Like any conditioning of the body, whether by exercise, diet or other means - consistency is king. As we've referenced (1) in other SFuels material, it's fat (well talk about what type soon) in our diet-training, plus the duration (length) of our workouts, that researchers call out as the most determinate factors impacting fat-oxidation efficiency.
In our own athletes, we have seen how consistency in training and diet improves fat-oxidation efficiency rates, in some cases by over 300%.
Recent research (2) has demonstrated that in as little as 4-weeks, a consistent higher-fat diet in athletes, can enable very high fat-oxidation rates (>2gr/min), even during high-intensity Vo2Max workloads.
A few weeks back we covered the critical importance of Zone 2 Aerobic workouts - and how to fuel them - you can watch that here. But, what about the 'diet side' of influencing your fat-oxidation rates?
Almost 30 years ago, researchers (3) began to show (albeit in animal models) that endurance (time to exhaustion) could be improved by over 10%, depending upon the type of fat consumed. Animals consuming mostly medium-chain fatty acids (MCT) measured significant (~20%) improvements in key mitochondrial enzymes, and utilization/oxidation of ketones bodies, when compared to control animals that were consuming only long-chain fats.
In 2011, (4) researchers compared animals over a four-week period, on a diet of long-chain fats, versus animals on MCT fats. It was shown, that those animals on long-chain fats exclusively, suffered from impaired exercise performance and reduced mitochondrial efficiency, whereas, there was no negative impact to mitochondrial efficiency or exercise performance in animals consuming medium-chain MCT fats. We will come back to this later, but note that the long-chain fat diet, was mostly made up of the palmitic acid fat.
Interestingly, more recent studies (5) have shown how MCT can provide some protection, from exercise-induced heat impairment. The researchers highlighted the up-regulation of specific protein levels involved in mitochondrial biogenesis, as an explanation behind the protection from heat-impairment. In a recent podcast with Dr. Dan Plews, I asked how long do you need to exercise before heat begins to impair performance - his response, 'anything beyond a minute'.
Most importantly though, for these animal studies, the consumption of the MCTs was for an extended period - several weeks.
So, the effect (of fats in the diet), isn't a case of acute consumption enabling an acute benefit. Rather, the consistency of intake is what drives these physiological adaptions.
Most recently, in 2023, a distinguished research team (2) conducted a highly controlled cross-over study to look at the effects of ~4 weeks of a lower-carb, higher-fat diet, vs. a higher-carb lower-fat diet on performances, and fat-oxidation of highly trained middle-aged athletes. The study showed that a high-carb diet offered no performance improvement (at high Vo2Max intensities), over the low-carb higher-fat diet. Notably, fat-oxidation rates dramatically rose on the low-carb high-fat diet, blood-glucose levels were in healthy ranges, and total HDL-LDL (total cholesterol) increased.
Again, note the time period here of the study-diet, was four weeks. This is actually a short period of time, though in reviewing the diet used in the study, it was essentially a 'keto' (~40-50gr Carbs/Day) diet. So now we see two factors, 1) higher fat consumption, and 2) low-carbohydrate consumption.
While a whole other topic, it's also worth noting that in the same 4-week period of the study, the high-carb diet triggered clinical signs of pre-diabetes (fasting blood-glucose >100mmol, as measured via CGM) in 30% of athletes.
All that said, there is some evidence of 'acute' benefits of fats for the athlete to consider.
In a 1985 study researchers (6) demonstrated a more acute-response (improved time-trial performance) to including MCTs to a carbohydrate beverage. Researchers suggested that oxidation of the MCTs in the beverage had directly or indirectly reduced glycogen oxidation - which may explain the improved performance (ability to finish strong).
Additionally, in 1992 (7) researchers demonstrated that in all beverage formulations where MCT was added to a glucose-polymer (maltodextrin) solution, subjects experienced faster gastric emptying time, verse a maltodextrin-only solution. This is thought to be explained via either increased osmolality (with the MCT fats), and/or, better water-solubility and absorption of MCT fats.
Finally, in a study in 2018 of high-intensity workloads of cross-country skiers, blood samples showed evidence of high lipolysis (fat breakdown and release into the circulation) of medium-chain fatty acids, while there was little evidence of long-chain fatty acid lipolysis in blood samples.
Uniquely, MCT fats are able to rapidly traverse cell membranes without transporters (as required for long-chain fats, and carbohydrates). This has contextual relevance in the use of this fatty acid for endurance exercise, in relation to its rapid movement across digestive system membranes and systemic (liver, muscle etc.) mitochondrial membranes.
4 Best Practices
1) Increase fat in your Diet:
As multiple studies and meta-analyses now show, purely increasing the ratio of fats to other macronutrient substrates (namely carbohydrates) in the overall diet, will raise your fat-oxidation efficiency. As a general guide, a cold-keto transition (~4 weeks) would have ~70% calories coming from fat, and carbohydrates at ~50gr/day.
2) Use MCT fats in Diet & Fueling:
Animal and human studies would suggest a performance enhancement and mitochondrial genesis/efficiency outcome through the use of MCT fats. Again most of these positive adaptions came about after about 4 weeks of consistent intake. We recommend the daily use of the most ketogenic forms of MCT oils, the C8 and C10 forms. Specific inclusion of these fats, can be found in -
- SFuels Keto3 Breakfast Cereal
- SFuels Revival Shake mix
- SFuels TRANSFORM (Smoothies, shakes, salad dressings, cooking sauces, pancake supplement etc.),
- SFuels fuel-hydration training drink: SFuels TRAIN
3) Choose healthy fats, beyond MCTs:
Focus on adding the healthy mono-unsaturated forms (Avocado, Olives/Olive oil, Almonds, peanut), and the better poly-unsaturated sources (Flaxseed, Walnuts, and Fatty Fish) through the daily diet.
4) Limit palmitic acid-based Fats:
The Palmitic acid (C16:0) form of fat has been shown (8) to have a reducing effect on fat-oxidation efficiency when tested over a 4-week period. Since the body can produce this fat, our guidance would be to let the body decide how much to produce, rather than over-consume it. Over-consumption can happen easily, with Palmitic acid making up 50-60% of the total fat in every-day foods like meats, dairy, and butter. Easy areas to limit its use would be, 1) use avocado over butter, 2) increase your fish consumption versus pork/chicken/beef.
Finally in closing - we haven't said anything about nutrients that can stimulate fat-oxidation. You can watch our SFuels video on Caffeine, and other specific nutrients for enhanced fat-oxidation here.
SFuels MCT C8-C10 Based Products
1. Jeffrey A. Rothschild, Andrew E. Kilding, Tom Stewart, Daniel J. Plews. Factors
Influencing Substrate Oxidation During Submaximal Cycling: a Modelling Analysis. Sports Medicine 2022 Jul.
2. Philip J Prins, Timothy D Noakes, Alex Buga, Dominic P D'Agostino, Jeff S Volek, Jeffrey D Buxton, Kara Heckman, Dalton W Jones, Naomi E Tobias, Holly M Grose, Anna K Jenkins, Kelli T Jancay, Andrew P Koutnik. Low and high carbohydrate isocaloric diets on performance, fat oxidation, glucose and cardiometabolic health in middle age males Frontiers in Nutrition. 2023 Feb
3. T Fushiki, K Matsumoto, K Inoue, T Kawada, E Sugimoto. Swimming endurance capacity of mice is increased by chronic consumption of medium-chain triglycerides. The Journal of Nutrition. 1995, Mar.
4. Andrew J Murray, Nicholas S Knight, Sarah E Little, Lowri E Cochlin, Mary Clements,and Kieran Clarke. Dietary long-chain, but not medium-chain, triglycerides impair exercise performance and uncouple cardiac mitochondria in rats. Nutrition and Metabolism. 2011, Aug.
5. Ying Wang, Zhenzhen Liu, Yi Han, Jiping Xu, Wen Huang, Zhaoshen Li. Medium Chain Triglycerides enhances exercise endurance through increased mitochondrial biogenesis and metabolism. PloS One. 2018, Feb.
6. C G Van Zyl, E V Lambert, J A Hawley, T D Noakes, S C Dennis. Effects of medium-chain triglyceride ingestion on fuel metabolism and cycling performance. Journal of Applied Physiology. 1996, Jun.
7. E J Beckers, A E Jeukendrup, F Brouns, A J Wagenmakers, W H Saris. Gastric emptying of carbohydrate--medium chain triglyceride suspensions at rest. International Journal of Sports Medicine. 2992, Nov.
8. C Lawrence Kien, Janice Y Bunn, Figen Ugrasbul. Increasing dietary palmitic acid decreases fat oxidation and daily energy expenditure. American Journal of Clinical Nutrition. 2005, Aug.