Low capacity to oxidize fat and body weight

Area of Science:

• Metabolism and Obesity Research
• Human Physiology

Background:

• The low fat oxidation hypothesis posits that reduced fat oxidation capacity contributes to weight gain.
• This is based on observations of higher respiratory quotient (RQ) in obesity-prone (OP) versus obesity-resistant (OR) individuals and its predictive value for weight gain.

Purpose of the Study:

• To critically evaluate the experimental evidence supporting the low fat oxidation hypothesis.
• To re-examine the physiological significance of respiratory quotient (RQ) in the context of weight gain and fat metabolism.

Main Methods:

• Systematic review of 42 studies investigating the relationship between RQ, obesity, and weight gain.
• Power analysis to assess the feasibility of experimentally confirming the hypothesis.
• Re-examination of the determinants of 24-hour and fasting RQ.

Main Results:

• No convincing experimental evidence was found to support the low fat oxidation hypothesis.
• Power analysis indicated that extremely large sample sizes would be required to statistically validate the hypothesis.
• The 24-hour RQ is primarily determined by dietary intake (food quotient, FQ) and energy balance, not fat oxidation capacity.

Conclusions:

• The low fat oxidation hypothesis is not supported by current experimental data.
• The interpretation of RQ as a direct indicator of fat oxidation capacity is flawed.
• Factors such as diet and energy balance are the primary determinants of RQ, irrespective of obesity status or predisposition.