MCT Oil for Endurance: Fast Fuel or Overhyped?

Look, I've seen the marketing: "MCT oil turns you into a fat-burning machine!" But here's a stat that makes me pause. A 2023 meta-analysis in the Journal of the International Society of Sports Nutrition (doi: 10.1186/s12970-023-00516-1), which pooled data from 18 studies with over 500 trained athletes, found that while MCTs can increase blood ketones by about 0.3 mmol/L on average, that boost didn't consistently translate to measurable performance gains in time trials or VO₂ max tests for most participants. Your body doesn't read the ads—it responds to what you actually put in it. So let's cut through the hype.

I had a marathoner client—Sarah, 38, a teacher—who came to me convinced MCT oil was her secret weapon. She was dumping a tablespoon into her morning coffee, hoping to "train her body to burn fat." By mile 18 of her long runs, she was bonking hard. Her problem? She was under-fueling carbs and overestimating what MCTs could do alone. We adjusted her strategy, and her story is a perfect example of why context matters.

What the Research Actually Shows (And What It Doesn't)

Okay, let's get into the data. The theory is solid: MCTs are absorbed directly into the portal vein and metabolized rapidly by the liver, potentially providing a quick energy source and elevating ketones, which some brain cells can use. Sounds perfect for endurance, right? Well...

A 2021 randomized crossover study (PMID: 34564321) had 20 trained cyclists complete a 2-hour ride at 65% VO₂ max followed by a time trial. One trial used a carb+ MCT drink (providing 85g carbs + 30g MCTs), another used carbs alone. The result? No significant difference in time trial performance. Blood ketones were higher with the MCT mix, but that didn't make them faster. This is the gap between a biochemical effect and a real-world outcome.

But it's not all negative. Published in Medicine & Science in Sports & Exercise (2022;54(5):789-798), a different team looked at ultra-endurance athletes during a 5-hour treadmill walk. They found that adding MCTs to a carb drink reduced perceived muscle fatigue by about 15% compared to carbs alone in the latter stages. The sample was small (n=12), but it hints at a potential benefit for subjective endurance, not necessarily raw power output.

Here's my take, after reading these and dozens of other papers: MCTs might help you feel better during very long, sub-maximal efforts by providing an alternative fuel stream and possibly sparing some muscle glycogen. But if you're expecting it to replace carbs or make you significantly faster in a race, the evidence just isn't there yet. Your body's primary high-octane fuel is still glucose.

Dosing, Timing, and How to Actually Use It

So you want to try it. Here's exactly how I advise my athletes, based on what works in practice, not just in a lab.

Start Low, Go Slow: Your gut needs to adapt. Begin with 5-10 grams (about 1 teaspoon) mixed into a pre-workout meal or drink, 60-90 minutes before exercise. If you tolerate it well (no GI distress—cramps or urgency are common if you jump in too fast), you can gradually work up to 15-30 grams for events lasting longer than 3 hours.

Never Take It Alone: This is critical. Always combine MCT oil with carbohydrates. A 2020 study (doi: 10.1123/ijsnem.2019-0321) with 18 runners showed that MCTs paired with carbs improved fat oxidation rates during running by 22% compared to fasted state, while MCTs alone did not. The synergy is the point. Think of it as adding a supplementary fuel line, not switching off the main one.

Form Matters: Get pure MCT oil (a blend of C8 and C10 is fine) or powder. Skip the "MCT powders" that are mostly filler fiber. I've seen athletes waste money on those. NOW Foods or Bulletproof are reliable. Do not just use coconut oil thinking it's the same—it's only about 15% MCTs.

Timing Protocol:

• Training Days (Long >90min): 10-15g MCT oil blended into a smoothie with 30-50g carbs (like oatmeal, banana) 60 min pre-exercise. During exercise, stick to your normal carb fueling strategy.
• Race Day: Tested protocol only! Maybe 15-30g in your pre-race meal, again with ample carbs. Some ultra-athletes use 5-10g per hour in their drink mix, but this requires serious gut training.

I'll admit, five years ago I was more bullish on MCTs as a standalone game-changer. The data since then has tempered that. It's a tool, not a miracle.

Who Should Probably Skip MCT Oil

This isn't for everyone. Honestly, if your workouts are under 90 minutes or are high-intensity intervals, you're complicating your fueling for likely zero benefit. Stick to carbs.

Avoid MCT oil if:

• You have a history of GI issues (IBS, Crohn's). MCTs can be a gut irritant.
• You have liver disease or gallbladder issues (requires medical clearance).
• You're following a very low-carb or ketogenic diet and are not fully fat-adapted. Adding a rapid fat source can overwhelm your system.
• You're an athlete who struggles with stomach sloshing or nausea during events. Adding oil is a risk.

I had a linebacker—big guy, powerful, but his training was all bursts under 60 seconds—who asked about MCTs for "energy." I told him to save his money and focus on his intra-workout carbs. Different engine, different fuel.

FAQs: Quick Answers

Q: Can MCT oil help me "get into ketosis" faster?
A: Temporarily, yes. It elevates blood ketones. But nutritional ketosis for performance is about metabolic adaptation over weeks, not a quick spike from a supplement. Don't confuse the two.

Q: Should I take it on rest days?
A: Probably not. There's no performance rationale. If you like it in your coffee for satiety, fine, but it's just extra calories then.

Q: MCT oil vs. carbs for energy during a marathon?
A: It's not vs. It's with. Carbs are non-negotiable for high-intensity marathon pacing. MCTs might offer a secondary, steady fuel source to help you feel more even late-race.

Q: I get diarrhea when I take it. What gives?
A: You took too much, too fast, or on an empty stomach. Start with a teaspoon (5g) with food. Your gut needs enzymes to adapt.

Bottom Line: Is It Worth It?

Here's my final call, across my desk:

• For ultra-endurance athletes (ironman, 100-milers, multi-hour events): It's a legitimate tool to experiment with in training. The potential subjective benefit for reduced fatigue perception is real for some.
• For marathoners and long-course triathletes: It's a maybe. If you've mastered carb fueling and want to explore a marginal gain, try it in training first. It's not a priority.
• For everyone else (runners under 2 hours, team sport athletes, weightlifters): Skip it. Focus on nailing your carbohydrate and protein intake first. That's where 95% of your fueling results will come from.

MCT oil is a fast-digesting fat that can provide auxiliary energy. It is not a replacement for carbohydrates, and the research on actual performance improvement is mixed at best. Start low, pair it with carbs, and see if your individual system responds. But don't expect magic—your body still runs best on the fundamentals.

Disclaimer: This is general information, not personalized medical advice. Consult with a healthcare provider before starting any new supplement, especially if you have underlying health conditions.