Nitrogen loss in normal and obese subjects during total fast

Area of Science:

• Metabolic research
• Human physiology
• Nutritional science

Background:

• Therapeutic fasting is utilized for weight management and certain medical conditions.
• Understanding nitrogen balance during prolonged fasting is crucial for patient safety.
• Previous studies have indicated variable nitrogen loss patterns during caloric restriction.

Purpose of the Study:

• To investigate urinary nitrogen excretion patterns in healthy and obese individuals during fasting.
• To determine the relationship between plasma glucagon levels and nitrogen loss.
• To compare nitrogen losses between sexes and weight categories.

Main Methods:

• Fasting protocols were applied to healthy volunteers (12 men, 12 women) for 6 days.
• Obese subjects (20 men, 28 women) underwent fasting for 6 to 28 days.
• Urinary nitrogen loss, plasma glucagon levels, and energy expenditure were measured.

Main Results:

• Urinary nitrogen loss significantly increased from day 1 to day 3, then steadily decreased.
• Early nitrogen excretion increases correlated with elevated plasma glucagon, suggesting increased gluconeogenesis.
• Men showed greater nitrogen losses than women at equivalent body weights.
• Obese subjects did not exhibit higher absolute nitrogen losses compared to normal-weight individuals despite higher energy expenditure.

Conclusions:

• Nitrogen loss during fasting follows a biphasic pattern, with an initial rise and subsequent decline.
• Plasma glucagon appears to play a role in the early phase of increased nitrogen excretion.
• Sex and body weight influence nitrogen metabolism during fasting, with implications for therapeutic fasting management.