Exercise capacity and nitrogen loss during a high or low carbohydrate diet

Area of Science:

• Exercise Physiology
• Nutritional Science
• Obesity Research

Background:

• Very-low-calorie diets (VLCDs) are used for weight reduction.
• The impact of carbohydrate content in VLCDs on exercise capacity is not fully understood.
• Obesity is associated with reduced aerobic fitness and altered lipid profiles.

Purpose of the Study:

• To compare the effects of high-carbohydrate (HC) versus low-carbohydrate (LC) VLCDs on exercise performance and body composition in obese women.
• To assess changes in aerobic capacity (peak VO2) and endurance during sub-maximal exercise.
• To evaluate the impact of these diets on blood lipid profiles and nitrogen balance.

Main Methods:

• Twelve obese women underwent maximal and endurance exercise tests.
• Participants were assigned to either an HC (71% carbohydrate) or LC (33% carbohydrate) VLCD (530 kcal/day) for 4 weeks.
• Supervised exercise sessions (60% peak VO2) were conducted 3 times per week.
• Exercise tests and body composition measures were repeated after 4 weeks of VLCD.

Main Results:

• Both HC and LC groups achieved significant weekly weight loss (1.7-2.0 kg/week).
• Time to exhaustion during endurance exercise improved by 36% in both groups.
• Serum cholesterol and HDL-cholesterol decreased, but their ratio improved.
• Absolute peak VO2 decreased, but relative VO2 was maintained; body protein loss occurred.

Conclusions:

• Both HC and LC VLCDs effectively reduce weight and improve blood lipid profiles in obese women.
• Supervised exercise is feasible and beneficial for endurance during VLCDs.
• VLCDs, regardless of carbohydrate content, can lead to a net loss of body protein.