Figure 8. Potential beneficial effects of energy intake restriction or low carbohydrate intake (compared with isocaloric high carbohydrate intake) on the respiratory and cardiovascular systems.

1. Cells oxidize food-derived nutrients delivered by the arterial blood together with oxygen. Cellular respiration generates CO₂ and other acidic metabolic waste (lactic acid, ketone bodies). 2. Lungs and kidneys cooperate to eliminate CO₂ (lungs) and acids (kidneys). 3. Respiratory elimination of CO₂ is under the control of the breathing center in the brainstem as part of a central chemoreceptor reflex. 4. Activation of central chemoreceptors stimulates breathing and enhances sympathetic output to the cardiovascular system, in essence increasing BP. 5. Carbohydrate oxidation generates more CO₂ than fat (fatty acid) oxidation. Therefore, in conditions with reduced lung function (e.g., chronic obstructive pulmonary disease patients) and reduced renal acid elimination (e.g., aldosterone deficient mice), and/or hypermetabolism (e.g., obese people), promoting fat oxidation (fasting, isocaloric increase in fat intake at the expense of carbohydrates) might improve cardiovascular and pulmonary function.