Oxidative Priority, Meal Frequency, and the Energy Economy of Food and Activity: Implications for Longevity, Obesity, and Cardiometabolic Disease
Interesting summary of research on fasting and oxidative priority of energy sources.
- A person's respiratory quotient (RQ) is defined as (volume CO2)/(volume O2), and can be used to measure his energy fuel mixture. Eg. an RQ of 0.85 indicates a 50/50 mix if carbohydrates and fat. Protein is estimated separately via urine/feces sample.
- Meals entail a 4-6 hour postpandrial change in metabolism to process the food
- The nature of the postpandrial change varies based on the type of food. Example: Protein causes higher rise in dietary induced thermogenesis, since there is no way to store proteins. It also causes a reduction in the use of stored carbs and fats
Oxidative order is based on how readily a fuel source can be stored:
- Alcohol has no storage capacity in the body, consumed first
- Protein has very limited storage capacity in tissue, consumed second
- Carbohydrates can be readily stored as glycogen, consumed third
Fat has almost unlimited storage in adipose tissue, consumed last
Above can be used to understand obesity in western diet. Excess carbohydrates pre-empt burning fat, while excess fat is steadily accumulated
- Fasting first burns through glycogen stores, then burns fat from adipose tissue
- "Chronic postpandrial state" due to ready availability of food at all times
- Cold changes metabolism to favor burning fat. The authors have a separate article entirely dedicated to this topic.