactation, the body undergoes significant metabolic changes to support milk production and meet the nutritional demands of the newborn. This period is characterized by increased energy expenditure, altered glucose and lipid metabolism, and enhanced renal function to excrete excess electrolytes and water.

**Why the Correct Answer is Right**
The increased demand for certain nutrients during lactation is due to the high energy requirements for milk synthesis, which involves the breakdown of glucose, fatty acids, and proteins. The body also requires more calcium and phosphorus to support the growth and development of the infant's bones and teeth. Furthermore, the kidneys need to excrete excess electrolytes, such as sodium and potassium, to maintain fluid balance and prevent hyponatremia. The increased renal function during lactation is essential to meet these demands.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the requirement for protein during lactation is actually lower compared to pregnancy, as the body is not building a new organ (the placenta) or supporting the growth of a fetus. However, the correct answer is not provided, so we will proceed to analyze the other options.

**Option B:** This option is incorrect because the requirement for calcium and phosphorus during lactation is actually higher compared to pregnancy, as these minerals are essential for milk production and the growth and development of the infant's bones and teeth.

**Option C:** This option is incorrect because the requirement for water during lactation is actually higher compared to pregnancy, as the body needs to produce and excrete excess fluid to maintain milk production and prevent dehydration.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that lactation is a catabolic state, characterized by increased energy expenditure and breakdown of glucose, fatty acids, and proteins. This is in contrast to pregnancy, which is an anabolic state, where the body builds a new organ (the placenta) and supports the growth of a fetus.

**Correct Answer: B. Calcium and phosphorus requirements are lower during lactation compared to pregnancy.**