Does the utilization of fatty acid (FA) versus carbohydrate as a fuel source impact basal metabolic rate (BMR)?

From the Guidelines

The utilization of fatty acid (FA) versus carbohydrate as a fuel source does impact basal metabolic rate (BMR), as the body's preference for carbohydrate oxidation over fat retention can influence energy expenditure.

Key Points

• The body tends to preferentially oxidize carbohydrates over fats, and excess energy intake will generally result in the retention of dietary fat in adipose tissue 1.
• Insulin released in response to carbohydrate intake helps promote fat storage, and high-carbohydrate diets can lead to increased de novo lipogenesis and circulating levels of saturated fatty acids (SFAs) 1.
• Low-carbohydrate diets, on the other hand, can increase rates of whole-body fat oxidation and reduce circulating SFAs, potentially leading to improved metabolic outcomes 1.
• The gut microbiome may also play a role in the metabolic differences between low-fat and low-carbohydrate diets, with low-carbohydrate diets potentially leading to unfavorable changes in gut microbiota and metabolic profiles 1.

Evidence-Based Rationale

The evidence suggests that the type of fuel source utilized by the body can have significant impacts on metabolic rate and overall health.

• A study published in the Journal of the American College of Cardiology found that dietary carbohydrate intake and insulin resistance can modulate the health effects of saturated fat, and that low-carbohydrate diets may be more effective for weight loss and improving metabolic outcomes 1.
• Another study published in Cell Host and Microbe found that low-carbohydrate diets can lead to unfavorable changes in gut microbiota and metabolic profiles, and that microbiome-targeted approaches may be necessary to improve the health outcomes of these diets 1.
• The Proceedings of the Nutrition Society study found that dietary fat typically provides about one-third of the energy, and that an excess energy intake will generally result in the preferential oxidation of carbohydrate over fat and the retention of dietary fat in adipose tissue 1.

Clinical Implications

In clinical practice, the choice of fuel source can have significant implications for patient outcomes.

• Healthcare providers should consider the potential benefits and drawbacks of low-carbohydrate and low-fat diets, and work with patients to develop personalized nutrition plans that take into account their individual needs and health status.
• Additionally, healthcare providers should be aware of the potential role of the gut microbiome in modulating the metabolic effects of different diets, and consider the use of microbiome-targeted approaches to improve patient outcomes.

From the Research

Impact of Fatty Acid versus Carbohydrate on Basal Metabolic Rate

• The utilization of fatty acid (FA) versus carbohydrate as a fuel source can impact basal metabolic rate (BMR) 2.
• A study found that a diet with a high polyunsaturated to saturated fatty acid ratio resulted in a relatively high resting metabolic rate (RMR) and high diet-induced thermogenesis (DIT) 2.
• The study showed that RMR after a period with a high P/S diet was significantly higher than after a period of a low P/S diet, with an average difference of 3.6% of RMR 2.
• Another study found that adaptation to a high-fat diet for 7-10 days can alter substrate utilization during submaximal exercise, but does not appear to alter the rate of working muscle glycogen utilization during prolonged, moderate intensity exercise 3.

Metabolic Changes with Fatty Acid Utilization

• High-fat dietary conditioning can result in metabolic changes consistent with greater lipolysis and fuel availability, including lower plasma insulin concentration before exercise and higher plasma glucose concentration during exercise 4.
• The peak fat-oxidation rate was 2.5-fold to 2.9-fold higher in the high-fat conditions compared to the high-carbohydrate condition 4.
• The glucose/fatty acid cycle plays an important role in ensuring that marathon runners can continue beyond the theoretical limit of 100 minutes, by reducing the rate of glucose utilization through the oxidation of fatty acids 5.

Effects on Exercise Performance

• High-fat dietary conditioning may enhance ultra-endurance cycling performance, although the main effects were not statistically significant 4.
• The ingestion of a high-fat diet for 7-10 days can alter substrate utilization during submaximal exercise, but does not appear to consistently improve performance 3.
• The availability of fatty acids for oxidation as early as possible in exercise can allow the use of both fuels (fatty acids and glucose) for a longer period of time, potentially delaying fatigue 5.