adult men (Taivainen et al., 1995). Nonetheless, 6 hours after ingestion, there was an antidiuretic phase, which lasted up to 12 hours post-alcohol ingestion (Taivainen et al., 1995). This could have been a result of a high serum osmolality that stimulated arginine vasopressin, resulting in water reabsorption (Taivainen et al., 1995). The effects of ethanol appear to change during the course of the day and may depend on the amount of water consumed at prior meals (Stookey, 1999). Thus, based on these limited data, it appears that the effect of ethanol ingestion on increasing excretion of water appears to be transient and would not result in appreciable fluid losses over a 24-hour period.
Urea, a major end product of metabolism of dietary proteins and amino acids, requires water for excretion by the kidneys. Renal excretion of 1 g of urea nitrogen (2.2 g of urea) requires 40 to 60 mL of water. Thus, if a person consumes 63 g of protein in a diet that contains 2,100 kcal, the volume of water required increases by 0.4 to 0.6 L/day above the basal osmolar excretory requirement of 0.5 and 0.75 L/day in younger and older individuals, respectively. Increasing dietary protein did not affect water intake or urine volume in eight men fed constant diets with 80 versus 180 g/day of protein for 7 days while energy and sodium intake remained constant (Luft et al., 1983). Ad libitum water intake was reported to be 2.8 and 2.7 L/day and urine volume was 2.1 and 2.0 L/day, respectively. Although changes in solute and urea nitrogen excretion were reported, these changes were appropriate for the changes in protein intake. Thus increased protein intake did not affect water intake or urine volume in the setting of ad libitum water consumption.
Like protein, the presence of dietary carbohydrate may also affect water requirements. On average, 100 g/day of carbohydrate is needed to prevent ketosis (IOM, 2002/2005). This amount of carbohydrate has been shown to decrease the body water deficit by decreasing the quantity of body solutes (ketone bodies) that need to be excreted (Gamble, 1947). This response is similar when ketosis occurs with consumption of very low carbohydrate diets.
Fecal water losses are increased with increased dietary fiber. The effects of adding 5.1 g/day of crude fiber to the diet of 20 nuns who ranged in age from 25 to 72 years were evaluated (Baird et al., 1977); mean total daily crude fiber intake was 8.4 g (Baird et al., 1977). After 12 weeks, consumption of a high-fiber biscuit resulted in a significant increase in fecal water loss compared with a placebo