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Underfueling Before the Season Can Ruin Your Performance
Many runners believe that being leaner equals being faster, leading us to try to manipulate our weight or body composition before or during key competitions. If you’ve got weight to lose, this could be a good strategy, but a new study on collegiate female distance runners shows that starting a season in an energy-deficient state leads to worse performance and slower fitness gains.
Researchers tracked 38 female collegiate runners throughout a competitive season. Before the season started, they categorized them into two groups based on metabolic health:
Energy deficient (low resting metabolic rate, indicating underfueling)
Energy sufficient (normal metabolic rate, indicating proper fueling)
Then, they measured VO₂max, 5k time trial performance, and key metabolic markers at the start and end of the season.
Runners who started the season underfueled were significantly slower. Their 5k times were 2 minutes slower than their well-fueled teammates and they didn’t improve over the season. VO₂max also stagnated in the energy-deficient group. Well-fueled runners gained aerobic capacity during the season, but those in a deficit didn’t see the same improvement. Lower total triiodothyronine (TT3) was linked to worse performance. TT3 is a key metabolic hormone, and low levels were related to slower times and poor training adaptation.
What this means for runners
Fueling matters before the season starts. If you enter training underfueled, your body will prioritize survival over performance, making it harder to build fitness. Even in the offseason or preseason, prioritizing nutrition is crucial. The best way to train hard is to eat enough to support it. Instead of focusing on weight, focus on fueling for adaptation. It’s a concept that takes a while to learn—and one I wish I’d have realized earlier on in my career as a long-distance runner.
Can “Too Much” Running Increase Your Risk of Heart Disease?
Most runners assume that logging more miles makes them immune to heart disease. After all, exercise improves cholesterol, lowers blood pressure, and strengthens the heart. But what if—paradoxically—long-term endurance training could increase heart disease risk? A new review explores the complex relationship between running and heart health, revealing that some athletes—especially those training at high volumes for decades—may develop more coronary calcification than expected. But there’s a lot of nuance involved.
Researchers conducted a state-of-the-art review of cardiac imaging studies assessing coronary artery calcification (CAC) and atherosclerotic plaque in endurance athletes. They compared highly trained runners and cyclists to less active populations to determine whether years of intense training increase or decrease the risk of heart disease.
The big question is whether endurance exercise protects against or contributes to coronary artery disease, the leading cause of sudden cardiac death in athletes over 35. Some of the findings challenge conventional wisdom.
For one, endurance athletes have a higher prevalence of coronary plaques than non-athletes. Multiple studies find that high-volume endurance athletes have more CAC and a higher prevalence of plaques than non-athletic control groups. However, not all plaques are created equal. While athletes have more total plaque burden, the composition of their plaques is less dangerous than what is typically seen in sedentary individuals. Endurance-trained individuals tend to develop densely calcified, stable plaques, which are less likely to rupture and cause heart attacks than the soft, lipid-rich plaques that are common in sedentary people. For example, in one study, 68% of the plaques found in endurance athletes were calcified, compared to only 47% in non-athletes.
Training intensity and volume seem to influence plaque development. Studies tracking athletes over time found that vigorous exercise was linked to increased CAC scores, but exercise volume alone did not drive plaque progression.
Despite more plaque, athletes have fewer cardiac events. Even in athletes with higher CAC scores, studies show that higher fitness levels (think VO₂max) are associated with a dramatically lower risk of heart attacks and cardiovascular events.
What this means for runners
Running won’t make you immune to heart disease, but higher fitness levels offer significant protection—even for those with coronary plaques.
Should you get a check-up? The authors did not recommend routine coronary artery scans for symptom-free athletes, as high CAC scores in endurance athletes do not necessarily translate to higher event risk. However, athletes with multiple risk factors (e.g., family history, high blood pressure, abnormal cholesterol) or symptoms should consider screening.
Do Super Shoes Really Improve Running Economy? And What About Ketones?
Super shoes—high-tech, carbon-plated racing shoes—have transformed running performance, promising better energy return and improved efficiency. At the same time, ketone supplements have been marketed as a metabolic enhancer that could improve endurance by offering an alternative fuel source. But do either of these actually improve running economy? What about combining them? A new study tested both advanced footwear technology and ketone monoester ingestion to determine their effects on running economy (RE), time-to-exhaustion (TTE), and metabolic efficiency.
Researchers conducted a study with 18 trained middle- and long-distance runners (10 men, 8 women, VO₂max: ~60).
Each participant completed four different trials on a treadmill, each consisting of five 8-minute stages of submaximal running (the men ran at a speed progressing from 10–14 km/h and women ran at a speed progressing from 9–13 km/h followed by a ramp test to exhaustion to measure time-to-exhaustion and peak oxygen uptake.
Each trial involved a combination of footwear and supplementation:
Standard running shoes (Nike Pegasus Turbo) + Carbohydrate (CHO) drink
Standard running shoes + ketone monoester drink
Super shoes (Nike ZoomX Vaporfly Next% 3) + CHO drink
Super shoes + ketone monoester drink
Participants ingested either a ketone supplement or a 10% carbohydrate solution before and during each session.
Super shoes (not surprisingly) improved running economy—ketones didn’t. Wearing the Vaporfly Next% 3 reduced oxygen consumption by 2.5-4.0% at submaximal speeds compared to the standard running shoes. This means runners used less energy to maintain the same pace, making them more efficient. The improvement was most pronounced at faster running speeds (third, fourth, and fifth stages). Super shoes also improved time-to-exhaustion—runners lasted 7% longer in the Vaporfly+CHO condition (381 sec) compared to Pegasus+CHO (356 sec). With ketones, the Vaporfly group improved time-to-exhaustion by 14% over Pegasus+KME.
Ketones alone did NOT improve running economy or endurance. There were no significant differences in economy between the carbohydrate and ketone trials despite elevated blood ketone levels. Time-to-exhaustion was actually lower in the ketone condition when runners wore the standard shoes.
What this means for runners
Super shoes genuinely improve running economy and extend time-to-exhaustion, making them one of the few equipment-based performance enhancers that live up to the hype. Ketone supplements, on the other hand, do not deliver on their performance promises and may be more useful for promoting post-exercise recovery or cognitive benefits.
HERE’S WHAT ELSE YOU WOULD HAVE RECEIVED this week if you were a subscriber to the complete, full-text edition of “Run Long, Run Healthy.”
What is "zone 2" training? Experts weigh in.
Do supershoes and ketones improve running performance?
How to break world records at 76 years old
That’s all for now. Thanks for reading. As always—Run Long, Run Healthy.
~Brady~