A study of 20 healthy young male volunteers confirmed the existence of a quantitative and temporal relationship between food and fluid intake, and assessed the effects of fluid restriction on food acceptability and intake under scheduled eating conditions. Fluid restriction and thirst were significantly correlated with a reduction of food intake. Possible explanations of the relation between food and fluid intake are discussed.

Two healthy men were evaluated before and after a 56 day raft voyage to determine endocrine and metabolic status immediately after and during the recovery phase after long term caloric, protein, and water deprivation. Daily intake during the trip consisted of no protein, 300 ml water, and for the first 40 days, 300 Kcal glucose. The subjects lost weight from 84.1 to 58.1 and 78.3 to 57.7 kg, respectively. Other variations were measured including rate of excretion, diurnal patterns, serum testosterone levels, plasma insulin levels, serum glucose concentrations, triglyceride content, liver function, fat and xylsoe absorption, and renal function.

Hunger and thirst have distinct goals but control similar ingestive behaviors, and little is known about neural processes that are shared between these behavioral states. We identify glutamatergic neurons in the peri-locus coeruleus (periLCⱽᴳᴸᵁᵀ² neurons) as a polysynaptic convergence node from separate energy-sensitive and hydration-sensitive cell populations. We develop methods for stable hindbrain calcium imaging in free-moving mice, which show that periLCⱽᴳᴸᵁᵀ² neurons are tuned to ingestive behaviors and respond similarly to food or water consumption. PeriLCⱽᴳᴸᵁᵀ² neurons are scalably inhibited by palatability and homeostatic need during consumption. Inhibition of periLCⱽᴳᴸᵁᵀ² neurons is rewarding and increases consumption by enhancing palatability and prolonging ingestion duration. These properties comprise a double-negative feedback relationship that sustains food or water consumption without affecting food- or water-seeking. PeriLCⱽᴳᴸᵁᵀ² neurons are a hub between hunger and thirst that specifically controls motivation for food and water ingestion, which is a factor that contributes to hedonic overeating and obesity.

Six ponies were deprived of drinking water and food and compared over 24 hours with nondeprived ponies, ponies deprived of water but with food available, and ponies deprived of food but with water available. When food was eaten during water deprivation, plasma osmolality rose 4% from 284 mOsm/kg to 295 mOsm/kg. During water and food deprivation, plasma osmolality failed to rise, even over 24 hours, and usually fell. Packed cell volume was higher when food but not water was available. Food and/or water deprivation had no significant effect on plasma protein concentration. When food was available, the ponies drank three times more water (13.1 ± 2.1 kg) than when water but not food was available (3.5 ± 1.4 kg). Blood volume changes were calculated from packed cell volume and plasma protein data, and it was found that blood volume did not change significantly with deprivation. Urine volume did not vary with deprivation, but free water clearance changed significantly, falling when food but not water was available. Under these conditions, blood volume is maintained, but the mechanisms are not clear. When deprived of both drinking water and food, ponies failed to develop the hyperosmolality expected under these conditions. Water deprivation while food is available is a more powerful challenge to water and electrolyte homeostasis than deprivation of both food and water.

In a factorial experiment, fifth-instar Locusta migratoria (L.) (Orthoptera: Acrididae) were given either dry food (lyophilized grass) and drinking water, food only, water only, or neither food nor water. Food consumption and insect weight were measured daily, and the behaviour of each locust was recorded for 5 h on each of four consecutive days and for 2.5 h on the fifth. Consumption declined progressively in locusts given food only, and those given water only were not observed to drink after the first day of food deprivation. The decline in food consumption on the first day was accounted for by a decrease in the average duration of feeds, which remained constant thereafter. The further decline in consumption over subsequent days was due to a progressive decline in the number of feeds. Although food availability did not slow weight loss relative to locusts given neither food nor water, the availability of water without food did. The proportion of time locomoting increased in all deprivation treatments, but the pattern of change across the five observation days differed markedly between treatments. Locusts given food but no water increased locomotion from 20% of the time budget (the value for controls) to 30% on the first day of deprivation, and by the second day had reached a plateau of approximately 65%, which was maintained until the experiment was terminated on day 5. In contrast, locusts given water but no food approached the 65% level of locomotion on the first day, which was statistically greater than the 55% observed in those deprived of both food and water. This increase was due both to an increase in the number of locomotion bouts initiated and an increase in the average duration of locomotion bouts. On the second and third days, all deprivation treatments maintained locomotion at around 65%. By day 4, locomotion had decreased to approximately 15% in locusts deprived of both food and water, but not in those deprived of food only or water only. Unlike those given only food, locusts given only water showed a reduction in locomotion of c. 15% on the fifth day.

The high intake of dietary sodium (Na⁺) has been associated with obesity and insulin resistance, sparking the hypothesis that the consumption of salty foods affects food intake (FI) and postprandial blood glucose (BG) response. Therefore, we conducted 2 randomized repeated-measures experiments to examine the acute effects of the Na⁺ content of solid food and beverage on FI, water intake (WI), subjective appetite, thirst, and BG. FI and WI were measured at ad libitum pizza test meals; appetite, thirst, and BG were measured at baseline and at regular intervals before and after meals. In the first experiment, 16 males (mean body mass index (BMI), 22.2 kg·m⁻²) consumed a low-Na⁺ (71 mg) bean preload (300 kcal) with or without 740 mg or 1480 mg of added Na⁺ 120 min prior to the pizza meal. Participants ate 116 kcal more at the test meal after consuming beans with 740 mg of added Na⁺ than after beans with 1480 mg of added Na⁺. In the second experiment, 19 males (mean BMI, 23.2 kg·m⁻²) consumed a low-Na⁺ (62 mg) tomato beverage (73 kcal) with or without 500, 1000, 1500, or 2000 mg of added Na⁺ 30 min prior to a pizza meal. The beverage with 2000 mg of added Na⁺ led to higher WI during the pizza meal than the beverage with 500 mg of added Na⁺. However, compared with the control conditions (no added Na⁺), added Na⁺ treatments had no effect on dependent measures in either experiment. In conclusion, the acute intake of Na⁺, in a solid or liquid form, did not affect short-term subjective ratings of appetite or thirst, ad libitum FI or WI, or BG in healthy young men.